2012 Annual Report
1a.Objectives (from AD-416):
Develop elite hard winter wheat genotypes that incorporate multiple resistance genes that are effective against new African races of wheat stem rust.
1b.Approach (from AD-416):
Bread wheat germplasm lines with effective major gene and/or minor gene resistance against new African races of stem rust are being developed by USDA-ARS as well as many other institutions. These resistance donors will be crossed with multiple local elite breeding lines with high yield potential, grain quality, and tolerance to biotic and abiotic stresses. Good stewardship of valuable new resistance genes requires that they not be exposed singly in commercial cultivars. Endemic stem rust resistance genes, such as Sr24, Sr36, or Sr1A.1R, while very useful against most races, are not effective against all African races, and are not sufficient protection for new resistance genes. Therefore, the goal is to combine two or more new major genes into elite backgrounds. Minor gene or adult plant resistance genes are recommended as a supplement to major gene resistance. Minor genes are expected to be much more durable and do not require special stewardship protocols.
In order to produce commercially competitive varieties of the future, new stem rust resistance genes must be incorporated into a forward breeding program. In addition, a backcross breeding program is required both for parent-building and as a hedge if commercially acceptable resistant varieties are needed in the short term. Rapid breeding methods, such as doubled haploids, will be needed to achieve results as quickly as possible.
Phenotypic selection for resistance using common North American races will be difficult in most backgrounds due to the high frequency of endemic stem rust resistance genes. Therefore, marker-assisted selection for new resistance genes will be necessary. Molecular markers are available or under development for virtually all new sources of stem rust resistance. Marker genotypes will be generated locally or in a high throughput facility at the USDA-ARS Regional Small Grains Genotyping Laboratory in Manhattan, KS. Resistance of advanced lines against African races of stem rust will be confirmed by field testing at cooperative research facilities in Kenya or at the USDA-ARS Cereal Disease Laboratory. Testing for agronomic traits, yield, and quality will be performed as usual by the breeding program.
The first Oklahoma statewide replicated yield trial with Ug99-resistant materials was successfully performed in 2012, featuring alien resistance genes Sr22, Sr35, Sr39, Sr40 introgressed singly into adapted backgrounds (courtesy of USDA-ARS, Manhattan, KS). We tested 40 F2:5 lines putatively containing different alien genes initially backcrossed into the HRW cultivars Duster, Fuller, and 2174, or combinations thereof. From the 2012 field trial we identified lines agronomically equivalent to several elite HRW cultivars (Fuller, Duster, Endurance, and Garrison). Unexpectedly, the most desirable experimental lines carried Sr40 based on marker genotype, and the least desirable lines carried Sr22. However, the yield comparison is likely biased by genetic background, because Sr22 was introgressed into 2174 (inferior cultivar in 2012) whereas Sr40 was introgressed into a stacked background of Fuller and 2174. Generally, lines which were not confirmed to be Sr-resistance gene carriers based on markers performed superior to those confirmed to be carriers. Exceptions occurred, namely experimental line OK11870 and OK00876 (pedigree: Fuller*2//RL6088/2174*2), which performed superbly in the main body of Oklahoma thanks to high levels of resistance to endemic races of leaf rust and stripe rust. These and other selections from 2012 will provide focal points for future crossing with the objective to further generate 2- and 3-gene combinations for stem rust resistance. The most worthy selections will be made available as Great Plains-adapted gene donors to cooperators on this project, as deemed appropriate by the ARS project leader.
Six unique crossing blocks were established in 2011-2012 to further introgress Ug99 resistance from divergent and multiple donors. More than 120 single, three-way, and double crosses were completed using the adapted donors mentioned above, plus Kingbird, KSWGGRC52, and new sources of resistance featuring Sr26 and Sr39. Our primary emphasis in the 2012 crossing program was to hybridize confirmed 2-gene combinations with adapted recipient lines showing field resistance (source unknown) to Ug99 and other races in Kenya. The recipient lines included locally adapted elite inbreds.