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Black pod rot, caused by several species of Phytophthora, is responsible for greater losses than any other disease affecting cacao. Breeders use various approaches to screen material for resistance to Phytophthora spp., however, the method used to assess disease reaction can influence outcomes. To determine how screening methods affect results, disease reactions of four cacao clones (BE 10, HY 271419, RIM 15 [MEX], and EET 236 [ECU]) were compared using incidence under field conditions, and lesion area following artificial inoculation. Disease incidence differed significantly among clones (p < 0.0007), ranging from 6.1% for BE 10 to 24.0% for HY 271419. Differences among clones were also detected based on lesion area (p < 0.032), however, their relative ranking differed: BE 10 (53.9 cm2), HY 271419 (80.64 cm2), RIM 15 [MEX] (95.7 cm2), and EET 236 [ECU] (102.4 cm2). These apparent differences observed in disease reaction among clones when comparing methods may be due to interactions with environmental conditions or differences in the pathogen species/isolates present. The improved understanding of the how screening methods used can affect the disease reaction determination and breeding outcomes in cacao germplasm will benefit breeders and farmers. |
