Identification in saudi arabia of pseudomonas corrugata the tomato pith necrosis pathogen and assessment of cultivar resistance and seed treatment

Y.Y. Molan, Y.E. Ibrahim, A.A. Al-Masrahi
doi: 10.4454/jpp.v92i1.32
Tomato pith necrosis disease was observed on tomato plants grown in the AL-Kharj region of Saudi Arabia. Symptoms were yellowing and wilting of lower leaves, brown areas on stems and yellowish-brown discoloration of the pith. Three bacterial strains were isolated from the stems of tomato cv. Red Gold. These strains were identified as Pseudomonas corrugata based on morphological, physiological, biochemical, and pathogenicity tests, as well as Biolog analysis. Seven commercial tomato cultivars were evaluated for resistance to P. corrugata. Of these cultivars, Alambra was the only cultivar tested that was considered resistant, Antinea was partially resistant, Agora, Farah and JV15 were susceptible whereas Newton and Red Gold were highly susceptible. Chemical seed treatments were evaluated for efficacy of disinfestation of tomato seed that had been inoculated with P. corrugata. Bacteria were not detected when seeds were treated with 5% hydrogen peroxide for 5 or 15 min. Treatment of seed with 0.52% sodium hypochlorite for 5 and 15 min was relatively ineffective. When sodium hypochlorite was used at a 1% concentration for 15 min, the level of bacterial infestation was reduced by 92%. Hydrogen peroxide treatments at a 5% concentration reduced seed germination up to 11.4% compared with controls. However, no significant differences in seed germination were observed between control treatments (inoculated and non-inoculated seeds and non-treated seed) and any of the other chemical seed treatments when seeds were sown in sterilized soil in the greenhouse. Effective management strategies for pith necrosis caused by P. corrugata should include planting of a resistant cultivar, where feasible, and seed treatment with hydrogen peroxide (5% for 15 min) or sodium hypochlorite (1% for15 min).