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Perfecting a simplified method for assessing cacao productivity

Tahi G.M., N'Goran J.A.K., Sounigo O., Lachenaud P., Eskes A.. 2009. In : Eskes Albertus (ed.), Efron Yoel (ed.), End M.J. (ed.), Bekele Frances L. (ed.). Proceedings of the international workshop on cocoa breeding for farmers' needs, 15th - 17th October 2006, San José, Costa Rica. Reading : INGENIC, p. 156-156. International Workshop on Cocoa Breeding for Farmers¿ Needs. 5, 2006-10-15/2006-10-17, San José (Costa Rica).

Productivity is a primordial selection criterion for new varieties of cocoa. Evaluation at the research station by the usual methods is restrictive and requires a lot of work. The aim of this work was to evaluate the efficiency of simple methods which are applicable to cocoa selection. To do this, the "classical" method of harvesting from individual trees (based on counting and weighing fruits on a monthly basis) has been compared with counting and visually scoring, on a scale of 0 to 5, of the quantity of fruits on the tree before the main harvest and before the mid-crop during two agricultural years (Septemeber 2002 to June 2004). The number of peduncles and fruit-bearing cushions were also counted and visually scored at the end of the one campaign (June 2003). Black pod infection level was estimated with the same methods as applied for pod yield during one harvesting campaign (2003/04). Highly significant correlations have been established between the first three methods to assess pod yield (i.e. "classical" method, counting and scoring the number of fruits). The use of counting and especially scoring the pod load before the main harvesting periods would make it possible to significantly reduce staff requirements and to still be able to obtain good quality information, useful for selection of individual trees and hybrid families. Counting and scoring of rotten pods before harvest campaigns seemed to be informative for the actual degree of infection during the harvest campaign, especially at the level of mean family values. On the other hand, the simplified method is less well correlated with the cumulated degree of infection over several years. The counting and scoring of active flower cushions at the end of the mid crop (Methods 4 and 5) appeared also to be promising for estimating average family pod production for the same harvesting campaign and for cumulated pod production (r = 0.78 to 0.89). However, the correlation at individual tree level was much lower (r = 0.49 to 0.61). This would suggest that the error variance at individual tree level for scoring of active flower cushions is larger than for family means. The results suggest that simplified methods can be efficient in the evaluation of relative pod production, as well as for the estimation of the proportion of diseased pods (in our case this was Phytophthora, but the same may apply to other diseases such as monilia and witches' broom). This would allow for savings of up to 80% of time and of financial resources to select new varieties in hybrid or clone trials, or to select promising trees within segregating populations. The use of simple and cost-efficient methods will be especially of interest in the evaluation of trials established at distant sites (such as on-farm trials), for which it is very difficult to collect yield data at monthly intervals. (Texte integral)

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