RESISTANCE TO SUNFLOWER RUST AND ITS INHERITANCE IN WILD SUNFLOWER SPECIES

Resistance to the prevailing races of sunflower rust, Puccinia heliant hi Schw., is lacking in the commercial hybrids (Helianthus annuus L.). The objective of this study was to identify new sources of resistance to the four North American rust races in wild Helianthus species, and to determine their mode of inheritance. Seventy-eight accessions of H . annuus L., H. argophyllus Torrey and Gray, and H. petiolaris Nutt. w ere evaluated in the greenhouse. Resistance to races 1, 2, 3, and 4 wa s observed in 25, 28, 15, and 26% of the plants, respectively, and 10% of the plants were resistant to all four races. Seven accessions that had a high percentage of resistant plants to all the four races were selected and one resistant plant from each accession was crossed with susceptible inbred line HA89. Three to four F1 plants resistant to all four races from each cross were backcrossed with HA89. F1 plants from PI 413118 x HA89 and PI 413175 x HA89 were resistant to all four race s. The PI 413023 x HA89 F1 plants were 100 % resistant to races 3 and 4 and segregated in a 3 : 1 resistant (R) to susceptible (S) ratio to races 1 and 2. The other four F, combinations segregated 3R : 1S ratio s to all four races. BC1F1 progenies revealed that plants from PI 4130 48, PI 413037, PI 413038, and PI 413171 used in the crosses possessed two dominant genes in heterozygous condition for resistance to each of the four races, whereas plants from PI 413023 possessed two dominant genes in heterozygous condition for resistance to each of races 1 and 2, and one dominant resistance gene in homozygous condition for each o f races 3 and 4. Plants from PI 413118 and PI 413175 carried a single dominant gene in homozygous condition for resistance against each of t he four races.