Infectivity of Psyringae pv. lachrymans to cucurbits as affected by gibberellic and/or salicylic acids

摘要

Cucumber plantations in the open fields of different Minia regions showed angular leaf spot symptoms. Seven infective bacteria! isolates were isolated and identified as Pseudomonas syn'ngae pv. lachrymans. Virulence of bacterium was varied with isolates and inoculation methods. The highest pathogenic isolate was PS4 while PS3 reacted as the weakest one. Leaf inoculation showed the highest severity (52.2 percent) of angular leaf spot followed by cotyledons inoculation (20.6 percent), while seed infestation showed the lowest severity (15.7 percent). Efficiency of salicylic acid (SA) to enhance resistance in cucumber plants was varied with application methods. Seed soaking for 12 h in SA solution before planting gave the greatest resistance against P. syringae pv. lachrymans infection as compared by leaf spraying and cotyledon injection. In contrast, gibberellic acid (GA3) increased cucumber susceptibility to P. syringae pv. lachrymans infection specially at 50 and 100 ppm. Other cucurbits variouslyreacted to infection and AS and/or GA3. Melon plants cv. Kahera 6 showed the least severity while watermelon plants cv. Giza 1 was the most susceptible to infection. Melon plants showed no effect for SA towards infection. SA increased resistance in watermelon plants against P. syringae pv. lachrymans and GA3 enhance the susceptibility. In addition, SA decreased the bacterial population in infected cucumber leaves while GA3 showed the opposite effect.