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

Authors: MANLEY, AURORA - Texas A&M Agrilife; RAVELOMBOLA, WALTRAM - Texas A&M University; Adams, Curtis; TROSTLE, CALVIN - Texas A&M Agrilife; CASON, JOHN - Texas A&M Agrilife; PHAM, HANH - Texas A&M Agrilife; SHRESTHA, RAJAN - Texas A&M Agrilife; MALANI, SHUBAM - Texas A&M Agrilife

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/11/2023
Publication Date: 4/24/2023
Citation: Manley, A., Ravelombola, W., Adams, C.B., Trostle, C., Cason, J., Pham, H., Shrestha, R., Malani, S. 2023. Evaluating USDA guar [Cyamopsis tetragonoloba (L.) Taub.] genotypes for Alternaria leaf blight resistance under field conditions. Euphytica. 219. Article 56. https://doi.org/10.1007/s10681-023-03185-2.
DOI: https://doi.org/10.1007/s10681-023-03185-2

Interpretive Summary: Guar is a drought-and heat-tolerant legume that is the source of “guar gum,” which is used in many industrial and food applications. Alternaria leaf blight is a plant disease that negatively impacts guar production. Development of natural genetic resistance to the disease is the most effective and affordable way to manage it. Therefore, the objective of this study was to evaluate resistance to Alternaria leaf blight in a pool of 196 guar accessions from the USDA germplasm collection, with the ultimate goal to utilize resistant genotypes in breeding better guar varieties. To accomplish this, a two-year field study was conducted in Chillicothe, TX and Lubbock, TX in 2021 and 2022. Twelve guar genotypes were found to be resistant to the disease across locations and years, making them good candidates for guar breeding. The heritability (broad sense) of the resistance trait was high, indicating that breeding for resistance can be efficient and effective.

Technical Abstract: 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.