Infectivity Titrations of Pseudomonas solanacearum on Tomato

Abstract

The dose of Pseudomonas solanacearum was controlled by injecting various amounts of bacteria directly into the plant. Ten varieties of tomato (30 days old) were injected with 6 levels of Pseudomonas solanacearum (10³-10⁸ cfu/ml) by a micropipette containing 0.1 ml (100 µl ). Each inoculum was inserted diagonally into stem at the third leaf axil from the top. Finally the total number of bacteria in each plant was 10²-10⁷ cfu/ml. Disease index rating were recorded daily for 3 weeks. The results indicated that the varieties 245,373,390 and TK-70 were susceptible (S). Most of them had ED50 value around 10²-10⁴ cfu/plant. On the opposite variety 285 was resistant (R). The varieties 8, 15 and 366 were moderately resistant (MR) to moderately susceptible (MS). The degree of resistance of variety 95 in correlated to the concentration of the inoculum. At low concentrations of bacteria, this variety showed resistant but became more susceptible rapidly when the concentration of bacteria increased. On the other hand, the variety 96 had little or no correlation between the concentration of bacteria and % wilt. This experiment showed that Micropipette technique was highly accurate in evaluating bacteria wilt resistance since it could determine the effect of dose on the degree of wilt in each tomato variety. This technique was recommended for intensive work.