Development of an epidemiological model and decision support system for the management of Karnal bunt of wheat

Environmental conditions favouring germination of primary inoculum & survival of the sporidial colony of Tilletia indica in wheat field did not correlate with disease incidence in Punjab from 1992–2005, as the expected disease deviated significantly from that observed in the farmers field. Linear models developed to explain disease incidence obtained on boot inoculations also failed to validate the disease incidence obtained in other varieties and poorly correlated with incidence on farmers field. Amount of sporidial inoculm formed in the field by actively growing colonies of the pathogen during heading of wheat crop correlated better and best fit polynomial equations were developed for the range (8–21°C temperature and 64–100% RH) and mean (temperature 14.5±1°C and RH 82±5 percent) of weather parameters, favouring maximum sporidial inoculum production at GS 51 - 65 of wheat, when first spike visible to half way anthesis. Mean weather parameters explained 92% and 85% variation in the disease incidence. This epidemiological model was further refined by considering the duration of the favourable conditions during the susceptible window of the host (GS 51- 65) and explained 89–91% the variations in the disease incidence on farmers field from 1996–2005, when PBW 343 was the predominant variety. The efficacy of epidemiological model to manage the disease was experimentally demonstrated by simulating favourable conditions for disease development (adequate sporidial inoculum and susceptible stage of the host). No disease was observed when boot inoculations (GS 47) were done 24 hours before the recommended fungicide was sprayed, but incidence increased as the gap of fungicide spray and inoculations increased. But on spray inoculations at GS 51 to 65, no disease was observed and with droplet inoculations (GS 51–57), when fungicide was sprayed 96 hrs before inoculations or when inoculum droplet was placed after 56 hrs of fungicide spray. Since spray and droplet inoculations were natural methods, it is expected that disease can be managed by spraying fungicide, with the onset of favourable conditions if these coordinates with the susceptible stage of the crop. This pre-harvest method of prediction can be developed as a “decision support system” using the information technology tools and weather forecast for the management of karnal bunt of wheat and implemented by extension advisory services.