Genetic Analyses of Root-knot Nematode (Meloidogyne floridensis) Resistance in _Flordaguard' Peach Rootstock

The peach (Prunus persica) cultivar ‘Flordaguard’ is the predominant rootstock for peach production in Florida.  It is effective as a rootstock due to its low-chill requirement and ability to withstand infection by the endemic peach root-knot nematode (RKN), Meloidogyne floridensis (Mf). The RMia gene present in  the rootstocks ‘Nemared,’ ‘Nemaguard,’ and ‘Okinawa’ rootstocks does not confer resistance to M. floridensis.  A source of broad spectrum and dominant resistance against the major RKN including Mf was found in Myrobalan plum P.2175 (Prunus cerasifera) and  Japanese plum J.222 (Prunus salicina) carrying the Ma and Rjap genes, respectively.  However, these resistances cannot be readily incorporated into Southeastern US breeding programs due to these plums’ susceptiblity to peach tree short life, Armillaria root rot, and plum leaf scald.  In this study, we examine the genetic basis of resistance in ‘Flordaguard’ with the goal of identifying markers associated with nematode resistance.  We hypothesize that the resistance in ‘Flordaguard’ may be controlled by a recessive allele and that the wild peach, Prunus kansuensis, may have a resistance gene allelic to that found in ‘Flordaguard.’  To infer the allelic composition in ‘Flordaguard,’ F2 and BC1F1 populations were generated from crosses made between the resistant (‘Flordaguard’ or P. kansuensis) and susceptible (‘Okinawa,’ ‘UFSharp,’ and ‘Tardy Nonpareil’) cultivars. Parental polymorphism was measured using an initial set of 30 SSR markers evenly distributed throughout the eight linkage groups based on the Prunus (interspecific ‘Texas’ almond x ‘Early gold’ peach) reference map available from the Genome Database for Rosaceae.  The populations were genotyped using the polymorphic SSR markers.  The segregating progenies are being evaluated for Mf resistance to identify associations between the polymorphic SSR markers and the resistance phenotype.  The information obtained in this study will clarify the inheritance of the nematode resistance phenotype of ‘Flordaguard’ and will indicate if it is allelic to nematode resistance genes in other Prunus rootstocks.