. 2008. The relationship of LT 50 to prolonged freezing survival in winter wheat. Can. J. Plant Sci. 88: 885Á889. Twenty-six wheat (Triticum aestivum L.) lines were tested for their ability to withstand remaining frozen for extended periods of time. Survival of acclimated seedlings was evaluated after remaining frozen at (58C for 15 or 20 wk. Survival after 15 wk ranged from 0 to 100% and after 20 wk ranged from 0 to 33%. The relationship of survival and LT 50 scores, the temperatures at which 50% of the plants were predicted to die, was examined with linear regression analysis. The linear relationship was highly statistically significant after 15 wk and after 20 wk. The cultivars Norstar and Froid survived being frozen for 20 wk nearly twice as well as the other cultivars; about 33% vs. 17% for the next best cultivar. These results indicated that the LT 50 score, which can be estimated in about 8 wk, reliably predicts the ability to survive in the frozen state for as long as 20 wk, and that Norstar and Froid possess a long-term freezing tolerance mechanism that is far superior to the other cultivars tested. Ces re´sultats indiquent que la LT 50 , qu'on peut estimer en a`peu pre`s 8 semaines, pre´dit de manie`re fiable la capacite´de survie au gel pendant un maximum de 20 semaines et que les cultivars Norstar et Froid posse`dent un me´canisme de tole´rance au gel nettement supe´rieur a`celui des autres varie´te´s teste´es.

The inheritance of freezing tolerance in F 2 -derived F 4 populations from all possible crosses of winter wheat cultivars ÔKestrelÕ, ÔEltanÕ, ÔTiberÕ, ÔFroidÕ and germplasm line Oregon Feed Wheat #5 (ORFW) was investigated. When frozen to a temperature equal to the LT 50 of the least freezing tolerant parent (ORFW), survival frequency distributions were skewed to greater survival in six of the 10 crosses, however, very few of the progeny from the four crosses to ORFW survived. The inheritance of this freezing sensitivity was investigated with freezing of F 2:4 populations from the crosses of ORFW to ÔEltanÕ or ÔTiberÕ to the LT 50 of the hardier parent. Very few of the F 2:4 populations survived as well as ÔEltanÕ or ÔTiberÕ, indicating a small number of strongly dominant genetic factors in ORFW that conditioned freezing sensitivity. Molecular analysis indicated these factors were not spring-type vernalization alleles.

The pathogenic nematodes Pratylenchus neglectus (Rensch, 1924) Filipjev and Schuurmans Stekhoven, 1941 and Pratylenchus thornei Sher and Allen, 1953 cause severe yield losses in wheat (Triticum aestivum L.). The objectives in this study were to assay a collection of Iranian landrace accessions collected from 12 provinces in Iran to identify novel sources of resistance to both species and to characterize agronomic traits critical for consideration in wheat breeding. Seventy‐eight accessions were assayed for dual resistance to parasitic nematodes P. neglectus and P. thornei in controlled environment assays. Field trials conducted in Pullman, WA, and Pendleton, OR, evaluated stripe rust (Puccinia striiformis f. sp. tritici) resistance, days to heading, grain volume weight, plant height, seed protein content, seed kernel characterization, glume tenacity, and pubescence. The accessions were assayed with simple‐sequence repeat (SSR), single‐nucleotide polymorphism (SNP), and known vernalization markers for hierarchical cluster analysis to identify relatedness among accessions. Thirty‐two accessions were identified as resistant or moderately resistant to both Pratylenchus species. Six were identified with moderate adult plant resistance to stripe rust in the field. The range of mean agronomic traits over locations was 53 to 105 cm for plant height, 46 to 84 d for post planting days to heading, and 151 to 728 kg m−3 for grain volume weight. The genetic cluster analysis identified three clusters based on the number of rare polymorphisms in the subset. The nematode resistance was distributed over the three clusters. The diversity within this subset could be useful for wheat breeders to integrate genetic variation and resistance to both Pratylenchus spp.

Understanding the genetic basis of root traits provides essential information on a largely untapped resource for crop improvement, as roots are instrumental for the uptake of water and nutrients. However, breeding for improved root traits is challenging due to laborious and time‐consuming root phenotyping in soil. Our studies sought to uncover spatiotemporal root‐growth dynamics of mature plant root systems in five spring wheat (Triticum aestivum L.) cultivars, Louise, Alpowa, Hollis, Drysdale, and Dharwar Dry, and a facultative spring landrace, AUS28451 using the in situ minirhizotron technique. The 2‐yr greenhouse study revealed that the root system grows rapidly after early node elongation to gain maximum size during anthesis, after which root growth slows and transitions to senescence. We were able to detect quantifiable differences among wheat cultivars in root traits in both 5‐d old seedlings and root systems at anthesis. Furthermore, the positive correlation of the observed root traits with grain yield and the consistency in root traits observed using minirhizotrons and through extraction of young and mature root systems has reinforced the experimental results. A negative correlation was found between root number, area, and length and root diameter. We found that the spring wheat cultivars, AUS28451, Dharwar Dry, and Alpowa, had increased root number, area, and length, but also increased time to heading. The results from this study can be further leveraged to screen breeding lines for root traits of interest, as well as assess the heritability of root traits for dryland farming in the inland Pacific Northwest.