<![CDATA[This study aimed to evaluate the potential of three Streptomyces spp. isolates obtained from the rhizosphere of Avicennia marina at the Mangrove Botanical Garden, Surabaya, for suppressing bacterial leaf blight (BLB) development under in vivo conditions and assessing their effects on plant growth. In a previous study, the three Streptomyces spp. isolates (St8, St9, and St19) demonstrated strong inhibitory activity in in vitro assays. The present study was conducted using a factorial Completely Randomized Design (CRD), with the first factor consisting of Streptomyces spp. isolates (St8, St9, and St19) and the second factor consisting of biological agent suspension doses (5, 10, and 15 ml plant⁻¹). A diseased control treatment was included for comparison. Each treatment was replicated three times, resulting in a total of 30 experimental units. The collected data were analyzed using analysis of variance (ANOVA) with IBM SPSS Statistics 24 software at a 5% significance level. The in vivo efficacy assay showed that the application of Streptomyces spp. isolate St19 at a dose of 5 ml plant⁻¹ only delayed the incubation period of X. oryzae by 1.1 days and was unable to suppress BLB disease severity. The same treatment significantly affected rice tiller number, reaching 13.6 tillers at 56 days after transplanting (DAT), but did not affect plant height throughout the observation period. The results indicate a discrepancy between the in vitro and in vivo assay outcomes. The potential of the tested Streptomyces spp. isolates as biological control agents remains limited; however, they showed a significant effect on rice tiller development.]]>
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