| Summary: | 博士 === 中興大學 === 植物病理學系所 === 94 === A total of 396 rhizobacterial strains isolated from different crops in central Taiwan were screened by a petri dish-blotter paper system and then by a peat moss-plug system in growth chamber for their effects on tomato growth following seed bacterization (seed coating). Fourteen strains consistently increased the seed germination and root length, among which, strains RS4, RS65, and RS70 performed best. These three strains significantly increased not only root length, but also stem length, plant fresh weight and dry weight (except strain RS65). In a commercial nursery using the peat moss-plug system, these three strains also showed their ability to promote seedling growth following either seed bacterization or peat moss drenching, and their populations in peat moss maintained at high levels (except strain RS65 for 30 min seed soaking ) within 21 days after seeding. The above 14 strains that were capable of promoting tomato growth were tested for their ability to control bacterial wilt of tomato. Among these 11 strains did not inhibit the growth of Ralstonia solanacearum PS152 on three media tested, but 9 strains significantly reduced the disease severity of bacterial wilt in growth chamber and greenhouse tests. Strains RS4, RS65, and RS70 which were better in the ability to promote tomato growth also performed better in the efficiency of disease control. Strain RS4 was identified as Chryseobacterium sp. and strains RS65 and RS70 as Streptomyces spp. The disease control mechanism might be related to the induce systemic resistance, because the severity of bacterial wilt was significantly reduced when top leaves of tomato were syringe-infiltrated with Streptomyces sp. RS70 and 7 days later roots were challenge-inoculated by drenching with R. solanacearum PS152. The induction of effective resistance required at least six days after leaf treatment with RS70. However, the induced resistance persisted only for several days. RS70 treatment could induce PR-1 gene expression in noninoculated leaves, and in a 10-day test period, the quantity of PR-1 mRNA increased over with time, reaching highest at the 8th day and then slightly decreased. Accumulation of PR-1 mRNA in noninoculated leaves was observed not only by leaf treatment but also by root treatment with RS70, indicating that the signal for PR-1 gene expression induced by RS70 may transport downward and upward from the inoculated site. The effectiveness of strains RS4, RS65, and RS70 for increasing yield of tomato was conducted in greenhouse and field. In greenhouse summer crop, these three strains enhanced the early growth, increased yield ( except for strain RS70) and single fruit weight, and reduced culls ratio. Analyses of nutrient content (N, P, K, Ca, Mg) of leaves at growing and harvest stage showed that the three strains differed in the ability to enhance the plant to absorb the nutrients, however, the variation in the nutrient content of leaves was not related to the yield of fruits. In greenhouse fall crop, only strain RS4 enhanced the early growth and increased yield, but these three strains also increased single fruit weight. Analyses of nutrient content of fruits showed that Ca and Mg in the three strains treatments, P and K in RS70-treated and N in RS4- and RS70-treated plants had higher concentrations than untreated controls. In the field test, these three strains applied by root-dip or soil-drench increased the yield and number of marketable fruits and reduced the yield (except for strain RS4 in soil-drench treatment) and number of culls. They also improved fruit quality except for a few treatments. Treatments with these three strains generally have higher concentrations of N, P, K, Ca and Mg in leaves and fruits at harvest stage than those of untreated controls. Populations of the three strains on tomato roots declined with plant growth, and varied with strains.
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