Semi-dwarfing alleles in Canadian wheat cultivars result in shorter coleoptiles but exceptions exist

Pandey, M., Singh, A. K., DePauw, R. M., Bokore, F. E., Ellouze, W., Knox, R. E. and Cuthbert, R. D. 2015. Coleoptile length, gibberellin sensitivity, and plant height variation of durum wheat in Canada. Can. J. Plant Sci. 95: 1259-1264. Thirty-three durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] and three hexaploid wheat (Triticum aestivum L.) cultivars and introduced germplasm were evaluated for coleoptile length (CL), gibberellin (GA) sensitivity, and plant height in the laboratory, greenhouse and field. The semidwarf durum cultivars, AC Navigator and Commander, had short CL (<7.0 cm) and were insensitive to GA. All the tall and conventional-height durum had long CL (>9.0 cm) and expressed sensitivity to exogenous GA. The CL was not associated with plant height and seedling dry matter mass among the tall and conventional-height durum genotypes.

In hexaploid wheat (Triticum aestivum) analysis of the F2 generation of the cross of Minister Dwarf and Chinese Spring showed that insensitivity to gibberellic acid, a characteristic of Minister Dwarf and other dwarf wheats, was determined by a single gene, Gai3. The short coleoptiles, which are also a feature of these dwarf wheats, was also identified as being predominantly controlled by a single gene which was probably identical to the gene Gai3. F2 monosomic analysis located Gai3 on chromosome 4A and demonstrated that the allele of Gai3 for insensitivity was an active allele rather than a deletion or a null allele, since plants nullisomic for chromosome 4A were not insensitive. The transmission rates of 20 chromosome gametes deficient for chromosome 4A was found to be higher than normally expected. Gai3 was also epistatic to genes for increasing coleoptile length carried by other chromosomes than 4A, indicating that selection for acceptable coleoptile lengths in breeding programmes may be difficult in the presence of Gai3.

Coleoptile length variation of near-isogenic Rht lines of modern CIMMYT bread and durum wheats

Heat stress can reduce the production potential of wheat (Triticum aestivum L.) by affecting the various developmental stages of wheat including the seedling stage. Understanding the genetic basis of heat stress tolerance can help in breeding resilient wheat cultivars with improved productivity. Here, evaluation of a diverse panel of spring wheat landraces and cultivars under non‐heat stress (23°C) and heat stress (36°C) treatments in a controlled environment revealed large phenotypic and genetic variations. Heat stress negatively affected all seedling traits with the maximum reduction in root length (85.6%) and the least reduction in coleoptile length (15.44%). Moreover, based on seedling performance, we identified six highly heat tolerant (PI 366905, Kzyl Sark, Rang, Perico S, Bohr Gamh, and PI 620689) and six highly heat susceptible (CItr 17470, CItr 13270, Coeruleum, Shashi, Hallany, and Currawa) genotypes. Genome‐wide association analysis using 302,524 single nucleotide polymorphisms identified 23 marker‐trait associations (MTAs), of which 16 were associated with various seedling traits under heat stress. Gene annotation and expression analysis indicated 35 differentially expressed genes, of which 13 were considered as high‐confidence genes with functional relevance to heat stress including protein kinase, basic‐leucine zipper, UDP‐glucosyltransferase, pyrophosphate‐energized proton pump, fatty acid hydroxylase, and other classes of proteins. The MTAs and candidate genes identified in this study hold promise for developing heat‐resilient wheat cultivars through the selection of favorable alleles with gene‐specific molecular markers.

Pandey, M., Singh, A. K., DePauw, R. M., Bokore, F. E., Ellouze, W., Knox, R. E. and Cuthbert, R. D. 2015. Coleoptile length, gibberellin sensitivity, and plant height variation of durum wheat in Canada. Can. J. Plant Sci. 95: 1259–1264. Thirty-three durum wheat [Triticum turgidum L. subsp. durum (Desf.) Husn.] and three hexaploid wheat (Triticum aestivum L.) cultivars and introduced germplasm were evaluated for coleoptile length (CL), gibberellin (GA) sensitivity, and plant height in the laboratory, greenhouse and field. The semidwarf durum cultivars, AC Navigator and Commander, had short CL (<7.0 cm) and were insensitive to GA. All the tall and conventional-height durum had long CL (>9.0 cm) and expressed sensitivity to exogenous GA. The CL was not associated with plant height and seedling dry matter mass among the tall and conventional-height durum genotypes.

Early and deep sowing practices have revolutionised Australian winter cropping. Oats (Avena sativa ) are the only winter-cereal with a mesocotyl, potentially allowing them to successfully emerge from deep sowing. This study examined the genetic differences in mesocotyl and coleoptile length, the effect of temperature on these traits, and undertook a field validation of deep-sown oats compared to selected wheat (Triticum aestivum ) and barley (Hordeum vulgare ) genotypes. A controlled environment experiment on 195 oat genotypes revealed long combined mesocotyl and coleoptile lengths (112-219 mm) with significant genotypic variation. A further controlled environment study compared the mesocotyl and coleoptile lengths of 42 genotypes across four temperatures (15-30°C). This revealed that temperatures exceeding 20°C reduced coleoptile and mesocotyl length by 3.7mm and 1.1mm per °C. Five field experiments compared the emergence of 19 oat, four wheat, and two barley genotypes from deep (110mm) and shallow sowing (40mm). Oats had greater emergence at depth compared to wheat and barley genotypes. The results indicate that oats are highly suited to early and deep sowing conditions due to their long mesocotyl and combined mesocotyl and coleoptile length.

Fusarium head blight (FHB) resistance in wheat is often associated with undesirable agronomic traits such as tall plant height and a propensity for lodging. Plant height in wheat is genetically controlled by some semi-dwarfing alleles that alter the plant's sensitivity to gibberellins (GAs). The presence of semi-dwarfing alleles increases the frequency of anther retention, which may contribute to FHB susceptibility by providing an initiation site for infection. The application of plant growth regulators (PGRs) may enable farmers to grow the most resistant cultivars while controlling plant height to minimize lodging risk. In this study, five spring wheat cultivars that differed in level of FHB resistance, height, and semi-dwarfing alleles were tested to determine the effect of PGRs, specifically Manipulator™ and Ethrel™, on plant height, anther retention, and FHB resistance level and the interactions between them in Winnipeg and Carman, Manitoba in 2019 and 2020. Combined field results showed that Ethrel™ significantly reduced plant height. Both PGRs did not affect the anther retention or FHB resistance levels of the tested cultivars under dry conditions. There were significant interactions between variables, but they were relatively small compared to the main treatment and cultivars. Based on the results of this study, producers could benefit from the higher levels of FHB resistance often associated with tall cultivars and use PGRs to manage plant height and lodging without increased risk of FHB.

The opening of a new durum wheat (Triticum turgidum L. var. durum) mill in Ohio and the premium prices paid for durum led to an examination of the feasibility of successfully producing Hungarian winter durum wheat in Ohio and the rest of the soft red winter reheat (Triticum aestivum L.) (SRWW) region. The grain yields and agronomic characteristics of three promising Hungarian winter durum wheat cultivars, 'Basa', 'Minaret', and 'Pannondur', were compared to those of Ohio SRWW cultivars, 'Cardinal' and 'Dynasty', in seven field trials from 1989 to 1991, at Wooster, OH. Mean Hungarian winter durum grain yields were 20%, 48%, and 53% of Ohio SRWW in 1989, 1990, and 1991, respectively. Mean plant densities for the Hungarian durums improved from 49% in 1989, to 71% and 93% in 1990 and 1991, respectively [...]

Successful plant establishment is critical to the development of high-yielding crops. Short coleoptiles can reduce seedling emergence particularly when seed is sown deep as occurs when moisture necessary for germination is deep in the subsoil. Detailed molecular maps for a range of wheat doubled-haploid populations (Cranbrook/Halberd, Sunco/Tasman, CD87/Katepwa and Kukri/Janz) were used to identify genomic regions affecting coleoptile characteristics length, cross-sectional area and degree of spiralling across contrasting soil temperatures. Genotypic variation was large and distributions of genotype means were approximately normal with evidence for transgressive segregation. Narrow-sense heritabilities were high for coleoptile length and cross-sectional area indicating a strong genetic basis for differences among progeny. In contrast, heritabilities for coleoptile spiralling were small. Molecular marker analyses identified a number of significant quantitative trait loci (QTL) for coleoptile growth. Many of the coleoptile growth QTL mapped directly to the Rht-B1 or Rht-D1 dwarfing gene loci conferring reduced cell size through insensitivity to endogenous gibberellins. Other QTL for coleoptile growth were identified throughout the genome. Epistatic interactions were small or non-existent, and there was little evidence for any QTL x temperature interaction. Gene effects at significant QTL were approximately one-half to one-quarter the size of effects at the Rht-B1 and Rht-D1 regions. However, selection at these QTL could together alter coleoptile length by up to 50 mm. In addition to Rht-B1b and Rht-D1b, genomic regions on chromosomes 2B, 2D, 4A, 5D and 6B were repeatable across two or more populations suggesting their potential value for use in breeding and marker-aided selection for greater coleoptile length and improved establishment.

and yield components for wheat cultivars during 2004-2006 at one site in Van Province in Eastern Turkey. Grain yield and yield components were found to positively correlate with coleoptile length, with marked declines observed in grain yield and yield components among varieties with shorter coleoptiles in deepest sowing. Wheat sown at 5 cm gave greater yields than wheat sown at 3, 7 and 9 cm by 19.9, 22.3 and 62.5%, respectively. The highest grain yield (2.98 T ha-1) was obtained with the Alparslan cultivar sown at a depth of 5 cm. Grain yield of all varieties tested was drastically reduced when sown at depths of 9 cm, with the exception of the local Tir and Alparslan varieties, both of which, when compared to the other varieties tested, had longer coleoptiles.

Growth stage-based modulation in antioxidant defense system and proline accumulation in two hexaploid wheat (Triticum aestivum L.) cultivars differing in salinity tolerance

Successful stand establishment is prerequisite for optimum crop yields. In some low-precipitation zones, wheat (Triticum aestivum L.) is planted as deep as 200 mm below the soil surface to reach adequate soil moisture for germination. To better understand the relationship of coleoptile length and other seed characteristics with emergence from deep planting (EDP), we evaluated 662 wheat cultivars grown around the world since the beginning of the 20th century. Coleoptile length of collection entries ranged from 34 to 114 mm. A specialized field EDP test showed dramatic emergence differences among cultivars ranging from 0–66% by 21 days after planting (DAP). Less than 1% of entries had any seedlings emerged by 7 DAP and 43% on day 8. A wide range of EDP within each coleoptile length class suggests the involvement of genes other than those controlling coleoptile length. Emergence was correlated with coleoptile length, but some lines with short coleoptiles ranked among the top emergers. Coleoptiles longer than 90 mm showed no advantage for EDP and may even have a negative effect. Overall, coleoptile length accounted for only 28% of the variability in emergence among entries; much lower than the 60% or greater reported in previous studies. Seed weight had little correlation with EDP. Results show that EDP is largely controlled by yet poorly understood mechanisms other than coleoptile length.

Lack of moisture near the soil surface commonly delays sowing, reducing grain yields of Australian wheat (Triticum aestivum) crops. Deep sowing would allow growers to make use of soil moisture lying below the drying topsoil, but the short coleoptiles of semidwarf wheats reduce emergence when sowing at depths greater than 5 cm. Selection of longer, thicker coleoptiles would help in improving emergence in hard or crusted soils, or when deep sowing, yet little is known of genetic control of coleoptile size in wheat. A diallel mating design was generated from crosses between 12 Australian and overseas wheats, and assessed for coleoptile size at different temperatures (11, 15, 19, and 23°C). Repeatabilities for coleoptile diameter and length were moderate to high on an entry-mean basis (R2 = 0.48 and 0.77, respectively), reflecting large genotype and small genotype × temperature interaction variances. Genotypic variation among parents translated into large and significant (P < 0.01) differences among F1 progeny (94–142 mm and 1.56–1.84 mm for length and diameter, respectively). General (GCA) and specific combining ability (SCA), and reciprocal effects were significant (P < 0.01) for length and diameter. Baker’s GCA/SCA ratio was high (0.62–0.77) for coleoptile length but intermediate for diameter (0.38–0.64), indicating strong additive genetic control for length. Further, GCA effects and parental means were strongly correlated (r = 0.81–0.91, P < 0.01) indicating parent length to be a useful predictor of progeny performance. Coleoptile lengths for progeny derived from Rht8, Rht9, and Rht12 dwarfing gene donors were generally shorter (c. –7 to –13%) but were still an average 47% longer than coleoptiles of Rht-B1b and Rht-D1b controls. The genetic correlation for coleoptile length and diameter was small (rg = –0.25 ± 0.15n.s.) suggesting that the two traits are genetically independent. Development of wheats with longer, thicker coleoptiles should be readily achieved in selection among partially inbred families from crosses targetting improved establishment.

Coleoptile length and culm length inheritance were studied in F1 and F3 populations from spring wheat (Triticum aestivum L.) crosses involving ‘Olesen's Dwarf’ and five tall cultivars with relatively long coleoptiles. In F2 populations studied both characters were quantitatively inherited. Broad‐sense heritability estimates were high for culm length and coleoptile length. Dominance for short culm length was expressed in the O D X ‘Lee’ F1, and coleoptile lengths of the F1 of O D X Lee, O D X ‘10‐VI‐5’, and O D X ‘Chris’ exceeded those of their midparents. Both additive and nonadditive gene action was detected in all crosses except one. Calculated minimum gene numbers were higher for culm length than for coleoptile length. Significant correction correlations were obtained between culm length and coleoptile length; however, coefficient of determination values (r2) were low.

Variation in coleoptile length within and between 2 cultivars of semidwarf wheat (Triticum aestivum) was related to seed size. Seeds of cvv. Banks and Kite were separated by sieving for width into the size classes of >2.75, 2.75-250, 2.50-2.25 and 2.25- 2.00 mm. The mean grain weights of ungraded samples were 43.1 mg (Kite) and 34.3 mg (Banks), and for the subsamples were 52.4, 37.9, 30.4 and 20.7 mg (Kite) and 41.4, 33.2, 25.8 and 19.1 mg (Banks). The effect of size class on coleoptile length was significant (P<0.01). Over both cultivars, coleoptile length declined by 0.37 mm per mg reduction in seed weight. Kite produced the longer coleoptiles overall, 87.5 mm compared with 59.0 mm for Banks. However, only 3.3 mm of this difference can be accounted for by the mean difference in seed weight (8.8 mg) and the effect of seed weight on coleoptile length (0.37 mm/mg). Genetic differences, apart from adult plant height, appear to explain most of the difference in coleoptile length between the cultivars. There was considerable genetic variability within genotypes. In Banks, with seed width >2.75 mm (41.4 mg per seed), the lengths of coleoptiles ranged from 24-89 mm (mean 65.1 mm), suggesting considerable scope for the selection of genotypes with longer coleoptiles.