Population Genetics, Lethal Yellowing Disease, and Relationships among Mexican and Imported Coconut Ecotypes

Abstract

Lethal Yellowing (LY) is one the main diseases affecting coconut worldwide, making the research for resistant germplasm vital to production. Study objectives were to: (i) estimate diversity and genetic structure within four commercial Mexican ecotypes and five imported ecotypes; (ii) analyze the genetic relationships between Mexican ecotypes and the main coconut gene pools identified worldwide; and (iii) measure the correlation between the genetic distance among these ecotypes and Malayan Yellow Dwarf and their percentage mortality due to LY. The Mexican pool had high genetic diversity (pl = 94; HT = 0.34 ± 0.02) similar to that of the populations imported from the world's main gene pools (pl = 94; HT = 0.36 ± 0.01). Both molecular variance and Wright's index of differentiation indicated strong differentiation among Mexican ecotypes (FST = 0.32) despite significant gene flow (Nm = 1.4 to 5.6). UPGMA analysis and exact tests of differentiation suggested that the Indo‐African gene pool is found along the Caribbean and Gulf of Mexico coasts, while the Asian‐Pacific pool is found on the Pacific coast. High positive correlations were found between genetic distance and LY mortality percentages under severe incidence conditions during 9‐ and 14‐yr periods (r2 = 0.80; P = 0.02; r2 = 0.78; P = 0.04), suggesting that genetic distance may be useful for the estimation of the potential LY mortality in regions as yet unaffected and identification of potential parents for LY resistance breeding.