Screening and biochemical profiling of 'Mac-07' crosses for resistance to CLCuD under field and glasshouse conditions.

Cotton is a valuable crop for the textile industry yet, its production is significantly affected by Cotton Leaf Curl Disease (CLCuD), a major cotton constraint. The present study was conducted under field trials and glasshouse conditions to analyze the effect of CLCuD in cotton. Single plant progeny rows (SPPRs) of different cotton accessions were grown in the field. In the glasshouse, two sets of cotton plants were maintained in a controlled environment. One set was kept healthy, while the other was graft-inoculated with a Cotton Leaf Curl Virus (CLCuV) infected plant. After 90 days post-inoculation, SPPRs and grafted plants were screened for symptom development using a disease rating scale from 0 to 6. Estimation of antioxidants and metabolites revealed significant differences in CLCuD-resistant and susceptible varieties. Elevated levels of total phenolic content (TPC), tannins, total oxidant status (TOS), total soluble proteins (TSP), and malondialdehyde (MDA) were observed by CLCuD-susceptible genotypes in the field and glasshouse. In contrast, increased antioxidants for example, peroxidase (POD), ascorbate peroxidase (APX), and, catalase (CAT) were observed in CLCuD- resistant varieties. Under field conditions, CLCuD-resistant varieties showed elevated antioxidant enzymes, with CAT, POD, and APX activities increasing by 32%, 3%, and 8% respectively, while superoxide dismutase (SOD) activity decreased by 25% compared to susceptible lines. Under glasshouse conditions, resistant genotypes showed stronger antioxidant responses than susceptible ones; for instance, POD and APX activities were ~ 62% and ~ 6% higher, respectively, while CAT and SOD increased by 15% and 3%. Principal component analysis (PCA) of the field experiment indicated that five key factors contributed to 80.26% of the variation observed among genotypes. Analysis of the glasshouse experiment explained 74.24% of the total cumulative variability. These factors were identified as the most influential in explaining differences in morphological and biochemical traits. In our study, genotypes Mac-07, T7-1-2, and T7-2-5, showed high chlorophyll a, lycopene, TPC, tannins, MDA, and antioxidant enzymes in the field. Under glasshouse conditions, their un-inoculated plants exhibited elevated level of chlorophyll a and b, total chlorophyll, lycopene, APX, SOD, CAT, and POD. Overall, Mac-07, T7-1-2, and T7-2-5 demonstrated superior performance against CLCuD across both conditions and can be considered strong candidates for future CLCuD-resistant cotton breeding programs.