Genetic control, combining ability and heritability of resistance to stem canker in cacao (Theobroma cacao L.)

Stem canker caused by Phytophthora palmivora and Phytophthora megakarya is a serious disease of cacao ( Theobroma cacao L.). Studies of the genetics of resistance to this disease is important to identify an effective procedure to use in breeding resistant varieties. The objective of this study was to determine mode of inheritance, combining ability and heritability of resistance to stem canker in cacao. A 6 × 6 full diallel mating design was used to generate 36 F1 hybrids which were evaluated for resistance to stem canker with three replications under artificial inoculation with 1 mm 2 agar plug taken from actively growing colonies of 10-day old cultures of P. palmivora and P. megakarya . Twelve months later, the canker lesions on outer bark of the stem of the seedlings were measured and the canker lesions inside was also measured after scraping the bark. There were significant (p