Faba bean (Vicia faba L.) is one of the oldest grain legumes and is grown in many countries for both human consumption and animal feed. Faba bean rust, caused by Uromyces viciae-fabae, is a serious disease of faba beans in the subtropical agricultural region of Australia. Experiments were conducted to assess the genetic variation for rust resistance in Australian faba bean germplasm and to determine the genetic basis of rust resistance in selected germplasm. Resistant lines were identified, subsequently crossed to agronomically suitable parents and the ensuing progeny were evaluated for resistance. Many derived lines showed a higher level of resistance than the current cultivars, although none were rated immune. This level of resistance was considered adequate for reliable crop production when combined with limited fungicide application. Genetic studies from the seedling test of F2 and F3 progenies derived from two crosses based on two different sources of resistance showed three distinct responses; highly resistant, moderately resistant and susceptible. However, no homozygous family with a moderate response was found in the F3 progeny test, hence, this infection type could not be attributed to independent gene(s). The segregation ratio in both F2 and F3 in the population derived from Doza#12035, a selection from the commercial cultivar Doza, indicated a single dominant gene was responsible for conferring resistance. In the other population developed from the resistant parent Ac1655, it is likely that also a single dominant gene confers resistance even though the F3 segregation ratio deviated significantly from a one gene hypothesis. An allelism test revealed that each of the resistant parents (Doza#12035 and Ac1655) carried a single and independent gene for resistance, thus providing at least two genes for breeders to choose or pyramid for improving the rust resistance in faba bean.
Faba bean is gaining attention in Australia as a rotation grain legume where most of the country’s produce is exported. Rust, caused by Uromyces viciae-fabae, is a major constraint to Faba bean production in eastern Australia and its chemical control results in increased cost of production. The deployment of diverse sources of resistance in new cultivars underpins economic and eco-friendly control of rust diseases of crops. A selection from cultivar Doza (Doza#12034) and a European accession Ac1655 exhibited seedling rust resistance against U. viciae-fabae pathotype 24–40. Doza#12034 and Ac1655 were crossed with a susceptible genotype Fiord and recombinant inbred line (RIL) F6 populations were generated. Rust tests on Fiord/Doza#12034 and Fiord/Ac1655 F4 and F6 populations demonstrated monogenic inheritance of resistance in both crosses and the underlying resistance loci were named Uvf-2 and Uvf-3, respectively. Genetic mapping of both RIL populations located Uvf-2 and Uvf-3 in chromosomes III and V, respectively. The SNPs that showed linkage with Uvf-2 and Uvf-3 were converted into kompititive allele specific PCR (KASP) assays. Markers KASP_Vf_0703 and KASP_C250539 flanked Uvf-2 at 4.9 cM and 2.9 cM distances, whereas Uvf-3 was flanked by KASP_Ac×F165 (2.5 cM) and KASP_vf_1090 (10.1 cM). Markers KASP_Vf_0703 and KASP_Ac×F165 can be used for marker-assisted selection of Uvf-2 and Uvf-3, respectively, after confirming parental polymorphisms.
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