Influence of Weather, Vector and Variety on Incidence of Yellow Leaf Disease in Sugarcane

Yellow leaf disease of sugarcane (Saccharum spp.) caused by the Sugarcane yellow leaf virus (SCYLV), vectored by aphids has attained epidemic proportions causing severe yield losses, ranging from 20 to 40 % in susceptible varieties. Yellow leaf spread by aphids depends on cultivar susceptibility as well as weather parameters and thus the present studies were conceptualized. The observations on meteorological parameters were taken from the observatory at the station. The data on incidence of vector(aphids) and yellow leaf disease were recorded at weekly interval during the entire crop growth period on three sugarcane varieties viz., 2005 A 128, 2001 A 63 and 2003 V 46. The data on vector and disease incidence was correlated with weather parameters. The aphid incidence on 2005 A 128 initiated (4.6 per leaf) at 30 SMW and gradually increased to 19.1 per leaf at 40 SMW. In the variety 2001 A 63, the aphid incidence was first observed (2.2 per leaf) at 27 SMW and reached the peak population of 19.1 per leaf at 38 SMW. The aphid incidence on 2003 V 46 initiated (2.1 per leaf) at 29 SMW and gradually increased to 18.1 per leaf at 42 SMW. With regard to yellow leaf disease the incidence was first observed (1.0 per cent) at 26 SMW and reached the peak (28.7 per cent) at 37 SMW in the variety 2005 A 128. In the variety 2001 A 63, the incidence of yellow leaf disease was 1.8 per cent at 26 SMW which later on increased up to 29.4 per cent by 46 SMW. The incidence of yellow leaf disease was 3.5 per cent at 28 SMW which later on increased up to 27.6 per cent by 44 SMW in the variety 2003 V 46.The observations on incidence of aphids and YLD in susceptible varieties revealed that aphids contribute significantly to the initial spread of YLD, from initial incidence of aphids and YLD in 29-30 SW up to 42-44 SMW when the aphids reach peak incidence and YLD also leaps to above 25 per cent. The aphid population exhibited positive correlation with maximum temperature (r2=0.62), minimum temperature (r2=0.55) and relative humidity I (r2=0.65), whereas, negative correlation with rainfall (r2=-0.63). The yellow leaf disease exhibited positive correlation with minimum temperature (r2=0.75) and relative humidity I (r2=0.67), whereas, negative correlation with rainfall (r2=-0.63). The leaf and aphid samples were collected at peak incidence of Yellow leaf disease and were tested and found positive for presence of virus using ELISA reader at 405 nm.