CHARACTERIZATION OF THE CAUSAL ORGANISM OF BLACKLEG AND SOFT ROT OF POTATO, AND MANAGEMENT OF THE DISEASE WITH BALANCED FERTILIZATION

摘要

Based upon colony morphology, physio-biochemical tests and polymerase chain reaction (using species or subspeciesspecificprimers) studies, 20 isolates (out of a total of 42) were found to be Erwinia carotovora subspecies atroseptica (Eca),19 were identified as Erwinia carotovora subspecies carotovora (Ecc), and 3 as Erwinia chrysanthemi (Ech). Results ofthe subspecies-differentiating biochemical tests indicated that majority of the candidate Ecc isolates did not produce acidfrom α-methyle glucoside (as expected) but their reaction to the production of reducing substances from sucrose wasvariable. Likewise, some of our Eca and Ecc strains (unexpectedly) were sensitive to erythromycin. Also, most of our Ecastrains unexpectedly grew at 36oC. Our strains slightly deviate from the standard description in some of their minorcharacteristics but they still remain the valid members of the Eca, Ecc or Ech group as similar variations in minorcharacteristics have been found by other workers. The occurrence of intermediate forms of Eca and Ecc (sharing some of thecharacteristics of both the groups) indicates variability happening among these strains. This variability indicates the potentialability of the pathogen to break the resistance of the host. The results of the effect of balanced nutrition in controllingblackleg and soft rot of potatoes indicated that the fertilizer combination of N3P1K3 (262/252/262 kg.ha-1) which is slightlyhigher than the normally practiced dose (247/247/247 kg.ha-1) was the best in bringing the disease to a minimum andsubsequently increasing the yield.