Need for efficient healthy nursery programme to sustain sugarcane cultivation through mechanized cane cultivation

Abstract

Sugarcane production is affected by different diseases caused by fungal, bacterial, viral and phytoplasmal pathogens in the country. Major fungal diseases such as red rot and smut are managed through deploying disease resistant varieties. Due to vegetative propagation the viral pathogens along with other non-fungal pathogens causing RSD and GSD gradually increase in their load in the canes over the generations. Such a high population of different pathogens leading to ‘varietal degeneration’ i.e. loss in vigour of sugarcane varieties. Due to this, longevity of many elite sugarcane varieties was reduced in the past. Since most of the pathogens are transmitted through seed in sugarcane, greater emphasis are given to seed health to manage the diseases. Hence disease-free nursery programmes form the basis of healthy crop in the field. Otherwise, the disease severity aggravates in the ratoons, scope of multi-ratooning and mechanization depends on the use of healthy planting material. In the past, impact of these diseases was ignored in the past due to lack of precise diagnostic techniques and clarity in symptoms caused by different viral diseases in sugarcane. Ever since yellow leaf disease (YLD) became a serious threat to sugarcane cultivation, ICAR-SBI has given more emphasis on healthy seed programme to address varietal degeneration by elimination of systemic virus infections through tissue culture combined with molecular diagnosis. At ICAR-SBI sensitive diagnostic techniques such as RT-PCR and PCR techniques were developed for the specific detection of the RNA viruses and phytoplasmas infecting sugarcane, respectively. These techniques have been applied to detect the pathogens in the tissue culture derived in vitro clones. Although the pathogen titre is expected to be very low, these techniques are highly sensitive to detect such a low titre in young plantlets. When tissue culture derived seedlings are utilized for commercial planting without diagnosis for the designated pathogens, the process also facilitates spread of the diseases far and wide and this will have a catastrophic effect in the field on crop health. Hence production of disease-free seedlings through tissue culture should be indexed for the designated viruses and phytoplasmas. Such virus-free seedlings are to be used as breeder seed in the three-tier seed nursery programme as they cannot be directly planted for commercial cultivation. Canes from this nursery can be used to raise single bud settlings in protrays under shade-net and such healthy settlings are used for planting in the field either for commercial cultivation or subsequent multiplication. Large scale adoption of such nurseries in Erode and Namakkal Districts in Tamil Nadu resulted in significant jump in cane yield as compared to the conventional planting. Critical monitoring of YLD-free fields revealed that the disease-free fields always maintained a vigorous crop stand and the farmers realized an average increase of 37.5-50 tonnes/ ha in cane yield in the region. In addition, rapid multiplication of healthy planting materials is achieved through settlings in the nurseries. Ultimately this approach would increase land productivity, increase farmer’s income and sustain sugarcane productivity. Our interventions in producing virus-free seedlings have opened new vistas towards effective management of diseases and supply of healthy planting materials in sugarcane.