Leaf fleck, an emerging viral disease in sugarcane: surveillance under various geographical locations in India

Abstract

Sugarcane bacilliform virus (SCBV) causing leaf fleck was reported three decades ago in sugarcane and for many years its symptoms have not been clearly described. Initially, the symptoms of fleck, mottling and mild mosaic were suspected to be caused by virus infections in Saccharum spp clones and no clear information was available on virus infections and disease symptoms in hybrid varieties. As reported earlier, PCR assays targeting a 221bp amplicon is not reliable for virus diagnosis from the SCBV-suspected clones of sugarcane. Hence a comprehensive study was made on leaf fleck symptomatology in Saccharum spp clones in germplasm and Saccharum spp hybrid varieties under cultivation and new PCR assays for precise diagnosis of the virus were developed. Surveys to determine the incidence, diversity and distribution of SCBV were conducted in different geographical locations at Kerala, Tamil Nadu and Andhra Pradesh. It was observed that the leaf fleck symptoms varied among the Saccharum spp clones and hybrid varieties. When compared to Saccharum spp clones, hybrid varieties exhibited a severe expression of the disease. Symptoms initiated as sparse or intense flecks in the lamina progressed to chlorotic stripes or distinct chlorotic streaks, intense yellow streaks/ blotches, reddening of the streaks and pre-mature drying of leaves. The average disease incidence was observed between 12 and 42 % in Kerala and higher in other states. The newly designed virus specific primers were found to be highly specific and detected the virus in symptomatic and asymptomatic plants. The studies revealed extensive spread of the virus across Saccharum spp genotypes and hybrid varieties.