Location: Subtropical Horticulture Research
Project Number: 6631-21000-023-08
Start Date: Sep 01, 2013
End Date: Sep 30, 2015
Cacao production is plagued by very serious losses globally from diseases. BP, WB, FP, VSD and Ceratocystis have produced a significant decrease in cacao production worldwide. Five species of Phytophthora are the cause of BP disease causing severe losses around the world. In the Americas the cacao industry has undergone a severe production decline due to losses principally to BP, WB, and FP. For instance, in Brazil, the cacao industry was devastated by WB in the 1990s. This aggressive disease reduced Bahia’s cacao production from over 405,000 metric tons in 1986 to less than 130,000 metric tons in 1998. FP has caused serious losses in Ecuador, Peru, Bolivia, Colombia, and Central America. It has been estimated that up to 80% of the pods on some farms in Ecuador and Colombia are lost due to FP. WB and FP are not yet found in West Africa or South Asia. VSD is the cause of major production losses in South Asia and has not been found in the Americas yet. Currently, the most widely grown commercial cultivars in West Africa, which produce ~70% of the world’s cocoa, are susceptible to WB and FP. Thus uniform phenotypic disease data are crucial for obtaining precision in the results of marker association studies. If we do not have uniform phenotypic disease data, to use together with the sequence data from two cacao genomes, our marker association project results will lack the necessary precision to accomplish our primary goals which are: the development of cacao cultivars utilizing the new molecular genetic tools to increase the efficiency of the selection process, and to identify quantitative trait loci (QTL) for anthracnose resistance in mango, and resistance to Phytophthora root rot (PRR) and laurel wilt in avocado. Due to the non-uniformity of screening methodologies used, there are currently in the literature conflicting reports regarding the location of QTLs associated with BP. Resistance to BP has been evaluated in the field using percent pod rot and using the leaf disk inoculation method; however, only a weak correlation exists between the two methods of measuring resistance. Furthermore, different QTL were detected with each of the two methods, indicating perhaps different mechanisms of resistance or low repeatability of the assay. Therefore, a standardized, reliable and reproducible assay must be identified soon. Without such an assay, molecular markers that are used currently in the cacao breeding program may be uninormative.