Genetic analysis of resistance to scab in spring wheat cultivar Frontana.

The Brazilian spring wheat cv. Frontana is resistant to scab (caused by Fusarium graminearum [Gibberella zeae]) in Mexico and other countries. The number of genes involved in resistance to this disease was estimated. This was done by evaluating random inbred F₆ lines and their parents for scab resistance. The lines were derived from crosses of Frontana with susceptible, or moderately susceptible cultivars Inia 66, Opata 85 and Pavon 76. These evaluations took place in field experiments in Mexico with a mixture of Mexican isolates of G. zeae. Spikes were inoculated by placing a tiny tuft of cotton soaked with the inoculum in the middle spikelet close to the anthers just prior to anthesis. Glassine bags were placed over the inoculated spikes. These spikes were harvested 45 d after inoculation. Scab severity was determined by recording the number of infected and healthy spikelets. Analyses of variance showed significant differences in scab severities of the F₆ lines. The distribution of F₆ lines was continuous in each cross. The narrow-sense heritability estimates for the crosses evaluated during 1991 and 1993 were 0.66 and 0.93, respectively. Both quantitative and qualitative models were applied to estimate the number of segregating genes. The resistance of Frontana was controlled by the additive interaction of a min. of 3 minor genes. Transgressive segregants were identified in each cross, indicating that the susceptible (or moderately susceptible) parents also carry 1 (or 2) minor genes. The combinations of these genes with the genes in Frontana have given F₆ lines with significantly better scab resistance than that of Frontana. [1]

Molecular mapping of resistance to Fusarium head blight in the spring wheat cultivar Frontana

Fusarium head blight (FHB) is a destructive disease of wheat. The objective of this study was to characterise the FHB resistance of the Brazilian spring wheat cultivar Frontana through molecular mapping. A population of 210 doubled-haploid lines from a cross of Frontana (partially resistant) and Remus (susceptible) was evaluated for FHB resistance during three seasons. Spray and single-spikelet inoculations were applied. The severity, incidence and spread of the disease were assessed by visual scoring. The population was genotyped with 566 DNA markers. The major QTL effect associated with FHB resistance mapped to chromosome 3A near the centromere, explaining 16% of the phenotypic variation for disease severity over 3 years. The most likely position is in the Xgwm720–Xdupw227 interval. The genomic region on 3A was significantly associated with FHB severity and incidence in all years evaluated, but not with FHB spread, indicating the prominent contribution of this QTL to resistance against initial infection. The map interval Xgwm129–Xbarc197 on chromosome 5A also showed consistent association with FHB severity and accounted for 9% of the phenotypic variation. In addition, smaller effects for FHB severity were identified on chromosomes 1B, 2A, 2B, 4B, 5A and 6B in single years. Individual QTLs for resistance to FHB spread accounted for less than 10% of the variation in trait expression. The present study indicates that FHB resistance of Frontana primarily inhibits fungal penetration (type I resistance), but has a minor effect on fungal spread after infection (type II resistance). [2]

Methods to evaluate wheat cultivar testing environments and improve cultivar selection protocols

Analysis of cultivar by environment (C × E) interaction can improve efficiency of crop breeding efforts. Variety selection and recommendation based on wheat (Triticum aestivum L.) yield testing trials could possibly benefit from this type of analysis as well. The objectives of the present work were to evaluate methods to identify relevant testing environments and improve the predictive value of data from wheat cultivar yield trials in the eastern US. The data come from 32 site years of winter wheat yield trials conducted in Virginia. Biplot analysis revealed that all current testing sites were relevant and that most performed similarly within a year. The degree of relationship or dissimilarity among environments was also evaluated using straight-line distance between observations in variable space measured as the squared Euclidean distance (ED). Analysis using the ED method revealed that all environments contained the centroid and were thus representative testing environments, similar to results from the biplot analysis. Biplots were effective at identifying cultivars and testing locations that were major sources of C × E interaction. Biplots and best linear unbiased predictions (BLUPs) were used to compare cultivar performance across environments. In a separate evaluation, the ED from the centroid to a cultivar mean was used to weight past relative yields for that cultivar and increased the predictability of future yield of a cultivar in three of four seasons. Weighting by ED decreased the number of site years needed to develop confidence in the yield stability of a particular cultivar from six to three. Utilizing the BLUPs for future grain yields, predictive ability of future performance after 1 year was 40% better and overall was 25% better than that achieved by weighting with ED. Overall the BLUPS method of estimating future performance was more accurate and more reliable than weighting with ED. [3]

Water Use Efficiency Variation and Its Components in Wheat Cultivars

Genetic variations of water use efficiency (WUE) in wheat cultivar were studied in different models. These models in addition accumulating WUE; evaluate the contribution of its components. In this study, seven bread wheat cultivars were sown at four separate randomized complete block design with four replications at different moisture regimes in two growing seasons. Combined analysis of variance showed significant differences for total dry matter, WUE, relative water loss (transpiration efficiency), and initial water of flag leaves (uptake efficiency). Sardary, Sabalan and Alamut cultivars had the lowest WUE and total dry matter, but Zarrin and Shahriar were the highest values. Sardary with low uptake efficiency and Zarrin with high grain yield had the minimum and maximum transpiration efficiency. The WUE and evapotranspiration efficiency had a positive significant correlation with total dry matter and grain yield respectively. Results of path analysis showed that WUE (0.6) and total dry matter (0.31) had the highest direct effect on grain yield. Contribution of evapotranspiration efficiency (0.82) on WUE was higher than harvest index (0.30).[4]

Effects of Cadmium on Water Content, Soluble Protein, Proline Changes and Some Antioxidant Enzymes in Wheat (Triticum durum desf.) Leaves

The effect of Cadmium stress on plant growth, oxidative stress and antioxidant enzyme of wheat seedlings (Triticum durum Desf.) was evaluated in this study. Cadmium stress decreased plant growth, lowered the relative water content and caused oxidative damage, as characterised by increased antioxidative enzymes in wheat leaves such as ascorbate peroxidase (APX), guaÑ—acol peroxidase (POX) and catalase (CAT). As a response to increasing Cadmium supply particular increases in antioxidative mechanisms in wheat cultivar Simeto suggest that the high Cadmium sensitivity of Simeto is related to enhanced production and oxidative damage of reactive oxygen species. [5]

Reference

[1] Singh, R.P., Ma, H. and Rajaram, S., 1995. Genetic analysis of resistance to scab in spring wheat cultivar Frontana. Plant Disease, 79(3), pp.238-240.

[2] Steiner, B., Lemmens, M., Griesser, M., Scholz, U., Schondelmaier, J. and Buerstmayr, H., 2004. Molecular mapping of resistance to Fusarium head blight in the spring wheat cultivar Frontana. Theoretical and Applied Genetics, 109(1), pp.215-224.

[3] Thomason, W.E. and Phillips, S.B., 2006. Methods to evaluate wheat cultivar testing environments and improve cultivar selection protocols. Field Crops Research, 99(2-3), pp.87-95. [4] Eivazi, A. and Habibi, F., 2013. Water use efficiency variation and its components in wheat cultivars. Journal of Experimental Agriculture International, pp.718-730.

[5] Alayat, A., Souiki, L., Grara, N., Djebar, M.R., Boumedris, Z.E., Benosmane, S., Amamra, R. and Berrebbah, H., 2014. Effects of cadmium on water content, soluble protein, proline changes and some antioxidant enzymes in wheat (Triticum durum desf.) leaves. Annual Research & review in biology, pp.3835-3847.