Determination of resistant genotypes against to stem rot disease (caused by Sclerotium rolfsii) in groundnut and validation of marker linked to disease

Stem rot is one of most the important biotic stress factors in groundnut, and causes to high yield losses worldwide. In the present investigation 121 groundnut genotypes from different subspecies and botanical varieties were screened for resistance to S. rolfsii under field conditions. The five wild Arachis species, A. diogoi, A. ipaensis, A. botizocoi, A. duranensis and A. cordenosii, were also evaluated in greenhouse conditions. 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 with a grain-based medium. A disease score (DS) scale (1 to 5) was used to assess symptomatic plants. To validate the experimental assessments, leaf samples of the genotypes and wild type species were analyzed using a SSR marker, GM2350, associated with stem rot resistance. The traits of lesion length, lesion area and disease severity showed significant differences among the genotypes. The DS ranged from 2 to 5 with a general mean of 4.7. The 5.7% and 1.6% of the collection were found to be moderately susceptible and moderately resistant, respectively. The lowest DS results were identified on genotypes ACG 14 from subsp. fastigiata var. vulgaris and ACG 101 from subsp. hypogaea var. hypogaea. ACG 101 also had a similar pod yield to the control plot. The lowest DS was recorded as 2.5 for A. botizocoi and the average DS was 3.7 in wild species. There was no correlation between the molecular analysis and field phenotyping.