Malus germplasm varies in resistance or tolerance to apple replant disease in a mixture of New York orchard soils.

摘要

Forty apple seedling lots and 17 clonal accessions, representing 941 genotypes and 19 species or interspecific hybrids of Malus, were evaluated for resistance or tolerance to apple replant disease (ARD) in a mixture of 5 New York soils with known replant problems. Total plant biomass, root necrosis, root-infesting fungi, and root-lesion nematode (RLN; Pratylenchus penetrans) or dagger nematode (DN; Xiphinema americanum) populations were evaluated in apple seedlings and clones grown for～60 days inthe composite soil. In addition to phytophagous nematodes, various Pythium, Cylindrocarpon, Fusarium, Rhizoctonia and Phytophthora species were isolated from roots grown in the test soil. Plant growth response was categorized by a relative biomass index(RBI), calculated as total plant dry weight in the pasteurized field soil (PS) minus that in an unpasteurized field soil (FS), divided by PS. Nematode reproduction on each genotype was defined by a relative reproduction index (RRI), calculated as final nematode populations in roots and soil (Pf) minus initial soil populations (Pi), divided by Pi. The RBI, RRI, and other responses of accessions to ARD soil were used to rate their resistance, tolerance or susceptibility to apple replant disease. None of the accessions was completely resistant to ARD pathogens in the test soil. Seedling accessions of M. sieversii and M. kirghisorum appeared to have some tolerance to ARD, based upon their low RRIs and RBIs. Three clonal rootstock accessions (G.65, CG.6210and G.30) and 4 other clones (M. baccata 1883.h, M. xanthocarpa Xan, M. spectabilis PI589404 and M. mandshurica 364.s) were categorized as tolerant to ARD. The disease response of other accessions was rated as susceptible or too variable to classify. Itis concluded that sources of genetic tolerance to ARD exist in Malus germplasm collections and could be used in breeding and selecting clonal rootstocks for improved control of orchard replant pathogens.