Map Based Phylogenies, Linkage Disequilibrium and Association Mapping for Fruit Traits in Melon

Melon has tremendous fruit diversity, which is the product of complex interactions of consumer preferences of different countries and a wide range of agro-climatic zones. Understanding footprints of divergence underlying formation of various morphotypes is important to develop sustainable and high quality melons. Basic understanding of population structure and linkage disequilibrium (LD) is limited in melon and has lagged behind when compared to the other crops. Characterization of population structure and LD are essential for carrying out association mapping of QTLs underlying various complex traits. Mapped single locus microsatellite markers are known to be very valuable to resolve population structure and 268 of such markers were used in the current study to resolve population structure and LD pattern using 87 accessions of melons belonging to Eastern European, Euro-North American and Asian types. Mixed linear model (MLM) was implemented to detect QTLs for various fruit traits. Various levels of QTLs with high to moderate stringency were detected for fruit shape, fruit weight, soluble solids, and rind pressure and a majority of them found to be tallied with the previously published indicating that the association mapping can be very useful for melon molecular breeding. Minor discrepancies in the position, strength and the variation absorbed by the QTLs present between the methods of association and recombinant mapping approaches can be bridged if more melon groups and larger sets of accessions are involved in future studies combined with highthroughput marker panels.