Assessment of artificial inoculation methods for development of sorghum pokkah boeng caused by Fusarium subglutinans

Abstract

Pokkah boeng is an emerging disease of sorghum causing economical loss to the crop. No sources of resistance or screening tools are available for this disease currently. Four methods of inoculation were assessed on four genotypes of sorghum for artificial development of pokkah boeng under field conditions during the post-rainy seasons of 2012 and 2013. Inoculation methods were foliar spray of spore suspension, stem injection of spore suspension with hypodermic needle, application of pathogen colonized sorghum grains into the whorl, and untreated control. Disease incidence and severity of pokkah boeng was recorded at both vegetative and reproductive crop stages. Multiseason data were analyzed using conventional as well as genotype + genotype-environment (GGE) biplot method to understand complex interactions between host and the treatments. Both disease incidence and severity of disease increased from vegetative to reproductive stage. Stem injection produced highest disease incidence (43.5%) and severity index (26.4%) followed by whorl application (incidence 31.3%; severity index 18.2%) and stem injection was more stable than whorl application across years. Which-won-where analysis showed that SLR 30 was the most susceptible variety across all inoculation methods. Studies on interrelationship among traits by conventional correlation analysis and biplot analysis revealed that grain yield, plant height and earhead length were affected by the disease. Stem injection developed high amount of disease and caused grain yield loss of 25.8%. To our knowledge this is the first instance where a suitable artificial inoculation method has been identified for screening sorghum genotypes for pokkah boeng resistance.