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STUDIES ON PHYTOPHTHORA FRUIT ROT OF ASH GOURD (BENINCASA HISPIDA)

MN DHANORKAR1, VG RAO2 and ALAKA PANDE1

1Department of Mycology and Plant Pathology, ARI-MACS, Pune 411 004, India; 2Niku Bio-Research Lab, 613, Nana peth, Pune 2, India

Background and objectives
Ash gourd (Benincasa hispida, Cucurbitaceae) is an important vegetable grown in many parts of India. During regular surveys in field and Pune markets (west India), an unusual fruit-rot disease was observed on some fruits producing pale-brown, irregular, water-soaked areas with dirty white fungal growth. An examination and study of this fungus in the laboratory revealed it to be a species of Phytophthora.

Results and conclusions
Some detailed studies were undertaken in respect of isolation, pathogenicity, host range, morphology, cultural characters, temperature-growth relationship, germination of sporangia, etc. These studies revealed that the pathogen was characterized by irregular, coenocytic, granular, lobed mycelium measuring about 6.84-10.26 m in width, producing short to long sporangiophores bearing terminally typical lemon-shaped to elongate, papillate sporangia, measuring 46.7-100.7x21.6-43.1 m, which soon germinated to produce motile zoospores. Chlamydospores were thick-walled, pale brown, spherical, terminal or intercallary measuring 14.4-28.8x14.8-25.2 m. The fungus was pathogenic to various fruits, tubers and bulbs, showing a wide host range. It grew best in almost all vegetable media. In temprature-growth studies, the fungus could grow at low temperatures (starting at 15C), profusely at room temperature (25-28C) and also up to 35C. In germination studies, zoospore germination was maximum at 25C, while germination by germ tube was maximum at 30C. This correlates with the epidemic severity of the disease in nature during the rainy season when temperatures are low with high humidity. No oospores were produced either on the host or in culture.

Based on gross morphological characters, dimensions of various fruiting structures, pathogenicity, including host range, cultural characters and temperature-growth relationship, the Phytophthora sp. under study (isolated from ash gourd) appeared to be a typical strain of Phytophthora palmivora Butler and has been identified as such Thus this report of fruit rot of ash gourd incited by Phytophthora palmivora constitutes possibly the first report from India or elsewhere, as evident from the literature [1, 2]. The material has been deposited in the Mycological Herbarium at Agharkar Research Institute, Pune under No. AMH 8160.

References
1. Bilgrami KS, Jamaluddin S, Rizwi MA, 1991. Fungi of India. Today and Tomorrow's Printers and Publishers, New Delhi, p. 798.
2. Rao VG, 1970. Mycopathologia et Mycologia Applicata 42, 241-258.