| dc.description.abstract | Culture filtrates of antagonistic bacteria Bacillus sp.(CA5) and Streptomyces sp. (CS35) isolates
and their combination (CAS + CS3S) were tested for their ability to control bean rust fungus,
Uromyces appendiculatus, under field conditions. A systemic fungicide anvil of the triazole
chemical group was used as the standard check. The antibiotics in the two culture filtrates were
also tested for their ability to be translocated within the bean plant as well as their level of
persistence after application on the bean host in the greenhouse. The activity of the antibiotics in
the culture filtrates was checked by carrying out in vitro tests against Fusarium oxysporum and
Pythium sp .. which grow easily in media.
The culture filtrates from both CAS and (,S35 were round to be active against Pythium sp. and
Fusarium oxysporum in culture but the inhibition zones varied. The mean inhibition zone given
[1\ c·:\5 and ("S35 on l'vtlii um was I I. 72!l1111 and 15.53mm respectively while on Fusarium
oxn"{Jorum it was l-U Imrn and 12.00mm respecti vely. The inhibition zones were significantly
different (P::::U.U5). It was observed that apart Irorn the size or the inhibition zones. their clarity
was also different depending (l11 the culture filtrate and the test pathogen. CS35 on Pvthium and
CAS on Fusarium oxysporum showed very clear inhibition zones. However, CS35 and CAS -ri
CS35 Oil Fusarium oxvsporum showed a faint inhibition zone. CAS and CAS + CS35 on Pythium
had an inhibition zone that was neither clear nor faint ranking between the two extremes.
The abilitv of the antibiotics in the culture filtrates from CA5 and (S35 to be translocated within
the bean plant was assessed as the number of rust pustules on the non-treated leaflets or trifoliate
leaves .. -\ntibiotics from both culture filtrates were found to have trans-lamina and leaflet-to-
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leaflet translocation. However, they had no significant trifoliate-to-trifoliate translocation. For
the trans-lamina and leaflet-to-leaflet translocation, they inhibited rust pustule development by
100%.
The level of persistence of the antibiotics in the two culture filtrates was assessed as the number
of rust pustules on the antibiotic treated bean plants that developed after inoculation with rust.
Antibiotics from both culture filtrates significantly reduced rust pustules when the plants were
inoculated O. 4. and 8 days after application of the treatments. Only CAS was significantly
different from the untreated controls when inoculation was done 12 days after application of the
treatments. When the inoculation was done 16 days after application of the treatments, the
treatments were not statistically different from the untreated controls.
Disease incidence \\~IS assessed as percentage ()I' infected leaves to the total number or leaves per
plant. .-\11 the treatments. C.-\5. CS35, C.-\5 -CS35 and anvil reduced the disease significantly.
The best result was achieved by anvil followed bv C:\5. . . The least effective but still better than
control \\as CS_~5 and C:\5 - CS~5 during the short and long rains respectively
The modi tied Cobbs scale was used to rate disease severity ranging from 0-99%. The above
treatments reduced disease severity ranging from 50.5% with CS35 to 72.0% with anvil. During
the long rains. C\5 ~ CS35 had the lowest reduction in disease severity of 53.0%. On average.
early application of treatments improved disease control by 63% compared to late application.
Disease severitv values were used to calculate the Area under Disease Progress Curves(AUDPC)
Anvil had the lowest (59.96) while ('535 had the highest (l l l.4).
Increase in seed yield due to the treatment effects ranged from 15.95-58.7% (mean 23.565%).
Whereas anvil had the highest increase at 46.45%, the combination of CAS + CS3S had the
lowest at 15.95%. However, CS3S had higher seed yield increase (30.9%) than CAS (20.7).
The two culture filtrates compared favourably with the standard chemical anvil in the control of
bean rust. Their combination showed no synergistic effect. However, culture filtrate from CAS
significantly reduced disease incidence and severity without a corresponding increase in seed
yield for the variety Samantha suggesting some negative interaction between the two. Some
phytotoxicity appearing as scotched leaf margins was observed on the beans treated with the
culture filtrates in the greenhouse. | en |
