Ensuring productivity and food security through sustainable control of yellow rust of wheat in Asia

ACIAR funding supports ongoing and new research and capacity building activities at CIMMYT, ICARDA, PBIC-Sydney University to ensure productivity and food security through sustainable control of wheat yellow rust, caused by Puccinia striiformis tritici (Pst), in Asia. Development of new near-isogenic lines (NIL) for greenhouse and field monitoring has been initiated to fill the gaps in the existing NIL set. NILs for genes Yr28, Yr29, Yr30, Yr31, and reselections for Yr8, were completed during 2005. Specific gene combinations (Yr1+9, Yr1+27, Yr9+27) were grown in segregating populations and will be selected in 2006. Data from yellow Rust Trap nurseries planted at key sites in South Asia and CWANA regions indicated significant variations in Pst populations within region. Virulence for resistance gene Yr27 has spread in the region and poses a major threat as several popular cultivars carry this resistance gene. Northwestern Pakistan suffered with a severe epidemic during 2005 on the major cultivar Inquilab 91. Likewise virulence on Yr1 first detected in 1999 in Tajikistan is now widespread. Yr1 virulence has likely contributed to the high susceptibility of yellow rust on winter and facultative winter wheats in Central Asia. Race with Yr10 virulence, detected in Yemen, Syria and Azerbaijan, has resulted in compatibility on most commercial durum wheat cultivars in West Asia. Virulence for Yr17, first detected in Central Asia is now spread to Afghanistan and Pakistan, however absent in India.

Several wheat cultivars grown and newly released in various Asian countries were evaluated in the field together with the Avocet NILs. Cultivars showing good level of resistance were identified. Evaluation in Mexico of individual F2 derived-F3 lines from crosses of yellow rust susceptible Avocet with four Chinese cultivars that show moderate levels of resistance in China but immunity in Mexico indicated that each cultivar carried 1 or 2 major genes and 2-3 minor genes. Presence of leaf tip necrosis in Chuan Mai 107 indicated the presence durable slow rusting gene Yr18. Multi pathotype studies at PBIC among 32 wheats from Central Asia have shown the presence of Yr1, Yr6, Yr7, Yr9, and possibly Yr27, with additional adult plant resistance. Populations from the crosses of Avocet with 10 bread wheat lines that have shown complete or partial resistance to yellow rust across CWANA region over the past 10 years were studied at ICARDA. Preliminary results indicate that 6 lines carry 2 to 3 resistance genes. Seedling tests indicated the presence of Yr1+Yr15 and Yr17+Yr15, respectively in two lines.

Significant progress was made in incorporating durable resistance into several cultivars. Because these cultivars are highly resistant in Mexico but either susceptible or moderately resistant in China, we used a shuttle breeding strategy to speed up the breeding as well as select under high yellow rust pressure in China. In the first group of materials we attempted to incorporate resistance in five Chinese cultivars. Advanced generation materials from 50 BC1-derived F6 lines developed entirely in Mexico to F3, followed by F4-F6 selection in China, were compared in the field in Chengdu, China. Several lines showed good agronomic features and high to adequate levels of resistance to yellow rust in, China, irrespective of the two selection strategy. However, the shuttle breeding strategy was better as higher frequency of lines were resistant and adapted to Chengdu environment. Moreover, it also develops local capacity to continue the work in the future. Several lines showed higher yield potential than Chinese cultivars in yield trials in Mexic, However results indicated that yield evaluations must be carried out in China since it was evident that Chinese parents were not well adapted in Mexico. Seeds of 62 new BC1-derived-F5 populations involving 13 additional Chinese cultivars from Sichuan and Yunnan Provinces were sent to China after selection in Mexico in F3 and F4 generations. Additional 125 BC1 populations involving a total of 25 cultivars were developed and selected.

Evaluation of 22 advanced lines (developed in Mexico for high yield potential, adult plant resistance to yellow and leaf rusts and good grain quality) in India and Pakistan indicated that at least 4 lines had 10-20% higher yield potential that local checks and possessed high levels of adult plant resistance. These and some additional lines are being tested at multiple sites during the 2005-2006 crop season. A new yield trial containing 28 high-yielding entries and resistant to rusts was formed and distributed for planting at 16 sites in India, Pakistan, Afghanistan, Iran and Turkey to find replacement for cultivars that are now susceptible to new races of yellow rust. Incorporation of yellow rust resistance in 21 facultative/winter wheat cultivars from Central Asian countries was also initiated.

ACIAR funding supports ongoing and new research and capacity building activities at CIMMYT, ICARDA, and PBIC-Sydney University to ensure productivity and food security through sustainable control of wheat yellow rust, caused by Puccinia striiformis tritici (Pst), in Asia. Development of new near-isogenic lines (NIL) for greenhouse and field monitoring for genes Yr2, Yr3, Yr4, Yr33, Yr34, Yr35, Yr36 is progressing to fill the gaps in the existing NIL set. NIL for gene Yr8 purified and multiplied and for Yr17 purified. Specific gene combinations are also under progress. Data from Yellow Rust Trap nurseries planted at key sites in South Asia, China and CWANA regions indicate significant variations in Pst populations in these areas. Virulence for Yr17, first detected in Central Asia, is now widely spread. Increasing virulence for Yr3 and its distribution in Pakistan and Afghanistan is a threat to the variety 'Tatara' the sown area of which has increased recently after the epidemic on 'Inquilab 91' during 2005. Lack of virulence for some genes that were ineffective previously is a major concern to progress in yellow rust breeding. A unified Yellow Rust Trap Nursery will now be planted in all countries except China which forms a different epidemiologic region with very different cultivars.

Several facultative/winter wheat cultivars grown, or newly released, in various countries of the CWANA region indicated that only a few were resistant at all sites except in Pakistan. This further demonstrated their vulnerability to diverse pathotypes predominant in different areas. Seedling gene postulation work on Central Asian cultivars conducted in Australia identified some of the commonly occurring genes, which have little or no value to provide resistance to some of the races known to occur in the region. Evaluation in Mexico of individual F2 derived-F5 lines from crosses of yellow rust susceptible Avocet with four Chinese cultivars that show moderate levels of resistance in China but immunity in Mexico confirmed F3 results that each cultivar carried 1 major gene and 2-3 minor genes.

Significant progress was made in incorporating durable resistance into several cultivars from China. Because these Chinese cultivars are highly resistant in Mexico but either susceptible or moderately resistant in China, we used a shuttle breeding strategy to speed up the breeding as well as select under high yellow rust pressure in China. During 2006 we identified 119 advanced lines with yellow rust resistance and desirable agronomic traits and planted them in replicated yield trials in farmers' fields during the 2006-2007 season. Selections were done on 62 new BC1-derived-F5 populations involving 13 additional Chinese cultivars from Sichuan and Yunnan provinces during 2006 in Chengdu and over 1000 advanced lines were planted for further evaluation and selection during 2006-2007. An additional 94 F4 populations were planted in Chengdu and Kunming following selection in the F2 and F3 generations in Mexico.

The '1st Elite Bread Wheat Yield Trial', containing 28 high-yielding entries with resistance to rusts, was grown at a total of 16 sites in India, Pakistan, Afghanistan, Iran and Turkey to find replacements for cultivars that are now susceptible to new races of yellow rust. Several new lines showed significantly higher yield potential and resistance at most of the sites in each country and were selected by the co-operators for further testing. Seed of high yielding entries for the '2nd Elite Bread Wheat Yield Trial' was multiplied during 2006 and planted at 30 sites in 11 countries. About half of the entries have shown high to moderate levels of resistance to the Ug99 race of stem rust pathogen.

Incorporation of yellow rust resistance in 21 facultative/winter wheat cultivars from Central Asian countries has been progressing well in Mexico. Populations in various generations from F1 to F3 were planted for either backcrossing or selection under yellow rust pressure in the 2006-2007 winter season at Toluca, Mexico.

A training course was organized in Uzbekistan for 20 scientists, mostly from Central Asia, to enhance their capacity in managing rust diseases of wheat and breeding for resistance. A Chinese scientist, Mr. Huazhong Zhu, attended a 3-month advanced training course on wheat improvement in Mexico. R.P. Singh, C. Wellings and A. Yahyaoui interacted with various scientists during visits to various breeding and pathology programs in China and Central Asia.

ACIAR funding supports ongoing and new research and capacity building activities at CIMMYT, ICARDA, and PBIC-Sydney University to ensure productivity and food security through sustainable control of wheat yellow rust, caused by Puccinia striiformis tritici (Pst), in Asia. The goals of this project were combined with the goals of the "Borlaug Global Rust Initiative" especially to disseminate and breed spring wheat materials with durable resistance to all three rusts and to conduct training. This became necessary due to the threat that the Ug99 race of stem rust pathogen poses to wheat production in most of the countries within the scope of the ACIAR project.

Development of new near-isogenic lines (NIL) for greenhouse and field monitoring for genes Yr2, Yr3, Yr4, Yr33, Yr34, Yr35, Yr36 is progressing to fill the gaps in the existing NIL set. Some NILs are undergoing purification/ further backcrossing as they were found to carry the slow rusting adult plant resistance gene Yr18. The development of NILs with specific gene combinations is in progress. Data from the Unified Yellow Rust Trap Nursery planted at key sites in various countries indicated significant variations in Pst populations. Several spring and facultative/winter wheat cultivars grown in various countries of the CWANA region indicated that only a few were resistant. This demonstrated their vulnerability to diverse pathotypes predominant in the epidemiologic region. This, combined with their susceptibility to the Ug99 race of stem rust, warrants efforts to identify and release new resistant varieties together with an aggressive seed production and dissemination strategy.

Significant progress was made in incorporating durable resistance into several cultivars from China. Because these Chinese cultivars are highly resistant in Mexico but either susceptible or moderately resistant in China, we used a shuttle breeding strategy to speed up selection as well as to select under high yellow rust pressure in China. Yield trials conducted during the 2006-07 season in the Sichuan Province identified about eight lines with yield potential similar to the check. One of these lines will be promoted for wider testing in Provincial Yield Trials during 2007-08. Sixty additional lines were planted for yield tests during the 2007-08 season. Selection was also conducted in additional breeding materials.

Multi-site (25 sites) testing of high yielding spring wheat lines with resistance to all three rusts (including the Ug99 race of stem rust), across seven countries, has identified 2-3 lines with significantly superior yield performance to that of current varieties. These lines are being tested widely by National Programs and simultaneous seed multiplication has been initiated. Seed of high yielding entries for the '3rdElite Bread Wheat Yield Trial' was multiplied during 2007 and the replicated yield trial (30 entries) and was distributed to 21 countries.

Incorporation of yellow rust resistance into 21 facultative/winter wheat cultivars from Central Asian countries is progressing in Mexico. Populations in various generations from BCF1 to F4 were planted for selection under yellow rust pressure in the 2007-08 winter season at Toluca, Mexico. Seed of F3 and F4 populations was sent to Turkey and Kazakhstan for selection under local environments.

Two scientists, one each from Turkey and Kazakhstan, spent 3 months at PBIC, Sydney University learning gene postulation and yellow rust management. Two courses (of 2 and 3 month duration) were organized by CIMMYT in Mexico for intensive wheat improvement training. These courses were attended by 4 scientists from India, 1 from Nepal, 1 from Pakistan, and 2 from Iran. A short training course on disease management, organized by ICARDA in Tunisia, was attended by 20 scientists. External funding was obtained to support these courses.