Effects of loose kernel smut caused by Sporisorium cruentum onrhizomes of Sorghum halepense

Abstract

The effect of loose kernel smut fungus Sporisorium cruentum on Sorghum halepense (Johnson grass) was investigated in vitro and in greenhouse experiments. Smut infection induced a decrease in the dry matter of rhizomes and aerial vegetative parts of the plants evaluated. Moreover, the diseased plants showed a lower height than controls. The infection resulted in multiple smutted buds that caused small panicles infected with the fungus. In addition, changes were observed in the structural morphology of the host. Leaf tissue sections showed hyphae degrading chloroplasts and vascular bundles colonized by the fungus. Subsequently, cells collapsed and widespread necrosis was observed as a symptom of the disease. The pathogen did not colonize the gynoecium of Sorghum plants until the tassel was fully developed. The sporulation process of the fungus led to a total disintegration of anthers and tissues. When panicles were inspected before emergence, fungal hyphae were observed on floral primord. Histological sections of panicles showed fungal hyphae located in the parenchyma tissue and the nodal area. Infection occurred in the floral primordium before the tassel had fully developed and emerged from the flag leaf. Grains were replaced by sori surrounded by a thin membrane that usually was broken before or after the emergence of the panicle. The results, together with the significant decrease of the dry matter of rhizomes and seeds of S. halepense, suggest that S. cruentum could be considered as a potential biocontrol agent in the integrated management of this weed.