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Karnal bunt caused by Tilletia indica is a quarantine disease of wheat causing huge economic losses due to the ban on the import of bunted grains. This study was designed to characterize pathogenicity, aggressiveness and genetic diversity of 68 Tilletia indica isolates collected from different geographic regions of Pakistan. Forty-six isolates were tested for their pathogenicity on eight wheat varieties, out of which three were non-aggressive. The coefficient of infection (CI) ranged from 15.73% (PB-25) to 10% (PB-68, PB-60, and PB-43). The isolates collected from central Punjab showed higher infestation compared to other isolates. Among the wheat varieties used for the aggressiveness study, WL-711 showed susceptible reaction with 10.88% CI, while NIFA-Barsat, HD-29, Janbaz, Bakhtawar-92, Tatara, and AARI 2011 showed resistance to the highly resistant response. These isolates were amplified using 31 random amplified polymorphic DNA (RAPD) markers and 32 inter-simple sequence repeat (ISSR) markers for diversity analysis. The principal component analysis (PCA) and analysis of molecular variance (AMOVA) showed greater divergence among isolates collected from Punjab and Khyber Pakhtunkhwa (KPK), with a moderate level of admixture. The isolates from Faisalabad (Punjab) were more aggressive compared to isolates from KPK and were clearly separated based on PCA, indicating the significant genetic distance in the populations. Our findings will assist breeders and pathologists in better understanding the pathogenic variability in Tilletia indica and in subsequent disease management. [ABSTRACT FROM AUTHOR]

Popcorn (Zea mays L. var. Everta) is the most ancient type of cultivated maize. However, there is little known about the genetics of popping-related traits based on genotyping-by-sequencing (GBS) technology. Here, we characterized the phenotypic variation for seven popping-related traits in maize kernels among 526 CIMMYT inbred lines (CMLs). In total, 155 083 high-quality single nucleotide polymorphism (SNP) markers were identified by a GBS approach. Several trait-associated loci were detected by genome-wide association study for color, popping expansion volume, shape, pericarp, flotation index, floury/vitreous, and protein content, explaining a majority of the observed phenotypic variance, and these were validated by a diverse panel comprising 764 tropical landrace accessions. Sixty two of the identified loci were recognized to have undergone selection. On average, there was a 55.27% frequency for alleles that promote popping in CMLs. Our work not only pinpoints previously unknown loci for popping-related traits, but also reveals that many of these loci have undergone selection. Beyond establishing a new benchmark for the genetics of popcorn, our study provides a foundation for gene discovery and breeding. It also presents evidence to investigate the role of a gradual loss of popping ability as a by-product of diversification of culinary uses throughout the evolution of teosinte–to–modern maize. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a devastating wheat disease worldwide. To decipher the genetic architecture of FHB resistance in Chinese germplasm, a Wheat Association Panel for Scab Research (WAPS) consisting of 240 leading Chinese wheat cultivars and elite lines was genotyped using the 90K single nucleotide polymorphism (SNP) arrays. The FHB response was evaluated in the field nurseries in Wuhan in Hubei Province over four consecutive years from 2014 to 2017. Five quantitative trait loci (QTL) were consistently identified on chromosome arms 1AS, 2DL, 5AS, 5AL, and 7DS using a mixed linear model (MLM), explaining 5.6, 10.3, 5.7, 5.4, and 5.6% of phenotypic variation, respectively. The QTL on 5AS, 5AL, and 7DS QTL are probably novel. The allelic frequency analysis indicated that cultivars from the Middle and Lower Yangtze River Valleys harbored more favorable alleles and were therefore more resistant than those from other regions. To facilitate in-house germplasm screening and marker-assisted selection (MAS), SNP-derived PCR markers were developed for the QTL regions on 1AS, 5AS, and 5AL QTL. In addition to the above five QTL, the WAPS population had a very low frequency of Fhb1, confirming that the gene is not widely used in Chinese wheat breeding programs. The resistant lines and molecular markers developed in this study are resources and information for enhancing FHB resistance in breeding populations by marker-assisted recurrent selection and gene stacking. [ABSTRACT FROM AUTHOR]

Background and aims: Chromium (Cr) toxicity is a rapidly increasing environmental concern and poses a major threat to plant growth as well as food chain. This study was carried out to screen spring wheat diversity panel against Cr toxicity to assess yield reduction, grain contamination extents and genomic regions associated with tolerance to Cr toxicity.Methods: The diversity panel was planted in control and Cr stress (26 mg Cr/kg soil) in paved plots, and several morphological and physiological traits were recorded. Wheat 90 K Infinium iSelect SNP array was used to identify genomic regions underpinning tolerance to Cr toxicity.Results: Some wheat cultivars (Khosar-95, Miraj-08, Millet-11, Sarsabaz and NARC-11) had Cr concentration within international edible threshold limit (1 ppm), but showed greater reduction to grain yield (63–95%) due to higher leaf Cr concentrations (2.35–8.95 ppm). Contrastingly, wheat cultivars Auqab-00 and Pakistan-13 had lower yield reduction up to 9% and 39%, respectively but had higher concentration of Cr in seeds (2.1 and 3.5 ppm, respectively). Genome-wide association studies identified 71 loci linked with yield related traits under Cr stress and 48 loci for differences between control and Cr stress treatments. Further, gene ontology of trait-associated SNPs revealed proteins with significant importance in plant development and tolerance against heavy metal stress.Conclusion: To our knowledge, this is the first study for identification of genomic regions linked to Cr stress, suggesting that this could be useful to identify complex architecture of genetic factors as well as molecular breeding opportunities for tolerance to Cr stress. [ABSTRACT FROM AUTHOR]

Adaptation of wheat (Triticum aestivum L.) to high temperature could be improved by introgressions from wild relatives. The response of 137 D genome synthetic hexaploid wheats (SHWs) to high temperature was evaluated to determine their potential for wheat improvement. Field experiments were conducted in two temperature scenarios (normal sowing time [NOR] and late sowing time to expose the plants to heat stress [HS]) for 2 yr at three locations to assess the effect of terminal high temperature on yield-related traits. High temperature stress overall led to a 46.9% reduction in grain yield and significant reductions of 25.2% in days to heading, 26.6% in plant height, 16.1% in grain number per square meter, and 18.3% in thousand grain weight. In ridge regression analysis, agronomic traits explained 8.74 to 35.2% of the variation in grain yield in the HS treatments with an average of 30.47%. In NOR treatments, agronomic traits explained 8.85 to 45.5% of the variation in grain yield, with an average of 34.5%. Days to heading was negatively correlated with grain yield in the heat-stressed environments but did not explain significant variation in grain yield in optimal environments. Thousand-grain weight explained the highest variation in grain yield in all environments, followed by grain number per square meter. The top ten highest grain-yielding SHWs in the HS treatment were also tolerant to heat stress, with a heat susceptibility index ranging from 0.33 to 0.40. These SHWs could be a promising source to introduce yield-related traits to develop high-yielding wheat cultivars for heat-stressed environments. [ABSTRACT FROM AUTHOR]

Seedling emergence is the preliminary factor defining wheat adaptability and stability under salt stress. This study was led to assess the salinity tolerance amongst 226 synthetic hexaploid wheats (SHWs) evaluated against two check cultivars, the tolerant ‘S-24’ and the susceptible ‘PBW-343’ at three sodium chloride treatments (0, 100 and 200 mM). Highly significant and positive correlation was observed between germination % and germination index (r = 0.85), and between seedling height and weight (r = 0.85). All four traits across three treatments were transformed into the salt tolerance trait index and salt tolerance index (STI). STI had significant positive correlation with all four parameters indicating reliability of this index for ranking the tolerance levels. STI-based 20 best performing genotypes were known as being promising candidates for wheat breeding. Local tolerant check was amongst the top three tolerant accessions. Two SHWs, AUS30288 {Croc_1/Aegilops squarrosa (466)} and AUS34444 {Ceta/Ae. squarrosa (872)} outperformed S-24 with STI of 61.8 and 55.7, respectively. SHW with same durum parents were included in tolerant and susceptible categories indicating that tolerance is contributed by the Ae. squarrosa syn. tauschii parent of SHWs. In conclusion, this baseline study revealed that continuous variation in the seedling emergence traits under salt stress is a conduit towards implementing genome-wide association studies. Likewise, new diversity has implications in development of salt tolerance germplasm after genetic dissection permitting unique Ae. squarrosa accessional diversity validation to target SHW donors for breeding. [ABSTRACT FROM AUTHOR]

Understanding the key characteristics associated with genetic gains achieved through breeding is essential for improving yield-limiting factors and designing future breeding strategies in bread wheat (Triticum aestivum L.) cultivars. The objective of the present study was to investigate the genetic progress in yield-related and physiological traits in cultivars released from 1950 to 2012 for irrigated conditions in the southern Yellow and Huai Valleys Winter Wheat Zone. Field trials including 26 leading cultivars from 1950 to the present time were conducted at Zhengzhou and Zhoukou in Henan Province, during the 2013-2014 and 2014-2015 cropping seasons, providing data from four environments. Grain yield (GY) was significantly increased by the linear rate of 57.5 kg ha-1 yr-1 or 0.70% (R2 = 0.66, P < 0.01) and significantly correlated with increased thousandkernel weight (TKW) (r = 0.48, P < 0.05), spike number m-2 (r = 0.44, P < 0.05), kernels m-2 (r = 0.56, P < 0.01), aboveground biomass (AGBM) (r = 0.80, P < 0.01), harvest index (HI) (r = 0.84, P < 0.01), watersoluble carbohydrate at 10 d postanthesis (WSC-10) (r = 0.80, P < 0.01), and reduced plant height (PH) (r = -0.85, P < 0.01). There was no significant change in kernel number per spike, heading date, normalized difference in vegetation index at anthesis and at 10 d postanthesis, leaf area index at anthesis and at 10 d postanthesis, and canopy temperature depression at anthesis during the past 60 yr. Soil plant analysis development (SPAD) estimates of chlorophyll content at 10 d postanthesis (Chl-10) increased with year of release and were significantly correlated with GY (r = 0.69, P < 0.01), PH (r = -0.76, P < 0.01), AGBM (r = 0.52, P < 0.01), HI (r = 0.71, P < 0.01), and WSC-10 (r = 0.73, P < 0.01). Cultivars conferring Rht-D1b and Rht- D1b + Rht8c showed increased GY, TKW, AGBM, HI, WSC-10, and Chl-10. Stem water solubility content can be used as a selection criterion for further improving yield potential. [ABSTRACT FROM AUTHOR]

Identification of genes for yield components, plant height (PH), and yield-related physiological traits and tightly linked molecular markers is of great importance in marker-assisted selection (MAS) in wheat breeding. In the present study, 246 F8 RILs derived from the cross of Zhou 8425B/Chinese Spring were genotyped using the high-density Illumina iSelect 90K single nucleotide polymorphism (SNP) assay. Field trials were conducted at Zhengzhou and Zhoukou of Henan Province, during the 2012-2013 and 2013-2014 cropping season under irrigated conditions, providing data for four environments. Analysis of variance (ANOVA) of agronomic and physiological traits revealed significant differences (P < 0.01) among RILs, environments, and RILs × environments interactions. Broad-sense heritabilities of all traits including thousand kernel weight (TKW), PH, spike length (SL), kernel number per spike (KNS), spike number/m² (SN), normalized difference in vegetation index at anthesis (NDVI-A) and at 10 days post-anthesis (NDVI-10), SPAD value of chlorophyll content at anthesis (Chl-A) and at 10 days post-anthesis (Chl-10) ranged between 0.65 and 0.94. A linkage map spanning 3609.4cM was constructed using 5636 polymorphic SNP markers, with an average chromosome length of 171.9cM and marker density of 0.64 cM/marker. A total of 866 SNP markers were newly mapped to the hexaploid wheat linkage map. Eighty-six QTL for yield components, PH, and yield-related physiological traits were detected on 18 chromosomes except 1D, 5D, and 6D, explaining 2.3-33.2% of the phenotypic variance. Ten stable QTL were identified across four environments, viz. QTKW.caas-6A.1, QTKW.caas-7AL, QKNS.caas-4AL, QSN.caas-1AL.1, QPH.caas-4BS.2, QPH.caas-4DS.1, QSL.caas-4AS, QSL.caas-4AL.1, QChl-A.caas-5AL, and QChl-10.caas-5BL. Meanwhile, 10 QTL-rich regions were found on chromosome 1BS, 2AL (2), 3AL, 4AL (2), 4BS, 4DS, 5BL, and 7AL exhibiting pleiotropic effects. These QTL or QTL clusters are tightly linked to SNP markers, with genetic distances to the closest SNPs ranging from 0 to 1.5 cM, and could serve as target regions for fine mapping, candidate gene discovery, and MAS in wheat breeding. [ABSTRACT FROM AUTHOR]