AN INTEGRATED GENETIC-LINKAGE MAP OF AVOCADO

An avocado genomic library was screened with various microsatellite re peats. (A/T)(n) and (TC/AG)(n) sequences were found to be the most fre quent repeats. One hundred and seventy-two positive clones were sequen ced successfully of which 113 were found to contain simple sequence re peats (SSR). Polymerase chain reaction primers were designed to the re gions flanking the SSR in 62 clones. A GenBank search of avocado DNA s equences revealed 1 sequence containing a (CT)(10) repeat. A total of 92 avocado-specific SSR markers were screened for polymorphism using 5 0 offspring of a cross between the avocado cultivars 'Pinkerton' and ' Ettinger'. Both are standard avocado cultivars which are normally outc rossed and highly heterozygous. Fifty polymorphic SSR loci, 17 random amplified polymorphic DNA (RAPD) and 23 minisatellite DNA Fingerprint (DFP) bands were used to construct the avocado genetic map. The result ing data were analyzed with various mapping programs in order to asses s which program best accommodated data from progeny of heterozygous pa rents. The analyses resulted in 12 linkage groups with 34 markers (25 SSRs, 3 RAPDs and 6 DFP bands) covering 352.6 cM. This initial map can serve as a basis for developing a detailed genomic map and for detect ion of linkage between markers and quantitative trait loci.