Resistance to Yellow Leaf Disease in Sugarcane Genotypes as Influenced by Physico-chemical Traits

Field investigation was carried out to evaluate the reaction of sugarcane genotypes to yellow leaf disease (YLD) under natural field conditions to characterize their associated biophysical and biochemical responses. Correlations among disease expression, the vector (aphid) incidence and weather parameters were also assessed. Pooled data of three years (2022-23 to 2024-25) showed that six genotypes viz. 2015A311, 2017A553, CoA20321, CoA20323, CoA20325, and CoV19359 exhibited resistant (R) reactions with disease severity scores between 0.0 and 1.0. Nine genotypes exhibited moderately resistant (MR) reactions with disease severity >1.0–2.0, while others such as CoA19322 and 2001A63 were moderately susceptible (MS). The variety, 2003V46, was highly susceptible (S) with disease severity >3.0. Resistant genotypes typically exhibited semi-erect leaves (22°–28°), medium to medium-wide leaf blades, and light-green foliage with SPAD values of 28–31. They also recorded higher phenol content (33.67–40.34%) and silica levels (1.64–2.41%) than the susceptible check 2003V46, which showed greater leaf droopiness (42°), higher sucrose (17.62%), and reduced phenols (28.32%) and silica (1.30%). DAS-ELISA confirmed SPLCV infection in both resistant and susceptible lines, with absorbance values of 3.693–3.957 in positive samples. Aphids collected from susceptible genotypes alone tested ELISA-positive, confirming vector-mediated transmission. Aphid population and YLD incidence were positively correlated with maximum temperature and relative humidity. Rainfall showed a significant negative correlation, indicating that warm, dry conditions favored aphid activity and disease spread. Overall, the genotypes 2015A311, 2017A553, and CoA20323 were identified as stable YLD-tolerant sources, making them promising candidates for resistant breeding programmes in sugarcane.