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baking quality traits. This genome also supports the wide adaptation that allows wheat cultivation even in Wild ancestors of common wheat (Triticum aestivum L.) have semiarid areas (Zohary et al., 1969). been reported to have higher maximum photosynthetic rates than modern wheat cultivars. Synthetic hexaploids, obtained by crossing Synthetic hexaploid wheat is a relatively new germtetraploid wheat and Aegilops tauschii Coss., have proven useful as plasm obtained by artificially crossing durum wheat, a source of resistance or tolerance to biotic and abiotic stresses. This Triticum turgidum L. ssp. durum (Desf.) Husn. (2n ϭ study was conducted to determine whether synthetic hexaploids also 4x ϭ 28, AABB) and Aegilops tauschii Coss. (2n ϭ could contribute genetic diversity to enhance leaf photosynthetic rate 14, DD), [Syn. Triticum tauschii (Coss.) Schmal]. This and other physiological traits. Three different populations of BC 2 F 2:6 germplasm has proven to be very useful as a source of synthetic-derived lines were evaluated at the Agricultural Research resistance to diseases and pests, as well as for tolerance Center for the Northwest (INIFAP) Experimental Station, near Ciuto environmental stresses (Gorham, 1990; Limin and dad Obregon, Sonora, Mexico. Differences in maximum photosyn-Fowler, 1993). Synthetic hexaploids are routinely thetic rate were detected among genotypes. Several synthetic-derived crossed and backcrossed with common wheat (2n ϭ lines showed higher photosynthetic rates than their recurrent parent. Staygreen, determined as days between senescence and physiological 6x ϭ 42, AABBDD) to achieve acceptable agronomic maturity, of most synthetic-derived lines did not differ from the recur-types. rent parents. Maximum photosynthetic rate was negatively associatedNet assimilation of CO 2 through the process of photowith leaf area and positively associated with stomatal and mesophyll synthesis is the initial step for biomass production. Some conductances, and leaf temperature depression. Mesophyll conducauthors (Austin et al., 1989; Carver and Nevo, 1990) tance accounted for 85% of the variation in maximum photosynthetic proposed the utilization of genes for higher photosynrate. These results suggest that synthetic-derived wheat can be also thetic rate, commonly present in wild relatives, to ina source of genetic diversity for important physiological traits such crease grain yield of wheat. Domestication and breeding as enhanced photosynthetic rate.

Wild relatives of wheat (Triticum aestivum L.) have primarily been used as sources of genes for biotic and abiotic stress resistance. A more direct approach to grain yield improvement has been sought by using exotic germplasm to enhance quantitative traits, including grain yield. This study was conducted to determine whether synthetic hexaploids, developed from artificial hybridization of durum wheat [Triticum turgidum ssp. durum (Desf.) Husn.] with Aegilops tauschii Coss., can enhance yield or yield components of wheat. Two hundred eighty‐two BC2F2‐derived lines, involving six crosses between different synthetic hexaploids and four spring wheat cultivars, were evaluated for grain yield and its components. These synthetic‐derived lines were compared with their recurrent parent in field experiments conducted during the 1995 to 1996 and 1996 to 1997 crop seasons near Ciudad Obregón, Sonora, Mexico. More than 80% of the synthetic‐derived lines were significantly superior to their recurrent parent for kernel weight. Eight lines had significantly higher grain yield compared with their recurrent parent. Grain yields of superior lines were up to 11% higher than those of their recurrent parents. A strong association between grains m−2, biomass, spikes m−2, and grain and biomass production rates and grain yield was observed in all populations. Path coefficient analyses of yield components revealed a strong direct effect of spikes m−2 and grains spike−1 on grain yield. Results indicate that synthetic hexaploids can be a valuable source of alleles to improve kernel weight.

During the past decade Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe has resulted in severe grain yield and quality losses of wheat (Triticum aestivum L.) in the Northern Great Plains of the U.S. Given the complexity of breeding for FHB resistance, molecular markers associated with this trait will be valuable in accelerating efforts to breed resistant cultivars. The objective of this study was to identify molecular markers linked to quantitative trait loci (QTL) for FHB resistance in wheat using a set of lines obtained by several cycles of crossing to North Dakota adapted genotypes, which derived their resistance from cv. Sumai 3. Microsatellite markers spanning the wheat genome were used to screen parents and derived lines. Polymorphisms for parental alleles were compared to disease scores for Type II resistance. The probability of linkage between markers and introgressed resistance genes was calculated using a binomial probability formula based on the assumption that a molecular marker at a specific distance from the introgressed gene, in a near-isogenic line (NIL), will carry the donor-parent allele as a function of the distance between marker and gene and the number of backcrosses/selfs performed in deriving the NIL. Microsatellite loci Xgwm533 and Xgwm274 were significantly associated with QTL for FHB resistance.

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