Aluminum Toxicity and Stem Rust in the Pacific Northwest

Cassidy Shamseldin

doi:10.7273/000005093

Wheat (Triticum aestivum) in the Pacific Northwest of the United States (PNW) faces multiple environmental factors that harm it’s ability to produce yield. Of these factors, aluminum toxicity and stem rust (Puccinia graminis f. sp. tritici) are discussed in this paper. Incredibly abundant in the earth’s crust, aluminum dissolves in acidic conditions into reactive compounds that can negatively affect wheat crop yield. More than 50% of arable land worldwide is acidic, and farm practices that increase acidity have resulted in aluminum toxicity. Aluminum is becoming an increasing threat to the production of wheat in the Pacific Northwest, of which 22-27mg kg-1 has been known to negatively affect yield. Farming practices lower pH, releasing toxic levels of volatile aluminum into the soil resulting in reduced root growth and thereby reduced biomass in a drought-like phenotype in wheat that decreases crop yield. Some wheat cultivars contain genes that confer tolerance whose roots grow more than in sensitive cultivars, these plants retain a higher biomass than their counterparts in aluminum toxic soils. Aluminum tolerance within local winter wheat germplasm remains unknown without tested methods of tolerance identification. Our objective is to identify a method of screening for wheat aluminum tolerance in the greenhouse, which would allow for year-round screening. Five sets of near-isogenic lines of spring and winter wheat, with genes similar, except for a variation in aluminum tolerance were chosen for these experiments. These tolerant and sensitive sister lines, and a set of checks were planted in the WSU Plant Growth Facility greenhouse in a selection of soils collected from four farms (Rockford WA, Moscow ID (Parker Farm), Pullman WA (Spillman Farm), and Farmington WA) that contain 5ppm to 488ppm aluminum and a pH of 5.08 to 4.02. Additionally, these same near isogenic lines were planted at the Rockford site where soil was collected. The biomass of the wheat cultivars planted in soil from Parker Farm with the highest bioavailable aluminum of 488ppm shows a wider range of biomass than those planted in Rockford soils with the second most aluminum of 162ppm, and the wheat cultivars show differing results. it may be better in future studies to use soil from Parker farm for a more comprehensive view of aluminum tolerance. The cultivars AlumPair-11-R and PI561725 have the highest biomass among the paired lines, and the local cultivars Alum, Chet and Seahawk all have a high biomass and therefore high tolerance in aluminum toxic soils. The genes TaALMT1 and TaMATE for aluminum tolerance are known to confer the greatest tolerance, therefore, local cultivars containing one or both genes are desired. There are likely multiple sources of aluminum tolerance genes within local germplasm, it is known that the spring AlumPair lines differ for the presence of Almt1, further steps would include the identification of genes present in the winter lines for breeding purposes and for the orientation of ancestral connections of local cultivars to other world regions. The greenhouse method used here allows for increased temporal flexibility in testing for aluminum tolerance and can aid in future germplasm selections for aluminum tolerance. Stem rust of wheat, a heteroecious pathogen, has been known to cause yield losses of up to 50%. Global efforts against the spread of a highly virulent stem rust race from east Africa, TTKSK, or Ug99 have encompassed the concern for stem rust for several decades. A new issue is arising, stem rust epidemics are occurring with increasing frequency in the PNW. It is unknown whether this is due to the presence of the alternate host, to climate change, or to the susceptibility of local commercial wheat cultivars, or a combination of the three. The conditions of the PNW including moisture, moderate temperatures, and the presence of the alternate hosts, barberry (Berberis vulgaris) and mahonia (Mahonia sp.) promote the sexual cycle of stem rust resulting in genetic recombination and expanded interpopulation diversity, as opposed to the areas in the Midwest where only the asexual cycle occurs, limiting the evolution of stem rust to mutations. Stem rust races are identified largely by screening differentials, which are a group of wheat genotypes containing a single source of resistance. Knowing the impact of stem rust isolates upon specific genes allows for the positive identification of genes within local wheat germplasm. In order to gauge the resistance, lines of the Washington State University wheat variety trials have been screened in the greenhouse against a stem rust isolate collected from a local farm. Using the Sr differential set, the Stem rust isolate has been tentatively named CTHJC. Sr5 and Sr36 have been found to be most resistant to CTHJC. The level of resistance has been compared to that of the variety trials, and similarities in rust infection may indicate the presence of particular resistance genes. Cultivars WA8355 and AP Coachman have been shown to have the highest resistance of those tested, more so than the Sr differential lines, indicating a combination of resistance genes may be present. Further research is required to discover exactly which resistance genes are contained within the most resistant lines, and which gene combinations prove to be effective against new stem rust races.

Aluminum Toxicity and Stem Rust in the Pacific Northwest

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