Abstract
The fungus
Blumeria graminis
f. sp.
tritici
causes wheat powdery mildew disease. Here, we study its spread and evolution by analyzing a global sample of 172 mildew genomes. Our analyses show ...that
B.g. tritici
emerged in the Fertile Crescent during wheat domestication. After it spread throughout Eurasia, colonization brought it to America, where it hybridized with unknown grass mildew species. Recent trade brought USA strains to Japan, and European strains to China. In both places, they hybridized with local ancestral strains. Thus, although mildew spreads by wind regionally, our results indicate that humans drove its global spread throughout history and that mildew rapidly evolved through hybridization.
Wheat yellow mosaic disease is a soilborne disease caused by wheat yellow mosaic virus (WYMV). Symptoms include yellow mosaic coloring of leaves, stunting, and growth inhibition. Here we conducted a ...detailed analysis of resistance to this virus in winter wheat ‘Hokkai 240’ by carrying out inoculation tests of WYMV and conducting field tests. The resistance level observed in ‘Hokkai 240’ was compared with those in varieties harboring known resistance genes. In the inoculation tests, ‘Hokkai 240’ showed resistance to WYMV Pathotypes I and II and partial resistance to Pathotype III. This result was contrary to the sensitive responses to the three pathotypes exhibited by the variety harboring resistance gene on chromosome 2DL. In fields infected with WYMV Pathotypes II and III, ‘Hokkai 240’ plants exhibited few disease symptoms and little proliferation of the virus. By analyzing the quantitative trait loci (QTLs) in recombinant inbred lines from a cross between ‘Hokkai 240’ and ‘Nanbukomugi’, a single major QTL, Q.Ymhk, from ‘Hokkai 240’, which had significant effects on Pathotypes II and III of the virus, was detected in the proximity of snp4212 and snp4215 mapped on chromosome 2AS. These results indicate that Q.Ymhk may be useful for developing broad resistance to WYMV in wheat breeding programs.
The timing of heading is largely affected by environmental conditions. In wheat, Vrn-1 and Ppd-1 have been identified as the major genes involved in vernalization requirement and photoperiod ...sensitivity, respectively. To compare the effects of Vrn-1 and Ppd-1 alleles on heading time under different environments, we genotyped Vrn-1 and Ppd-1 homoeologues and measured the heading time at Morioka, Tsukuba and Chikugo in Japan for two growing seasons. A total of 128 Japanese and six foreign varieties, classified into four populations based on the 519 genome-wide SNPs, were used for analysis. Varieties with the spring alleles (Vrn-D1a or Vrn-D1b) at the Vrn-D1 locus and insensitive allele (Hapl-I) at the Ppd-D1 locus were found in earlier heading varieties. The effects of Vrn-D1 and Ppd-D1 on heading time were stronger than those of the other Vrn-1 and Ppd-1 homoeologues. Analysis of variance revealed that heading time was significantly affected by the genotype-environment interactions. Some Vrn-1 and Ppd-1 alleles conferred earlier or later heading in specific environments, indicating that the effect of both alleles on the timing of heading depends on the environment. Information on Vrn-1 and Ppd-1 alleles, together with heading time in various environments, provide useful information for wheat breeding.
A quantitative trait locus (QTL) controlling wheat grain protein content (GPC) and flour protein content (FPC) was identified using doubled haploid (DH) lines developed from a cross between the hard ...red winter wheat variety ‘Yumechikara’ with a high protein content used for bread making, and the soft red winter wheat ‘Kitahonami’ with a low protein content used for Japanese white salted noodles. A single major QTL, QGpc.2B-yume, was identified on the short arm of wheat chromosome 2B for both the GPC and FPC over 3 years of testing. QGpc.2B-yume was mapped on the flanking region of microsatellite marker Xgpw4382. The DH lines grouped by the haplotype of the closest flanking microsatellite marker Xgpw4382 showed differences of 1.0% and 1.1% in mean GPC and FPC, respectively. Yield-component-related traits were not affected by the haplotype of QGpc.2B-yume, and major North American hard red winter wheat varieties showed the high-protein haplotype. Unlike Gpc-B1 derived from tetraploid wheat, QGpc.2B-yume has no negative effects on yield-component-related traits and should be useful for wheat breeding to increase GPC and FPC.
A low cadmium (Cd) concentration in wheat grain is desirable because of Cd toxicity to humans. Grain Cd concentrations in Japanese wheat differed among the varieties in previous study. In this study, ...we hypothesized that the varieties with a low concentration of Cd in grain have (1) low Cd uptake from the soil through the roots during early growth and/or (2) low Cd translocation from the roots to shoots, and also, that (3) Cd uptake from soil is affected by root morphology. These hypotheses were verified by investigating the concentration and quantity of Cd in root, shoot and leaf tissues, and examining the root morphology of young seedlings of wheat varieties with high and low grain Cd concentrations. Seedlings of 'Kitahonami' and 'Nanbukomugi' which had low grain Cd concentration (low Cd/G varieties) had a lower Cd quantity in whole plant tissues than 'Nishikazekomugi' and 'Kitakamikomugi' which had high grain Cd concentration (high Cd/G varieties) during early growth. Low Cd/G varieties also showed lower root to shoot (aerial parts) translocation of Cd than high Cd/G varieties. Seedlings of low Cd/G varieties showed less root branching than high Cd/G varieties. Root frequency showed a significant positive correlation with Cd quantity in whole plant tissues. These results suggest that low Cd/G varieties used in this study have low Cd uptake and translocation from the roots to shoots during early growth, and furthermore, that low Cd uptake at the seedling stage may relate to slow and/or limited development of branching roots.
Yellow mosaic disease, caused by wheat yellow mosaic virus (WYMV), is one of the most serious diseases of winter wheat (
Triticum aestivum
L.) in Japan. WYMV pathotype I is distributed mainly in ...western and central Japan, pathotype II in northern Japan, and pathotype III on a part of the southern island of Japan. Major resistance genes and quantitative trait loci for WYMV were previously identified on wheat chromosomes 2DL, 3BS, and 5AL. We evaluated a total of 165 modern Japanese wheat varieties, released by the Ministry of Agriculture, Forestry and Fisheries, for response to the three pathotypes in field trials, and genotyped them using microsatellite markers associated with the three WYMV resistance genes. Based on the data, we propose a model for the relationship between the three resistance genes and WYMV pathotypes. The results strongly suggest that the resistance conferred by the gene on 5AL has broken down with emergence of pathotype III, which may be derived from pathotype I.
Fusarium head blight (FHB) remains a serious problem due to yield loss and mycotoxin accumulation in wheat production worldwide. We previously reported that the closed‐flowering (no anther extrusion) ...characteristic was effective for increasing resistance to FHB infection. In this study, we investigated the relationships between the degree of anther extrusion (AE) and FHB damage using double haploid lines (DHLs), derived from F1 plants from crosses between closed‐flowering and opened‐flowering varieties. These DHLs exhibited various degrees of AE, and the degree of AE was significantly different among DHLs, regardless of the year and environment (pot‐ or field‐grown). FHB severity was the lowest in closed‐flowering DHLs, and DHLs with partially extruded anthers showed significantly higher FHB symptoms than those with closed‐flowering phenotypes. In general, DHLs with partially extruded anthers also had relatively severe FHB symptoms compared with those exhibiting full anther extrusion. FHB severity was significantly correlated with Fusarium‐damaged kernels and deoxynivalenol concentration. The results of this study showed that partially extruded anthers were considered to be a source of FHB infection. The closed‐flowering phenotype improved resistance to FHB infection. Meanwhile, phenotypes with rapid anther extrusion and ejection also could contribute to the avoidance of FHB infection.
In wheat (Triticum aestivum L.), Fusarium head blight (FHB) resistance is an important breeding target to reduce yield losses and mycotoxin contamination. We hypothesized that cleistogamous (CL, ...closed flowering) cultivars have a lower risk of FHB infection than chasmogamous (CH, opened flowering) cultivars because FHB infection usually occurs in the inside of florets or extracted anthers and FHB resistance in CL cultivars decreases mycotoxin accumulation. To test these hypotheses, we produced 126 recombinant inbred lines (RILs) derived from a cross between common wheat varieties ‘U24’ (CL variety) and ‘Saikai 165’ (CH variety). Although ‘U24’ and ‘Saikai 165’ are both resistant to FHB infection, ‘U24’ is susceptible to FHB spread, grain deterioration, and mycotoxin accumulation compared with ‘Saikai 165’. Among the RILs, there were significant differences in all of the tested traits. Although the CL RILs showed less initial FHB infection than CH RILs, there were no significant differences in grain deterioration and mycotoxin accumulation between the 2 groups. An FHB-resistant quantitative trait locus (QTL) located on chromosome 3BS increased resistance to FHB spread, grain deterioration, and mycotoxin accumulation; however, not all CL RILs with this QTL accumulated less mycotoxin than ‘Saikai 165’.
Waxy wheat lines carrying null alleles at the loci Wx‐A1 and Wx‐B1 and a mutated Wx‐D1 allele (Wx‐D1f) generate unique pasting curves on a Rapid Visco Analyzer. The initial pasting temperature, peak ...viscosity, and final viscosity are found to not differ markedly between waxy wheat carrying Wx‐D1b and waxy wheat carrying Wx‐D1f, but the hot‐paste viscosity is more stable in the case of waxy wheat carrying Wx‐D1f. The study seeks to determine the cause for this unique starch property. Whereas amylopectin chain‐length distribution is similar in wheat lines #211 (Wx‐A1b, Wx‐B1b, Wx‐D1a) and #234 (Wx‐A1b, Wx‐B1b, Wx‐D1f), #234 contained 7.0% amylose and 1.3% extra‐long chains (ELCs) of amylopectin, levels corresponding to 1/3 and 2/3 of the content of amylose and ELCs of amylopectin in #211, respectively. Moreover, #234 contains a small‐chain amylose not detected in #211. Therefore, this study concludes that the unique starch characteristics of waxy wheat carrying Wx‐D1f may be due to the relatively high quantity of ELCs of amylopectin and/or the low‐molecular‐weight amylose.
Waxy wheat with null alleles at the Wx‐A1 and Wx‐B1 loci and a mutated allele of Wx‐D1 (Wx‐D1f) is not amylose‐free and has a unique starch pasting property. These characteristics of Wx‐D1f may be due to the relatively high quantity of ELC and/or the small amylose chain size.
Specific gravity selection using calcium chloride solution was effective in improving the grain traits for bread-wheat breeding. There were positive effects on the protein content, seed hardness, and ...test weight. Specifically, the protein content of the next generation seeds was increased by 0.5% in the F3 and F4 populations of the materials that we used. On the other hand, the effects of volumetric weight and seed hardness differed depending on the selected generation. In contrast, the seed weight and seed size showed a tendency to be decreased by the selection. To avoid less yield selection, small grains from the population must be removed using sieves when applying specific gravity selection to the breeding population.
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