Infectivity and management of dry rot, eye rot and soft rot of ginger (Zingiber officinale Rosc.)

Abstract

Dry rot and eye rot of ginger are post-harvest infections noticed as caused by Macrophomina phaseolina and Fusarium oxysporum, respectively. To investigate whether these pathogens cause damage to the crop only during the cropping period and then remain latent, or are purely post-harvest in nature, an experiment was undertaken by artificially inoculating the pathogens and comparing them with soft rot caused by Pythium myriotylum. The results of the study indicate that M. phaseolina could infect ginger plants during the cropping period and cause rhizome infection, manifested as yellowing of the pseudostem and the pathogen reside inside the rhizome and develop latent infection as dry rot during storage. The pathogen could be re-isolated and proved Koch’s postulates. However, none of the Fusarium challenged plants showed symptoms either manifested as yellowing or rotting of the pseudostem. In Macrophomina-challenged plants, the infection appeared only during the post-monsoon period that coincides with the yellowing of the leaves during maturity. This observation was supported by the occurrence of natural infection by Macrophomina in harvested fresh rhizomes during 2018 and manifested as scattered elongated streaks with black mycelia inside the rhizomes, which extended from the cut end to the tip. But Pythium inoculated plants succumbed to infection as rotting of the basal portion of the pseudostem and yellowing of the lower leaves. The intensity of infection varied from 0-63 per cent. In vitro testing of seven fungicides in four different concentrations showed that metalaxyl-Mz, copper oxychloride (COC), and mancozeb even at 500 ppm are not inhibitory to M. phaseolina. But carbendazim and carbendazim-mancozeb were highly effective, giving complete inhibition even at 50 ppm. In the case of P. myriotylum, metalaxyl-Mz, COC, and Bordeaux mixture showed >70 per cent inhibition at 500 ppm. Mancozeb alone at 500 ppm was not effective against Pythium. In planta evaluation was done with fungicides individually and in combinations along with a systemic insecticide, dimethoate. Most of these treatments resulted in reduction of Macrophomina infection, of which metalaxyl-Mz alone or in combination with carbendazim (0.2%) and dimethoate (0.05%) showed 100 per cent reduction in infection. Metalaxyl-Mz (0.125%) with dimethoate (0.05%) was highly effective in reducing the infection caused by P. myriotylum.