|Rouse, Matthew - Matt|
|Bonman, John - Mike|
Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/21/2012
Publication Date: 7/1/2013
Publication URL: http://apsjournals.apsnet.org/doi/abs/10.1094/PDIS-02-12-0200-RE
Citation: Newcomb, M.S., Acevedo, M., Bockelman, H.E., Brown Guedira, G.L., Goates, B., Jackson, E.W., Jin, Y., Njau, P., Rouse, M.N., Singh, D., Waynera, R., Bonman, J.M. 2013. Field resistance to the Ug99 race group of the stem rust pathogen in spring wheat landraces. Plant Disease. 97:882-890. Interpretive Summary: Stem rust disease is a threat to wheat production worldwide. Many US wheat cultivars are vulnerable to new races of the stem rust pathogen (‘Ug99’ and its variants) that have recently appeared in East Africa and spread to the Middle East and Southern Africa. As part of an international effort to reduce this threat, the National Small Grains Collection (NGCG) is screening accessions against the new races in Kenya. Through this work we have found 246 ‘landrace’ wheats from the NSGC that are naturally resistant to the new races. There are a few known genes for resistance to Ug99, so the next step will be to determine if the resistant accessions have known genes for resistance or novel genes for resistance. Also, since these landraces are likely not adapted to US agriculture, further work is needed to transfer any novel resistance into productive genetic backgrounds. Once identified and transferred, novel resistance to the stem rust pathogen will be useful to wheat breeders for developing new disease resistant wheat cultivars.
Technical Abstract: Wheat landraces provide a useful source of genetic variability for breeding and germplasm enhancement. The emergence and spread of newly detected and highly virulent races of the stem rust pathogen (Ug99 and its variants) threaten wheat production globally. Spring wheat landraces from the NSGC were screened for resistance in eight field seasons at the Kenya Agricultural Research Institute, Njoro, where the Ug99 race group has become endemic. Accessions showing resistance in one season were re-tested in the field and also screened with molecular markers associated with rust resistance genes Sr2, Sr24, Sr36, Lr34/Yr18, two height-reducing genes, and a photoperiod insensitivity allele. Of 2509 accessions tested, 278 were categorized as resistant based on results from at least two field seasons. Thirty-two of these resistant accessions were positive for one or more of the markers diagnostic for the Sr2, Sr36, Rht-B1b or Rht-D1b, indicating that they do not fit the definition of ‘landrace’ since these genes were likely introduced via modern breeding practices. Thus, 246 resistant accessions were identified that fit the ‘landrace’ classification. The landraces that were screened were originally collected from 67 countries, with 37 countries having more than 5 tested accessions. For 9 of these 37 countries (Afghanistan, Iran, Portugal, Ethiopia, Uzbekistan, Greece, Tajikistan, Bosnia and Herzegovina, and Serbia), at least 10 percent of the tested accessions were resistant to the Ug99 race group. Future research will characterize the resistance to determine its novelty and incorporate novel genes into improved breeding lines.