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Characterization of Isolates of Phytophthora Colocasiae Collected from Andhra Pradesh and Telangana Causing Leaf Blight of Taro

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Characterization of Isolates of Phytophthora Colocasiae Collected from Andhra Pradesh and Telangana Causing Leaf Blight of Taro Int.J.Curr.Microbiol.App.Sci (2017) 6(10): 1901-1912 International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 6 Number 10 (2017) pp. 1901-1912 Journal homepage: http://www.ijcmas.com Original Research Article https://doi.org/10.20546/ijcmas.2017.610.229 Characterization of Isolates of Phytophthora colocasiae Collected from Andhra Pradesh and Telangana Causing Leaf Blight of Taro G. Padmaja1*, G. Uma Devi1, B. Kanaka Mahalakshmi3 and D. Sridevi2 1Department of Plant Pathology, Prof Jayashankar Telangana State Agricultural University, Rajendranagar, Hyderabad - 500 030, Telangana, India 2Department of Entomology, College of Agriculture, Prof Jayashankar Telangana State Agricultural University, Rajendranagar, Hyderabad - 500 030, Telangana, India 3Vegetable Research Station, Sri Konda Laxman Telangana State Horticulture University, Agriculture Research Institute, Rajendranagar, Hyderabad - 500 030, Telangana, India *Corresponding author ABSTRACT K e yw or ds The oomycetous fungus Phytophthora colocasiae that causes taro leaf blight is one of the most devastating diseases of taro and is widely Leaf blight, Phytophthora distributed in India. Characterization of morphological and cultural was colocasiae , used to characterize 4 isolates of P. colocasiae obtained from different sporangium, oospore, culture medium locations of Andhra Pradesh and Telangana. Considerable differences in Article Info morphological parameters were observed. This study confirms that isolates of P. colocasiae are highly dynamic in nature and a considerable degree of Accepted: diversity exists among them. A detailed knowledge of the morphological 17 September 2017 Available Online: characters of P. colocasiae will help in developing suitable control 10 October 2017 strategies against the taro leaf blight disease. Introduction Taro [Colocasia esculenta (L.) Schott] a Leaf blight disease is prevalent in almost all tropical aroid is an important staple crop in the major taro growing districts of Andhra the developing countries especially in Africa Pradesh and Telangana with varying and South East Asian countries. Leaf blight intensities on different varieties causing yield caused by Phytophthora colocasiae loss of 10-55 per cent (Laxmi et al., 2012). Raciborski is the most important disease of The disease appears with the onset of Taro and was recorded for the first time by monsoon and spreads the entire field during Butler and Kulkarni (1913) in India. Leaf rainy season through zoospores and sporangia blight has become a limiting factor for (Misra et al., 2007). Reports have revealed, production in all taro growing areas in India however, that P. colocasiae is relatively short moderate to severe form causing 25% to 50% lived in infected leaf tissue like any other yield loss every year (Misra et al., 2007). foliar pathogen of taro. The fungus seems to 1901 Int.J.Curr.Microbiol.App.Sci (2017) 6(10): 1901-1912 have a poor competitive saprophytic ability. Extract Agar (HLA), Corn Meal Agar This contributes to the lack of success in (CMA), Papaya Sucrose Agar (PSA) were isolating and growing P. colocasiae in an used along with Carrot agar medium for artificial medium. In order to culture the fungi investigation of cheap source and suitable in the laboratory, it is necessary to medium for mycelial growth of Phytophtora supplement in the medium, those essential colocasiae. The isolated pathogen was elements and compounds needed for their identified as Phytophthora colocasiae based growth and other metabolic processes. Hence on its mycelial and sporangial characters different media were tried in the present through standard mycological keys investigation to select the best medium (Waterhouse, 1963; Hemmes, 1993) and by suitable for the growth of the pathogen. CMI descriptions. Also, we studied the variation in growth and Pathogenicity test sporulation among P. colocasiae isolates from processing taro fields. The objective of this The pathogenicity test was conducted in pots study was to investigate cultural and under glass house. The taro variety Satamukhi morphologic variation among isolates of P. susceptible to Phytophthora colocasiae leaf colocasiae isolated from taro fields of blight disease was raised in pots and 20 day different regions. old culture grown on CA broth suspension containing zoospores was inoculated to taro Materials and Methods plant at 3-5 leaf stage with hand sprayer and covered with polythene covers. Isolation and identification of the pathogen Variability studies Diseased leaves showing typical symptoms of Taro plants were collected from different Morphological characteristics Taro growing areas of Andhra Pradesh and Telangana (ARI, Rajendranagar, Hyderabad, The morphology of mycelium, sporangium, East and West Godavari districts) (Table 1). oospore of Phytophthora were studied in These leaves were put in sterilized polythene seven day old culture of each isolate grown bags and brought to the laboratory for on carrot potato agar medium and stained isolation and identification of the organism with 0.1 per cent lacto phenol cotton blue and involved. Taro leaves showing typical observed under compound microscope (40X). symptoms of the disease were selected and Observations on size and shape of washed with sterile water. sporangium, presence of papillae, size of Oospore and Zoospore were recorded. The surface sterilized leaf bits were transferred aseptically into sterilized Cultural characteristics Petridishes containing solidified carrot agar medium and incubated at 18±20C. After 3 Observation on colony colour, growth rate, days of incubation mycelial growth was was recorded at 24 hrs interval and mycelial absorbed along with diseased leaf bits. dry weight of each isolate was recorded at 7 Hyphal tips from the advancing mycelia were days after incubation at 18±20C. transferred to the carrot agar medium slants. Characteristics like sporulation and colour of Also studied different composition of media spore were observed and recorded at 10 days viz., Potato Dextrose Agar (PDA), Carrot after incubation. Potato Agar (CPA), V8 agar, Host Leaf 1902 Int.J.Curr.Microbiol.App.Sci (2017) 6(10): 1901-1912 Colony diameter and growth rate per day Kovvuru (West Godavari), Bahadurguda, (Ranga Reddy), Rajendranagar (Hyderabad), Twenty ml of carrot potato agar medium was and Thiruvananthapuram (Kerala) (Table 1). poured in sterilized Petriplates and allowed to The leaves showing typical symptoms of leaf solidify. Mycelial disc of 5mm diameter were blight were surface sterilized and kept on cut from the margin of the 7 day old culture carrot agar medium for isolation of the of Phytophthora colocasiae placed in the pathogen. The pathogen isolated on carrot center of the Petriplate under aseptic agar (CA) medium was identified with the conditions. The plates were incubated for 8 help of descriptions given by Waterhouse days in an incubator at 18±20C and the (1963). The colony was submerged or fluffy diameter of the colony was measured and and rosette in its growth and the colour was recorded. Three replications of each isolate whitish or dull white. Mycelium was aseptate, were maintained for the study. Growth rate hyaline, 1µm in width. Sporangiophore was per day of each isolate was calculated by simple, aseptate, hyaline and the sporangia dividing the colony diameter with number of were hyaline, ovoid, and semipapillate. Based days kept for incubation. on colony character and sporangial nature the pathogen isolated was identified as Dry weight of mycelium Phytophthora colocasiae. The characteristics of the pathogen were similar to the The dry weight of the mycelium of each descriptions given by Waterhouse (1963). isolate fifty ml of carrot potato agar both was poured in 150 ml conical flask, plugged and The pathogen was further sub cultured on sterilized. Mycelial disc of 5 mm diameter carrot agar medium and the culture was was cut from the margin of the seven day old purified by using hyphal tip method and kept culture of each isolate of the pathogen and on carrot agar medium slants and preserved at transferred to the conical flask containing the 18 + 20C for further studies sterilized medium under aseptic condition. Effect of different media on the growth of The flasks were incubated at 18±20C in an Phytophthora colocasiae incubator for 8 days. The mycelial mat was removed aseptically, washed thoroughly with In order to culture the fungi in the laboratory, distilled water and dried in blotters and kept it is necessary to supplement in the medium, in an oven at 500C for 12 hours. Dry weight those essential elements and compounds of the mycelium of each isolate was taken and needed for their growth and other metabolic recorded using digital electronic balance. processes. Neither all media are equally good for all fungi nor there will be an artificial Length, width and size of sporangium medium on which all fungi grow. Hence different media were tried in the present Morphological characters such as length, investigation to select the best medium width and the size of sporangium (L x B) suitable for the growth of the pathogen. Eight were measured by using micrometer. different media viz., Potato Dextrose Agar (PDA), Carrot Potato Agar (CPA), Carrot Results and Discussion Agar (CA), Papaya Sucrose Agar (PSA), Oat Meal Agar (OMA), Host Leaf Extract Agar The disease samples of leaf blight of Taro (HLEA), Corn Meal Agar (CMA) and Water were collected from farmer’s fields at Agar (WA) were used. 1903 Int.J.Curr.Microbiol.App.Sci (2017)
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