ASSESSMENT OF STORAGE FUNGI OF ONION AND ITS EFFECTS ON FIELD CONDITION

Abstract

Two experiments were conducted to assess purple blotch disease in the experimental field (November, 2015 to April 2016) and association of storage fungi with onion bulb in the laboratory (July, 2016 to October, 2016) of the Department of Plant Pathology and Seed Science, SAU, Sylhet. A total of six onion where four Indian viz. Accession 1, Accession 2, Accession 3, Pusa Red and two deshi varieties Faridpuri and Zitka were used in these experiments. The experiments were arranged in Randomized Complete Block Design (RCBD) with three replications. In field experiment, three Indian accessions were sown in two different times as timely sown and late sown. Purple blotch disease was assessed in the field and disease incidence and severity was recorded at four different times (35 DAT, 50 DAT, 65 DAT and 80 DAT) at an interval of 15 days. Accession-1 showed the highest disease incidence 32.4% in timely sown (17 November, 2015) and 38.0% in late sown (21 January, 2015). Highest disease severity was 15.4% in timely sown and 22.27% in late sown among the accessions tested. Disease development was at the highest level in all the accessions at 80 DAT. All accessions showed significant disease development at aged plant and disease development less at timely sown compared to late sown. Disease development of stored onion bulbs was observed at 45 days of storage (DOS) using all six onions in the laboratory. Three important storage fungi namely Aspergillus niger, Penicillium spp. and Fusarium oxysporum were found to be associated with the onion bulbs that caused black mould, blue mould and Fusarium bulb rot disease, respectively. All onions were found to be susceptible to the storage fungi. The lowest (10.34%) disease incidence was found in Zitka variety where the highest (26.6%) was in Pusa Red variety. Black mould disease showed the highest disease incidence among the three diseases. Alternaria porri the causal agent of purple blotch disease was not found in the stored onion bulb. Percent weight loss was measured at three different time (15, 30, 45 DOS) for all the onions at an interval of 15 days. All varieties were significantly different regarding weight loss at 15 days interval in storage condition. Pusa Red variety showed the highest (35.7%) weight loss at 45 days of storage where the lowest (8.7%) was recorded in Zitka. All Indian onions showed higher weight loss compared to deshi onions.