Kegunaan pseudomonas species sebagai agen kawalan biolo gi bipolaris maydis penyebab penyakit hawar daun jagung selatan

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Date
1993-12
Authors
Mohamed Masthan Ghani, Seeni
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Abstract
Of the two hundred and fourty eight bacterial isolates from soi 1 and the maize phyllopl ane tested in in vitro, 67.2% of fluorescent pseudomonad and 66.2% nonfluorescent pseudomonad were inhibitory to radial growth of Bipolaris maydis on at least one of the media types used. Isolates from the phylloplane inhibited growth of B. maydis by 72.6% compared to soil isolates which inhibited in the region of 64.6%. Twenty-eight isolates (20 fluorescent and 8 nonfluorescent isolates) from 106 isolates tested in planta were found to effectively control this disease giving a disease rating of below 2 as compared to a rating of 5 for control plants. The seven best isolates were selected for further studied in vitro and in planta are strain P0402, P0904, PJ0205, PJ0210 and PJ0304 which were identified as Pseudomonas fluorescens and K0801 and NJ0104 which were identified as P. putida. A number of tests in agar media, cavity slides, acetone extraction, the addition of nutrients in vitro or in planta and the use of siderophore negative mutant have shown that competition for nutrients and not antibiosis was involved in the inhibition of B. maydis growth. i i i 1 ~ general, control of SCLB by the 7 isolates decreased when t~e concentration of B. maydis spores increased whereas, the • reverse occurred when the concentration of bacterial antagonists increased with a fixed concentration of 8/' :·~- maydis. The antagonists that were tested were able to colonize and survive on the maize leaves and also able' to reduce disease up to 15 days after initial application in the plant house. Histopathological studies demonstrated that 8. maydis spores were able to germinate, g,row and penetrate leaf tissue either through appresorial formation or directly through stomata to initiate infection. The additional of antagonists together with 8. maydis spores on the maize leaf also reduced the rate of B. maydis growth and subsequent infection. Strain PJ0210 gave a better control of SCLB compared to P0904 at a mini-field study. A. rifampicin resistant mutant of PJ0210 and P0904 were reisolated from maize leaves up to 25 and 15 days respectively, after the initial application. The number of mutant PJ0210 cells which be reisolated from rnaize 1 eaves increased when 1 eaves were wet but adversed effect was found when the leaf surface was dry. In planta, strain PJ0210 reduced new spores production by 50% up to 30 days. A mutant strain of PJ0210 resistant to rifampicin was reisolated from infected and rotted leaf debris up to 30 days.
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Keywords
Pseudomonas species , Bipolaris maydis
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