Different aerated steam therapy (AST) regimes on the development of grassy shoot disease symptoms in sugarcane

Abstract

Aerated steam therapy (AST) treatment of seed cane for a period of 1 h at 50°C is given to eliminate grassy shoot disease (GSD) incidence in sugarcane. However, there are reports that this treatment was found ineffective in reducing GSD in plant crop to a significant level. Hence, enhanced treatment duration from 1 h to 3 h at 50°C and increased temperature regimes from 50 to 52 °C for 1 h were evaluated for sugarcane sett germination and GSD development in plant crop. Effect of grassy shoot phytoplasmas infection on sett germination revealed that in 8 out of 12 genotypes, phytoplasma infection reduced sett germination. AST at 50°C for 1 h recorded higher per cent germination of setts as compared to the untreated setts. When treatment temperature was increased from 50 to 52 °C, sett germination was affected in 3 out of 7 genotypes. Similarly increased treatment time from 1 h to 3 h at 50°C also resulted in reduced germination of setts in all the 5 genotypes. In the first trial, disease build up was slower in plots planted with setts treated at 50°C for 1 h and healthy setts as compared to the diseased setts. However, by the 12th month almost all the 12 genotypes except Co 8340, Mosaic-1 and M84-074 showed 100 per cent disease incidence in all the treatments. When treatment temperature was increased from 50 to 51 and 52 °C for 1 h or treatment at 50 °C for 2 or 3 h significant reduction in GSD build up was noticed in the field. By 12th month these treatments recorded either no disease or very restricted development of GSD as compared to untreated controls and AST treatment for 1 h at 50 °C. Reduced disease incidence by altered temperature regimes from 50 to 52 °C and enhanced treatment duration at 50 °C for 2 or 3 h significantly increased the number of millable canes and cane yield in the plant crop. Although higher temperature regimes or enhanced treatment time affected sugarcane sett germination to a certain extent, these treatments markedly enhanced cane yield as compared to conventional treatment at 50 °C for 1 h or untreated controls.