Varietal degeneration in sugarcane and its management in India

Abstract

Vegetative propagation in sugarcane favours accumulation of pathogens inside the canes and carryover of pathogenic inoculum through planting materials. Except foliar diseases, disease-infected setts serve as a primary source for disease spread for most of the diseases in the crop. In case of fungal diseases, planting infected setts leads to disease builds up in plant crop and probably death of the affected clump. However, in case of non-fungal diseases continuous accumulation of pathogens systemically leads to loss of vigour in sugarcane varieties referred to as ‘varietal degeneration’ and this result in loss of yield potential in elite commercial varieties. Past decades witnessed many such instances of degeneration in popular sugarcane varieties and their replacement with new varieties. With the development of precise molecular diagnostic tools the associated pathogens are being precisely identified. Under Indian conditions, it was found that combined or separate infections of viruses causing mosaic and yellow leaf (YL), phytoplasmas causing grassy shoot and leaf yellows and bacterium causing ratoon stunting disease (RSD) are associated with varietal degeneration. The degeneration was rapid and severe when all these pathogens infect sugarcane together as compared to their separate infections. However, among all these diseases, YL contributes more towards degeneration of sugarcane varieties. The disease occurrence to epidemic levels in different states is a serious concern for sugar industry and due to that longevity of the affected varieties in the field is threatened. Meristem-tip culture combined with hot water treatment and molecular diagnosis was found effective to detect and free the cane from these pathogens. Developing disease-free nurseries is imperative to sustain productivity of sugarcane and to realize yield potential of popular sugarcane varieties in India.