V.S. Sohu

Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat

To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience.

Genetic dissection of grain zinc concentration in spring wheat for mainstreaming biofortification in CIMMYT wheat breeding

Wheat is an important staple that acts as a primary source of dietary energy, protein, and essential micronutrients such as iron (Fe) and zinc (Zn) for the world’s population. Approximately two billion people suffer from micronutrient deficiency, thus breeders have crossed high Zn progenitors such as synthetic hexaploid wheat, T. dicoccum, T. spelta, and landraces to generate wheat varieties with competitive yield and enhanced grain Zn that are being adopted by farmers in South Asia. Here we report a genome-wide association study (GWAS) using the wheat Illumina iSelect 90 K Infinitum SNP array to characterize grain Zn concentrations in 330 bread wheat lines. Grain Zn phenotype of this HarvestPlus Association Mapping (HPAM) panel was evaluated across a range of environments in India and Mexico. GWAS analysis revealed 39 marker-trait associations for grain Zn. Two larger effect QTL regions were found on chromosomes 2 and 7. Candidate genes (among them zinc finger motif of transcription-factors and metal-ion binding genes) were associated with the QTL. The linked markers and associated candidate genes identified in this study are being validated in new biparental mapping populations for marker-assisted breeding.

Harnessing genetic potential of wheat germplasm banks through impact-oriented-prebreeding for future food and nutritional security

The value of exotic wheat genetic resources for accelerating grain yield gains is largely unproven and unrealized. We used next-generation sequencing, together with multi-environment phenotyping, to study the contribution of exotic genomes to 984 three-way-cross-derived (exotic/elite1//elite2) pre-breeding lines (PBLs). Genomic characterization of these lines with haplotype map-based and SNP marker approaches revealed exotic specific imprints of 16.1 to 25.1%, which compares to theoretical expectation of 25%. A rare and favorable haplotype (GT) with 0.4% frequency in gene bank identified on chromosome 6D minimized grain yield (GY) loss under heat stress without GY penalty under irrigated conditions. More specifically, the ‘T’ allele of the haplotype GT originated in Aegilops tauschii and was absent in all elite lines used in study. In silico analysis of the SNP showed hits with a candidate gene coding for isoflavone reductase IRL-like protein in Ae. tauschii. Rare haplotypes were also identified on chromosomes 1A, 6A and 2B effective against abiotic/biotic stresses. Results demonstrate positive contributions of exotic germplasm to PBLs derived from crosses of exotics with CIMMYT’s best elite lines. This is a major impact-oriented pre-breeding effort at CIMMYT, resulting in large-scale development of PBLs for deployment in breeding programs addressing food security under climate change scenarios.

Correction to: Strategic crossing of biomass and harvest index—source and sink—achieves genetic gains in wheat

The original article was corrected. Author Muhammad Kundi should instead read: Muhammad Sohail.

Stability Performance of Bread Wheat Genotype for Grain Yield, Zinc and Iron Concentrations

The primary aim of plant breeding is to improve stability in yield and to obtain varieties with good quality. For this reason, a study of wheat genotypes was conducted at three different locations: Bathinda, Gurdaspur and Ludhiana during 2015-16 in Punjab (India). Grain yield and its components with quality traits were assessed in 21 wheat genotypes with 3 checks using analysis of variance and regression analysis. The combined analysis of variance for environment (E), genotype (G) and (G×E) interaction was highly significant for all studied traits, suggesting differential responses of the genotypes and the need to stability analysis. Results revealed that high yielding genotypes can also be stable. The check HD 3086 and PBW 725 and genotypes BWL 6003, BWL 6065, BWL 6066, BWL 6068 and BWL 6069 for grain yield/ plot had desired performance in term of high mean, unit regression coefficient (bi) and least deviation from regression (S2d), indicating the role of linear portion of GxE interaction and average stability in the performance of these genotype. The value of regression coefficient (bi) of genotypes BWL 6008, BWL 6011 and checks HD 3086, PBW 725 for grain Fe concentration; genotypes BWL 6006, BWL 6007, BWL 6013 and BWL 6062 for grain Zn concentration were have high mean, unit regression coefficient (bi) and least deviation from regression (S2d), indicating that these genotypes were considered specially adopted to unfavorable environments

Marker assisted stacking of drought tolerance QTL and rust resistance genes in an elite Indian wheat genotype

Backcross population derived from a cross between Triticum aestivum advance breeding line PBW703 (PBW343+Lr24+Lr28+Yr10+Yr15) and Babax, a drought tolerant line from CIMMYT was used for introgression of drought tolerance QTL (quantitative trait loci) regions in a leaf and stripe rust resistant background. Out of 24 polymorphic SSR markers reported to be linked to drought tolerance in earlier studies and 15 markers showed introgression on different chromosomes with minimum of two and maximum of nine introgressed regions in different BC2F1 plants. For phenotypic analysis, 364 BC2F4 progenies from best performing selected BC2F1 plants were evaluated for rust reaction, chlorophyll content, canopy temperature, stay green, plant height, number of tillers per meter, number of spikelets per spike, number of grains per spike, 100 grain weight under restricted irrigated conditions. Correlation analysis showed that there was significant and positive correlation between these morphological traits. Transgressive segregants were observed for all the traits which were out performing the recipient parent PBW703. A total of 42 plants carrying the Babax specific alleles for drought tolerance QTL and all the four rust resistance genes Lr24, Lr28, Yr10 and Yr15 were finally selected for agronomic evaluation. Selected improved lines for drought tolerance are being evalauted in the wheat breeding programme.

Genetic variation for grain zinc and iron concentrations and quality parameters in wheat (Triticum aestivum L.) genotypes

Grains of fifty lines of bread wheat (Triticum aestivum L.) representing diverse genotypes were analyzed in the year 2015 for variation in their micronutrient concentrations. Both grain Zn and Fe concentrations correlated negatively with grain yield and 1000-grain weight. Zn concentration also correlated significantly but negatively with phenol reaction score and plant height. Grain Fe concentration correlated significantly but positively with plant height, grain Zn and grain protein concentration. However, the correlations of Fe content with days to heading, grain appearance score, sodium dodecyl sulphate (SDS) sedimentation value and phenol reaction score and correlations of Zn content with days to heading, grain appearance score, SDS and grain protein were weak. Both Fe and Zn concentration showed negative direct on grain yield. Significant differences between bread wheat genotypes were found for grain Fe and Zn concentrations. Five entries namely 448, 412, 420, 414 and 419 showed high values for both Fe and Zn concentration. For Zn, an increment of 33.3% (54.4 ppm) over check (40.8 ppm) was observed. For Fe, an increment of 28.1% (45.1 ppm) was observed over check (35.2 ppm). The information generated could be used for developing micronutrient biofortification strategies.

Genetic characterization of resistance to stripe rust, leaf rust, Karnal bunt and cereal cyst nematode in a multiple disease resistant wheat stock W8627

Genetic analysis of multiple disease resistance was carried out in segregating populations of bread wheat line W8627 and PBW343 against stripe rust (Puccinia striiformis), leaf rust (Puccinia triticina), Karnal bunt (Tilletia indica) isolates and cereal cyst nematode (Heterodera avenae). Seedling response of W 8627, PBW 343 and F1 against 78S84 race of Puccinia striiformis, 77-5 race of P. triticina reflected that the wheat line W8627 possessed seedling resistance genes against both the races. Based on the segregation pattern of F2 generation and F3 families, two complementary recessive genes for resistance to 78S84 race of Puccinia striiformis and one recessive gene each for resistance to 77-5 race P. triticina, mixture of Tilletia indica isolates and Ha 41 biotype of H. avenae were identified. Co-segregation studies revealed no linkage between concerned resistance genes.