AN IN VITRO BIOASSAY TO EVALUATE SWEET CHERRY RESPONSE TO INOCULATION WITH PSEUDOMONAS SYRINGAE PV. SYRINGAE

An excised leaf bioassay from sweet cherry tissue culture plantlets was developed to test for a necrotic response to inoculation with Pseudomonas syringae pv. syringae. The four treatments in this bioassay included a water control, a low virulence 10⁸cfu/ml P. syringae inoculation, and a 10⁶ or a 10⁸cfu/ml mixed pathogenic treatment. Leaves were inoculated and then incubated for 7 days. Evaluation of the necrotic response used a rating scale of 0 to 4 with 0 denoting necrosis surrounding the wound site only and 4 denoting necrosis of the entire leaf. None of the evaluated genotypes exhibited any necrosis when inoculated with the water control, yet a few genotypes exhibited negligible necrosis when inoculated with a low virulence strain, JL2000. Several of the genotypes tested had necrotic responses statistically the same as the susceptible control (‘Corum’) when inoculated with either mixed pathogenic treatment. Weiroot genotypes had a high necrotic rating, Pi-KU and Giessen/GiSelA genotypes had variable ratings, and Mazzard x Mahaleb (MxM) genotypes had very low necrotic ratings.