Characterization of a groundnut collection to stem rot disease caused by Sclerotium rolfsii

Stem rot caused by Sclerotium rolfsii is a destructive disease that induces serious yield losses in groundnut (Arachis hypogaea L.) around the world. This study used a multifaceted approach to screen 121 groundnut genotypes from different subspecies and botanical varieties for resistance to S. rolfsii under field conditions. Five wild species of Arachis were also assessed in a greenhouse study. In both experiments, 60 to 65 days after planting, plants were inoculated with an aggressive isolate of S. rolfsii using a combined agar disk technique. Disease assessments were made using a disease score (DS) scale of 1 to 5 based on the percentage of symptomatic plants. The genotypes and wild species were also screened using a SSR marker associated with fungal resistance. In the first year of study, significant variations were observed among the genotypes with respect to disease related traits. The DS results varied from 2 to 5 with a general mean of 4.7. Under heavy disease pressure, 5.7% and 1.6% of the collection were found to be moderately susceptible and moderately resistant, respectively. In the second year of study, the selected moderately susceptible and moderately resistant genotypes were assessed in similar field conditions. The overall result showed that the lowest DS was observed in the genotypes ACG 14 and ACG 101, from subsp. fastigiata var. vulgaris and var. subsp. hypogaea var. hypogaea, respectively. They also had similar pod yield with controls. For the wild Arachis species, the average DS was 3.7, A. batizocoi having the lowest DS of 2.5, followed by A. duranensis and A. cardenasii. There was no correlation between the molecular marker analysis and field phenotyping. New validated resistance related markers should be developed for further studies to select truly resistant/susceptible genotypes.