Studies on sunflower rust. X. Specialization of Puccinia helianthi on wild sunflowers in Texas

Abstract

Sunflower rust (Puccinia helianthi) was collected in Texas on wild Helianthus spp. believed to be ancestors of the cultivated sunflower (Helianthus annuus). Race 1, the least pathogenic on the standard "Canadian" differentials, was the most common. Races 1 and 2 predominated on H. annuus and H. debilis, race 2 on H. praecox, and race 4 on H. petiolaris. Most host species proved to be heterozygous for rust resistance; cross-infectivity tests between them were inconclusive. Puccinia helianthi shows a high degree of adaptive variability, which suggests that local specialization may be relatively unimportant.