No abstract

Recent epidemics of fusarium head blight (FHB), caused by Fusarium graminearum Schwabe (telomorph: Gibberella zeae), in the USA and Canada have caused severe yield and quality losses in wheat (Triticum aestivum L.). Development of resistant cultivars has been difficult because of the complex inheritance of resistance and confounding environmental effects. This study was conducted to identify and map DNA markers linked to genes associated with FHB resistance. A population of 112 F5‐derived recombinant inbred (RI) wheat lines from the cross ‘Sumai 3’ (resistant)/‘Stoa’ (moderately susceptible) was evaluated in two greenhouse experiments for Type II resistance (spread within the spike). On the basis of restriction fragment length polymorphism (RFLP) marker analyses, five genomic regions were significantly (P < 0.01) associated with FHB resistance, three derived from Sumai 3 and two from Stoa. Regions on Chromosomes 3BS (from Sumai 3) and 2AL (from Stoa) were identified by interval analysis using a LOD threshold of 3.0. These two quantitative trait loci (QTL) have been assigned the gene designations QFhs.ndsu‐3B and QFhs.ndsu‐2A, respectively. Recombinant inbred lines with these two QTL had a median severity of 20.9%, compared with 36.2% for all RI lines. The best RFLP marker in the 3BS region explained 15.4% of the variation and a multiple regression model consisting of three QTL explained 29.5% of the variation. These results indicate that resistance to FHB is inherited in a quantitative manner and that marker‐assisted selection may aid the development of FHB‐resistant cultivars.

Recent results have shown that mutations in genes coding for puroindoline a and b (PinA and PinB) are associated with the expression of the hard texture of wheat (Triticum aestivum L.) grain. A majority of hard wheats have a glycine‐to‐serine mutation in puroindoline b (allele PinB‐D1b), or they are devoid of puroindoline a (allele PinA‐D1b). Hard wheats with PinA‐D1b tend to be harder than those with PinB‐D1b Grain hardness is known to affect milling and baking traits. Our objective was to determine the influence of allelic variation in PinA and PinB on milling and bread quality traits in a recombinant inbred population segregating for PinA‐D1b and PinB‐D1b One hundred thirty‐nine recombinant inbred lines from the cross ‘Butte 86’ (PinA‐D1b allele)/ND2603 (PinB‐D1b allele) and parents were grown in a field trial with two replications at two locations. Grain hardness was measured by near‐infrared reflectance (NIR) and the single‐kernel characterization system (SKCS). Grain was milled and baked for each line. Puroindoline allele type was determined for each line. The PinB‐D1b group had significantly softer grain, higher break flour yield, flour yield, milling score, and loaf volume, and lower flour ash and crumb grain score (low score being desirable) than the PinA‐D1b group. Significant genetic variability was detected within allelic classes for all traits. The proportion of variation among entry means attributed to puroindoline classes was 34% for break flour yield, 26% for NIR hardness, and 22% for SKCS harness index. Grain hardness was negatively correlated with break flour yield, flour yield, and mixing score and positively correlated with flour ash. Grain hardness was not correlated with loaf volume or crumb grain score. The PinB‐D1b allele was more desirable for milling and bread baking, although superior milling and bread quality genotypes could be selected within either class.

The grain fill (GF) period of spring wheat (Triticum aestivum L.) grown in the Northern Great Plains coincides with periods of drought and high temperature stress, whicho ften reduce crop yield and quality. Rate and duration of GF were determined for 20 spring wheat genotypes in four rainfed North Dakota environments to evaluate genotypic variation for rate and duration of GF, and to examine relationships between estimated GF parameters, environmental limitations, wheat productivity, and stress tolerance in environments prone to postanthesis drought and high temperature stresses. A quadratic polynomial was used to describe the relationship between kernel weight and accumulated growing‐degree days from anthesis to maturity. Rate and duration of GF were estimated from fitted curves. Genotypes varied for both GF rate and duration, but increasing temperatures during GF tended to stop grain growth prematurely and to hasten physiological maturity. Rate, but not duration of GF, was correlated with kernel weight. Increasing kernel weight by extension of the GF period does not appear to be a promising strategy for increasing grain yield in these environments. Rate and duration of GF were not associated in these genotypes. Results suggest that simultaneous selection for high GF rate and high kernel weight is possible without lengthening GF duration, and that selection for high GF rate through selection for high kernel weight is possible. High rate and short duration of GF appeared to contribute to increased stress tolerance in these genotypes, but only one of the 20 genotypes investigated had both characteristics. High GF rates with short to medium GF durations appear to be desirable objectives in environments in which the growing season frequently is shortened because of severe stress.