Populations of Pseudomonas glumae on Rice Plants.

Abstract

The populations of Pseudomonas glumae on rice leaf blades and rice leaf sheaths were studied. When rice plants were inoculated by spray application of bacterial suspension at 27 days before heading time, the pathogen was recovered from the inoculated rice leaf blades only immediately after inoculation, but was recovered from the inoculated leaf sheaths regardless of the sampling time. Moreover, when rice plants were inoculated by spray application of the bacterial suspension at 22 days before heading time, P. glumae was recovered from all the inoculated leaf sheaths, the succeeding leaf sheaths which had not emerged at the time of inoculation and 1 of 3 flag leaf sheaths at 3 days after heading time. Population level of the bacterium on inoculated leaf sheaths and the succeeding leaf sheaths was about 106cfu/g (fresh weight of leaf sheath) regardless of inoculum densities, but was about 103cfu/g on flag leaf sheaths. P. glumae was recovered from 13 of 14 top leaf sheaths at 13 days before heading time when inoculated at the 6th leaf stage, 31 days before heading time. Thereafter, P. glumae was recovered from all the 3rd leaf sheaths under the flag leaf, 2 of 9 flag leaf sheaths and one panicle within 2 flag leaf sheaths on which the bacterium was detected at 2 days before heading time. The population level of P. glumae on the leaf sheaths and panicles was less than 106cfu/g and it was suggested that the bacterial populations were lognormally distributed. P. glumae was recovered at each sampling time from all the leaf sheaths of the rice plants inoculated with 107cfu/ml of the bacterial suspension at 41 days before heading time, but the frequency of recovery of P. glumae from leaf sheaths of rice plants inoculated with 105 or 103cfu/ml was low. These results suggest that bacteria reproducing in the lower to the upper leaf sheaths play an important role in the outbreak of bacterial grain rot of rice.