Cotton resistance to white mold (Sclerotinia sclerotiorum) evaluated by the oxalic acid method

The white mold (Sclerotinia sclerotiorum) is one of the most destructive cotton disease. Genetic resistance is one of the main strategies to control this disease. Thus, this study aimed to determine an appropriate period of exposition and concentration of oxalic acid to identify levels of physiological resistance to white mold in white fiber cotton genotypes. The study was implemented in two periods (August to October and November to January) in randomized complete block design, in a split-split-plot factorial in time, with five replications, where the plot factor was the concentration of oxalic acid (20; 40 mM) and the sub-plot factor was the 20 cotton genotypes, the sub-sub-plot factor was the time of exposure to oxalic acid (24h; 48h; 72h). The experimental units, or plots, were composed of test tubes with one cotton plant shoot partially immersed in oxalic acid solution. The biomass of the cotton shoots was evaluated at 24, 48, and 72 h. The loss of water caused by the exposure to oxalic acid indirectly indicates the level of cotton resistance to white mold. The results suggest that the most appropriate exposition time and concentration of oxalic acid for cotton evaluation of resistance to white mold were 20 mM at 48 hours, respectively. In these conditions, the cotton genotypes that presented the greatest average fresh mass were: UFU-14 A, UFU-14 B, UFU-14 F, UFU-14 H, and UFU-14 S, which could be used as sources of resistance to white mold in cotton breeding programs