STUDIES ON INTENSITY, VARIABILITY AND EPIDEMIOLOGY OF CITRUS CANKER IN HIMACHAL PRADESH
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Date
2019-10-22
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COLLEGE OF HORTICULTURE AND FORESTRY, DR Y S P UHF, NERI, HAMIRPUR
Abstract
The present investigations entitled “Studies on intensity, variability and epidemiology of citrus canker in Himachal Pradesh” was undertaken to record the occurrence of the disease, study physiological and epidemiological variability of pathogen and study the epidemiology of the disease. Citrus canker was prevalent on different Citrus spp. in moderate to severe form at various locations in three districts (Hamirpur, Kangra and Sirmour) surveyed in Himachal Pradesh. Disease incidence was found to be ranging between 40 to 100 per cent whereas, disease severity was found to be ranging between 2.78 to 50.55 per cent. Nine pathogen isolates were collected and purified and were identified as Xanthomonas axonopodis pv. citri on the basis of cultural characters and various biochemical tests. All the isolates tested positive both for protein digestion as well as esculin hydrolysis and gave negative reaction to Gram’s staining. Out of five different media tested, Wakimoto medium was found to the best medium for the growth of all isolates. Temperature of 25˚C and pH 7.0 was found to be optimum for the growth of all isolates. During pathogenicity test of all isolates under in vitro conditions on Kagzi lime as detached leaf assay, the incubation period and final symptom development was found to be ranging between 3.00 to 5.00 days and 14.00 to 16.00 days, respectively. All the nine isolates produced light yellow, yellow, pale, dark yellow, circular colonies with varied elevation and colony diameter ranging between 1.00 to 6.00mm on various solid media tested. Leaves of all age groups in nursery of K. lime were found to be susceptible towards the pathogen. Among different inoculation methods, pink prick method of inoculation was found to be best with shortest incubation period (4.18 days) under in vitro conditions. A temperature range of 25 to 35˚C and relative humidity more than 80 per cent was found to be optimum for symptom development under in vitro conditions exhibiting incubation periods between 2.00 to 5.00 days. All nine isolates exhibited considerable amount of variability in terms of various cultural and epidemiological traits under study. The periodical investigations of K. lime nursery at College of Horticulture and Forestry Neri, Hamirpur revealed that maximum disease incidence (88.45%) and disease severity (15.06%) was recorded during August, 2018 when the mean monthly temperature, relative humidity and cumulative rainfall were 26.54˚C, 76.43 per cent and 407.8 mm, respectively. Disease incidence as well as severity were found to be significantly and positively correlated with mean monthly temperature, average monthly relative humidity and cumulative monthly rainfall and these three factors were found to influence disease incidence and severity up to 91.16 and 79.94 per cent, respectively.
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