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Coleoptile length, in wheat, is a significant agronomic trait impacting yield by facilitating the successful establishment of seedlings. In arid regions, varieties possessing longer coleoptile can evade harsh conditions by deep sowing, paving the way for improved yield. However, the study of genes involved in coleoptile development is insufficient. In this study, a high-density 660 K SNP array was used for genome-wide association study (GWAS) on coleoptile length in 150 wheat varieties. The findings revealed the detection of 353 significantly associated SNPs across all environments. The integration of linkage disequilibrium analysis and haplotype analysis mined 23 core QTLs capable responsible for the stable regulating coleoptile length in wheat. In wheat varieties characterized by extended coleoptile length, 6,600, 11,524, and 6,059 genes were found to be differentially expressed at three distinct developmental stages within the coleoptile, respectively. Through GWAS, gene expression levels, and functional annotation, we concluded the identification of two candidate genes (TraesCS2B02G423500, TraesCS2B02G449200) regulating wheat coleoptile length. By employing WGCNA and protein interactions prediction, discovered that the 19 genes were found to interact with candidate genes and participate in plant hormone metabolism and signaling, cell elongation or proliferation, which collectively contributing to coleoptile elongation. Additionally, two KASP markers were developed which can be used in breeding. These results offer a basis for understanding the genetic regulatory network responsible for wheat coleoptile length formation. The QTLs and candidate genes identified in this study can be further utilized for genetic improvement of wheat coleoptile length. [ABSTRACT FROM AUTHOR]

To stably produce domestic wheat under water-scarce environmental conditions due to climate change, root characteristics with excellent water utilization rates are crucial. In this study, we analyzed the root and grain phenotypes of 37 domestic wheat varieties over a two-year period by combining the results of genetic mutations related to semi-dwarfing and grain size. Root length was positively correlated with maximum root depth (r=0.76**) and total seminal root length (r=0.54**), whereas it was negatively correlated with the number of roots (r=-0.33**) and root angles (r=-0.51**). The thousand-kernel weight was positively correlated with embryo width (r=0.34**) and embryo area (r=0.33**) but was not correlated with other root traits. Embryo length was positively correlated with the number of roots (r=0.34**) and coleoptile length (r=0.42**). Phenotypic analyses of roots and grains, along with genotypic analyses of semi-dwarfing (Rht-B1 and Rht-D1) and grain size (TaCWI-4A, TaCWI-5D, TaGW2-6A, TaSus2-2B) genes, revealed that the Rht-D1b genotype led to reduced root depth, increased root angles, and reduced coleoptile length. TaCwi-A1, TaCWI-5D, TaSus2-2B, and TaGW2-6A, possessing the alleles TaCwi-A1a, Hap-5D-C, Hap-L, and Hap-6A-G associated with a larger grain size, resulted in an increased number of roots and root depth. Domestic wheat varieties were categorized into three clusters based on root, grain, and coleoptile trait characteristics, with 15 varieties in Cluster I, 9 in Cluster II, and 13 in Cluster III. The results of this study can be utilized in basic research to develop varieties that can produce stable domestic wheat by selecting resources with excellent root growth and seed characteristics. [ABSTRACT FROM AUTHOR]

The length of coleoptile is crucial for determining the sowing depth of oats in low-precipitation regions, which is significant for oat breeding programs. In this study, a diverse panel of 243 oat accessions was used to explore coleoptile length in two independent experiments. The panel exhibited significant variation in coleoptile length, ranging from 4.66 to 8.76 cm. Accessions from Africa, America, and the Mediterranean region displayed longer coleoptile lengths than those from Asia and Europe. Genome-wide association studies (GWASs) using 26,196 SNPs identified 34 SNPs, representing 32 quantitative trait loci (QTLs) significantly associated with coleoptile length. Among these QTLs, six were consistently detected in both experiments, explaining 6.43% to 10.07% of the phenotypic variation. The favorable alleles at these stable loci additively increased coleoptile length, offering insights for pyramid breeding. Gene Ontology (GO) analysis of the 350 candidate genes underlying the six stable QTLs revealed significant enrichment in cell development-related processes. Several phytochrome-related genes, including auxin transporter-like protein 1 and cytochrome P450 proteins, were found within these QTLs. Further validation of these loci will enhance our understanding of coleoptile length regulation. This study provides new insights into the genetic architecture of coleoptile length in oats. [ABSTRACT FROM AUTHOR]

Wheat is an important cereal crop constrained by several biotic and abiotic stresses including drought stress. Understating the effect of drought stress and the genetic basis of stress tolerance is important to develop drought resilient, high-yielding wheat cultivars. In this study, we investigated the effects of drought stress on seedling characteristics in an association panel consisting of 198 germplasm lines. Our findings revealed that drought stress had a detrimental effect on all the seedling characteristics under investigation with a maximum effect on shoot length (50.94% reduction) and the minimum effect on germination percentage (7.9% reduction). To gain a deeper understanding, we conducted a genome-wide association analysis using 12,511 single nucleotide polymorphisms (SNPs), which led to the identification of 39 marker-trait associations (MTAs). Of these 39 MTAs, 13 were particularly noteworthy as they accounted for >10% of the phenotypic variance with a LOD score >5. These highconfidence MTAs were further utilized to extract 216 candidate gene (CGs) models within 1 Mb regions. Gene annotation and functional characterization identified 83 CGs with functional relevance to drought stress. These genes encoded the WD40 repeat domain, Myb/SANT-like domain, WSD1-like domain, BTB/POZ domain, Protein kinase domain, Cytochrome P450, Leucine-rich repeat domain superfamily, BURP domain, Calmodulin-binding protein60, Ubiquitin-like domain, etc. Findings from this study hold significant promise for wheat breeders as they provide direct assistance in selecting lines harboring favorable alleles for improved drought stress tolerance. Additionally, the identified SNPs and CGs will enable marker-assisted selection of potential genomic regions associated with enhanced drought stress tolerance in wheat. [ABSTRACT FROM AUTHOR]

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Wheat is an important cereal crop constrained by several biotic and abiotic stresses including drought stress. Understating the effect of drought stress and the genetic basis of stress tolerance is important to develop drought resilient, high-yielding wheat cultivars. In this study, we investigated the effects of drought stress on seedling characteristics in an association panel consisting of 198 germplasm lines. Our findings revealed that drought stress had a detrimental effect on all the seedling characteristics under investigation with a maximum effect on shoot length (50.94% reduction) and the minimum effect on germination percentage (7.9% reduction). To gain a deeper understanding, we conducted a genome-wide association analysis using 12,511 single nucleotide polymorphisms (SNPs), which led to the identification of 39 marker-trait associations (MTAs). Of these 39 MTAs, 13 were particularly noteworthy as they accounted for >10% of the phenotypic variance with a LOD score >5. These high-confidence MTAs were further utilized to extract 216 candidate gene (CGs) models within 1 Mb regions. Gene annotation and functional characterization identified 83 CGs with functional relevance to drought stress. These genes encoded the WD40 repeat domain, Myb/SANT-like domain, WSD1-like domain, BTB/POZ domain, Protein kinase domain, Cytochrome P450, Leucine-rich repeat domain superfamily, BURP domain, Calmodulin-binding protein60, Ubiquitin-like domain, etc. Findings from this study hold significant promise for wheat breeders as they provide direct assistance in selecting lines harboring favorable alleles for improved drought stress tolerance. Additionally, the identified SNPs and CGs will enable marker-assisted selection of potential genomic regions associated with enhanced drought stress tolerance in wheat.

Hypoxia is a key limiting factor for seedling emergence and establishment of direct-seeded rice (DSR) under submergence. The anaerobic germination (AG) tolerance, therefore, is one of the most critical traits in DSR breeding programs. However, the genetic basis of AG is still unclear. In this study, 229 single segment substitution lines (SSSLs) were arranged in an augmented design in field planting. We evaluated the anaerobic germinability by measuring the SSSLs' coleoptile length (CL) under submergence, and then identified AG QTLs. AG was a typical quantitative trait based on the results of five cropping seasons. We repeatedly detected 19 SSSLs with putative AG QTLs in at least two cropping seasons. Moreover, substitution mapping identified 11 integrated AG QTLs on nine chromosomes, including six positive and five negative QTLs with additive effect contributions ranging from 6.8 to 18.5%. Among the 11 QTLs, qAG4 and qAG11 were novel ones, qAG9 was cloned in a previous study, and the remaining eight QTLs overlapped with reported AG QTLs. Overall, we identified some genetic loci controlling AG in multiple environments, which may be useful for developing varieties suitable for DSR. [ABSTRACT FROM AUTHOR]

Wheat coleoptile is a sheath-like structure that helps to deliver the first leaf from embryo to the soil surface. Here, a RIL population consisting of 245 lines derived from Zhou 8425B × Chinese Spring cross was genotyped by the high-density Illumina iSelect 90K assay for coleoptile length (CL) QTLmapping. Three QTL for CL were mapped on chromosomes 2BL, 4BS and 4DS. Of them, two major QTL QCL.qau-4BS and QCL.qau-4DS were detected, which could explain 9.1%-22.2% of the phenotypic variances across environments on Rht-B1 and Rht-D1 loci, respectively. Several studies have reported that Rht-B1b may reduce the length of wheat CL but no study has been carried out atmolecular level. In order to verify that the Rht-B1 gene is the functional gene for the 4B QTL, an overexpression line Rht-B1b-OE and a CRISPR/SpCas9 line Rht-B1b-KO were studied. The results showed that Rht-B1b overexpression could reduce the CL, while loss-of-function of Rht-B1b would increase the CL relative to that of the null transgenic plants (TNL). To dissect the underlying regulatory mechanism of Rht-B1b on CL, comparative RNA-Seq was conducted between Rht-B1b-OE and TNL. Transcriptome profiles revealed a few key pathways involving the function of Rht-B1b in coleoptile development, including phytohormones, circadian rhythm and starch and sucrose metabolism. Our findings may facilitate wheat breeding for longer coleoptiles to improve seedling early vigor for better penetration through the soil crust in arid regions. [ABSTRACT FROM AUTHOR]

In arid and semi-arid regions, coleoptile length is a vital agronomic trait for wheat breeding. The coleoptile length determines the maximum depth that seeds can be sown, and it is critical for establishment of the crop. Therefore, identifying loci associated with coleoptile length in wheat is essential. In the present study, 282 accessions from Shanxi Province representing wheat breeding for the Loess Plateau were grown under three experimental conditions to study coleoptile length. The results of phenotypic variation indicated that drought stress and light stress could lead to shortening of coleoptile length. Under drought stress the growth rate of environmentally sensitive cultivars decreased more than insensitive cultivars. The broadsense heritability (H2) of BLUP (best linear unbiased prediction) under various conditions showed G x E interaction for coleoptile length but was mainly influenced by heredity. Correlation analysis showed that correlation between plant height-related traits and coleoptile length was significant in modern cultivars whereas it was not significant in landraces. A total of 45 significant marker-trait associations (MTAs) for coleoptile length in the three conditions were identified using the 3VmrMLM (3 Variance-component multi-locus random-SNP-effect Mixed Linear Model) and MLM (mixed linear model). In total, nine stable genetic loci were identified via 3VmrMLM under the three conditions, explaining 2.94-7.79% of phenotypic variation. Five loci on chromosome 2B, 3A, 3B, and 5B have not been reported previously. Six loci had additive effects toward increasing coleoptile length, three of which are novel. Molecular markers for the loci with additive effects on coleoptile length can be used to breed cultivars with long coleoptiles. [ABSTRACT FROM AUTHOR]

The cold tolerance studies were carried out in a bi-parental F2 population of a cross between tolerant and susceptible parents (SKUA-529 and HEERA, respectively). The purpose was to screen the individuals of a population for primary cold-tolerance-related attributes. The information generated has a direct application and use in identifying cold tolerance quantitative trait loci (QTLs) and further can be used for genotyping with an appropriate marker system. The screening was carried out on F2-derived F3 seeds and F3 plants for seedling and agronomic traits, respectively. Two tests measuring cold tolerance were conducted. In experiment I, seeds were germinated for 28 days at 13 °C and 7 days at 28 °C, and in experiment II, the seeds were germinated for 72 h at 28 °C, 96 h at 13 °C, and once more for 72 h at 28 °C. Coleoptile length, germination percentage, and radical reduction percentages were all measured in experiment I. The radicle and coleoptile regeneration in experiment II were measured after the cold period. The improvement in cold tolerance was achieved through radicle regrowth, as evidenced by the difference between the second and first measurements. The individual lines from the F2:3 population that recorded high germination (%) were #21, #13, #14, and #15. The percentage of coleoptile length (PERCOL %) was observed to be between the ranges of 23.33% to 53.00%. The reduction in coleoptile length (REDCOL %) was also obtained, and there was less reduction in #15, #16, and #14 and it had a range between 38.46% and 75%. Radicle regrowth (REDRAG) was high at 13 °C in #7, #11, #30, #35, and #36. Survival of the seedling range was between 33.33% and up to 100%, and the highest survival rate was observed in #16. The main objective of this rotation in temperature was to emulate field conditions where there has been a drop in temperature. The evaluations were done for primary cold stress tolerance traits, and it was found that most of these traits exhibited high variability. The mapping population developed may be utilized to generate a linkage map and locate QTLs for tolerance to cold stress in rice. Further, the identified donors for cold tolerance may be utilized for breeding programs aimed at the transfer of low-temperature stress tolerance into susceptible backgrounds. In general, a genotype with improved seedling germination rates, growth rates, and leaf yellowing scores; high seedling survival; lesser reduction in coleoptile length and in radicle development; and recovery following a cold shock at the seedling stage demonstrated its cold resistance. Genotypes with a low germination percentage, a greater number of days to germination, slow growth rate and higher leaf yellowing score, high reduction in coleoptile and radicle growth, and reduced seedling survival indicated cold susceptibility. [ABSTRACT FROM AUTHOR]

Successful crop stand establishment is critical to realize high yield potential, which is dependent on depth of seed placement to access soil moisture. The coleoptile determines sowing depth by its length and ability to emerge from depth. This study was conducted to assess coleoptile length among three sets of three Great Plains winter small grain cereals—wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and triticale (X triticosecale Wittm.)—and to evaluate the effect of the Rht-B1b dwarfing allele on coleoptile length in wheat and triticale. Fifty seeds of each genotype were sown in wet germination paper in two replications utilizing a randomized complete block design, which were placed in dark growth chambers at 25°C. Measurements were conducted after 7 d, and analysis of variance and comparison of least square means for coleoptile length among and within each set of genotypes were performed in Statistix 8.1 software using Fisher's protected least significance difference at the α = 0.05 significance level. Results revealed that triticale had the longest coleoptiles, which were significantly longer (P < 0.05) than those measured in both barley and wheat. Additionally, significant variation in coleoptile length (P < 0.05) was also found within each set of wheat (3.52–6.41 cm), barley (4.32–6.63 cm) and triticale (4.05–6.92 cm) genotypes, respectively. These findings confirm other reports that the presence of the Rht-B1b allele was pleiotropic for coleoptile length, but development of semi-dwarf wheats with longer coleoptiles is possible if breeders deploy concurrent selection strategies. [ABSTRACT FROM AUTHOR]

Submerged germination ability is a key trait of rice (Oryza sativa L.) in the success of water direct seeding. Therefore, mining submerged germination‐related loci and seeking high tolerant rice germplasms are important for developing rice direct seeding breeding strategies. Here, we treated 272 recombinant inbred lines (RILs, F15) from a cross from Luohui 9 (indica) and RPY geng (japonica) with simulated submergence for 7 days. We successfully bred several superior homozygous RILs with high submergence resistance, namely, R53, R137, R148, R176, and R180, via indica and japonica hybridization strategies. Then, the QTL mapping of coleoptile length trait was performed by R/qtl and IciMapping softwares based on the high‐density bin marker genetic map and two QTLs responsible for coleoptile length were detected in chromosomes 1 (qCL‐1.1) and 3 (qCL‐3.1). The haplotype results of RILs showed that the aggregation of elite alleles of these two QTLs in an individual was beneficial to improving the rice submergence tolerance. According to contrasting genotype of qCL‐1.1 and qCL‐3.1 with different coleoptile lengths, RIL07 (R07) and R180 were selected to further RNA‐seq analysis for analyzing the possible molecular mechanisms of rice under submergence stress. Finally, LOC_Os01g04430, LOC_Os01g04530, and LOC_Os03g22720 for qCL‐1.1 and qCL‐3.1 were characterized to affect submergence stress by the overlapped analysis of two independent sets of RNA‐seq data, qRT‐PCR verification, and gene sequence alignments. In this study, the submerged germination‐related QTLs/genes and high submergence‐tolerant RILs provided new genetic resources for breeding rice varieties suitable for direct seeding via molecular breeding strategies in the immediate future. [ABSTRACT FROM AUTHOR]

Unknown genetic architecture makes it difficult to characterize the genetic basis of traits and associated molecular markers because of the complexity of small effect quantitative trait loci (QTLs), environmental effects, and difficulty in phenotyping. Seedling emergence of wheat (Triticum aestivum L.) from deep planting, has a poorly understood genetic architecture, is a vital factor affecting stand establishment and grain yield, and is historically correlated with coleoptile length. This study aimed to dissect the genetic architecture of seedling emergence while accounting for correlated traits using one multi-trait genome-wide association study (MT-GWAS) model and three single-trait GWAS (ST-GWAS) models. The ST-GWAS models included one single-locus model [mixed-linear model (MLM)] and two multi-locus models [fixed and random model circulating probability unification (FarmCPU) and Bayesian information and linkage-disequilibrium iteratively nested keyway (BLINK)]. We conducted GWAS using two populations. The first population consisted of 473 varieties from a diverse association mapping panel phenotyped from 2015 to 2019. The second population consisted of 279 breeding lines phenotyped in 2015 in Lind, WA, with 40,368 markers. We also compared the inclusion of coleoptile length and markers associated with reduced height as covariates in our ST-GWAS models. ST-GWAS found 107 significant markers across 19 chromosomes, while MT-GWAS found 82 significant markers across 14 chromosomes. The FarmCPU and BLINK models, including covariates, were able to identify many small effect markers while identifying large effect markers on chromosome 5A. By using multi-locus model breeding, programs can uncover the complex nature of traits to help identify candidate genes and the underlying architecture of a trait, such as seedling emergence. [ABSTRACT FROM AUTHOR]

Abstract Background Drought is projected to become more frequent and severe in a changing climate, which requires deep sowing of crop seeds to reach soil moisture. Coleoptile length is a key agronomic trait in cereal crops such as barley, as long coleoptiles are linked to drought tolerance and improved seedling establishment under early water-limited growing conditions. Results In this study, we detected large genetic variation in a panel of 328 diverse barley (Hordeum vulgare L.) accessions. To understand the overall genetic basis of barley coleoptile length, all accessions were germinated in the dark and phenotyped for coleoptile length after 2 weeks. The investigated barleys had significant variation for coleoptile length. We then conducted genome-wide association studies (GWASs) with more than 30,000 molecular markers and identified 8 genes and 12 intergenic loci significantly associated with coleoptile length in our barley panel. The Squamosa promoter-binding-like protein 3 gene (SPL3) on chromosome 6H was identified as a major candidate gene. The missense variant on the second exon changed serine to alanine in the conserved SBP domain, which likely impacted its DNA-binding activity. Conclusion This study provides genetic loci for seedling coleoptile length along with candidate genes for future potential incorporation in breeding programmes to enhance early vigour and yield potential in water-limited environments.

Abstract Submerged germination ability is a key trait of rice (Oryza sativa L.) in the success of water direct seeding. Therefore, mining submerged germination‐related loci and seeking high tolerant rice germplasms are important for developing rice direct seeding breeding strategies. Here, we treated 272 recombinant inbred lines (RILs, F15) from a cross from Luohui 9 (indica) and RPY geng (japonica) with simulated submergence for 7 days. We successfully bred several superior homozygous RILs with high submergence resistance, namely, R53, R137, R148, R176, and R180, via indica and japonica hybridization strategies. Then, the QTL mapping of coleoptile length trait was performed by R/qtl and IciMapping softwares based on the high‐density bin marker genetic map and two QTLs responsible for coleoptile length were detected in chromosomes 1 (qCL‐1.1) and 3 (qCL‐3.1). The haplotype results of RILs showed that the aggregation of elite alleles of these two QTLs in an individual was beneficial to improving the rice submergence tolerance. According to contrasting genotype of qCL‐1.1 and qCL‐3.1 with different coleoptile lengths, RIL07 (R07) and R180 were selected to further RNA‐seq analysis for analyzing the possible molecular mechanisms of rice under submergence stress. Finally, LOC_Os01g04430, LOC_Os01g04530, and LOC_Os03g22720 for qCL‐1.1 and qCL‐3.1 were characterized to affect submergence stress by the overlapped analysis of two independent sets of RNA‐seq data, qRT‐PCR verification, and gene sequence alignments. In this study, the submerged germination‐related QTLs/genes and high submergence‐tolerant RILs provided new genetic resources for breeding rice varieties suitable for direct seeding via molecular breeding strategies in the immediate future.

Bread wheat cultivars with longer coleoptile are desired for cultivation in drought prone environments where moisture is available in the deeper layers of the soil. Although there exist several studies about coleoptile length, its relations with important agronomic traits are not clear. In the present research, a diallel mating was generated of seven Iranian and overseas wheat cultivars to evaluate coleoptile length, yield and yield related traits during 2 years, and assess relationships between coleoptile length and important agronomic traits. Roshan, Iranian landrace containing Rht8, had the longest coleoptile length (8.81 cm). High narrow sense heritability (0.53 and 0.66 in 2016 and 2017, respectively) of coleoptile length indicated strong additive genetic control of this trait. Selection for longer coleoptile indirectly increased plant height (r = 0.75**), biological yield (r = 0.56**), fertile tiller numbers (r = 0.37*), days to flowering (r = 0.57**) and awn length (r = − 0.64**). Except for days to flowering and awn length, these indirect responses are appropriate in drought stress condition. Coleoptile length of gibberellic acid sensitive cultivars possessing Rht8 and Rht13 were 42% longer than gibberellic acid insensitive cultivars containing Rht1 and Rht2. [ABSTRACT FROM AUTHOR]

Successful seedling establishment depends on the optimum depth of seed placement especially in drought-prone conditions, providing an opportunity to exploit subsoil water and increase winter survival in winter wheat. Coleoptile length is a key determinant for the appropriate depth at which seed can be sown. Thus, understanding the genetic basis of coleoptile length is necessary and important for wheat breeding. We conducted a genome-wide association study (GWAS) using a diverse panel of 298 winter wheat genotypes to dissect the genetic architecture of coleoptile length. We identified nine genomic regions associated with the coleoptile length on seven different chromosomes. Of the nine genomic regions, five have been previously reported in various studies, including one mapped to previously known Rht-B1 region. Three novel quantitative trait loci (QTLs), QCL.sdsu-2AS, QCL.sdsu-4BL, and QCL.sdsu-5BL were identified in our study. QCL.sdsu-5BL has a large substitution effect which is comparable to Rht-B1's effect and could be used to compensate for the negative effect of Rht-B1 on coleoptile length. In total, the nine QTLs explained 59% of the total phenotypic variation. Cultivars ‘Agate’ and ‘MT06103’ have the longest coleoptile length and interestingly, have favorable alleles at nine and eight coleoptile loci, respectively. These lines could be a valuable germplasm for longer coleoptile breeding. Gene annotations in the candidate regions revealed several putative proteins of specific interest including cytochrome P450-like, expansins, and phytochrome A. The QTLs for coleoptile length linked to single-nucleotide polymorphism (SNP) markers reported in this study could be employed in marker-assisted breeding for longer coleoptile in wheat. Thus, our study provides valuable insights into the genetic and molecular regulation of the coleoptile length in winter wheat.

Background: Drought is projected to become more frequent and severe in a changing climate, which requires deep sowing of crop seeds to reach soil moisture. Coleoptile length is a key agronomic trait in cereal crops such as barley, as long coleoptiles are linked to drought tolerance and improved seedling establishment under early water-limited growing conditions. Results: In this study, we detected large genetic variation in a panel of 328 diverse barley (Hordeum vulgare L.) accessions. To understand the overall genetic basis of barley coleoptile length, all accessions were germinated in the dark and phenotyped for coleoptile length after 2 weeks. The investigated barleys had significant variation for coleoptile length. We then conducted genome-wide association studies (GWASs) with more than 30,000 molecular markers and identified 8 genes and 12 intergenic loci significantly associated with coleoptile length in our barley panel. The Squamosa promoter-binding-like protein 3 gene (SPL3) on chromosome 6H was identified as a major candidate gene. The missense variant on the second exon changed serine to alanine in the conserved SBP domain, which likely impacted its DNA-binding activity. Conclusion: This study provides genetic loci for seedling coleoptile length along with candidate genes for future potential incorporation in breeding programmes to enhance early vigour and yield potential in water-limited environments. [ABSTRACT FROM AUTHOR]

Successful seedling establishment depends on the optimum depth of seed placement especially in drought-prone conditions, providing an opportunity to exploit subsoil water and increase winter survival in winter wheat. Coleoptile length is a key determinant for the appropriate depth at which seed can be sown. Thus, understanding the genetic basis of coleoptile length is necessary and important for wheat breeding. We conducted a genome-wide association study (GWAS) using a diverse panel of 298 winter wheat genotypes to dissect the genetic architecture of coleoptile length. We identified nine genomic regions associated with the coleoptile length on seven different chromosomes. Of the nine genomic regions, five have been previously reported in various studies, including one mapped to previously known Rht-B1 region. Three novel quantitative trait loci (QTLs), QCL.sdsu-2AS , QCL.sdsu-4BL , and QCL.sdsu-5BL were identified in our study. QCL.sdsu-5BL has a large substitution effect which is comparable to Rht-B1 's effect and could be used to compensate for the negative effect of Rht-B1 on coleoptile length. In total, the nine QTLs explained 59% of the total phenotypic variation. Cultivars 'Agate' and 'MT06103' have the longest coleoptile length and interestingly, have favorable alleles at nine and eight coleoptile loci, respectively. These lines could be a valuable germplasm for longer coleoptile breeding. Gene annotations in the candidate regions revealed several putative proteins of specific interest including cytochrome P450-like, expansins, and phytochrome A. The QTLs for coleoptile length linked to single-nucleotide polymorphism (SNP) markers reported in this study could be employed in marker-assisted breeding for longer coleoptile in wheat. Thus, our study provides valuable insights into the genetic and molecular regulation of the coleoptile length in winter wheat. [ABSTRACT FROM AUTHOR]

Nepal is facing more intense early-season drought stress associated with climate change. The introgression of reduced height (Rht) alleles to enable stem dwarfism in bread wheat (Triticum aestivum L.) inadvertently reduced coleoptile length and growth plasticity in seedlings, making improved varieties less suitable for deep seeding; these alleles may have also reduced seedling root length. Therefore, with the long-term objective of breeding wheat for early-season drought stress, a Nepali spring wheat panel was evaluated to assess allelic variation at the most common dwarfing-associated loci (Rht-B1, Rht-D1) and their impact on coleoptile/seedling root traits, and to identify accessions with longer and/or more GA-responsive coleoptiles as parents for future breeding. Here, Kompetitive Allele Specific PCR (KASP) was used to genotype accessions. The panel was phenotyped using the cigar-roll method in the presence/absence of GA3. Plant height was measured under field conditions. The results showed that Nepali landraces had a significantly higher frequency of the non-dwarfing allele Rht-B1a. The dwarfing alleles Rht-B1b and Rht-D1b had negative effects on coleoptile length but positive effects on the length of the longest seedling root. However, 40 potential semi-dwarf accessions (possessing Rht-B1b and/or Rht-D1b alleles) with long and/or more plastic coleoptiles suited for deep sowing were identified. This included 12 accessions that exhibited significant changes in coleoptile length in response to GA3 treatment.

Climate change has increased the risk of drought, which significantly limits plant productivity. Various ways of increasing water availability and sustaining growth of crop plants in drought-prone environments are available. Genetic advances in grain yields under rainfed conditions have been achieved with the introduction of dwarfing genes. A thorough understanding of the effects of different dwarfing genes on root growth, coleoptile length, grain yields and water using efficiency (WUE) will provide opportunities to select appropriate Rht genes for breeding high WUE and grain yield cultivars. This review focuses on the mechanism involved in Rht genes that reduce plant height and affect root and coleoptile length, their consequent effects on grain yields and WUE, and suggests that for rainfed and irrigation-limited environments, combining GAR and GAI dwarfing genes in breeding may help boost WUE and yields, and more materials from different parental sources should be collected to assess opportunities for potential comprehensive application of specific Rht genes.

The present study was conducted during years 2017-18 and 2018-19 involving 60 wheat genotypes including advance lines and released varieties. Based on the coleoptile length, these were categorised for coleoptile length as short (2.5-4.5 cm), medium (4.6-6.5 cm) and long (6.6-9 cm) respectively. Small and medium coleoptile length genotypes had comparable plant height (100.07cm and 99.29 cm, respectively) whereas, longer coleoptile genotypes were in general taller (103.78cm) numerically and for each class, the speed of germination was almost similar.A set of linked SSRs markers was used to screen the genotypes for molecular characterization based on GA responsive genes. In wheat, longer coleoptile length with reduced height is primarily controlled by GA responsive reduced height genes like Rht8, Rht12 etc., therefore, the material was screened to identify genotypes possessing GA responsive reduced height genes with available molecular markers. Molecular screening for Rht genes revealed five Rht8 positive genotypes having longer coleoptile length and good seedling vigour. Thus, Rht8 genes had positive effect on coleoptile length and had no detrimental effect on root length of seedling and provided better field emergence in field. Hence, these genotypes can be used for the development of variety for dryland agriculture and underconservation agriculture practices.

A total of 124 recent winter wheat accessions of European origin were screened for coleoptile length and plant height. Most of the accessions (74.2%) possessed a coleoptile length ranging between 5.00 and 7.00 cm. The German varieties Ebi, Pegassos, Flair without Rht genes had a coleoptile length of 9.08, 9.43, 9.56 cm and a plant height of 97, 95 and 98 cm, respectively. The Serbian variety Pobeda possessing Rht8 had a coleoptile length of 9.14 cm and a plant height of 71 cm. The varieties possessing Rht-B1b, Rht-D1b had a significantly shorter mean coleoptile length (5.45 cm) and mean plant height (84.5 cm) than the varieties without Rht genes (7.41 and 99.6 cm). The correlation between coleoptile length and plant height was medium (r = 0.613, p < 0.01) when the calculation excluded the varieties from Central and Southern Europe. The similar plant height, but not coleoptile length of the varieties possessing different dwarfing factors enables development of novel varieties with desirable height and coleoptile length from the European winter wheat germplasm.

به منظور بررسی اثر تیمار بذور با گلایسین­ بتائین بر تخفیف اثرات تنش شوری در مرحله جوانه­ زنی و رشد اولیۀ گیاهچه ذرت، آزمایشی به صورت فاکتوریل درقالب طرح کاملاً تصادفی با سه تکرار انجام شد. ابتدا بذور در محلول­ های تهیه شده گلایسین­ بتائین در 5 سطح (صفر، 2، 4، 8 و 16 میلی­مولار) خیسانده شده و پس از گذشت 24 ساعت در پتریدیش قرار داده شدند. سپس برای اعمال تنش شوری از محلول­های نمک کلرید­سدیم در سطوح صفر، 5، 10، 15 و 20 دسی­ زیمنس بر متر استفاده شد. نتایج نشان داد کلیه پارامتر­های مورد ارزیابی به شوری واکنش منفی معنی­ داری نشان دادند. اما تیمار بذور با گلایسین­ بتائین موجب افزایش معنی­ داری در پارامتر­های درصد جوانه­ زنی و طول و وزن تر ریشه­ چه و ساقه­ چه گردید. این آزمایش نشان داد که تیمار بذور با گلایسین­ بتائین، اثر مثبتی در تخفیف اثرات تنش شوری داشت و کاربرد گلایسین­ بتائین تا سطح شوری 10 دسی­ زیمنس بر متر نسبت به تیمار عدم کاربرد آن برتری یافت. مقایسات میانگین نشان داد که غلظت 4 میلی­ مولار گلایسین ­بتائین، مطلوب­ترین وضعیت را در مقابله با تنش شوری در مرحلۀ جوانه ­زنی ایجاد کرده و در بالاترین سطح آماری قرار گرفت. لازم به ذکر است که گلایسین ­بتائین در غلظت بالا (16 میلی ­مولار) اثر منفی بر خصوصیات جوانه­ زنی داشت.

Sucrose synthase, which catalyzes uridine diphosphate (UDP)-dependent cleavage of sucrose into fructose and UDP-glucose, is induced by oxygen deficiency in rice seedlings and is considered to play an important role in energy production under hypoxic conditions. In this study, we analyzed the relationship between coleoptile elongation and sucrose synthase activity in rice (Oryza sativa L.) cultivars under submerged conditions. We also analyzed the activity of α-amylase, which digests starch reserves in the endosperm and is considered to be important for energy production in young seedlings. The results indicated that different rice cultivars had different sucrose synthase and α-amylase activities under submerged conditions. Moreover, sucrose synthase activity in whole seedlings was significantly correlated with coleoptile length under submerged conditions, whereas the correlation between α-amylase activity and coleoptile length was low. Sugar content of shoots differed with the cultivar. Correlation analysis demonstrated that sucrose content was highly correlated with coleoptile length and sucrose synthase activity, but not with α-amylase activity.

Establishment of seedlings is a key factor in achievement of uniform field stands and, consequently, stable yields. Under Mediterranean conditions, soil moisture in the upper layer is limited and seedlings may be exposed to frequent dehydration events. The presence of the Rht-B1b and Rht-D1b semidominant dwarfing alleles results in insensitivity to gibberellin (GAI) and, hence, poor emergence from deep sowing. Introduction of alternative dwarfing genes and, thereby, preservation of the gibberellin response (GAR) and coleoptile length, contributes to better emergence from deep sowing. Initially 47 wheat cultivars carrying different Rht alleles were screened for their ability to emerge from deep sowing, and then 17 of them were selected for detailed physiological characterization in the field. The modern wheat lines containing GAI alleles showed significantly lower percentages of emergence from deep sowing than the GAR lines, i.e. 52 and 74%, respectively. Differences in early developmental stages were associated with grain yield, as indicated by a reduction of 37.3% in the modern cultivars. Our results demonstrate the potential of alternative dwarfing genes for improving seedling establishment and grain yields in Mediterranean-like environments.

Wheat coleoptile is a sheath-like structure that helps to deliver the first leaf from embryo to the soil surface. Here, a RIL population consisting of 245 lines derived from Zhou 8425B × Chinese Spring cross was genotyped by the high-density Illumina iSelect 90K assay for coleoptile length (CL) QTL mapping. Three QTL for CL were mapped on chromosomes 2BL, 4BS and 4DS. Of them, two major QTL QCL.qau-4BS and QCL.qau-4DS were detected, which could explain 9.1%-22.2% of the phenotypic variances across environments on Rht-B1 and Rht-D1 loci, respectively. Several studies have reported that Rht-B1b may reduce the length of wheat CL but no study has been carried out at molecular level. In order to verify that the Rht-B1 gene is the functional gene for the 4B QTL, an overexpression line Rht-B1b -OE and a CRISPR/SpCas9 line Rht-B1b -KO were studied. The results showed that Rht-B1b overexpression could reduce the CL, while loss-of-function of Rht-B1b would increase the CL relative to that of the null transgenic plants (TNL). To dissect the underlying regulatory mechanism of Rht-B1b on CL, comparative RNA-Seq was conducted between Rht-B1b -OE and TNL. Transcriptome profiles revealed a few key pathways involving the function of Rht-B1b in coleoptile development, including phytohormones, circadian rhythm and starch and sucrose metabolism. Our findings may facilitate wheat breeding for longer coleoptiles to improve seedling early vigor for better penetration through the soil crust in arid regions., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Xu, Hao, Yang, Lv, Qin, Wang, Jia, Liu, Dai, Zeng, Zhang, He, Xia, Cao and Ma.)

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Longer coleoptile is a desirable trait in wheat for sowing under drought stress environments with moisture availability in the deeper layers of the soil. In the present study, WL711/C306 wheat RIL population and the parents were phenotyped for coleoptile length under deep sowing conditions in the field and plant growth chamber. C306, a tall traditional cultivar had longer coleoptile compared to the semi dwarf parent WL711 carrying Rht- B1b gene. The RIL population showed considerable variation, normal distribution and transgressive segregation for coleoptile length under field and controlled environment conditions. The genetic linkage map of WL711/C306 RIL population was constructed comprising of 346 markers. The total map distance was 4,526.8 cM with an averaged interval of 12.9 cM between the adjacent markers. Major novel consistent QTLs for coleoptile length were identified on 4BS, co-located with the Rht- B1b gene and on 3BS. Also major QTL was identified on chromosome 3BL for coleoptile length explaining up to 12.4 % of phenotypic variation. On comparison with the rice ( Oryza sativa L.) genomic DNA sequences syntenic to wheat chromosome 4BS and 3BS, two candidate genes were identified namely gibberellin C- 20 oxidase 1 and α- Expansin. These genes play a role in cell wall expansion in the young expanding tissue in the coleoptile. QTLs qCL.4B.1 and qCL.3B.1 emerge to be important for coleoptile length in the WL711/C306 RIL population suggesting their potential value for use in marker assisted selection after validation for longer coleoptile length and improved establishment. [ABSTRACT FROM AUTHOR]

Establishment of seedlings is a key factor in achievement of uniform field stands and, consequently, stable yields. Under Mediterranean conditions, soil moisture in the upper layer is limited and seedlings may be exposed to frequent dehydration events. The presence of the Reduced height (Rht)-B1b and Rht-D1b semi-dominant dwarfing alleles results in insensitivity to gibberellin (GAI) and, hence, poor emergence from deep sowing. Introduction of alternative dwarfing genes and, thereby, preservation of the gibberellin response (GAR) and coleoptile length, contributes to better emergence from deep sowing. Initially 47 wheat cultivars carrying different Rht alleles were screened for their ability to emerge from deep sowing, and then 17 of them were selected for detailed physiological characterization in the field. The modern wheat lines containing GAI alleles showed significantly lower percentages of emergence from deep sowing than the GAR lines, i.e., 52 and 74%, respectively. Differences in early developmental stages were associated with grain yield, as indicated by a reduction of 37.3% in the modern GAI cultivars. Our results demonstrate the potential of alternative dwarfing genes for improving seedling establishment and grain yields in Mediterranean-like environments. [ABSTRACT FROM AUTHOR]

Low temperature is the most important abiotic stress affecting rice (Oryza sativa L.) yield in Chile. Rice in Chile is usually planted when the minimum air temperatures are below 12 °C. This temperature is lower than the optimum needed for normal rice germination. Therefore, the aim of this study was to evaluate cold tolerance in 20 experimental lines from the Rice Breeding Program of the Instituto de Investigaciones Agropecuarias (INIA), Chile, at the germination stage. Coleoptile length reduction (CRED), coleoptile length after cold treatment (CLEN), coleoptile length recovery (CREC), and coleoptile regrowth (CREG) were evaluated at 13 °C for 4 d using 'Diamante-INIA' as the cold-tolerant control. To find genotypes with cold tolerance (low CRED value and high CLEN, CREC, and CREG values), genotypes were ranked, a biplot of principal components, and cluster analysis were performed. No differences were found among genotypes in the ranking based on CREC value so this trait was not considered. Analysis showed that only three experimental lines had cold tolerance similar to that of 'Diamante-INIA'; all other experimental lines exhibited intermediate to low cold tolerance These results showed low cold tolerance of some Chilean genotypes at the germination stage, thus confirming the need to evaluate the rest of the germplasm from the Rice Breeding Program. [ABSTRACT FROM AUTHOR]

In arid and semi-arid regions, coleoptile length is a vital agronomic trait for wheat breeding. The coleoptile length determines the maximum depth that seeds can be sown, and it is critical for establishment of the crop. Therefore, identifying loci associated with coleoptile length in wheat is essential. In the present study, 282 accessions from Shanxi Province representing wheat breeding for the Loess Plateau were grown under three experimental conditions to study coleoptile length. The results of phenotypic variation indicated that drought stress and light stress could lead to shortening of coleoptile length. Under drought stress the growth rate of environmentally sensitive cultivars decreased more than insensitive cultivars. The broad-sense heritability ( H ) of BLUP (best linear unbiased prediction) under various conditions showed G × E interaction for coleoptile length but was mainly influenced by heredity. Correlation analysis showed that correlation between plant height-related traits and coleoptile length was significant in modern cultivars whereas it was not significant in landraces. A total of 45 significant marker-trait associations (MTAs) for coleoptile length in the three conditions were identified using the 3VmrMLM (3 Variance-component multi-locus random-SNP-effect Mixed Linear Model) and MLM (mixed linear model). In total, nine stable genetic loci were identified via 3VmrMLM under the three conditions, explaining 2.94-7.79% of phenotypic variation. Five loci on chromosome 2B, 3A, 3B, and 5B have not been reported previously. Six loci had additive effects toward increasing coleoptile length, three of which are novel. Molecular markers for the loci with additive effects on coleoptile length can be used to breed cultivars with long coleoptiles.2 ) of BLUP (best linear unbiased prediction) under various conditions showed G × E interaction for coleoptile length but was mainly influenced by heredity. Correlation analysis showed that correlation between plant height-related traits and coleoptile length was significant in modern cultivars whereas it was not significant in landraces. A total of 45 significant marker-trait associations (MTAs) for coleoptile length in the three conditions were identified using the 3VmrMLM (3 Variance-component multi-locus random-SNP-effect Mixed Linear Model) and MLM (mixed linear model). In total, nine stable genetic loci were identified via 3VmrMLM under the three conditions, explaining 2.94-7.79% of phenotypic variation. Five loci on chromosome 2B, 3A, 3B, and 5B have not been reported previously. Six loci had additive effects toward increasing coleoptile length, three of which are novel. Molecular markers for the loci with additive effects on coleoptile length can be used to breed cultivars with long coleoptiles., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Wei, Zhang, Liu, Wang, Wu, Zhao, Qiao, Zheng, Wang and Zheng.)

Barroso J, Loureiro I, Escorial MC & Chueca MC (2010). The response of Bromus diandrus and Lolium rigidum to dalapon and glyphosate I: baseline sensitivity. Weed Research 50, 312–319. The establishment of Bromus diandrus and Lolium rigidum baseline sensitivity to glyphosate and dalapon herbicides was studied for the North Central region of Spain. A rapid method in Petri dishes and a plant assay method were evaluated. The studied populations of both weed species showed sensitivity to both herbicides. The rapid method to establish the sensitivity baseline for these species worked properly for dalapon and a good correlation was found between Petri dish and plant assays. In the case of glyphosate, the rapid method was not sensitive enough, so baseline sensitivity establishment would have to be determined with plant assays. The baseline sensitivities will allow us to determine quickly and accurately any variation in the sensitivity of these weeds against these herbicides over time and to detect, at an early stage, the beginning of any trends towards resistance. [ABSTRACT FROM AUTHOR]

Abstract: Sixty-eight rice germplasms were used for cold tolerance evaluation at the germination stage in laboratory. Seeds of rice germplasms germinated at three different temperatures containing low temperature (constant 13°C for 28 days), alternative temperature (a temperature cycle of 12 h at 20°C and 12 h at 23°C for 14 days) and control (constant 26°C for 7 days). Analysis of variance revealed that temperature had a significant effect on germination rate, coleoptile length and radicle length. Germination rate was strongly affected by the low temperature and alternative treatments. Stress of low temperature at the germination stage on the tested rice germplasms caused a reduction in final germination rate and the lengths of coleoptile and radicle. The normal and healthy seeds began to germinate within 36 h after imbibition and germination were completed on the 7th day in the control, but delayed under the low and alternative temperature treatments. The low and alternative temperature treatments delayed the growth of coleoptile and radicle compared to the control, and the average lengths of coleoptile and radicule were strongly inhibited with the decreasing temperature in all of the tested germplasms. Taichung, a semi-dwarf, low amylose content and early maturing rice variety, showed a significantly higher germination rate at the three temperature treatments and its coleoptile length was significantly higher than other germplasms. [Copyright &y& Elsevier]

Higher seedling vigour and greater coleoptile length are important for early establishment of wheat crops and subsequently higher grain yield in many dry environments. Seedling vigour includes those seed properties that determine the potential for rapid, uniform emergence and development of normal seedlings under a wide range of field conditions. Genotypes with the widely used gibberellic acid (GA)-insensitive dwarfing genes Rht-B1b and Rht-D1b have good partitioning and grain yield under optimal conditions, but may perform poorly under stressed conditions due to poor crop establishment. Breeding programmes are in search of GA-sensitive dwarfing genes that do not affect seedling vigour under dry conditions. This study evaluated 40 genotypes currently used in wheat breeding programmes of south Asia for seedling vigour-related traits in greenhouse and field experiments during 2006-2007 at IAAS, Rampur, Nepal. Wide variation in coleoptile length, seedling vigour, as well as sensitivity to GA was observed. Among the genotypes studied, there were positive correlations among coleoptile length, leaf width and plant height. Genotypes, SW89-5193, SW89-5422/NL251 and SW89-5422, were found to have longer coleoptile, higher seedling vigour and response to GA application. This shows a promise for their further applications in the breeding programmes. [ABSTRACT FROM AUTHOR]

Selection of winter wheat cultivars with long coleoptiles is an important component of improving emergence, weed suppression and grain yield in low rainfall regions of the world. Seven winter wheat cultivars were hybridized in a Griffing’s half-diallel mating design, method 2 (reciprocals excluded, parents included), model 1 (fixed), and the progeny analyzed for coleoptile length in the F1 through F4 for response to selection, general combining ability (GCA), specific combining ability (SCA) and heritability. Highly significant differences existed for GCA among progeny in each generation. SCA was highly significant in the F1, F2 and F4, although SCA estimates were inconsistent among generations in each progeny population. The SCA/GCA ratio was 0.15, 0.11, 0.06 and 0.04 in the F1 through the F4, respectively, indicating that additive effects increased with homozygosity. Broad-sense heritability for coleoptile length was estimated at 0.86, 0.76, 0.60 and 0.78 for the F1 through the F4, respectively. Realized heritabilities ranged from −0.16 to 0.85 with a mean of 0.32 in the F3 and ranged from −0.68 to 0.68 with a mean of 0.13 in the F4. Spearman’s rank correlation coefficients (RS) were significant for all generation comparisons except the F1:F2, indicating that changes in rank for coleoptile length were insignificant. Cultivars with long coleoptiles and high GCA were the best parents for improving coleoptile length. Sustained selection over generations for coleoptile length was more effective than one generation of selection for genotypes both with and without reduced height genes. [ABSTRACT FROM AUTHOR]

Abstract: By using a set of recombinant inbred line (RIL) population involving in 195 lines derived from a cross of Zhenshan 97B (lowland variety) and IRAT109 (upland variety), the correlation analysis between coleoptile length (CL) and drought resistance index (DRI) and their QTL identification were conducted. There existed a significantly positive relationship between CL and DRI with the correlation coefficient of 0.2206** under water stress conditions. Under normal and water stress conditions, a total of eleven and four QTLs for CL and DRI, respectively, were detected on chromosomes 1, 2, 4, 5, 6, 7, 9, 11 and 12 by using a linkage map including 213 SSR markers, which explained 4.84% to 22.65% of phenotypic variance. Chromosomes 1 and 9 possessing the QTLs for DRI harbored simultaneously QTLs for CL, and qCL9 shared the same chromosome location with qDRI9 (RM160-RM215). Comparing the QTLs related to drought resistance in other studies, QTLs for CL and DRI were located in the same or adjacent marker interval as those related to root traits, such as number, dry weight, depth, and length of root. Moreover, sixteen and three pairs of epistatic loci for CL and DRI were found, which accounted for 56.17% and 11.93% of the total variation in CL and DRI, respectively. [Copyright &y& Elsevier]

Abstract: High soil temperatures at planting time can seriously reduce plant populations in the semi-arid tropics where surface temperatures can exceed 50°C leading to loss of crop yield. Seedling heat tolerance is critical for adequate crop establishment. Because field screening for emerging seedling heat tolerance is tedious, inconsistent, and seasonally limited, it is essential for genetic improvement to have effective and validated techniques to identify sources of tolerance and for evaluating breeding material. The objective of this research was to define a simple laboratory procedure for evaluating sorghum seedlings for their capacity to survive a controlled heat shock and resume growth, and to determine if there were significant differences for heat tolerance among the cultivars tested. Seven genotypes were grown between vertical transparent plexiglass plates in a growth chamber at 30°C, exposed to direct heat shock via a water bath at 50°C for 0, 10, 20 and 30min and then returned to the 30°C growth chamber. Coleoptile growth was measured at 8, 20, 32, and 44h after the heat treatment. Heat tolerance per se was expressed by a heat tolerance index (HTI) defined as a ratio of resumed coleoptile growth after the controlled heat shock, compared to normal growth. Ten minutes heat exposure-separated genotypes better across the time interval for coleoptile recovery compared to other exposures. Genotype×exposure interaction for HTI was significant at P &#60;0.001 and &#60;0.05 for 32 and 44h intervals, respectively. The technique for heat screening at 50°C, 10min of exposure and measuring coleoptile length after 32h of recovery was the best treatment combination. This method is relatively simple and inexpensive and can be used to screen a large number of genotypes. [Copyright &y& Elsevier]

Nepal is facing more intense early-season drought stress associated with climate change. The introgression of reduced height (Rht) alleles to enable stem dwarfism in bread wheat (Triticum aestivum L.) inadvertently reduced coleoptile length and growth plasticity in seedlings, making improved varieties less suitable for deep seeding; these alleles may have also reduced seedling root length. Therefore, with the long-term objective of breeding wheat for early-season drought stress, a Nepali spring wheat panel was evaluated to assess allelic variation at the most common dwarfing-associated loci (Rht-B1, Rht-D1) and their impact on coleoptile/seedling root traits, and to identify accessions with longer and/or more GA-responsive coleoptiles as parents for future breeding. Here, Kompetitive Allele Specific PCR (KASP) was used to genotype accessions. The panel was phenotyped using the cigar-roll method in the presence/absence of GA3. Plant height was measured under field conditions. The results showed that Nepali landraces had a significantly higher frequency of the non-dwarfing allele Rht-B1a. The dwarfing alleles Rht-B1b and Rht-D1b had negative effects on coleoptile length but positive effects on the length of the longest seedling root. However, 40 potential semi-dwarf accessions (possessing Rht-B1b and/or Rht-D1b alleles) with long and/or more plastic coleoptiles suited for deep sowing were identified. This included 12 accessions that exhibited significant changes in coleoptile length in response to GA3 treatment. [ABSTRACT FROM AUTHOR]