Heritability of the tolerance to Phytophthora megakarya Bras. and Grif. of Theobroma cacao L. in terms of their necrosis length, phenolic contents and activity of enzymes
By: Manga Ndjaga Jude, Effa Onomo Pierre, Ondobo Martine Louise, Djoko Kouam Jules Christian, Djocgoue Pierre François
Key Words: Theobroma cacao, Phytophthora megakarya, heterosis, heritability, tolerance.
Int. J. Biosci. 8(5), 249-261, May 2016.
Plant breeding through selected biochemical markers requires the genetic amelioration programs. Therefore, this study focused on the heritability of the necrosis length, phenolic contents and activity of enzymes during Theobroma cacao/Phytophthora megakarya interactions. Length of necrosis were measured after leaves infection by Phytophthora megakarya in 20 genotypes of Theobroma cacao L. derived from intercrossing of T79/467 and ICS40 parental clones. Total polyphenols (TPP), total flavonoids (TF) and variation in peroxidase (POX), polyphenoloxidase (PPO) and phenylalanine ammonialyase (PAL) activities in imparting tolerance to P. megakarya were estimated according to standard methods. The outcome showed heterosis linked to length of necrosis manifest a hybrid vigor (90% for 2013, 85% for 2014 and 80% for 2015). The F90.34, F90.35 and F95.36 genotypes showed a significant increase (P˂0.05) of biochemical components correlated with tolerance rates and this increase was genotype-dependent. Principal component analysis (PCA) and hierarchical classification displayed two clusters where the first categorized 17 tolerant individuals and the second five susceptible ones. Heritability of the necrosis [narrow sense heritability (h²: 0.231 for F90 and 0.243 for F95) and broad-sense heritability (H²: 0.291 for F90 and 0.336 for F95)] and the metabolites studied from the two reciprocal crossings didn’t show any significant difference implying the absence of maternal effect in the transmission of these characters.