Sugarcane is one of the most important crops grown in India as well as in Assam. In India, sugarcane is grown in an area of 5.07 Million hectares with a productivity of 70.317 tonnes per hectare.
In Assam, it occupies an area of 29083 hectares with a productivity of 36.06 tonnes per hectare (Anon., 2014). Sugar industry is the 2nd largest agro-based industry in India, supporting 50 million farmers. India is world’s 2nd largest producer after Brazil producing nearly 15 and 25 per cent of global sugar and sugarcane respectively. The sugar industry contributes 1.
1 per cent of the Indian GDP from an area of 2.57 per cent of gross cropped area of the country (Solomon, 2016).Sugarcane crop is attacked by a number of pathogens like fungi, bacteria, viruses, phytoplasmas and nematodes causing about 55 diseases (Rott et al., 2000).
Among these diseases of the crop, sugarcane grassy shoot (SCGS) disease is becoming a serious threat for the crop and its occurrence has been reported from countries like Bangladesh, India, Malaysia, Nepal, Pakistan, Sri Lanka and Thailand (Sdoodee, 2001). The Sugarcane grassy shoot disease is caused by sugarcane grassy shoot phytoplasma that belongs to 16SrXI group (Nasare et al., 2007 and Rao et al., 2008). Plants affected with grassy shoot disease become bushy, with pale yellow and chlorotic leaves that remain thin, narrow, reduced in size, soft textured. Infected stools produce tillers with short internodes and side shoots are developed from bottom to top of the canes.
Grassy shoot infected sugarcane plants do not produce millable cane. Ratoon crops are most affected by the disease as compared to plant cane (Rao et al., 2007). The disease may cause 5 to 70 per cent yield loss in plant crop and the losses may rise up to 100 per cent in the ratoon crop (Vishwanathan and Rao, 2011).
Sugarcane grassy shoot disease is transmitted through the infected setts and by the leaf hopper vectors. Several leafhoppers have been confirmed as vectors for transmission of the disease (Arocha et al., 2005 and Srivastava et al., 2006).Grassy shoot disease of sugarcane is becoming a serious problem in many sugarcane growing states of India (Rao et al., 2008).
The phytoplasma has beenspreading very rapidly to newer locations with the help of infected planting material and leafhopper vectors. Hence, it would be important to diagnose and manage the SCGS phytoplasma at an early stage of the crop growth to avoid further spread and significant losses caused by them. It is also important to identify and characterize the responsible insect vectors for the secondary spread of phytoplasma in nature.
Though, grassy shoot phytoplasma suspected symptoms have been observed frequently on sugarcane crop in Assam but not much attempt has been made for a systematic study to record the incidence, economic damage and the etiology of the diseases. Therefore, there was a long felt need to carry out systematic study on the various aspects of the sugarcane grassy shoot diseases in Assam.