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PLANT GENETIC RESOURCES

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

Centro de Investigación Científica de Yucatán (CICY), Calle 43 No. 130, Col. Chuburná de Hidalgo, 97200 Mérida, Yucatán, México

^* Corresponding author (zizumbo{at}cicy.mx)

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; H_T = 0.34 ± 0.02) similar to that of the populations imported from the world's main gene pools (pl = 94; H_T = 0.36 ± 0.01). Both molecular variance and Wright's index of differentiation indicated strong differentiation among Mexican ecotypes (F_ST = 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.

Abbreviations: AFLP, Amplified fragment length polymorphism • AMOVA, analysis of molecular variance • ANOVA, one-way analysis of variance • D, genetic distance • F_ST, Wright index of population differentiation • H_E, expected heterozygosity • H_S, intrapopulation heterozygosity • H_T, total heterozygosity • HW, Hardy-Weinberg equilibrium • I, genetic identity • ISSR, Inter simple sequence repeat • ITSR, Inverse sequence-tagget repeat • pl, percentage of polymorphic loci • LY, Lethal Yellowing disease • MXAT, Mexican Atlantic Tall • MXPT, Mexican Pacific Tall • MYD, Malayan Yellow Dwarf • NJ, Neighbor-Joining analysis • Nm, number of migrants • PNT, Panama Tall • RAPD, Random amplified polimorphism • RFLP, Restriction fragment length polymorphism • RIT, Rennell Island Tall • SSR, Simple Sequence Repeat • TAT, Tahiti Island Tall • UPGMA, un-weighted pair group method with arithmetic mean • WAT, West African Tall