Evaluation of ginger germplasm for resistance to soft rot caused by Pythium myriotylum

Abstract

Ginger (Zingiber officinale Rosc.), an important spice crop is highly susceptible to soft rot caused by species of Pythium. The disease is of soil borne nature and the pathogen multiplies with the build up of soil moisture. Younger sprouts are more susceptible to the pathogen. At the early stage of infection, collar region of affected pseudo stem becomes water soaked which later spreads to the rhizome resulting in typical soft rot. Different species of Pythium viz,. P. vexans P. myriotylum, P. graminicolum, P. aphanidermatum, P. zingiberum,, P. ultimum and P. splendens were observed as pathogens from various ginger growing regions. Among the pathogens, P. myriotylum is found as the predominant pathogen in many parts of the country and outside (3, 9, 2, 5). Several fungicides have been reported as effective in controlling the disease. However fungicide drenching schedules and their effectiveness is severely hampered due to incessant rain when the crop is at the most vulnerable stage for infection. Since, many of these control measures are not that much effective, development of resistant varieties is the most effective alternative to escape from the heavy crop loss occurring due to this disease. In this study, ginger accessions maintained in the spice germplasm repository at IISR, Calicut were evaluated for identifying sources of resistance against soft rot disease. A total of 650 accessions were subjected to screening towards P.myriotylum. Prior to evaluation, the screening procedure was standardized to optimize the type and dose of inoculum. The method suggested by Dake and Edison (3) was followed with slight modifications. Three types of inocula with two different dosages were tested by soil inoculation method. In the first method homogenized mycelial suspension prepared from P. myriotylum culture grown for seven days in potato dextrose broth (PDB) was used. Here the mycelial mat was harvested from the broth and homogenized in warring blender for 1 minute in sterile distilled water and the inoculum density was adjusted optically at 500nm wave length as done by Tripathi and Grover (10).