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  • Author or Editor: A. Kamalakannan 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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Bittergourd yellow mosaic virus (BGYMV) is one of the virus affecting the bittergourd (Momordica charantia). It is transmitted by whitefly Bemisia tabaci Genn. Minimum of five whiteflies were required to transmit the virus. However, hundred per cent transmission of BGYMV disease was obtained when 45 whiteflies were released per plant. Twelve hours of acquisition access feeding period (AAFP) and inoculation access feeding period (IAFP) were required for the whiteflies to transmit the disease. The percentage of transmission increased with increase in both acquisition and inoculation feeding period. A pre-acquisition starvation period of 3.5 h ensured hundred per cent transmission, while post-acquisition starvation period affected the transmission.

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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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A new necrosis viral disease was observed in blackgram, showed brown necrotic rings along with veinal and stem necrosis. The virus was mechanically inoculated on the local lesion host, cowpea cv. 152 and maintained in the local lesion host throughout the study. Yield studies under pot culture experiment showed 10- to 30-day-old plants were highly susceptible and the yield became almost nil. By using Transmission Electron Microscope (TEM) and indirect Direct Antigen Coated-Enzyme Linked Immuno-Sorbent Assay (DAC-ELISA) studies the virus was identified as Tobacco streak virus (TSV). The ultraviolet absorbance of the purified virus was measured and the ratio of A260/A280 was determined as 1.41. Polyclonal antiserum was raised against blackgram necrosis virus in New Zealand white rabbit and the titre value was determined as 1: 200. Direct antigen coating-ELISA was used to detect the virus concentration in various plant parts and stem portion recorded maximum virus concentration. TSV in blackgram was not transmitted through seeds.

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Acta Phytopathologica et Entomologica Hungarica
Authors: A. Kamalakannan, L. Mohan, K. Kavitha, S. Harish, R. Radjacommare, S. Nakkeeran, V. K. Parthiban, R. Karuppiah and T. Angayarkanni

Five isolates of Trichoderma viride, Pseudomonas fluorescens and four isolates of Bacillus subtilis were evaluated for their ability to control Rhizoctonia solani, the causal agent of stem and stolon rot of peppermint (Mentha piperita Lin.). Of the various isolates of T. viride, P. fluorescens and B. subtilis tested, TVUV10, PFMMP and BSG3 showed the maximum inhibition of mycelial growth of R. solani. Among these isolates, P. fluorescens, PFMMP recorded the highest inhibition zone against R. solani in vitro and was very effective in reducing disease incidence in greenhouse condition. The effective isolates were evaluated for their ability to induce defense related enzymes and chemicals in plants. Increased activity of phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenoloxidase (PPO) and total phenolics were recorded in the biocontrol agents pretreated peppermint plants challenged with R. solani. P. fluorescens isolate PFMMP recorded early and increased synthesis of all defense related enzymes and total phenol. Thus, the present study shows that application of biocontrol agents; induce defense related enzymes involved in phenyl propanoid pathway in addition to direct antagonism which collectively contribute for enhanced resistance against invasion of R. solani in M. piperita.

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