Pre-harvest Sprouting Tolerance Research Articles

Development and validation of a Viviparous-1 STS marker for pre-harvest sprouting tolerance in Chinese wheats

Pre-harvest sprouting (PHS) of wheat reduces the quality of wheat grain, and improving PHS tolerance is a priority in certain wheat growing regions where conditions favorable for PHS exist. Two new Viviparous-1 allelic variants related to PHS tolerance were investigated on B genome of bread wheat, and designated as Vp-1Bb and Vp-1Bc, respectively. Sequence analysis showed that Vp-1Bb and Vp-1Bc had an insertion of 193-bp and a deletion of 83-bp fragment, respectively, located in the third intron region of the Vp-1B gene. The insertion and deletion affected the expression level of the Vp1 at mature seed stage, more correctly spliced transcripts were observed from the genotypes with either insertion or deletion than that of the wild type. Based on these insertions and deletions, a co-dominant STS marker of Vp-1B gene was developed and designated as Vp1B3, which in most cases could amplify either 845 or 569-bp fragment from the tolerant cultivars, and 652-bp from the susceptible ones. This Vp1B3 marker was mapped to chromosome 3BL using a set of Chinese Spring nulli-tetrasomic and ditelosomic lines. A total of 89 white-grained Chinese wheat cultivars and advanced lines, were used to validate the relationship between the polymorphic fragments of Vp1B3 and PHS tolerance. Statistical analysis indicated that Vp1B3 was strongly associated with PHS tolerance in this set of Chinese germplasm, suggesting that Vp1B3 could be used as an efficient and reliable co-dominant marker in the evaluation of wheat germplasm for PHS tolerance and marker-assisted breeding for PHS tolerant cultivars.

Isolation and characterization of Viviparous-1 genes in wheat cultivars with distinct ABA sensitivity and pre-harvest sprouting tolerance

Pre-harvest sprouting (PHS) of wheat reduces the quality and economic value of grain, and increasing PHS tolerance is one of the most important traits in wheat breeding. Two new Vp-1B alleles related to PHS tolerance were identified on the 3BL chromosome of bread wheat and were designated Vp-1Bb and Vp-1Bc. Sequence analysis showed that Vp-1Bb has a 193 bp insertion and Vp-1Bc has a 83 bp deletion located in the third intron region of the Vp-1B gene, and that they shared 95.43% and 97.89% similarity, respectively, with the sequence of AJ400713 (Vp-1Ba) at the nucleotide level. Their sequences were deposited in the GenBank under the accession numbers DQ517493 and DQ517494. Semi-quantitative RT-PCR analysis showed that alternatively spliced transcripts of the Vp-1A, Vp-1B, and Vp-1D homologues were present and there were no differences in the splicing patterns or abundances of Vp-1A and Vp-1D from embryos 35 d after pollination between PHS-tolerant and -susceptible cultivars. Although Vp-1Ba, Vp-1Bb, and Vp-1Bc could each produce a set of transcripts, only one was correctly spliced and had the capacity to encode the full-length VP1 protein and was more highly expressed with Vp-1Bb and Vp-1Bc than with Vp-1Ba. Comparison of the expression patterns of Vp-1Ba, Vp-1Bb, and Vp-1Bc on different days after pollination also revealed that the expression of these genes was developmentally regulated. Furthermore, genotypes with different levels of tolerance to PHS respond differently to ABA exposure and differences in transcript levels of Vp-1Ba, Vp-1Bb, and Vp-1Bc were observed after ABA treatment. The results indicated that insertion or deletion in the third intron region might affect the expression of the Vp-1B gene and its sensitivity to ABA, and thus resistance to PHS.

Increased grain dormancy in white-grained wheat by introgression of preharvest sprouting tolerance QTLs

White-grained wheat cultivars have long been recognized to be less resistant to preharvest sprouting (PHS) than the red-grained ones. Previously two QTLs for grain dormancy, QPhs.ocs-3A.1 (QPhs-3AS) and QPhs.ocs-4A.1 (QPhs-4AL) were identified in a highly dormant Japanese red wheat, Zenkoujikomugi (Zen). Aiming at improvement of PHS tolerance in white-grained wheat, the introgression effect of these two QTLs in a white-grained population consisting of 40 recombinant inbred lines (RILs) developed from a cross between Zen and white-grained Spica was examined here. Random 20 RILs with red grains were also developed from the same cross and used as a control population. The RILs were grown in the field and in the glasshouse to evaluate the grain dormancy by germination test. Several SSR markers closely linked to the QPhs-3AS and QPhs-4AL were used to estimate the alleles at the QTLs. Dormancy variation in the RILs was significantly associated with the differences for grain color and the alleles at QPhs-3AS over several years. Although allelic variation was detected in a SSR marker closely linked to QPhs-4AL there was no difference in germination data between the Zen-allele and the Spica-allele groups. As expected, the red-grained RILs with the Zen allele at QPhs-3AS were the most dormant. Some white-grained RILs with the Zen allele at QPhs-3AS showed higher dormancy compared to the red-grained RILs with the alternative allele. These results demonstrated that introgression of the QPhs-3AS gene could contribute to the increased grain dormancy in white-grained wheat.

Mapping of a major QTL for pre-harvest sprouting tolerance on chromosome 3A in bread wheat

Quantitative trait loci (QTL) analysis was conducted for pre-harvest sprouting tolerance (PHST) in bread wheat for a solitary chromosome 3A, which was shown to be important for this trait in earlier studies. An inter-varietal mapping population in the form of recombinant inbred lines (RILs) developed from a cross between SPR8198 (a PHS tolerant genotype) and HD2329 (a PHS susceptible cultivar) was used for this purpose. The parents and the RIL population were grown in six different environments and the data on PHS were collected in each case. A framework linkage map of chromosome 3A with 13 markers was prepared and used for QTL analysis. A major QTL (QPhs.ccsu-3A.1) was detected on 3AL at a genetic distance of approximately 183 cM from centromere, the length of the map being 279.1 cM. The QTL explained 24.68% to 35.21% variation in individual environments and 78.03% of the variation across the environments (pooled data). The results of the present study are significant on two counts. Firstly, the detected QTL is a major QTL, explaining up to 78.03% of the variation and, secondly, the QTL showed up in all the six environments and also with the pooled data, which is rather rare in QTL analysis. The positive additive effects in the present study suggest that a superior allele of the QTL is available in the superior parent (SPR8198), which can be used for marker-aided selection for the transfer of this QTL allele to obtain PHS-tolerant progeny. It has also been shown that the red-coloured grain of PHS tolerant parent is not associated with the QTL for PHST identified during the present study, suggesting that PHS tolerant white-grained cultivars can be developed.

Genetic basis of pre-harvest sprouting tolerance using single-locus and two-locus QTL analyses in bread wheat.

Quantitative trait loci (QTL) analysis for pre-harvest sprouting tolerance (PHST) in bread wheat was conducted following single-locus and two-locus analyses, using data on a set of 110 recombinant inbred lines (RILs) of the International Triticeae Mapping Initiative population grown in four different environments. Single-locus analysis following composite interval mapping (CIM) resolved a total of five QTLs with one to four QTLs in each of the four individual environments. Four of these five QTLs were also detected following two-locus analysis, which resolved a total of 14 QTLs including 8 main effect QTLs (M-QTLs), 8 epistatic QTLs (E-QTLs) and 5 QTLs involved in QTL x environment (QE) or QTL x QTL x environment (QQE) interactions, some of these QTLs being common. The analysis revealed that a major fraction (76.68%) of the total phenotypic variation explained for PHST is due to M-QTLs (47.95%) and E-QTLs (28.73%), and that only a very small fraction of variation (3.24%) is due to QE and QQE interactions. Thus, more than three-quarters of the genetic variation for PHST is fixable and would contribute directly to gains under selection. Two QTLs that were detected in more than one environment and at LOD scores above the threshold values were located on 3BL and 3DL presumably in the vicinity of the dormancy gene TaVp1. Another QTL was found to be located on 3B, perhaps in close proximity to the R gene for red grain colour. However, these associations of QTLs for PHST with genes for dormancy and grain colour are only suggestive. The results obtained in the present study suggest that PHST is a complex trait controlled by large number of QTLs, some of them interacting among themselves or with the environment. These QTLs can be brought together through marker-aided selection, leading to enhanced PHST.

Use of SAMPL for a study of DNA polymorphism, genetic diversity and possible gene tagging in bread wheat.

Selective Amplification of Microsatellite Polymorphic Loci (SAMPL) technology was used in bread wheat for the first time for a study of genetic diversity, genotype identification and gene tagging. The diversity studies involved 55 wheat genotypes and two SAMPL primer pairs (SAMPL-6 and SAMPL-7, each with a M-CAG primer), which together gave 43 polymorphic bands out of a total of 87 SAMPL bands. The average polymorphic information content (PIC) of SAMPL primers was 0.221 and that of SAMPL markers was 0.264. The marker index of SAMPL markers was 9.61. The genetic similarity (GS) coefficients for 1,485 pairs of genotypes ranged from 0.35 to 0.96 with an average of 0.65. A dendrogram was prepared on the basis of a similarity matrix using the UPGMA algorithm, which corresponded well with the results of principal component analysis (PCA). From a total of 55 genotypes, 54 could be distinguished using the SAMPL banding patterns of both primers. For gene tagging, 568 bands from a total of 1,185 SAMPL bands detected polymorphism between each of the three pairs of parents differing for grain protein content (GPC), pre-harvest sprouting tolerance (PHST) and grain weight (GW). An association of six bands with GPC, of seven bands with PHST and four bands with GW was observed using bulked segregant analysis (BSA).

Integrated physical maps of 2DL, 6BS and 7DL carrying loci for grain protein content and pre-harvest sprouting tolerance in bread wheat

SUMMARY In our two earlier studies on bread wheat, we identified three molecular marker loci - one (Xwmc41) associated with grain protein content (GPC) was located on 2DL and the other two (Xwmcl04 and XmstlOl) associated with pre-harvest sprouting tolerance (PHST) were located one each on 6BS and 7DL. These studies were extended using additional marker loci already known to be located on these arms. Seven STMS marker loci, that were already mapped on 2DL (Roder et al., 1998a), and 13 STMS marker loci that were already mapped on 6BS and 7DL were tested for possible genetic association with GPC/ PHST. Although, some of these markers did show polymorphism between the contrasting parents, none of them showed linkage with GPC/ PHST or with the markers associated with them. This encouraged us to undertake physical mapping of all the loci known to be located on 2DL, 6BS and 7DL. The marker loci and the regions to which they were mapped included the following: (i) Xwmc41 (an STMS locus), that was associated with a QTL for GPC, was assigned to the terminal 0.24 fraction of 2DL; (ii) from among two molecular marker loci associated with PHST, Xwmcl04 (an STMS locus) was assigned to terminal 0.76 fraction of the 6BS satellite and XmstlOl (an STS locus) was assigned to proximal centromeric 0.10 fraction of 7DL; (iii) 13 STMS marker loci, earlier genetically mapped on 6BS and 7DL, were also assigned to specific physical regions of these two arms. The marker loci that were physically mapped during the present study were integrated with those earlier mapped in a similar way, and integrated physical maps with 27 marker loci on 2DL, 42 marker loci on 6BS and 54 marker loci on 7DL were prepared. We believe that these integrated physical maps should prove useful for a variety of studies in future.

Genetic analysis of preharvest sprouting tolerance in three wheat crosses

Three recombinant inbred populations were assessed for tolerance to preharvest sprouting (PHS). Genetic analysis of the PHS scores, as assessed under artificial rain treatment, indicated that for 2 of the populations, tolerance to sprouting was simply inherited and was controlled by 2 independent genes, both of which are necessary for full tolerance. The data presented here show that in these 2 populations the trait is highly heritable under controlled environment situations. It was also demonstrated that the red seed colour gene, derived from Aus1490 and traditionally associated with tolerance, is not necessary for full tolerance to sprouting, although indirect selection for preharvest sprouting tolerance can be performed very effectively by selecting for red grain. The presence of white-seeded lines, recovered from this cross with a red-seeded donor of PHS tolerance, that are at least as tolerant as the most tolerant red-seeded individuals demonstrates that red-seeded donors of PHS tolerance should not be discarded for improvement of this trait.

Inheritance of Preharvest Sprouting Tolerance in Triticum aestivum and Its Transfer to an Amber-Grained Cultivar

Inheritance of Preharvest Sprouting Tolerance in Triticum aestivum and Its Transfer to an Amber-Grained Cultivar

Preharvest sprouting tolerance in three triticale biotypes

Preharvest sprouting is a major constraint to the utilization of triticale for human consumption in regions where moist, humid conditions prevail during harvest. To examine variation for different components of preharvest sprouting tolerance (PST), trials were conducted over six environments in Mexico. Seed dormancy, bract related chemical and mechanical inhibitory effects and falling number (FN) were measured in primary and secondary triticales and their wheat and rye progenitors. Seed dormancy contributed 78% to PST with significant variation among and within triticale biotypes and progenitor species for bract water soluble inhibitors, bract mechanical barriers and FN. Bract chemical inhibition was higher when soil moisture was non-limiting in moisture-stress/non-stress experiments, suggesting the presence of inhibitors other than abscisic acid. In combination, tolerance components enhanced PST. Substituted triticales [2D(2R)] showed higher seed dormancy and bract related tolerances compared with other triticale biotypes and displayed PST equivalent to wheat. The higher PST in wheat could be attributed to higher FN levels. Components of PST evident in the wheat and rye progenitors were suppressed by wheat/rye genomic interactions in primary triticales. The selection of triticales with high stable FN will be an important first step in the development of PST cultivars, by providing the building block upon which seed dormancy and other related factors can be introduced.

Breeding for Preharvest Sprouting Tolerance in White‐Seed‐Coat Spring Wheat

White seed‐coat is a desirable quality attribute for many uses of wheat (Triticum spp.). Unfortunately white seed coat has traditionally been associated with low tolerance to preharvest sprouting. The objective was to assess our breeding progress to improve the preharvest sprouting tolerance of white genotypes. In 1987 and 1988, two groups of white genotypes, developed in our breeding program, were compared with 20 genotypes differing in seed‐coat color (red or white), preharvest sprouting tolerance, and class of wheat. Three categories of tests were used to evaluate sprouting tolerance: (i) artificial rain (AR) treatment of intact heads, (ii) germination (G) of hand threshed heads, and (iii) field weathering (FW). The AR and G tests differentiated and ranked genotypes in agreement with previous information, while the FW test proved unsatisfactory, probably due to insufficient rainfall during the field weathering periods. The white genotypes developed from two tolerant parents (2TP) displayed higher levels of tolerance than those developed from a single tolerant parent (1TP). Only tolerant red genotypes and registered hard red spring cultivars had more tolerance than the 2TP group. The 2TP group was judged to be equal in tolerance to ‘Laura’, a hard red spring wheat with a reasonable level of sprouting tolerance, and better than eight groups comprised of 19 genotypes. The results suggest that white‐seed‐coat cultivars can be developed with high levels of preharvest sprouting tolerance. Observed differences between wheat classes probably reflect current cultivars and applied selection pressure, either direct or indirect during cultivar development, rather than inherent differences between classes.