~ 2044 ~ Journal of Pharmacognosy and Phytochemistry 2020; 9(3): 2044-2047 E-ISSN: 2278-4136 P-ISSN: 2349-8234 www.phytojournal.com JPP 2020; 9(3): 2044-2047 Received: 01-03-2020 Accepted: 03-04-2020 Vasumathi S Kalasingam University, Krishnankovil, Virudhunagar, Tamil Nadu, India P Ahila Devi National Pulses Research Centre, Vamban, Pudukottai, Tamil Nadu, India Corresponding Author: Vasumathi S Kalasingam University, Krishnankovil, Virudhunagar, Tamil Nadu, India Characterization of Fusarium oxysporum causing wilt disease in groundnut Vasumathi S and P Ahila Devi Abstract Richard’s agar and carrot dextrose agar supported the maximum mycelial growth of 9.00 cm at 7 DAI. Richard’s broth yielded the maximum mycelial dry weight of 914.00 mg. when carbon sources glucose ranked first in solid as well as liquid broth to promote the fungal growth with a mean mycelial diameter of 9.00 cm and mycelial dry weight of 453.40 mg respectively. In nitrogen sources, ammonium nitrate was found to be effective for the growth of F. oxysporumin solid and liquid media. The fungus grew well in pH 6.5 to 7.0. Keywords: Fusarium oxysporum, groundnut, richard’s Introduction Groundnut or peanut (Arachis hyphogaea L.) is an important leguminous oil seed crop, belonging to the family Fabaceae. Groundnut is grown on a large scale in almost all the tropical and subtropical countries of the world. Including China, India, Nigeria, Sudan and USA. Groundnut occupied on area of 26.46 million ha with an annual production of 26.4 million tonnes in the world (FAO, 2007) [2] . The crop was introduced into India by Portuguese. In India it is one of the most important food and cash crop with valuable source of all nutrients. India ranks first in the world with regard to area of groundnut (26.11 million ha) and second in its production (7.54 million tonnes). (www.india stat.com, 2011). In India, Gujarat is the largest producer of groundnut contributing to 25 per cent of its productionfollowedby Tamil Nadu with 22.48 per cent, while in productivity Tamil Nadu ranks first. In the State groundnut is cultivated in 11.29 lakh ha accounting for a production of 18.04 lakh tonnes with an average yield of 2681 kg/ha (www.india stat.com, 2011). Groundnut is susceptible to many foliar and soil-borne fungal diseases including early leaf spot caused by Cercosporaarachidicola Hori., late leaf spot caused by Phaeoisariopsispersonata (Bark and Curt.) v.Arx., rust incited by Puccinia orachidis Speg., dry root rot caused by Macrophominaphaseolina (Tassi) Goid., stem rot incited by Sclerotium rolfsii Sacc. and wilt caused by Fusarium oxysporum. Among these the soil- borne diseases viz., dry root rot, stem rot and wilt cause serious losses to the crop which is extensively grown under rainfed conditions (Kannaiyan et al., 1989) [11] . The pathogen Fusarium oxysporum that causes wilt of groundnut was first reported in Tansania by Armstrong et al. (1975) [3] . Fusarium oxysporum is a root pathogen colonizing the xylem and blocking them completely to effect wilting (Bateman et al., 1996) [4] . Fusarium induces vascular diseases in crops such as watermelon, cucumber, tomato, pepper, muskmelon, bean, cotton and groundnut (Rasheed et al., 2004) [16] . In a survey carried out in groundnut growing areas of Theni district, the crop was found to exhibit a disease syndrome which caused sudden wilting in plants. During sudden wilting, leaves of an entire plant turn greyish green and the taproots show vascular browning. The fungus isolated from the stem on potato dextrose agar (PDA) produced cottony white mycelium with microconidia, macroconidia and chlamydospores. The present investigation was undertaken with the following objectives. 1. Survey on the incidence of wilt in groundnut growing areas. 2. Isolation, identification of the pathogen, symptomatology and confirmation of pathogenicity. 3. Studies on the morphology and growth characters of the pathogen. Materials and Methods Collection of samples A survey was conducted during 2011 to assess the occurrence of Fusarium wilt of groundnut at Madurai, Sivagangai and Theni districts of Tamil Nadu. The disease incidence was assessed by counting the number of affected plants out of total number of plants in each field.