Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/18/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: Peanut smut, caused by the fungus Thecaphora frezzii, is the most problematic disease in Argentina and threatens peanut production worldwide. A major roadblock in breeding for peanut smut resistance is the current practice of manually opening pods to rate disease, which is slow and labor intensive. To address this problem, we developed and evaluated an X-ray imaging system as a potential alternative to hand-opening pods. Because the peanut smut pathogen is not present in the U.S., we made faux-infected pods by replacing all or one seed with finely ground coffee, corn starch, or corn smut (Mycosarcoma maydis) teliospores, as a substitute for T. frezzii teliospores. In addition, we made some pods with an artificial artificial sorus (a cluster of spores) on one seed. Over 3,300 pods, representing each of the four major market types, were scanned using the X-ray system, and the images were scored by ten raters as being healthy or “unhealthy” (faux-infected pods). Overall, the raters correctly scored 85% of the images, and healthy pods were easier to identify (89.5%) than faux-infected pods (82.6%). Raters had the most trouble with correctly scoring pods containing the artificial sorus (21.2%). However, pods with small/few sori and partially damaged seeds are reported to be relatively rare in both resistant and susceptible genotypes in Argentina. Therefore, the X-ray system’s inability to generate clear images of artificial sori may not be a significant detraction. These results indicate that the X-ray imaging system has potential for peanut smut phenotyping, but the system needs to be validated in Argentina with pods grown in T. frezzii-infested fields.

Technical Abstract: Peanut smut, caused by the fungus Thecaphora frezzii, is the most problematic disease in Argentina and threatens peanut production worldwide. A major roadblock in breeding for peanut smut resistance is the current practice of manually opening pods to rate disease, which is slow and labor intensive. To address this problem, we developed and evaluated a line-scan X-ray imaging system as a potential alternative to hand-opening pods. Since the peanut smut pathogen is not present in the U.S., suitable test phantom pods were developed to emulate infected pods. Faux-infected pods were made by replacing all or one seed with finely ground coffee, corn starch, or corn smut (Mycosarcoma maydis) teliospores, as a proxy for T. frezzii teliospores. In addition, one seed from some pods were made to contain an artificial sorus made from corn smut teliospores to mimic T. frezzii-infected pods with low levels of disease severity. Over 3,300 pods, representing each of the four major market types, were scanned using the X-ray system, and the images were scored by ten raters as being healthy or “unhealthy” (faux-infected pods). Rater accuracy varied from 82-89%, and overall, the ten raters correctly classified 85% of the images. Healthy pods were easier to identify (89.5%) than faux-infected pods (82.6%), but raters had the most difficulty in correctly scoring pods with the artificial sorus (21.2%). Because T. frezzii-infected pods with small/few sori and partially damaged seeds are reported to be relatively rare in both resistant and susceptible genotypes, the X-ray system’s inability to generate clear images of artificial sori may not be a significant detraction. These results indicate that the X-ray imaging system has potential for peanut smut phenotyping, however, the system needs to be tested in Argentina with pods grown in T. frezzii-infested fields.