STUDIES ON CITRUS CANKER

Abstract

Citrus bacterial canker disease (CBCD) is characterized by formation of ruptured, raised, crumpcnt lesions having water soaked margins on above ground parts of the plant. Samples of CBCD were collected from different citrus growing areas of Punjab and NYVFP isolations of the bacterium were made on Yeast dextrose calcium carbonate agar (YDCA), sucrose peptone agar (SPA) and Kasugamycin - cephalexin - chlorothalonil + Tween media. Forty isolates were stored each in sterile distilled water and phosphate buffered saline and twenty four in siliea gei in test tubes. To determine the pathogenic nature of these t lie isolates, hypersensitive reaction was performed on Nicntiana nistica plants by injection infiltration technique. Twenty four isolates gave positive reaction for KOII, U,S production, tyrosinase, aesculin hydrolysis, leeithinase, gelatin liquefaction, casein hydrolysis, tween-80 hydrolysis, pectin liquefaction, starch hydrolysis, potato plug test, citrate utilization, succinate, malonate dextrin, glycogen, glycerol, sucrose, mannose, galactose, fructose, glucose, xylose and arabinose. Negative results were observed for oxidase, methyl red, urease production, nitrate reduction, gluconate, arginine hydrolysis, inulin, sorbitol, ruHInose and rahanmose. xiv The sonicated and whole cell antigen gave a sharp band near the antigen well will the antisera XC-91, XC-93, XC-05188 blit faint reaction with XC-02. On the basis o reaction pattern two serovars were identified, serovar type 1, XC-58, XC-91. XC-93, XC 100. XC-101, XC-105, XC-107, XC-II4 and XC-125 gave a sharp are like band will ! antisera XC-91, XC-93, XC-05188, but serovar type II did not form are like band but faint reaction with heated and noil-heated antigen. In chemotaxis XC-93 was attracted towards leaf disc and leaf extract of Frost Marsh was most effective as compared to Shaddock Webber on sucrose peptone agar media in soft agar assay as well as capillary assay. In capillary assay number of bacteria attracted towards leaf extract increased with increase in incubation time. Inoculation by pin prick method resulted in much more consistent lesion development and greater number of lesions than brush and sand paper method. Pin prick method produced noteable infection in all citrus cultiyars 14 days after inoculation in Held. More lesions were noticed on upper leaves than lower and middle inoculated with pin prick method in the glass house and field assay. i Bacterial strains XC-98 and XC-101 were more virulent and formed more lesions on ; detached leaves of Kinnow/Rough lemon, Hamlin, Pixie, Frost Marsh and Mnrrava exotica as compared to XC-93, XC-97, XC-124, XC-126 and XC-I29 incubated at 24'C under 12 ; h illumination. Strain XC-57 formed significantly higher number of lesions on Kinnow/Sour orange and Blood red/Rongh lemon when incubated at 22'C under 12 h illumination as compared to XC-49, XC-5I, XC-53, XC-58, XC-60, and XC-62. Higher number of lesions were formed under low temperature (0 & 5"C) shock as compared to high temperature (35 & 4I)"C) shock. Low temperature shock for 5, 10, 20, and 30 minutes was identical but was significantly different from 45 minutes. Under low temperature lesions began to develop within 7 days, while under high temperature leave stalled rotteniug after 15 days. A preinoculation low temperature (5°C) shock to leaves and fruits showed significantly higher number of lesions as compared to those w hich developed w hen a shock of similar duration was given three days after inoculation. Among the agrochemicals tested for inhibition zones, the bacterium showed greatest sensitivity to Streptomycin sulphate, followed by Bordeaux mixture, Cuprosan, Trimiltox forte. Saudofan M, Polycom combi. Liromanzch, Kidomil and Score 250E. In field test, Streptomycin sulphate and Bordeaux mixture in comparison with Trimiltox forte and Cuprosan reduced the number of lesion significantly when applied 2 days after inoculation as compared to 7 days after inoculation. Every dose of active ingredient of streptomycin sulfate was highly significant in production of inhibition zones as well as protective and curative action on detached leaves and fruits.