Longer Coleoptiles Research Articles

High-throughput phenotyping of wheat root angle and coleoptile length at different temperatures using 3D-printed equipment

BackgroundInnovation in crop establishment is crucial for wheat productivity in drought-prone climates. Seedling establishment, the first stage of crop productivity, relies heavily on root and coleoptile system architecture for effective soil water and nutrient acquisition, particularly in regions practicing deep planting. Root phenotyping methods that quickly determine coleoptile lengths are vital for breeding studies. Traditionally, direct selection for root and coleoptile traits has been limited by the lack of suitable phenotyping methods, genetic and phenotypic complexity, and poor repeatability in sampling. In this study, we innovated a method utilizing 3D printing technology to measure root angle and coleoptile length in wheat seedlings. We evaluated seedlings from eight different wheat genotypes across varying temperatures and validated our findings through image processing techniques.ResultsThe analysis of variance in root architecture revealed significant differences among genotypes for root angle. Temperature treatments also significantly influenced shoot length, number of roots and total root length. The Tosunbey genotypes exhibited the highest root angle and the lowest root angle was observed in Altindane genotypes. Additionally, we observed that increasing the temperature led to an increase in seedling root length. Similarly, the coleoptile architecture analysis showed significant differences among genotypes in coleoptile length, leaf length, number of roots, and total root length. Temperature treatments and deep sowing applications significantly affected these traits as well. The Tosunbey and Müfitbey genotypes exhibited the longest coleoptile length, whereas the Nevzatbey genotype showed the shortest.ConclusionSelecting for a narrow root angle and a high number of seminal roots can result in deeper, more branched root systems. Furthermore, developing wheat genotypes with longer coleoptiles can enhance plant production and early vigor, particularly with deep sowing. Our method, using the eqiupments producing by 3D printing technology enables high-throughput phenotyping of wheat roots and coleoptiles, offering new insights into root and coleoptile system regulation at different temperature conditions. This method can be seamlessly integrated into breeding programs to enhance drought tolerance, rapidly phenotyping populations for root and coleoptile characteristics.

Identification of a novel and plant height-independent QTL for coleoptile length in barley and validation of its effect using near isogenic lines

Key messageThis study reported the identification and validation of novel QTL conferring coleoptile length in barley and predicted candidate genes underlying the largest effect QTL based on orthologous analysis and comparison of the whole genome assemblies for both parental genotypes of the mapping population.Coleoptile length (CL) is one of the most important agronomic traits in cereal crops due to its direct influence on the optimal depth for seed sowing which facilitates better seedling establishment. Varieties with longer coleoptiles are preferred in drought-prone areas where less moisture maintains at the top layer of the soil. Compared to wheat, genetic study on coleoptile length is limited in barley. Here, we reported a study on detecting the genomic regions associated with CL in barley by assessing a population consisting of 201 recombinant inbred lines. Four putative QTL conferring CL were consistently identified on chromosomes 1H, 5H, 6H, and 7H in each of the trials conducted. Of these QTL, the two located on chromosomes 5H and 6H (designated as Qcl.caf-5H and Qcl.caf-6H) are likely novel and Qcl.caf-5H showed the most significant effect explaining up to 30.9% of phenotypic variance with a LOD value of 15.1. To further validate the effect of this putative QTL, five pairs of near isogenic lines (NILs) were then developed and assessed. Analysis of the NILs showed an average difference of 21.0% in CL between the two isolines. Notably, none of the other assessed morphological characteristics showed consistent differences between the two isolines for each pair of the NILs. Candidate genes underlying the Qcl.caf-5H locus were also predicted by employing orthologous analysis and comparing the genome assemblies for both parental genotypes of the mapping population in the present study. Taken together, these findings expand our understanding on genetic basis of CL and will be indicative for further gene cloning and functional analysis underly this locus in barley.

Genome‐wide association analysis of coleoptile length and interaction with plant height in durum wheat

AbstractGenotypes with longer coleoptiles can be sown in deep soil layers to reach the underground moisture needed for germination in dry areas. Developing new varieties with longer coleoptiles and shorter plant heights would be novel for wheat breeding and production. In this study, coleoptile lengths of a panel of durum wheat (Triticum turgidum ssp. durum) genotypes were determined, and 14,255 DArTseq (SNP and Silico‐DArT) markers were used to identify coleoptile length‐associated markers by genome‐wide association study (GWAS). A wide genetic variation was accounted for both coleoptile length and plant height. The genetic relationships between coleoptile length and plant height were evaluated using plant height values from five different environments. Two environmentally stable MTAs were identified, one for coleoptile length (QCol.su.4BS) and one for plant height (QPh.su.4BS). These MTAs were located on the short arm of chromosome 4B, with LOD scores up to 12.00 and 17.00, respectively. A relatively high LD (r2 = 0.71) was accounted for between QCol.su.4BS and QPh.su.4BS. The LD block intervals of the MTAs overlapped with some genes with roles in plant growth and development. The functions of plausible candidate genes tell us that QCol.su.4BS may be controlling coleoptile length, whereas QPh.su.4BS may be regulating plant height. The combination of the two loci would be desirable. In conclusion, this study sheds light on the genetic control of coleoptile length and its relationship with plant height in durum wheat.

New semi-dwarfing alleles with increased coleoptile length by gene editing of gibberellin 3-oxidase 1 using CRISPR-Cas9 in barley (Hordeum vulgare L.).

The green revolution was based on genetic modification of the gibberellin (GA) hormone system with "dwarfing" gene mutations that reduces GA signals, conferring shorter stature, thus enabling plant adaptation to modern farming conditions. Strong GA-related mutants with shorter stature often have reduced coleoptile length, discounting yield gain due to their unsatisfactory seedling emergence under drought conditions. Here we present gibberellin (GA) 3-oxidase1 (GA3ox1) as an alternative semi-dwarfing gene in barley that combines an optimal reduction in plant height without restricting coleoptile and seedling growth. Using large-scale field trials with an extensive collection of barley accessions, we showed that a natural GA3ox1 haplotype moderately reduced plant height by 5-10 cm. We used CRISPR/Cas9 technology, generated several novel GA3ox1 mutants and validated the function of GA3ox1. We showed that altered GA3ox1 activities changed the level of active GA isoforms and consequently increased coleoptile length by an average of 8.2 mm, which could provide essential adaptation to maintain yield under climate change. We revealed that CRISPR/Cas9-induced GA3ox1 mutations increased seed dormancy to an ideal level that could benefit the malting industry. We conclude that selecting HvGA3ox1 alleles offers a new opportunity for developing barley varieties with optimal stature, longer coleoptile and additional agronomic traits.

An invasive weed-associated bacteria confers enhanced heat stress tolerance in wheat

Global temperatures are expected to increase due to climate change, and heat stress is one of the major limiting factors affecting future agriculture. To identify plant-associated microorganisms which can promote heat stress tolerance in wheat, we have screened several bacteria isolated from etiolated seedlings of the invasive noxious weed Parthenium hysterophorus. One isolate designated as Ph-04 was found to confer enhanced heat stress tolerance in wheat. The 16S rRNA gene sequence analysis showed that Ph-04 isolate shared highest sequence identity with Bacillus paramycoides species of the Bacillus cereus group. Ph-04 treated wheat seeds exhibited enhanced germination, longer coleoptile, radicle and seminal root length than control seedlings when grown in the dark at optimum and high temperatures. Similarly, under autotrophic conditions, Ph-04 treated plants also exhibited enhanced heat stress tolerance with a significant increase in membrane integrity and significantly reduced levels of H2O2 under heat stress compared to control plants. This observed heat stress tolerance is associated with constitutively higher basal levels of proline, and activity of antioxidant enzymes, catalase (CAT) and ascorbate peroxidase (APX) in Ph-04 treated plants grown under unstressed conditions with further increase under heat stress conditions compared to controls. Plant recovery after heat stress also showed that the Ph-04 treated plants exhibited significantly less damage in terms of survival percentage and exhibited better morphological and physiological characteristics compared to control plants. The study proves that invasive weeds can harbour potentially beneficial microorganisms, which can be transferred to non-native crop (host) plants to improve climate resilience characteristics.

Coleoptile length comparison of three winter small grain cereals adapted to the Great Plains

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.

Challenges of breeding for longer coleoptile in bread wheat (Triticum aestivum L.)

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.

Seedling elongation responses to gibberellin seed treatments in wheat

AbstractThe wheat (Triticum aestivum L.) Reduced height (Rht) alleles are widely used to prevent lodging through semi‐dwarfism. Seedling elongation and coleoptile length can be significantly decreased by some of these alleles, leading to reduced soil emergence after deep sowing in certain semi‐arid environments. Application of the elongation‐promoting hormone gibberellin A3 (GA3) as a seed treatment has been used as an alternative to improve seedling emergence. Seedling responses to GA3 seed treatment were investigated under controlled conditions in a collection of varieties differing for Rht dwarfing alleles and the ability to emerge from deep planting. Data between treated and untreated seed were collected on overall coleoptile length and emergence from deep planting in simulated pot studies. Gibberellin‐sensitive varieties, carrying either no dwarfing gene or the Rht8 dwarfing gene, responded to the GA3 seed treatment with increased coleoptile and subcrown internode elongation. Comparison of near‐isogenic lines carrying no dwarfing allele or the GA‐insensitive Rht‐B1b and/or Rht‐D1b semi‐dwarfing alleles showed that GA insensitivity was associated with reduced seedling response to GA3 seed treatment. However, there was variation in seedling elongation and GA3 response in a collection of GA‐insensitive varieties. Thus, it cannot be assumed that all Rht‐B1b and Rht‐D1b varieties will fail to respond to GA3 seed treatment. Interestingly, some better emerging GA‐insensitive varieties had longer coleoptiles after treatment, suggesting that selection for better emergence in semi‐arid regions of the U.S. Pacific Northwest may have led to responses in GA3 application independent of the dwarfing gene used.

Detection and characterization of quantitative trait loci for coleoptile elongation under anaerobic conditions in rice

ABSTRACT Low oxygen concentrations in flooded paddy fields cause poor seedling establishment in wet direct seeded rice. We aimed to identify novel genomic regions associated with coleoptile elongation under anaerobic conditions in order to improve seedling establishment. Chromosome segment substitution lines (CSSLs), substituted with Koshihikari (Japonica-type) in the IR 64 genetic background (Indica-type) were evaluated. These lines were imbibed with a hydroponic solution containing Oxyrase to create a stable anaerobic condition and coleoptile lengths were measured six days after incubation at 30°C. Among the CSSLs, only SL2111 had a significantly longer coleoptile (23.9 mm) than that of IR 64 (14.3 mm). From genotype and phenotype analyses, a novel QTL, referred to as qACE3.1, for coleoptile elongation under anaerobic conditions was detected on chromosome 3. To explore the molecular mechanism of qACE3.1, the expression levels of genes encoding enzymes involved in starch degradation and fermentation were assessed. In SL2111 coleoptiles, the expression levels of pyruvate decarboxylase were significantly higher than in IR 64 coleoptiles whereas those of alcohol dehydrogenase were lower. In contrast, no differences were observed in the expression levels of genes associated with starch degradation. These results imply that qACE3.1 may specifically affect fermentative metabolism. In addition, we evaluated the impact of qACE3.1 on seedling establishment under flooded conditions in a paddy field.

ВЛИЯНИЕ ДЛИНЫ КОЛЕОПТИЛЯ И ГЛУБИНЫ ПОСЕВА НА УРОЖАЙНОСТЬ ЯРОВОЙ ТРИТИКАЛЕ

Now triticale is referred to as a crop that is able to solve the problem of stabilizing the gross yield of cultivated feed and food grains around the world. Spring triticale in the Chuvash Republic is not cultivated in a small area and breeding for this crop is not conducted. The introduction of spring triticale in production is possible only when creating varieties that meet the soil and climatic conditions of the country. This problem can be solved only by selecting and creating the initial breeding material. The source material must be studied comprehensively. One of the important indicators in the evaluation of the source material may be the length of a coleoptile. The purpose of the research is to determine the influence of the length of the coleoptile and the depth of sowing of seeds on the yield of the source material of spring triticale. Presented studies conducted in 2017-2018. The varieties Ulyana, Rovnya, Khaykar, Saur and breeding lines 15-11-2, 15-48-11, 15-65-29 were evaluated. The short coleoptile had Rovnya and 15-11-2 line, the middle coleoptile had Ulyana, Saur and 15-65-29 line, the long coleoptile Khaykar and 15-48-11 line. The longest coleoptile was in 15-48-11 line, and the shortest - in 15-11-2 line. For forms with a short coleoptile with increasing sowing depth, field germination, plant safety, number of productive stems, productive bushiness, grain weight per spike, number of grains per spike, grain yield are significantly reduced. Their maximum manifestation in forms with an average coleoptile was found at a seeding depth of 5 cm. For forms with a long coleoptile, the seeding depth does not significantly affect the value of these indicators. For all the studied parameters with an increase in the depth of sowing, their dependence on the length of the coleoptile increases. High correlation is observed in field germination, plant safety, the number of productive stems, the mass of 1000 grains and yield.

Dissection of coleoptile elongation in japonica rice under submergence through integrated genome-wide association mapping and transcriptional analyses.

Rice is unique among cereals for its ability to germinate not only when submerged but also under anoxic conditions. Rice germination under submergence or anoxia is characterized by a longer coleoptile and delay in radicle emergence. A panel of temperate and tropical japonica rice accessions showing a large variability in coleoptile length was used to investigate genetic factors involved in this developmental process. The ability of the Khao Hlan On rice landrace to vigorously germinate when submerged has been previously associated with the presence of the trehalose 6 phosphate phosphatase 7 (TPP7) gene. In this study, we found that, in the presence of TPP7, polymorphisms and transcriptional variations of the gene in coleoptile tissue were not related to differences in the final coleoptile length under submergence. In order to find new chromosomal regions associated with the different ability of rice to elongate the coleoptile under submergence, we used genome-wide association study analysis on a panel of 273 japonica rice accessions. We discovered 11 significant marker-trait associations and identified candidate genes potentially involved in coleoptile length. Candidate gene expression analyses indicated that japonica rice genotypes possess complex genetic elements that control final coleoptile length under low oxygen.

Effects of combinational treatment with ethephon and gibberellic acid on rice seedling growth and carbohydrate mobilization in seeds under flooded conditions

ABSTRACTEarly seedling growth, including seedling emergence and vigor, is crucial in direct seeded rice. In this study, we examined the effects of gibberellic acid (GA3) and ethephon (ET) on the early growth of direct seeded rice, and on α-amylase activity and soluble sugar content in the seeds. Rice seeds were treated with water (control), ET, GA3, or ET+ GA3 and were allowed to grow for 21 days. The results showed that ET and GA3 synergistically improved the lengths of mesocotyl, coleoptile, mesocotyl+ coleoptile, and first leaf. Moderate synergistic effects of ET and GA3 were detected in the second and third leaves. ET+ GA3 treatment induced higher α-amylase activities during early post-germination growth, which is consistent with the longer coleoptile, mesocotyl, mesocotyl+ coleoptile, and first leaf. In addition, ET+ GA3 induced higher α-amylase activity in the seeds, and consequently, higher sucrose and glucose concentrations than other treatments. These results partially explain the regulatory mechanism underlying the synergistic interaction of ET and GA3 on rice seedling growth in terms of starch and sugar metabolism in the seeds, and this knowledge is expected to facilitate the practical use of ET and GA3 in direct seeded rice systems.

Ethylene-Inhibited Jasmonic Acid Biosynthesis Promotes Mesocotyl/Coleoptile Elongation of Etiolated Rice Seedlings.

Elongation of the mesocotyl and coleoptile facilitates the emergence of rice (Oryza sativa) seedlings from soil and is affected by various genetic and environment factors. The regulatory mechanism underlying this process remains largely unclear. Here, we examined the regulation of mesocotyl and coleoptile growth by characterizing a gaoyao1 (gy1) mutant that exhibits a longer mesocotyl and longer coleoptile than its original variety of rice. GY1 was identified through map-based cloning and encodes a PLA1-type phospholipase that localizes in chloroplasts. GY1 functions at the initial step of jasmonic acid (JA) biosynthesis to repress mesocotyl and coleoptile elongation in etiolated rice seedlings. Ethylene inhibits the expression of GY1 and other genes in the JA biosynthesis pathway to reduce JA levels and enhance mesocotyl and coleoptile growth by promoting cell elongation. Genetically, GY1 acts downstream of the OsEIN2-mediated ethylene signaling pathway to regulate mesocotyl/coleoptile growth. Through analysis of the resequencing data from 3000 rice accessions, we identified a single natural variation of the GY1 gene, GY1376T , which contributes to mesocotyl elongation in rice varieties. Our study reveals novel insights into the regulatory mechanism of mesocotyl/coleoptile elongation and should have practical applications in rice breeding programs.

Mapping gibberellin-sensitive dwarfing locus Rht18 in durum wheat and development of SSR and SNP markers for selection in breeding

Gibberellin-sensitive dwarfing gene Rht18 was mapped in two durum wheat recombinant inbred lines (RIL) populations developed from crosses, Bijaga Yellow/Icaro and HI 8498/Icaro. Rht18 was mapped within genetic interval of 1.8 cM on chromosome 6A. Simple sequence repeat (SSR) markers S470865SSR4, barc37 and TdGA2ox-A9 specific marker showed co-segregation with Rht18 in Bijaga Yellow/Icaro population consisting 256 RILs. Effect of Rht18 on plant height was validated in HI 8498/Icaro RIL population which segregated for Rht18 and Rht-B1b. Rht-B1b from HI 8498 showed pleiotropic effect on plant height and coleoptile length, on the other hand, Rht18 did not show effect on coleoptile length. The SSR and SNP markers linked to Rht18 were also validated by assessing their allelic frequency in 89 diverse durum and bread wheat accessions. It was observed that 204 bp allele of S470865SSR4 could differentiate Icaro from rest of the wheat accessions except HI 8498, suggesting its utility for selection of Rht18 in wheat improvement programs. Rht18 associated alleles of TdGA2ox-A9, IAW4371 and IAW7940 were absent in most of the tall Indian local durum wheat and bread wheat, hence could be used to transfer Rht18 to bread wheat and local durum wheat. SSR marker barc3 showed high recombination frequency with Rht18, though it showed allele unique to Icaro. Since semidwarf wheat with GA-sensitive dwarfing genes are useful in dry environments owing to their longer coleoptile, better emergence and seedling vigor, Rht18 may provide a useful alternative to widely used GA-insensitive dwarfing genes under dry environments.

Sowing quality and yielding capacity of spring wheat seeds depending on the pre-sowing treatment by protectants and microfertilizers

Aim. To determine seed quality indices of bread spring wheat under environments of Right-bank Forest-Steppe of Ukraine depending on pre-sowing seed treatment with protectants and microfertilizers.Materials and methods. The studies were carried out at the V.M. Remeslo Myronivka Institute of Wheat of NAAS (2012-2014) on the spring wheat varieties Elehiia myronivska and Simkoda myronivska. Scheme of experiment: 1) Control (no treatment); 2) Rankona 15, ME, 1.2 l/t; 3) Celeste Top 312.5 FS, 1.5 l t; 4) Tseovit Grain, 1 l/t; 5) Fertigrain Start, 1 l/t; 6) Rankona 15, ME, 1.2 l/t + Tseovit Grain, 1 l/t; 7) Rankona 15, ME, 1.2 l/t + Fertigrain Start, 1 l/t; 8) Celeste Top 312.5 FS, 1.5 l/t + Tseovit Grain, 1 l/t; 9) Celeste Top 312.5 FS, 1.5 l/t + Fertigrain Start, 1 l/t.Results. On average, over the years of research (2012-2014) on seed treatment variant for protectants Rankona 15 ME, 1.2 l/t and Celeste Top 312.5 FS, 1.5 l/t yielding capacity of the variety Elehiia myronivska increased by 0.26–0.30 t/ha, the variety Simkoda myronivska – by 0.21–0.26 t/ha in comparison with the variant no treatment. When the seeds were treated with microfertilizers Tseovit Grain, 1 l/t and Fertigrain Start, 1 l/t, the productivity of varieties increased by 0.24–0.25 t/ha and 0.18–0.22 t/ha, respectively. The highest yield of Elehiia myronivska (3.55–3.59 t/ha) and Simkoda myronivska (3.37–3.44 t/ha) was produced resulted from seed treatment with protectants together with microfertilizers. This treatment also increased the mass of 1000 seeds. Seed treatment with protectant of fungicidal-insecticidal action Celeste Top 312.5 FS, 1.5 l/t together with microfertilizer Fertigrain Start, 1 l/t was the most effective. Presowing treatment of bread spring wheat seeds with protectants and microfertilizers promoted the formation of seeds with high germination energy, laboratory germination, longer coleoptile and more germ rootlets in the next generation.Conclusions. The positive effect of protectants and microfertilizers on yielding capacity and sowing seed quality has been experimentally revealed. The yield, mass of 1000 seeds, activity of sprouting, energy of germination, laboratory germination, as well as the length of coleoptile and the number of embryonic rootlets increased with seed treatment with a mixture of Rankona 15, ME, 1.2 l/t and Celeste Top 312.5 FS, 1.5 l/t combined with microfertilizers Tseovit Grain, 1 l/t and Fertigrain Start, 1 l/t.

Genome-wide association study reveals genetic architecture of coleoptile length in wheat.

Eight QTL for coleoptile length were identified in a genome-wide association study on a set of 893 wheat accessions, four of which are novel loci. Wheat cultivars with long coleoptiles are preferred in wheat-growing regions where deep planting is practiced. However, the wide use of gibberellic acid (GA)-insensitive dwarfing genes, Rht-B1b and Rht-D1b, makes it challenging to breed dwarf wheat cultivars with long coleoptiles. To understand the genetic basis of coleoptile length, we performed a genome-wide association study on a set of 893 landraces and historical cultivars using 5011 single nucleotide polymorphism (SNP) markers. Structure analysis revealed four subgroups in the association panel. Association analysis results suggested that Rht-B1b and Rht-D1b genes significantly reduced coleoptile length, and eight additional quantitative trait loci (QTL) for coleoptile length were also identified. These QTL explained 1.45-3.18 and 1.36-3.11% of the phenotypic variation in 2015 and 2016, respectively, and their allelic substitution effects ranged from 0.31 to 1.75cm in 2015, and 0.63-1.55cm in 2016. Of the eight QTL, QCL.stars-1BS1, QCL.stars-2DS1, QCL.stars-4BS2, and QCL.stars-5BL1 are likely novel loci for coleoptile length. The favorable alleles in each accession ranged from two to eight with an average of 5.8 at eight loci in the panel, and more favorable alleles were significantly associated with longer coleoptile, suggesting that QTL pyramiding is an effective approach to increase wheat coleoptile length.

Characterization for drought resistance at early stages of wheat genotypes based on survival, coleoptile length, and seedling vigor

In order to develop genotypes having a stable higher yield, it is necessary to characterize genetic resources based on drought adaptation, determine the suitable genotypes, and use them in breeding programs. This study was carried out in greenhouses, plant growth chambers, and research farms of the Faculty of Agriculture at Ataturk University. A total of 64 certified and local bread wheat genotypes were used to test survival after drought, coleoptile length, and seedling vigor. There were significant differences with respect to the selection parameters in this study. Seedling survival ranged from 18.5% to 51.1% and coleoptile lengths were 39-74 mm. Leaf width and specific leaf area were 3.27-4.71 mm and 164.4-204.2 cm 2 /g, respectively. Genotypes Lancer, Kirac 66, Gerek 79, Mizrak, Harmankaya 99, Alparslan, Dagdas 94, and Dogu 88 had stable high seedling survival rates and were tolerant to early drought with respect to seedling survival after drought. Local genotypes and old cultivars had higher coleoptile length compared to modern cultivars. Genotypes Ak Bugday, Tir, Lancer, Sert Bugday, and Conkesme, having long coleoptiles, could be used as genitors for the breeding of new genotypes with short plant height and longer coleoptile. Genotypes Kirac 66 and Mufitbey, ranked best in terms of first leaf width and specific leaf area, could adapt themselves to places where early drought is observed and could be used as parents in breeding programs.

Overexpression of an S-like ribonuclease gene, OsRNS4, confers enhanced tolerance to high salinity and hyposensitivity to phytochrome-mediated light signals in rice

S-like ribonucleases (S-like RNases) are homologous to S-ribonucleases (S-RNases), but are not involved in self-incompatibility. In dicotyledonous plants, S-like RNases play an important role in phosphate recycling during senescence and are induced by inorganic phosphate-starvation and in response to defense and mechanical wounding. However, little information about the functions of the S-like RNase in monocots has been reported. Here, we investigated the expression patterns and roles of an S-like RNase gene, OsRNS4, in abscisic acid (ABA)-mediated responses and phytochrome-mediated light responses as well as salinity tolerance in rice. The OsRNS4 gene was expressed at relatively high levels in leaves although its transcripts were detected in various organs. OsRNS4 expression was regulated by salt, PEG and ABA. The seedlings overexpressing OsRNS4 had longer coleoptiles and first leaves than wild-type seedlings under red light (R) and far-red light (FR), suggesting negative regulation of OsRNS4 in photomorphogenesis in rice seedlings. Moreover, ABA-induced growth inhibition of rice seedlings was significantly increased in the OsRNS4-overexpression (OsRNS4-OX) lines compared with that in WT, suggesting that OsRNS4 probably acts as a positive regulator in ABA responses in rice seedlings. In addition, our results demonstrate that OsRNS4-OX lines have enhanced tolerance to high salinity compared to WT. Our findings supply new evidence on the functions of monocot S-like RNase in regulating photosensitivity and abiotic stress responses.

Relationship between coleoptile and mesocotyl elongation of upland rice (Oryza sativa L.) seedlings under submergence and soil-sand culture

In rice, the coleoptile and mesocotyl are two morphologically important structures for seedling emergence. After germination, coleoptile and or mesocotyl elongation projects the seedling tip out of the soil and water in which it is planted, allowing the leaves to make contact with the atmosphere thus enabling the seedling to develop into a normal rice plant. Rice genotypes with inherently longer coleoptiles and or mesocotyls are thought to emerge better than those with shorter ones. However, the patterns of elongation under submergence and in soil-sand culture remain unclear especially for upland rice. This study examined coleoptile and mesocotyl elongation in 63 upland rice genotypes comparing elongation patterns under submergence to elongation in soil-sand culture. Coleoptile and mesocotyl elongation in soil-sand culture differed from elongation under submergence. Coleoptile lengths were enhanced more under submergence and mesocotyls grew longer in soil-sand culture. This appeared to link seedling emergence under submergence more to coleoptile elongation, and emergence in drained soil-sand culture largely to mesocotyl elongation. We found no obvious relationship between coleoptile and mesocotyl elongation under submergence. But in soil-sand culture, increases in coleoptile length corresponded to increases in mesocotyl length, suggesting that simultaneously coleoptile and mesocotyl elongation contribute to seedling emergence in drained soils. Key words: Seedling emergence, mesocotyl elongation, coleoptile elongation, upland rice.

Elongation habit of mesocotyls and coleoptiles in weedy rice with high emergence ability in direct-seeding on dry paddy fields

Direct-seeding of rice on dry paddy soil could enable large-scale cultivation and cost-savings, but still has some problems including poor seedling establishment caused by low temperature and varied sowing depth. This research was performed to identify weedy rice genetic resources that may help to eliminate the problem of poor seedling establishment in direct-seeded rice on dry paddy soil in temperate regions. The genetic resources screened in this study were 128 genotypes consisting of 92 japonica weedy rices, 24 indica weedy rices, and 12 Korean bred cultivars. On average, weedy rice germplasm had superior abilities to emerge from greater depths than cultivated rices. Coleoptile and mesocotyl lengths were highly positively correlated with the emergence rate. Among the weedy rice germplasm, the japonica weedy rice WD-3 showed the highest level of emergence with the longest coleoptile and mesocotyl. The emergence ability of WD-3 was confirmed in both phytotron and field conditions. In the emerged plants in the field, the mesocotyl elongation increased with increasing burial depth in a logarithmic fashion, and coleoptile extension increased exponentially. The mesocotyl and coleoptile elongated to a length of seed burial depth, indicating that the mesocotyl and coleoptile of WD-3 could induce the safe development of the first leaf of the seedling at the soil surface. Therefore, the elongation habit of the mesocotyl and coleoptile of WD-3 could be one of the most important characteristics for the development of direct-seeding cultivars.