Sclerotinia Stem and Head Rot Resistant Germplasm Development Utilizing

Based on evaluations over two years, interspecific amphiploids are useful sources of resistance genes for both Sclerotinia stem rot and head rot. Interspecific amphiploids between wild perennial Helianthus gracilentus, H. hirsutus, H. strumosus, H. grosseserratus, H. maximiliani, and H. nuttallii, crossed with P21, plus one intercrossed amphiploid involving H. divaricatus and H. grosseserratus were evaluated. The results indicated that most amphiploids were more resistant to stem rot and head rot than the tolerant checks HA 410 and HA 441, respectively. The good F1 seed set between the amphiploids and HA 410 or HA 441 provided a sufficient number of plants for further backcrossing and chromosome reduction toward the 2n=34 of the cultivated sunflower