2011 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.
A second year of local evaluation of Ug99-resistant germplasm was achieved through a multi-location, single-replicate observation nursery was planted at three Oklahoma locations in 2010-2011. This set of germplasms contained 89 BC3F2:4 lines selected from a larger single-environment nursery in 2010. Pedigrees common to the 89 lines are listed below, and they feature single-gene resistance to Ug99 in adapted backgrounds, using crosses initiated by USDA-ARS, Manhattan, KS. The pedigree Duster*2//Mq(2)5*G2919-k/2174*2 (Sr35) produced desirable progeny with greatest frequency. Twenty-two lines were selected based on high yield performance, suitable agronomic phenotype, and molecular marker confirmation (USDA-ARS, Manhattan; L. Yan, OSU) of resistance genes Sr22, Sr35, Sr39, and Sr40. Additional quality data to be collected will allow further selection of the most desirable lines for intercrossing in 2012, with the goal to stack resistance genes in appropriate combinations. Because some of the 89 lines were segregating for molecular marker genotypes associated with Ug99 resistance, head selections were made in certain lines to continue agronomic selection among nearly 500 BC3F4:5 lines. This two-stage selection process should provide a highly suitable agronomic platform for the southern Plains from which to build and further incorporate multiple sources of stem rust resistance.
Four crossing blocks were established in 2010-2011 to further introgress Ug99 resistance from divergent and multiple donors. About 120 single or three-way crosses were planned and completed using the following donor parents: Kingbird; KSWGGRC52; BC3F4 derivatives from pedigrees listed above, plus others and about 17 accessions selected from the 1st WWSRRN based on field observations in 2010. Where appropriate, single plants were marker-selected prior to crossing to increase the probability of crossing with a resistant donor. Recipient lines included locally adapted pre-release inbreds confirmed to have field resistance (gene identity unknown) to Ug99 and other races in Kenya.
Progress on this agreement is monitored by regularly discussing program goals and approaches in face-to-face meetings, by email and phone conferences, and by reviewing annual accomplishments reports.