Identification of Haploid Seedlings In Low Chill Peach Germplasm

Peach is one of a few tree species capable of generating haploids.  Haploidy represents an important tool for the rapid generation of homozygous genotypes in peach breeding programs.  The potential impact is even greater in the case of peach rootstocks where it takes multiple generations to develop inbred lines that come true to seed. Spontaneous peach haploids are generated at a low frequency and have been reported previously.  All peach haploids available at the National Clonal Germplasm Repository for Fruit and Nut Crops were derived from high chill germplasm, and are of limited utility in our breeding program.  We have initiated an effort to identify and collect a panel of low chill haploids to determine the feasibility of using them in our rootstock breeding program.  Putative haploids were identified either as twin seedlings i.e. hemitwin embryos contained within a common seed coat, or by their reduced growth and narrow leaf phenotype.  An initial search of seedling populations identified 3 putative haploid seedlings belonging to 3 different low chill parents.  Two of the parents represented peach scion germplasm.   The third parent was an interspecific Prunus persica x P. kansuensis F1 hybrid used in rootstock breeding.   Flow cytometry was used to measure the nuclear DNA content and confirm the haploid status of the seedlings.  Microsatellite marker analysis with  37 SSR markers distributed evenly across the peach genome revealed that 2 of the 3 seedlings had a single SSR allele at all the SSR loci.