Evaluating USDA guar [ Cyamopsis tetragonoloba (L.) Taub.] genotypes for Alternaria leaf blight resistance under field conditions

Guar [ Cyamopsis tetragonoloba (L.) Taub] is a drought- and heat-tolerant legume that produces seed embryo galactomannan compounds for industrial, chemical, and food applications. Alternaria leaf blight, caused by Alternaria cucumerina var. cyamopsidis , is one of the major diseases affecting guar production worldwide. Development of guar varieties resistant to Alternaria leaf blight is the most affordable way to manage this disease. Objectives of this study were to evaluate responses of diverse guar germplasm to Alternaria leaf blight and identify germplasm with resistance, with the goal of incorporating them into the guar breeding program. A total of 196 USDA guar accessions were grown in single-row five-meter plots at the Texas A&M Agrilife Agricultural Experimental Station in Lubbock and Chillicothe, TX in the year of 2021 and 2022, respectively. A 1–5 scale was used for scoring, by two individuals, and began after disease symptoms were first observed. A significant location X year X genotype interaction was present ( p = 0.0137) and broad sense heritability ( H ) for disease susceptibility was 88.4%. Twelve genotypes were found to be resistant across locations and years (Table 4 ), with PI 288,429 being resistant across three location/year combinations. Overall, all lines tested are well adapted, selection can be done in early generations (F2), and potential parents for additional germplasm improvement were identified. To the best of our knowledge, this is the first report of field evaluation of Alternaria leaf blight involving 196 guar genotypes.