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  • Author or Editor: V. Shanmugam x
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Downy mildew of maize caused by Peronosclerospora sorghi was significantly controlled by seed treatment and foliar sprays of a talc-based formulation of a Pseudomonas fluorescens strain under greenhouse and field conditions. Leaf extracts of Prosophis chilensis and Azadirachta indica were found to be equally effective as P. fluorescens in controlling maize downy mildew, although the extracts were not as effective at inhibiting conidial germination as the pseudomonad or as metalaxyl. These treatments also suppressed sporulation of P. sorghi on diseased foliage. Enhanced induction of defense enzymes, chitinase and β-1,3-glucanase appeared to be associated with control mechanism and metalaxyl did not show such induction. The reduction in disease incidence under field condition resulted in increased yield. The inhibitory effect of P. fluorescens and extracts of P. chilensis or A. indica make them potential alternatives to metalaxyl for control of maize downy mildew, although their efficacy, practical application and cost needs to be explored in greater detail before they can be incorporated into an integrated pest management programme.

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Aspergillus niger was found to be the predominant pathogen associated with black mould rot of onion during storage. Market survey for the assess­ment of spoilage caused by the fungus recorded a loss of 2.9% to 12.09% during the period from June 1998 to February 1999. Application of higher doses of calcium in the form of gypsum (400 kg/ha) and lower dose of nitrogen in the form of urea (50 kg/ha) to the field and advancing the harvest of onion bulbs by fifteen days significantly reduced the spoilage of bulbs during storage. An inverse relationship existed between neck length of the bulbs and spoilage at storage. Bulb rotting was noticed when the storage temperature was between 30 °C and 40 °C and the relative humidity was above 80%. Further, A. niger infection caused reduction in pungency of onion bulbs which was more pronounced at grade 4 than grade 1. The culture filtrates of Aspergillus niger and Asper­gillus flavus isolated from onion as well as the extracts from onion bulbs infected with the above fungi were free from aflatoxin contamination.

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Acta Phytopathologica et Entomologica Hungarica
Authors: S. Babu, R. Nandakumar, S. Sriram, R. Jaisankar, V. Shanmugam, T. Raguchander, R. Samiyappan and P. Balasubramania

Mutants of Rhizoctonia solani were developed using UV irradiation of the mycelia of isolate RS7, which is the field isolate causing sheath blight in rice. The mutants showed reduced virulence, as compared to RS7 in detached leaf sheath and intact rice plants. All the mutants produced some toxin but in varied quantities. The amount of toxin produced by the mu­tants was positively correlated with disease development on rice plants and detached leaf sheaths. The wild isolate RS7 and mutant RSU7 pro­duced more quantity of toxic material, which in turn related to severe sheath blight symptoms. Sclerotial production on the infected rice sheath also showed significant variation among the mutants and the virulent and less virulent isolates. SDS-PAGE analysis of the mycelial proteins show­ed many proteins of different molecular weights varying among mutants and wild isolate at different stages of mycelial growth. Correlation bet­ween reduction in toxin production and disease severity is statistically significant.

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