Authors:A. Comeau, L. Nodichao, J. Collin, M. Baum, J. Samsatly, D. Hamidou, F. Langevin, A. Laroche and E. Picard
Literature confirms that using polyethylene glycol (PEG) as an osmotic agent to imitate water shortage was not so easy in practice, due to PEG toxicity effects and frequent contaminations. Two new approaches were developed to alleviate those problems, one using a raft covered with a membrane to prevent PEG entry in roots, and one using solidified PEG media. The raft trials were done on corn, hexaploid and tetraploid wheat, rye, triticale, oats, barley, Agrotricum; those in solid media, with corn, hexaploid and tetraploid wheat, barley, sorghum and pearl millet. Different species respond differently to PEG-induced osmotic stress. In our trials, the most sensitive cereal was corn, and this finding correlates with the lower osmotic pressure of the sap (a constitutive trait in corn seedlings). Corn responded to osmotic stress by a very poor rate of elongation of the coleoptile, especially when the highest stress (32% PEG) was used. This behavior was also observed in the field in dry years, for example in the Sahel area. Compared to this sensitive cereal species, all other cereals tested were more resistant. Hexaploid and tetraploid wheat, triticale, and Agrotricum kept capacity to elongate roots when submitted to a high osmotic stress, but the higher stress reduced root length considerably. Barley kept rooting ability like other cereals, but was able to develop more aerial biomass, seminal roots, and ramifications. Barley root hair was also longer and covered a higher proportion of the root. Those adaptive features likely explain part of the good adaptation of barley to dry Mediterranean areas. Preliminary results on solid media also showed relationships between drought resistance and the osmoresistance response, at least when comparing species. Roots of species adapted to hot climate, like pearl millet and sorghum, had few seminal roots but displayed a strong gravitropism under osmotic stress. The ease of use of solidified PEG media shows promise for future larger scale trials. Applications of solidified PEG media for research beyond cereal crops is envisioned.
Authors:A. Comeau, F. Langevin, V. Caetano, S. Haber, M. Savard, H. Voldeng, G. Fedak, Y. Dion, S. Rioux, J. Gilbert, D. Somers and R. Martin
It has proven to be an enduring and difficult challenge to generate useful germplasm that resists fusarium head blight (FHB) as effectively as Sumai 3. While focussed genetic approaches may follow a clear path to a well-defined goal of resistance, they run the risk of worsening traits not selected for. It was commonly believed that selecting for good performance under pressure from multiple diseases plus abiotic stress should be a harder task than focussing on the single goal of FHB resistance; and yet the complex, systemic approaches have now been shown to be capable of rapid progress. Moreover, the risks of worsening non-selected traits are lessened, because the selection matrices favour genes, or groups of genes, that are free of major defects arising from linkage or pleiotropy. However, even at the pre-breeding level, environments are needed that stress the tested germplasm abiotically and with multiple diseases, as a broad array of traits must be examined at the same time. Since as much as 98–99% of any population may need to be discarded, the widest possible genetic range of diversity should be investigated. As seen in several bread wheat examples, the critical factors that allow for rapid selection of germplasm resistant to most stresses are: a) use of an extensive range of available biodiversity; b) well-designed planning of numerous crosses; c) the astute application of combinations of biotic and abiotic stresses; and d) fast recycling of multiple-resistant lines into crossing blocks. Analyses of our first attempts (2003–07) with such systemic approaches show that as early as F1-F3, germplasm with minimal defects and resistant to the multiple biotic and abiotic stresses can be selected. This ability to identify and advance trait packages rather than just individual traits also improves efficiency for breeders. The selected germplasm resisted well all diseases of concern in Eastern Canada: FHB, barley yellow dwarf (BYD), rusts, powdery mildew, leaf spots, and root diseases. The best (e.g. FL62R1) had FHB resistance near equivalent to Sumai 3 while displaying good yield potential and agronomic traits. Milling quality still falls short of desired levels, but was a good improvement over Sumai 3. The systemic approach, so described because it integrates the pursuit of multiple traits in complex environments, has now demonstrated, in a Canadian setting, the success achieved earlier in Brazil. This confirmation and extension of the utility of systemic approaches support the case for their wider application.