Daryl J. Mares

Mapping components of flour and noodle colour in Australian wheat

Flour and noodle colour influence the value of wheat (Triticum aestivum L.) and are obvious targets for breeders seeking to improve quality, end-product range, and marketability of wheat. The objective of this investigation was to identify quantitative trait loci (QTLs) associated with flour and noodle colour traits and with individual components of colour. One hundred and sixty-three doubled haploid lines derived from Sunco x Tasman, white-grained, prime hard, and hard wheats adapted to the north-eastern region of Australia were used for the bulk of this study and were supplemented by doubled haploid populations derived from CD87 x Katepwa and Cranbrook x Halberd for comparisons of flour colour. Samples of Sunco x Tasman, together with parental lines, were grown at Narrabri, NSW, in 1998 and 1999 and at Roma, Qld, in 1998 and used for visible light reflectance measurements of flour brightness (CIE L*) and yellowness (CIE b*), and white salted noodle (WSN) and yellow alkaline noodle (YAN) brightness, yellowness, and colour stability. Xanthophyll content and polyphenol oxidase (PPO) activity were measured spectrophotometrically. No consistent QTLs were identified for flour L* or initial L* of WSN and YAN. Xanthophyll content was very strongly associated with QTLs located on chromosomes 3B and 7A and these QTLs also had a major influence on flour b*, WSN b*, and YAN b*. Noodle brightness at 2, 24, and 48 h and the magnitude of change in noodle L* and b* with time were affected by QTLs on 2D, contributed by Tasman, and, to a lesser degree, 2A. The QTL on 2D was clearly associated with control of grain PPO, an enzyme implicated in darkening of Asian style noodles. QTLs located on 2B, 4B, and 5B and associated with control of grain size or flour protein content also appeared to influence a number of colour traits.

A QTL located on chromosome 4A associated with dormancy in white- and red-grained wheats of diverse origin

Improved resistance to preharvest sprouting in modern bread wheat (Triticum aestivum. L.) can be achieved via the introgression of grain dormancy and would reduce both the incidence and severity of damage due to unfavourable weather at harvest. The dormancy phenotype is strongly influenced by environmental factors making selection difficult and time consuming and this trait an obvious candidate for marker assisted selection. A highly significant Quantitative Trait Locus (QTL) associated with grain dormancy and located on chromosome 4A was identified in three bread wheat genotypes, two white- and one red-grained, of diverse origin. Flanking SSR markers on either side of the putative dormancy gene were identified and validated in an additional population involving one of the dormant genotypes. Genotypes containing the 4A QTL varied in dormancy phenotype from dormant to intermediate dormant. Based on a comparison between dormant red- and white-grained genotypes, together with a white-grained mutant derived from the red-grained genotype, it is concluded that the 4A QTL is a critical component of dormancy; associated with at least an intermediate dormancy on its own and a dormant phenotype when combined with the R gene in the red-grained genotype and as yet unidentified gene(s) in the white-grained genotypes. These additional genes appeared to be different in AUS1408 and SW95-50213.

Mapping quantitative trait loci associated with variation in grain dormancy in Australian wheat

Preharvest sprouting is a problem in many regions of the world, resulting in downgrading of quality, substantial economic losses to wheat growers, and difficulties for grain handling and marketing agencies. Improvements in tolerance from the introduction of better grain dormancy at, or near, harvest-ripeness would be expected to have a significant impact on the incidence and severity of sprouting. Intermediate levels of dormancy in older Australian wheats, such as Halberd, and a small number of current cultivars could be used in the short term while more extreme dormancy is being introgressed into locally adapted germplasm. A doubled haploid population derived from Cranbrook (extremely non-dormant, very susceptible to sprouting) x Halberd (intermediate dormancy, moderately tolerant to preharvest sprouting) was grown in replicated experiments and ripe grain harvested for assessment of dormancy, measured as a germination index. Consistent differences were observed between the parents in both experiments. For the bulk of the progeny, the germination index fell within a range defined by Cranbrook at the upper and Halberd at the lower end. Significant quantitative trait loci, all contributed by the very susceptible parent, that explained 11%, 9%, and 9% of the phenotypic variation were identified on chromosome arms 2AL, 2DL, and 4AL, respectively. These QTLs offer the opportunity to develop molecular markers for grain dormancy and to develop a better understanding of the mechanisms involved in this trait.

Enzymes from rain-damaged and laboratory-germinated wheat I. Effects on product quality

A range of products was made from flours derived from five Australian wheats subjected to a laboratory wetting treatment in a rain-simulator and compared with others affected by field weathering. Severe product defects were observed in Cantonese and Korean noodles, while lesser but still deleterious effects were observed with Arabic flat-breads. However, the quality of pan breads made from rain-damaged grain was better than that from corresponding untreated wheats, although loaves made from the most damaged cultivar, Hartog, could not be sliced mechanically. Comparison of increased levels of enzyme activity for six enzymes (a-amylase, protease, catalase, peroxidase, lipoxygenase and phenol oxidase) from these varieties in grain and flour revealed that changes in flour properties and product defects were related to levels of flour protease and a-amylase. The significance of the levels of individual enzymes is considered in relation to aspects of individual product quality. Information on the tolerance and sensitivity to rain damage of a range of products is derived from the results.

Water movement into dormant and non-dormant wheat (Triticum aestivum L.) grains

The movement of water into harvest-ripe grains of dormant and non-dormant genotypes of wheat (Triticum aestivum L.) was investigated using Magnetic Resonance Micro-Imaging (MRMI). Images of virtual sections, both longitudinal and transverse, throughout the grain were collected at intervals after the start of imbibition and used to reconstruct a picture of water location within the different grain tissues and changes over time. The observations were supplemented by the weighing measurements of water content and imbibition of grains in water containing I2/KI which stains starch and lipid, thereby acting as a marker for water. In closely related genotypes, with either a dormant or a non-dormant phenotype, neither the rate of increase in water content nor the pattern of water distribution within the grain was significantly different until 18 h, when germination became apparent in the non-dormant genotype. Water entered the embryo and scutellum during the very early stages of imbibition through the micropyle and by 2 h water was clearly evident in the micropyle channel. After 12 h of imbibition, embryo structures such as the coleoptile and radicle were clearly distinguished. Although water accumulated between the inner (seed coat) and outer (pericarp) layers of the coat surrounding the grain, there was no evidence for movement of water directly across the coat and into the underlying starchy endosperm.

Wheat grain preharvest sprouting and late maturity alpha-amylase.

Preharvest sprouting (PHS) and late maturity α-amylase (LMA) are the two major causes of unacceptably high levels of α-amylase in ripe wheat grain. High α-amylase activity in harvested grain results in substantially lower prices for wheat growers and at least in the case of PHS, is associated with adverse effects on the quality of a range of end-products and loss of viability during storage. The high levels of α-amylase are reflected in low falling number, the internationally accepted measure for grain receival and trade. Given the significant losses that can occur, elimination of these defects remains a major focus for wheat breeding programs in many parts of the world. In addition, the genetic, biochemical and molecular mechanisms involved in the control of PHS and LMA as well as the interactions with environmental factors have attracted a sustained research interest. PHS and LMA are independent, genetically controlled traits that are strongly influenced by the environment, where the effects of particular environmental factors vary substantially depending on the stage of grain development and ripening. This review is a summary and an assessment of results of recent research on these important grain quality defects.

Dormancy in white-grained wheat: Progress towards identification of genes and molecular markers

Preharvest sprouting limits the consistent production of high quality wheat in many regions of the world. Improvements in tolerance from the introduction of better grain dormancy at, or near, harvest-ripeness would be expected to have a significant impact on the incidence and severity of sprouting. Genetic and molecular investigations have provided new evidence for the presence of dormancy genes on chromosome 3D of white-grained genotypes AUS1408 and N72.72 (T. sphaerococcumderivative), and identified a potential molecular marker for one of the dormancy genes in AUS1408. Analysis of a doubled haploid population derived from Cranbrook (extremely non-dormant, very susceptible to sprouting) × Halberd (intermediate dormancy, moderately tolerant to preharvest sprouting) identified three significant quantitative trait loci on chromosome arms 2AL, 2DL, and 4AL, all contributed by the very susceptible parent.

The interaction of yellow rust (Puccinia striiformis) with winter wheat cultivars showing adult plant resistance: macroscopic and microscopic events associated with the resistant reaction

Abstract The development of race 104 E 137 of Puccinia striiformis was observed in leaves of four winter wheat cultivars which were susceptible at the seedling stage but showed a graded series of reactions at later growth stages. The degree of resistance, measured by the reduction in area of sporulating tissue, increased gradually with successively appearing leaves on the main axis of Cappelle Desprez, Holdfast and Maris Widgeon. Resistant reactions were associated with reduced fungal colony growth rates, the appearance of scattered cells showing hypersensitive necrosis and with more general areas of chlorosis and browning of host tissue. The differences in resistance between cultivars were correlated with different frequencies of hypersensitively necrotic cells but the gradual increase of resistance in successive leaves of Maris Widgeon did not correspond with the occurrence of hypersensitive necrotic cells which appeared suddenly in the second leaf and remained similar in successive leaves. By contrast the rate of fungal colony growth during the latter half of the infection process and the development of tissue chlorosis and browning were well correlated with increasing resistance of successive leaves, final reaction type and relative differences in resistance between cultivars. The significance of these observations in terms of resistance mechanisms is discussed.

Measurement of dough surface stickiness associated with the 1B/1R chromosome translocation in bread wheats

The 1B/1R chromosome translocation which carries genetic material derived from cereal rye is associated with several quality problems in bread wheats, including dough stickiness and intolerance to over-mixing. An objective procedure based on the use of a Digital Gram Gauge push/pull tensiometer was developed to measure dough stickiness and tested using three 1B/1R translocation wheats together with their recurrent parent cultivars. The method gave a reproducible distinction between doughs of hard-grained 1B/1R wheats and their recurrent parent cultivars when the lines were grown at the same site and the doughs were prepared and tested under closely controlled conditions. By contrast, the one soft-grained 1B/1R derivative tested could not be reliably distinguished from its recurrent parent Egret. Stickiness was markedly influenced by factors such as protein content, dough mixing time, the water content of the dough and variation of the test parameters. Possible ways of improving the procedure are discussed.

Expression of late maturity α-amylase in wheat containing gibberellic acid insensitivity genes

SummaryTwo wheat cultivars, Spica and Lerma 52, which consistently produce high levels of α-amylase during the later stages of grain development (late maturity α-amylase), were crossed with a set of four near-isogenic lines carrying the tall (rht) allele or one of the dwarfing genes Rht1, Rht2 or Rht3 (GA-insensitive alleles). The F1 and F2 populations were developed and analysed for grain α-amylase and plant height. The Rht3 gene exhibited the strongest influence on plant height and strongly inhibited new α-amylase synthesis during the later part of grain ripening. By comparison, Rht1 and Rht2 had a less pronounced effect but still significantly reduced the expression of late maturity α-amylase. These observations suggest that gibberellic acid is involved either directly or indirectly in this phenomenon. The implications of the effect of dwarfing genes on expression of late maturity α-amylase are discussed in relation to cultivar improvement and to the identification and control of high α-amylase germplasm.