Pascal-Yan Sayegh

Yan Sayegh

Keywords: nationalism / citizenship, identity / Otherness, inclusion/ exclusion, discourse, collective imaginary, hybridity

come

Introduction:

In a nutshell, the aim of the project is to build a coherent framework of social and political theory around defined case studies of discourse analysis -an analysis of the representation of 'Otherness' in political and press discourse.

As this is an aim yet to be attained, I will be talking in the first part of my presentation about the theoretical background of this project, and in the second part, I will be presenting highlights of my recently engaged case studies.

Part 1: Nation-states, nationalism and democracy, or the "modern ideological cluster" (paradigm) I would like to start this presentation with a quote by the American sociologist, Craig Calhoun, which I persistently quote every time I write a presentation of this project:

"Is it possible to build states and even confederations of states in which cohesion and self-rule are established through public discourse across lines of difference? Can we conceive the growth of a cultural unity within such states or confederations that does not devalue or demand the obliteration of other sources of personal and political identity? Or must we fall back on nationalism alone as our shelter in a world grown too frightening, or as the one immediately satisfying identity with which to confront the globalization of capital?" 1 These questions, which I personally like to call the "Calhoun project", are the general questions in which my research is involved. It seems to me that 15 years or so since the "Calhoun project" was formulated, it remains a valid, and indeed increasingly valid. For instance, it seems that the contemporary issues related to pluralism -at least in the context I am concerned with -are not being answered "across lines of difference", but dangerously along these lines. In fact, despite the calculations of many globalist theories on the fall or decline of Nation-states, and despite the enlarged liberalized space of mobility in Europe, I think there is little doubt that the Nation-state remains the central political institution. Concurrently, and this is what I am concerned with, nationalism (as state ideology and self-determination ideology) remains the modern central mode of collective identification. 2 Of course, there is no denying that globalization or the European construction does have a major impact on modern institutions. In fact, these phenomena do put the Nation-state into question, but do not hamper its existence, and particularly its (imaginary/ideological) legitimacy.

The recent expressions and policies of exclusion we have witnessed in most European countries, the ongoing debates about immigration and the tightening of related laws for instance (in the Netherlands, in France, in Denmark…, but this is only the tip of the iceberg) follow and respond to the ideological stance of Nation-states: they show (they want to be perceived) as far as these issues are concerned, that they are "in power". This power is exercised along state ideology through (dominant) nationalist discourse. When the state's power or legitimacy is put into question, it relies on the ideological grounds of modern state legitimacy: national democracy.

It is in this sense that the "current state of affaires" I briefly mentioned before, is fostering the development for some and the repetition for others of nationalism (in its banal or "aggressive" forms). This is based on the belief that nationalism is the sole identity formation compatible with modernity, and hence the logical rampart against a cultural imperialism undercurrent in globalization. But why is this problematic in the light of the "Calhoun project"? It is because of what I would like to call the 2 Cf. e.g. Michel Sauquet, L'intelligence de l'autre (the intelligence of the other): "The simulatneaous existence of the same western cultural forms in certain sectors of certain cities in some of the four corners of the world can not be taken as proof that the world is homogeneous. The progressive alignment of dressing codes is a superficial phenomenon. A real homogenization would suppose a general mutation of representations and imaginaries, which does not correspond to what reality now is. La présence simultanée des mêmes formes culturelles occidentales dans certains secteurs de certaines villes de certains des quatre coins du monde ne peut guère être prise pour preuve que le monde est homogénéisé. L'alignement progressif des codes vestimentaires est un phénomène superficiel. Une véritable homogénéisation supposerait une mutation généralisée des représentations et des imaginaires, ce qui ne correspond pas à la réalité." "ideological cluster of modernity" (Zizek would call it a "symbolic field"), i.e. the circular legitimating of nationalism and democracy. In my mind, it does not answer the contemporary issues in the management of social pluralities: the inclusion of nonmajority communities, groups or individuals in a reciprocal cultural and political equality within the framework of the modern state (and this is the iceberg…). This is not only problematic in itself (i.e. from a theoretical point of view), it is more precisely problematic because societies, at least in Europe, are increasingly aware of their plurality -whether accepted or refused, a plurality increasingly complex given the fluidity (or hybridity) of peoples (geographically and imaginary). And this may be the most important influence of globalization for the purpose of my research, the fostering of social sensitivity towards identity issues (hence the national "revival").

But going back to nationalism, one of the central questions for modernity it claims to answer is "who are the people?": and the answer it provides is part of the selfdetermining process and of the democratic process i.e. as it gives an answer to the "self", it is a necessary prerequisite for the definition of democratic citizenship. [And in a certain sense, the process of democratization of the national communities in Europe have reached a certain paroxysm: we cannot on this basis include even more people in the community. ]

Yet, this answer does not involve the existence (or even potential) plurality of societies. It is, in a certain sense a contradiction, as the equal participation in the polis is based on nationality (it used to be even more exclusive, cf. gender equality), the boundary between participating in the affaires of the polis and cultural hegemony is constantly ambiguous.

In short, the linkage between state and society, between cultural and political community, between the polis and the nation, opens a certain gap. In John Breuilly's mind, it is through an ambiguity that nationalism appears to provide an answer to this problematic link. In fact, the ambiguous references of national discourse to the cultural community on the one hand and to the political community on the other overtake this problematic.

Part 2: Hypotheses, the collective imaginary and empirical references; or doxa and praxis.

This point forms the first hypothesis of my thesis that the case studies will need to confirm or discard. For this hypothesis, I assume that the discourse involved engages in an association of terms and significations that exclude other type of significations, like the differentiation between cultural community and political community for the purpose of pluralism. I would like at this point to give a short quote of Nicolas Sarkozy (NS) which provides with a quite astonishing example: "Si on veut vivre avec sa culture, on ne vient pas vivre sur le territoire de la République Française" ["If one wants to live with one's culture, one does not come to live on the territory of the French republic"] (Live on France 2, one of the largest French television network (France television), then interior minister, "A vous de juger", political talk show, 30 November 2006,)

What we see here is the juxtaposition in the same sentence of a (relativist) cultural reference to a (universalistic) political reference, all of this very carefully said at first with the impersonal pronoun, while the definite article (unambiguous, fix) then defines the reference to France.

The question contained in this first hypothesis is (paraphrasing Bauman): does political coexistence (or which form of political coexistence) necessarily entails a homogeneous culture (what mode of culture)? Or more pragmatically, do contemporary democratic communities have to necessarily be national? The answer to this question would involve an analysis of this "necessity" in terms of imaginary associations, or in other words, of the exclusiveness of imaginary associations (are there associations that are not necessarily exclusive? If yes, to what extent?3 ). This is when the collective imaginary comes in, as the national imaginary and the democratic imaginary, are both exclusive imaginaries on a cultural basis4 . It is in fact in this imaginary space that processes of exclusion take place. And discourse analysis can here provide elements that define the "grid of signification" (Foucault) discourse imposes on the imaginary.

The four countries involved in this study are Britain, France, Poland and Sweden. The choice of these countries has been determined through the will to engage in a study involving a varied panel of European societies. As Britain and France are often depicted as mainstream actors of the European concert of nations, I wanted to include countries that are not often considered as such.

What is also more interesting is that each is thought to represent a certain model of society. France is famous for its Jacobin republican model, often opposed to Britain's long running multicultural and liberal system. Both also represent post-colonial states and societies, with the particularly sensitive approach relative to these issues. Sweden for its part is famous for its attractive social model which has for long been thought of as a model of integration, and while it faces some difficulties, it is still looked up to.

Poland, despite a certain multicultural past and a relative immigration since 1991, is finally the only country not famous for an attractive model, but rather for its "tradition" of emigration. It is also an evident representative of central and eastern European countries, new to the European construction but where political discourse often presents an openly nationalist tone. Yet, many features bring these four countries together; one obvious is their involvement in European affairs, another is the migration and integration crisis that stirs the whole of the European community.

For my concern, I aim at analysing the extent to which there are common processes of exclusion despite the obvious differences.

The study of the dominant discourse will engage in the political discourse on the one hand with the discourse of media on the other, more precisely the daily national newspapers. It could be argued that narrowing the study to daily national presses would not be representative of the modern media (referring more specifically to television). Despite a certain decline of the printed press, it still represents the traditional means for information and formation of popular opinion. As it remains an important, accessible and modern medium, it plays a major role in the construction of stereotypes and representations of identity and otherness.

I would like to draw upon a case study I just started to describe my methodology concerning the imaginary, i.e. to describe some of the processes through which imaginary exclusion is performed. The case study concerns France, and particularly the discourse on immigration and national identity which has been on the front stage for a good few years now.

The debate has crystallized during the presidential election campaign earlier this year when the creation of a new ministry dealing both with immigration and national identity appeared as one the 15 points of NS presidential project ("immigration control"). The ministry for immigration, integration, national identity and codevelopment was finally created creation six months ago (31 May) and is widely being referred to in the media as the "ministry for immigration and national identity".

At first glance, it seems that it is the association of terms that has shaken the opinion and the opposition, but when we look closer, it is the creation of a single ministry (for two competences) that stirs the opinion rather than the name of it. What obviously overtones in the name of the ministry is that immigration is a threat to national identity; but threat discourse is far from being the monopoly of NS, e.g. it can also be found in the discourse of the political opposition, in Segolène Royal's presidential campaign project (the expulsion and foreigners when there are "dangerous criminals")5 .

As far as the mainstream press is concerned, I do not have enough references now to say more than that alternative readings are rare (I have in one week found only one article, an "expert analysis", that does in fact propose an alternative approach). But this is, in my mind, linked to my second hypothesis that dominant discourse calls for itself, and it is very hard to oppose it in different categories that those it "imposes".

Consequently, even though one can find opposing political stances, the grid of signification remains virtually untouched.

Coming back to the case study, one has also to note a very important aspect: NS had been interior minister for the previous government, and as interior minister he was then in charge of immigration policies. And this association has precedence: one of the first laws NS drafted was the "law related to immigration control, the sojourning of foreigners and nationality" (Loi no. 2003-119, 26 November 2003).

Since then the discourse of the would-be president and his supporters has grown very strongly around these themes. Here is a short sample of NS and the UMP's rationale about immigration that has been repeated throughout the past few years:

In the "banlieues", we are paying the price of an immigration policy that was neither chosen, nor wanted, nor claimed or organized; but the accumulation in certain neighbourhoods of sons and grandsons of foreigners who never had any formation, any education, any job has created real powder magazines. I conclude that one has to control immigration. 6 Public discourse was systematically filled with discourse on immigration and national identity, etc. In short, it has been banalized and it has consequently become part of the dominant discourse.

And it is in this light interesting to note that none of the policies from the new ministry do anything but mentioning the relationship (threat) of immigration with national identity. Here is an extract from the press conference the new minister for immigration and national identity, Brice Hortefeux (BH) gave on the 8 November 2007. It it is the starting point to the reasons why the minister sees new tougher immigration laws are necessary:

"First of all, let us be honest: the French integration system has failed. The proof is the much to high concentration of population of foreign origin in only three regions out of 22: 60% of foreigners live in Ile-de-France, Rhône-Alpes or in PACA, sometimes in real urban ghettos. Another proof is the average unemployment rate of foreigners, above 20%, which is more than twice the national average. In certain "banlieues", this rate reaches to 40%. We have to say the truth to the French people: our integration system is no more a model. And to success in integration, one has first to control immigration." 7 What I would like to point at here, both in the previous "sample" and in BH's declaration is the exact ellipsis we find in the laws. We can see of course that there is the same correlation that overtones immigration as threatening the national identity.

But more precisely, we see that the reason for a new (future) immigration policy is need because of the errors of the previous one(s). In short, we find in both cases the mention that there is a situation inside, and this is indeed very important because this were the ellipsis appears: while we find the acknowledgment that there is a situation that has to be answered, the answer leads us to immigration control and not to what 6 E.g. « Dans les banlieues, nous payons le prix d'une politique de l'immigration qui n'a été ni choisie, ni voulue, ni revendiquée, ni organisée ; mais l'accumulation dans certains quartiers de fils et petit fils d'étrangers à qui on n'a donné ni formation, ni éducation, ni emploi a conduit à de véritables poudrières. J'en tire la conclusion qu'il faut maîtriser l'immigration, qu'on ne peut pas accepter tout le monde pour donner la chance de l'intégration à ceux qui ne l'ont pas. » "A vous de juger", political talk show, 30 November 2006 7 « D'abord, osons regarder la vérité en face : le système français d'intégration a échoué. J'en veux pour preuve la concentration beaucoup trop forte de la population d'origine étrangère sur seulement trois régions sur vingt-deux : 60% des étrangers habitent en Ile-de-France, en Rhône-Alpes ou en Provence-Alpes-Côte d'Azur, parfois dans de véritables ghettos urbains. J'en veux aussi pour preuve le taux de chômage moyen des étrangers, supérieur à 20 %, soit plus du double de la moyenne nationale. Dans certaines banlieues, ce taux atteint les 40%. Il faut donc dire la vérité aux Français : notre système d'intégration n'est plus un modèle. Et pour réussir l'intégration, il faut d'abord maîtriser l'immigration. » http://www.premier-ministre.gouv.fr/iminidco/salle_presse_832/discours_tribunes _835/ discours_brice_hortefeux_presse_57958.html society inside is concerned with. It seems to me that it this "gap" in significations is very important the processes of imaginary exclusion. The "logic" of the linkage between immigration and national identity (or vice versa) imposes a grid if significations where the association (i.e. the inclusion) of a certain fringe (French citizens of foreign origins living in the poor suburbs 8 ) of the existing French society is made unthinkable, or in Foucault's words, is forbidden. We can describe it in formal terms through the logic of amalgamate ("population of foreign origins"/ "sons and grandsons of foreigners" become not integrated "foreigners"), but also in terms of imaginary processes of exclusion. The linkage between one the hand immigration (i.e. the question of newcomers) and national identity (the shared collective references, the shared grid of significations, etc.) aims at draw a line between those that can easily fit the grid of significations and those that would need an adjustment: the effect of this discourse of exclusion has a direct effect on the majority imaginary. But it aims at a secondary effect on the minority/stereotyped/excluded community: it renders their own imaginary unviable if including themselves in the French community. The space which is left in between is the important exclusive process as it is only in this space that inclusion can take effect. Before concluding, I would like to relate an interesting anecdote that came out after the suburban riots in France in 2005. Given a increased amount of identity checks in the so-called "dangerous" suburbs, there was this advice from some young people 9 (who are the main targets of the id checks) to have their electoral card at the front of their wallets. The aim was to show the policemen (representing the state authority, but indirectly NS as interior minister) that "we" are part of the same political community.

The effect of this was supposedly for the police to be less inclined to be hard on them.

What I find interesting here, is indeed the attempt to fill the imaginary space I have described, and that this effort has come from the "excluded" (yet, I cannot tell to what extent this fulfilled its aim or made it more complicated).

Conclusion

My aim here was to try raising some hypothesis: 8 To make it short, it is easily understood that the peoples NS points to are Muslims. Cf. His preference for a Christian/White Europe, and in his campaign video clip on immigration, the example he uses to describe French values (the rights of women). 9 NB. This was used later by Segolène Royal during her campaign to incite young people to vote (for her).

→ Through stereotyping, oversimplifying implications, scapegoating, threat and risk discourse, the ambiguity of who is included or not in the community, maintains the game of nationalist significations of confusion between political and cultural communities. The political motives are usually left out in the press mediation of this discourse: we end up with a culturalist grid of signification.

→ Dominant discourse calls for itself, the grid of signification it imposes excludes or renders no mediating space (hybrid, plural). It imposes a mode of using categories the "other" is compelled to understand and use to be himself understood or taken notice of, e.g. NS: "racism is not only French, it is also immigrant" (talking about French people of immigration origins). This process ends up in what I have described as an imaginary gap.

→ The paradigm of modernity (cf. the ideological cluster) plays a role in the exclusion processes as it is based on what Edgar Morin has called the hypersimplification of the modern mind. In this sense, the implications from the preivous two hypthesis would impact on this paradigm. For instance: what the dominant grid of signification excludes is a complexity (plurality) of society, in this sense the inclusion of diversity could mean the inclusion of complexity, in imaginary terms, a (more) complex grid of signification. It is on this level that an imaginary "mutation" (cf. footnote no.2) would take place.

[→ Following, the contemporary dominant discourse adds a third party to the game of significations which involves additional confusion to legitimize a certain exclusion/inclusion pattern: market economy/liberalism/neo-liberalism.] Yan Sayegh, Université de Lyon, IETT

"Nationalism and Civil Society: Democracy, Diversity and Self-determination"; paper first presented in June 1991 at the Hungarian Sociological Association. Last retrieved on 14.11.2007 from www.ssrc.org/staff/calhoun/publications/nationalism_and_civ_society.pdf. Cf. Craig Calhoun (ed.) Social Theory and the Politics ofIdentity, Oxford, Blackwell,

E.g. Scottish "new nationalism": the break-up Britain within the EU.

NB: democracy is exclusive through the "equality postulate": it is a historical fact that democratic forms of power have always been shared among "equals", i.e. people recognizing each other along lines of similarity, of identity. Consequently, there is no real example of the institutionalization of democracy with a non-homogeneous cultural community. That is why nationalism provides a very effective corollary to democracy: essentially, equality for "us".

She explained later that she was not "talking about those that have grown up in France, but those you have arrived not long ago."


Michel Ndoumbe Nkeng

Mousseni Ives

Bruno Efombagn

Lucien Bidzanga

M Ndoumbè-Nkeng

M I B Efombagn

S Nyassé

E Nyemb

I Sache

C Cilas
email: cilas@cirad.fr

Spatio-temporal dynamics on a plot scale of cocoa black pod rot caused

Keywords: Cross-correlation, epidemic risk, integrated protection, Phytophthora megakarya, Theobroma cacao. Résumé Corrélations croisées, risque épidémique, protection intégrée, Phytophthora megakarya, Theobroma cacao

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Pod rot, caused by different species of the genus Phytophthora, is widespread in all cacao producing countries. Worldwide, the most common species is P. palmivora. In Cameroon, studies revealed the existence of a single species, P. megakarya , that was responsible for the disease (Nyassé, 1992). Although this disease can affect different organs such as the roots or the trunk, it mainly attacks fruits. The different Phytophthora species all cause the same symptoms on pods, namely rotting black patches that sometimes spread to the entire fruit. Damage from pod rot can be up to 30% of the world harvest every year.

Disease expression in the field is influenced by numerous factors, both environmental and genetic such as environmental conditions (rainfall, wetness and temperature), pathogen survival and dispersal, pathogen species and strain involved, as well as host resistance [START_REF] Tarjot | De quelques facteurs favorisant le développement des pourritures de cabosse du cacaoyer en Côte d'Ivoire[END_REF][START_REF] Akrofi | Management of Phytophthora pod rot disease in cocoa farms in Ghana[END_REF][START_REF] Cilas | Disease incidence and field resistance[END_REF]. All these factors can interact to favour or to restrict disease development. For example, some genotypes of Theobroma cacao may appear resistant in an environment and susceptible in other ones. This phenomenon is known as "genotype x environment" interaction [START_REF] Cilas | Disease incidence and field resistance[END_REF].

The present study focuses on the incidence of environmental factors on dynamics of the disease.

Whether in Cote d'Ivoire [START_REF] Tarjot | De quelques facteurs favorisant le développement des pourritures de cabosse du cacaoyer en Côte d'Ivoire[END_REF][START_REF] Tarjot | -Etude de la pourriture des cabosses due au Phytophthora palmivora (Butl.) Butl. en Côte d'Ivoire. Lieux de conservation du parasite pendant la saison sèche[END_REF], Ghana (Asare-Nyako, 1973), Cameroon (Muller, 1974a(Muller, , 1974b)), Jamaica [START_REF] Henry | Primary sources of Phytophthora palmivora (Butl.) Butl. Inoculum in Jamaica and methods of control[END_REF] or Nigeria [START_REF] Gregory | Epidemiology of Phytophthora on cocoa in Nigeria[END_REF], epidemiological observations showed that Phytophthora pod rot appears when there is a conjunction between the presence of fruit on trees, whatever their growth stage, on one hand and rainy season on the other hand. The effects of climate on the epidemic process are only known in a macroscopic approach in cocoa producing zones [START_REF] Tarjot | De quelques facteurs favorisant le développement des pourritures de cabosse du cacaoyer en Côte d'Ivoire[END_REF]). In Cameroon for example, the incidence of disease tends to be higher in some agro-ecological zones with a mono-modal rainfall regime, compared to those with a bi-modal rainfall regime [START_REF] Ndoumbè-Nkeng | Incidence des facteurs agro-écologiques sur l'épidémiologie de la pourriture brune des fruits du cacaoyer au Cameroun: contribution à la mise en place d'un modèle d'avertissements agricoles[END_REF].

Similarly, a positive correlation has been found between the rate of pod infection and the potential production, implying that the environmental conditions determining both disease incidence and production capacity are similar (Muller, 1974a;[START_REF] Despréaux | Etude de la pourriture brune des cabosses du cacaoyer au Cameroun. Deuxième partie : contribution à l'étude de la maladie[END_REF]. However, this observation does not take into account the climactic variations observed for the whole production period, such as the alternating dry and wet periods and their impact on the process and intensity of the epidemics. Knowledge of the effects of climatic variations on pod rot incidence is useful, particularly to plan fungicide applications.

The objective of the study was to assess and quantify the effects of rain events and temperatures on the temporal development of the disease in the cocoa producing areas of Cameroon, like it was done on other crops [START_REF] Rapilly | L'épidémiologie en pathologie végétale[END_REF]. The questions addressed were (1) what are the relationships between climatic factors and disease expression? (2) Is there a threshold for these factors above which the disease occurs?

Materials and Methods

Study sites and experimental design

The study was conducted in three locations in Cameroon: Mbankomo (Centre Region, Mefou-et-Akono Division; coordinates: 3°78'0''N and 11°38'0''E), Goura (Centre Region, Mbam-et-Kim Division; coordinates: 4°55'60''N and 11°45'0''E), and Barombi-Kang (South-West Region, Meme Division; coordinates: 4°34'40''N and 9°27'21''E).

Mbankomo and Goura are situated at altitudes of 730m and 480m, respectively and belong to the agro-ecological zone with a bi-modal rainfall regime, characterised by two dry (from December to February and from June to August) and two wet seasons (from March to May and from September to November). The soils are ferralitic, average (base saturation of 35%) to highly (base saturation of 20%) unsaturated. Barombi-Kang, altitude 180m, belongs to an agro-ecological zone with a mono-modal rainfall regime. Barombi-Kang is characterised by a highly humid and hot climate, with a long wet season (March to November) and short dry season (December to February).

The sites chosen were thought to be representative of the agro-ecological conditions suitable for optimal cocoa production. On these sites, many farmers were prepared to allow experiments in their cocoa fields. Experimental plots were selected on the basis of accessibility, size and maintenance of the farm. Cocoa plantations studied were about 15 years old at Barombi-Kang and Goura and over 25 years of age at Mbankomo. The site at Barombi-Kang had traditional cocoa varieties (Amelonado). There are hybrids cocoa varieties (Amelonado x Trinitario) at Mbankomo and mixed traditional and hybrids varieties at Goura. At each of the three plots, 100 trees were randomly distributed. The plot was surrounded with a phytosanitary barrier made up of two rows of cocoa trees, to prevent chemical treatments and pathogen spread from neighbouring farms. For the purpose of field observations, the observed trees were divided into three levels: 0-0.5 m (level 1), 0.5-1.50 m (level 2) and > 1.50 m (level 3). Inside the same plantation, the spacing among trees varied from 2.5 x 2.5 m to 3 x 3m, corresponding to tree densities of 1111 to 1600 cocoa trees ha -1 .

Data collection

Rotten pods (caused by Phytophthora sp., ROT), wilted fruit (early desiccation, WILT), fruit damaged by rodents (DAM), fruit infected by diseases other than Phytophthora pod rot (OD), cherelles (fruit ≤ 4 cm length, CHER), young pods (fruit > 4 cm length but not yet at adult stage, YP), adult pods (but not yet mature, AP), and healthy mature pods (MP) were counted weekly. These variables were chosen for weekly estimation of pod rot rate (Number of rotten pods / Number of all the pods).

At each site, a rain gauge (high: 150 mm) was installed in an open area and two thermometers were placed outside the plantation and under the cocoa tree canopy within the plantation, respectively. Rainfall (mm) and temperature (°C) data were collected daily.

Observations were made over a period of three years (1999)(2000)(2001). Disease status and production data were collected weekly from mid-April, when the first pods appeared on the trees, to the end of the production season (mid-November) each year. In total, there were around 30 weeks of data collection per site and per year. After each round of observation, rotten or wilted fruit, as well as fruits damaged by rodents and other diseases were harvested from trees and removed from the farms.

Based on the data collected, the pod rot incidence (PRR), mean temperature and total rainfall were calculated from the variables measured in the field.

The calculation method for the weekly pod rot incidence (PRR), was adapted from the formula used by Berry and Cilas (1994b) [START_REF] De | Exploitation des résultats de l'étude « épidémiologie » sur la pourriture brune[END_REF]. The losses due to PRR were estimated using the potential production:

where PRRi = Pod rot rate at the week i ROTi = number of rotten pods at the week i MPi = number of mature pods at the week i

The minimum surrounding temperatures (SMinT) and those under the cocoa trees canopy (UCMinT), and the maximal ones (SMaxT, UCMaxT), expressed in degrees Celsius, represent

100 * ) ( MPi ROTi ROTi PRRi  
respectively, the averages of minimal and maximal temperatures of the week (7 days). The mean temperatures (SMeanT, UCMeanT) are the averages of both weekly minimum and maximum temperatures. The daily thermal amplitude (Amp) was calculated, by taking the difference between maximum and minimum daily temperatures.

Similarly, total rainfall per week (RAIN) was the cumulative rainfall calculated from the daily rainfall.

Statistical analyses

For each derived variable, an analysis of variance (ANOVA) was done per site and per year.

The data for three years were pooled to test the site and year effects. Logarithmic or angular transformations were sometimes necessary, to meet the requirements of the general linear model, particularly the homogeneity of variances.

When the test associated to the ANOVAs (F-test) lead to rejection of the null hypothesis, the means were compared by contrasts [START_REF] Gomez | Statistical procedures for agricultural research 2 nd edition[END_REF][START_REF] Tomassone | Biométrie. Modélisation des phénomènes biologiques[END_REF].

Set of variables measured each year for 30 successive weeks (T), could be seen as chronological series, with week as the lag period unit, meaning that the sequence of measurements did not follow a random order. Auto-correlations of variables were estimated with the purpose of understanding disease progress over time, the autocorrelation being defined as the correlation calculated between a series and a lagged version of itself. If the correlation coefficient is calculated for all lags k=0,1,2...N-1 the resulting series is called the autocorrelation series or the correlogram. Cross-correlations were calculated for different lags to identify the lag which allows to maximise the correlation between rainfall and PRR incidence, i.e. to determine the number of weeks between rainfall and disease expression.

The autocorrelation coefficient ρ, of lag (or period) k was calculated, considering the T-1 pairs of observations (y1 , y2), (y2 , y3), …,(yT-1 , yT), in the following manner [START_REF] Box | Forcasting and control[END_REF][START_REF] Tomassone | Biométrie. Modélisation des phénomènes biologiques[END_REF][START_REF] Bourbonnais | Econométrie[END_REF] : y represents the mean of the series.

All auto-correlation coefficients (ρk) were calculated with a lag k -k varying from 1 to 4 weeks [START_REF] Bourbonnais | Econométrie[END_REF][START_REF] Quenouille | The joint distribution of serial correlation coefficients[END_REF][START_REF] Ljung | On a measure of lack of fit in time series model[END_REF].

Cross-correlations were computed to evaluate the link between pod rot rate and the environmental variables. The cross-correlation r of k's lag between two series xi and yi is defined as follows [START_REF] Bourke | Cross correlation[END_REF]:

Where i = 0, 1, 2,…T-1 in week; x represents the mean of a series xi and y is the mean of the series yi. Multiple regression analysis was done to find the most parsimonious model to predict pod rot rate. In order to suppress the auto-correlation present in the series relative to disease incidence (PRR), the difference between two time points was used for the analysis [START_REF] Kendall | Time-series[END_REF]). An angular transformation of the variable PRR (Arcsine PRR ) was used to ensure the homogeneity of variance which is a requirement of general linear model [START_REF] Draper | Applied regression analysis[END_REF].

          T t t k T t k t t k y y y y y y 1 1 )² ( ) )( (            i k i i i i k i i k y y x x y y x x r )² (( ² ) (
) )( ( These analyses were carried out per site and per year and subsequently per site with combined the data of the three years. Data were analysed using Statistica and SAS (SAS, 2001), with REG and GLM procedures.

Results

The evolution of temperature, quantity of rainfall, and PRR incidence was monitored during three years (Figures 1 to 3). Temperature is not presented because it was more or less constant within each site and within each of the three years.

Temperature and rainfall

In Mbankomo, 2001 was cooler than 1999 and 2000 (P < 0.05). The reverse was observed in Goura where 2001 was warmer than the two previous years. In Barombi-Kang annual temperatures were not significantly different (P>0.05) between years (Table 1). At the three sites, annual rainfall (in mm) varied among years. In Mbankomo and Barombi-Kang, significant differences (P<0.01) in rainfall observed in 1999 and 2000 was observed. In addition, the year 2001 was the wettest in these two locations. In Goura, rainfall varied significantly during the three years (P<0.001) (Table 1). Mbankomo was the site where the lowest temperatures were recorded for all years. The temperatures at Goura and Barombi-Kang were similar. Barombi-Kang was the site that had the greatest total quantity of rainfall during the three years, and Goura had the lowest, with rainfall below seasonal norms in 2001.

Difference of temperature and rainfall means between Mbankomo and Goura (though situated in the same agro-ecological zone) was the outstanding point in the observation of environmental variables.

Production and Phytophthora pod rot rate

The number of healthy pods per tree, for each site and each year is shown in Table 2: in Goura in 2000 (21.31 fruit/tree), in Barombi-Kang in 1999 (21.9 fruit/tree) and in 2000 (19 fruit/tree). This was a high number of healthy pods per tree as compared to the average national production of 10 fruit/tree.

In each site, pod rot incidence (PRR) was significantly different of over the three years (P<0.01). The highest and the lowest rates were recorded in 2001 in Barombi-Kang and in Goura, respectively (Table 2). For each year, the pod rot incidence (PRR) was significantly different between sites (P<0.05); Goura was significantly less attacked by pot rot disease than the others sites.

Temporal analysis

The results of simple auto-correlation of rainfall at the three sites during the three years are shown in Table 3. The correlations were very low (P>0.05). This is characteristic of a white noise process, meaning that the successive rainfall events were not dependant. Conversely, observations of the data presented in Table 4 (auto-correlations of PRR) showed that the successive pot rot rate were dependant, with a significant autocorrelation (P<0.05). Overall the values of autocorrelation decreased progressively when the lag increased. So, there was a null risk to reject wrongly the hypothesis of nullity of ρk coefficients; this indicates that the series is not a white noise process, with dependence between successive pod rot rates.

The cross-correlation method allowed for identification of important environmental variables (and associated lags) that affect PRR. Figures 4 to 6 represent cross-correlations coefficients between PRR and the rainfall. During rain, the disease did not produce symptoms immediately. Overall, the highest significant correlations were obtained with a week lag time (P<0.05). This result suggests a latent period of one week for the expression of the disease.

Cross-correlations results of year 2001 in Goura were not presented, because of the low level of Phytophthora pod rot at the experimental plantation observed during this season.

Relationship between environmental variables and incidence of the disease

The best results determined by model selection (R²) were obtained with the step-by-step method. Among all the environmental variables, only RAIN (with one week lag) contributed significantly to the PRR incidence. Table 4 presents the results of regressions that described PRR incidence as a function of quantity of rainfall per site and per year and subsequently per site using the pooled data from the three years. In Goura, only data from 1999 and 2000 were pooled, as pod rot rate was almost zero in 2001. These results always showed that quantity of rainfall had a highly significant effect on PRR incidence. However, the coefficients of determination (R²), representing the percentage of variability explained by the model, were relatively low for the analysis done per year and per site. The R² were improved when the data of different years were pooled for each site.

From equations presented in Table 5, the quantity of rainfall can be used to predict PRR incidence at a cocoa farm. For example, it was observed that to reach a weekly pod rot rate of 1%, more rainfall was needed in Mbankomo (48 mm) than in Goura (39 mm) (Table 6).

Discussion

One of the objectives of this study was to establish the relationships between Phytophthora pod rot and two environmental factors. The results clearly showed that disease increased with increasing quantity of rainfall . The highest PRR incidence occurred in 2003 at the Barombi-Kang (70.3%) and Mbankomo (64.76%) sites when quantity of rainfall was very high (> 2200 mm). In contrast, the lowest losses were obtained in Goura in 2001 (1.15%) when rainfall was low (751 mm). However, in this case, the production of healthy pods per tree was also low, probably meaning that the rainfall was not sufficient to induce good fructification. It is generally indicated that a minimum of 1000 -1200 mm of rainfall is required in a cocoa plantation to get a good yield [START_REF] Mossu | Le cacaoyer[END_REF]. The best cacao yield is obtained with an intermediate rainfall regime (1100 -2000mm).

To better understand the effects of environmental conditions on disease development, two types of analyses were done: cross-correlation analysis and multiple regression analysis.

Results of the cross-correlation analysis showed that there was a lag of one or two weeks between rainfall and disease expression. This may be the result of a incubation period, which is the period from fruit infection and the first disease symptoms. In the case of Phytophthora megakarya, this period lasts six days in cocoa trees [START_REF] Ward | The epidemy on sprayed cocoa at Gambary[END_REF]. From the multiple regression analysis, it was possible to determine that the rainfall regime was the best indicator of PRR incidence which allows to better disease prediction. Among the different sites, mean temperature variations, which were relatively constant over the year did not influence the development of the epidemic.

These results are in agreement with those reported by [START_REF] Ward | The epidemy on sprayed cocoa at Gambary[END_REF]. These authors attempted to model disease development in the field by taking into account the change in the number of total pods per tree over time, the latency period (p) and the duration of active sporulation zone on each fruit (i). Considering (p)=6 days and (i)=15 days, the authors discovered that disease incidence on day (d) was correlated to the cumulative number of healthy pods on day (d), to rainfall on day (d-3) and to the cumulative duration of sporulation on pod on day (d-5).

The long term objective of this study was to contribute to the elaboration of disease forecasting models for cocoa. For this pupose we need to apprehend a great environmental variation and it will be then necessary to collect data over many years

Figure captions Figure 1 :Figure 4 :Figure 5 :Figure 6 :

 captions1456 Figure captions

Table 1 :

 1 Mean temperatures and rainfall in each site(April -November 1999[START_REF] Bourbonnais | Econométrie[END_REF][START_REF] Rapilly | L'épidémiologie en pathologie végétale[END_REF] 1

			Surrounding temperature (°C)	Under cocoa trees temperature (°C)
		Sites	Year						Rainfall (mm)
			SMinT	SMaxT	SMeanT	UCMinT	UCMaxT	UCMeanT
			† 19.44 ± 0.18a 22.10 ± 0.23b 20.77 ± 0.20ab	18.21± 0.18a	21.16 ± 0.16a	19.69 ± 0.17a	1762 ± 15.02 b
		Mbanko-
		mo
		Barombi	22.67 ±0.11a	23.61± 0.20a	23.14± 0.12a	21.65± 0.09a	22.09± 0.20a	21.87± 0.11a	2003 ± 13.80b
		-	22.49 ±0.14a	23.54± 0.12a	23.02± 0.12a	20.64± 0.10a	22.51± 0.27a	21.56± 0.14a	1960 ± 11.83b
		Kang	22.11 ±0.11a	23.76± 0.11a	22.94± 0.09a	20.83± 0.11a	22.75± 0.28a	21.79± 0.18a	2873 ± 9.29a
	2	† Values are means ± standard error
	3	For each variable at a given site, values followed by the same letter are not significantly different with Newman-Keuls test at 5% level
	4
	5
	6
	7
	8

Table 2 : Mean pod rot rate and production in each site

 2 For each variable at a given site, values followed by the same letter are not significantly different with Newman-Keuls test at 5% level 3 1

	(April -November 1999, 2000, 2001)

Table 3 : Auto-correlations of rainfall at different sites (1999 -2001) 1

 3

				White noise
	Site	Year	Lag (week)	Correlation
				† (P value)
			1	0.07769
			2	0.03813
		1999		0.5880
			3	0.27777
			4	0.18834
			1	-0.03364
			2	-0.12438
	Mbankomo	2000		0.2403
			3	-0.17005
			4	0.31207
			1	0.33633
			2	0.20602
		2001		0.4040
			3	0.06774
			4	0.10049
			1	0.04657
			2	-0.02783
		1999		0.8672
			3	0.14162
			4	0.20364
			1	0.01838
	Goura
			2	-0.01026
		2000		0.9663
			3	0.07725
			4	-0.02992
			1	0.36892
		2001		0.5298
			2	0.12501

Table 4 : Auto-correlations of pod rot rate at different sites (1999 -2001) 1

 4

				White noise
	Site	Year	Lag (week)	Correlation
				(P value)
			1	0.38177
			2	0.39539
		1999		0.0007
			3	0.49067
			4	0.24886
			1	0.81794
			2	0.68899
	Mbankomo	2000		<0.0001
			3	0.51443
			4	0.35122
			1	0.69931
			2	0.33266
		2001		<0.0001
			3	0.14526
			4	-0.07983
			1	0.73008
			2	0.52308
		1999		<0.0001
			3	0.32898
			4	0.20190
			1	0.45732
	Goura
			2	0.48730
		2000		0.0052
			3	0.34699
			4	0.02463
			1	0.39230
		2001		0.0174
			2	0.08095

Table 6 :

 6 Rainfall (mm) necessary to start a weekly pod rot rate of 1% per year in different sites (estimations based on the equations of Table4)

	Sites

Acknowledgments

Financial assistance from the FAC project (Fond d'Aide et de Coopération), set up by the French Ministry of Cooperation and the Government of Cameroon, is acknowledged. Sincere thanks are expressed to the staff of the Plant Pathology Laboratory at the Institute of Agricultural Research for Development, Cameroon (E. Bouambi, N. Bindzi, Late T. Simo, N. Essomo), who carried out the field trials. The authors also thank their colleagues (A. Kameni and M. Hoopen) who critically reviewed the manuscript.