Evaluation of Host Suitability in Prunus for Criconemella xenoplax

Methods were developed for screening Prunus selections for host suitability to Criconemella xenoplax. The relative host suitability of selections was based upon a doubling accumulation value (beta) that was defined as the number of degree-days (base 9 C) required for doubling of an increment of the initial nematode population. The beta value characteristic for C. xenoplax (139 +/- 8 degree-days) on suitable hosts was similar to the average beta value determined for several peach rootstocks known to be suitable hosts. The beta values were 144 +/- 21 for Halford, 141 +/- 16 for Lovell, and 138 +/- 10 for Nemaguard. A higher value for beta could indicate poorer host suitability or resistance of a selection to C. xenoplax. All of 369 Prunus accessions tested, including eight accessions that had survived well on a field site infested with C. xenoplax, were suitable hosts. Apparently, resistance to C. xenoplax was not a factor in survival of the accessions planted in the field. Seedlings from P. besseyi, P. pumila 'Mando', and two interspecific hybrids, Redcoat and Sapalta IR 549-1, failed to support nematode population increase in 44-81% of tests conducted, but all selections supported population increase in some tests. These accessions may have resistance mechanisms that are active only under specific conditions.