Submitted to: Dryland Agriculture Book
Publication Type: Research Technical Update
Publication Acceptance Date: 4/20/2013
Publication Date: 7/20/2013
Citation: Okubara, P.A., Mahoney, A., Hulbert, S.H. 2013. Pre-Breeding for Root Rot Resistance Using Root Morphology Traits. Technical Report. 13-1 / p. 31-32. Interpretive Summary:
Technical Abstract: Our goal is to identify new wheat varieties that display field resistance/tolerance to root rot diseases, such as those caused by Rhizoctonia and Pythium. We are tapping into the genetic diversity of ‘synthetic’ hexaploid wheats (genome composition AABBDD), which were generated at CIMMYT by artificial genome fusions of durum wheat genotypes (AABB) with wild diploid grasses (DD). Synthetic fusions can produce new combinations of genes not present in traditionally-bred hexaploid wheat. The synthetic wheat lines are screened in cool, wet soils under heavy disease pressure induced by green bridge (planting into ‘green’ strips) and compared with the same lines screened in strips in which the green bridge is removed (‘clean’ strips) (Photo 1). Six synthetic wheat lines were found that were not stunted under heavy disease pressure: two synthetic-derived lines, SPCB3104 and SPCB3220, and four synthetic lines, SYN30, SYN172, SYN182, and SYN201. We have advanced large BC1 Louise-derived families (backcrossed once to the recurrent parent, cv. Louise) under field and/or greenhouse selection for each of the six sources of resistance. Currently, advancement is in progress for BC2 plants of SPCB3104, SYN172, SYN201, and BC1 plants of SYN30, SYN182 and SPCB3220. A SPBC3104 x Louise BC1-F7 mapping population was evaluated and scored for resistance in the field in the spring of 2012. Initial mapping using SSR markers indicated one candidate resistance locus in this population. We have finished constructing BC1-F8 Louise-derived SPCB3104 for rescreening in the field this year. This year’s field-screened populations will be advanced by backcrossing into Louise; genotypic data will be collected using next generation genotyping platforms. The mapping population of SYN172 x Louise BC1-F8 will also be scored in green-clean strips this year. In addition to using green-clean comparisons, we plan to plant into ‘green’ strips with, and without, fungicides to create the disease pressure differential (green-green). Populations SPCB3104 x Louise BC1-F8, SYN30 x Louise BC1-F5 and SYN182 x Louise BC1-F5, and the six original parental synthetic lines will be evaluated in these green-green strips. In addition to field screens, we will compare the resistances of the six original synthetic lines along with the 10 best and 10 worst plants of the SPCB3104 x Louise population under controlled (greenhouse) conditions. Greenhouse assays showed that original lines SPCB3104 and SYN172 differed in numbers of seminal and lateral roots, morphology traits that can be linked to escape from the pathogen or recovery from pathogen damage. Since original lines vary widely in endogenous root development, advanced Louise-derived lines from the field will provide a common genetic background. Our cooperators are Tim Paulitz and Deven See.