Plant and Weather Factors on Resistance of Saccharum officinarum Germplasm Against Ring Spot Disease

Abstract

Ring spot caused by Leptosphaeria sacchari is a very common disease of sugarcane in humid tropical conditions. We have conducted a detailed study on status of disease resistance to the disease in our major Saccharum spp collections of Saccharum officinarum. All the S. officinarum clones exhibited ring spot disease with varying intensity as 70.14% clones showed resistant reaction, 24.3% clones showed intermediate reaction and 5.5% clones showed susceptible reaction. The disease appears in the month of June and remains until the harvest. Maximum average disease severity (29.33%) was observed in the July. The accessions analysed also showed significant difference with respect to origin. Multiple comparisons indicated that mean rank of Thailand accessions (682.50) was significantly highest as compared to those of other. Stalk height and leaf length showed significantly weak correlation with ring spot incidence, and other morphological factors were not significant. Disease severity with leaf colour and canopy type was found significant. Purple-leaved clones recorded lower disease incidence than other clones. Very strong positive correlation was observed with rainfall, evening relative humidity and rainy days, whereas maximum temperature showed significant negative correlation. This study clearly indicated the role played by the morphological factors, juice quality traits and weather factors in determining resistance in germplasm to ring spot disease in sugarcane.