M. A. C. Langham

Occurrence and Distribution of Triticum mosaic virus in the Central Great Plains

Wheat curl mite (WCM)-transmitted viruses-namely, Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV), and the High Plains virus (HPV)-are three of the wheat-infecting viruses in the central Great Plains of the United States. TriMV is newly discovered and its prevalence and incidence are largely unknown. Field surveys were carried out in Colorado, Kansas, Nebraska, and South Dakota in spring and fall 2010 and 2011 to determine TriMV prevalence and incidence and the frequency of TriMV co-infection with WSMV or HPV in winter wheat. WSMV was the most prevalent and was detected in 83% of 185 season-counties (= s-counties), 73% of 420 season-fields (= s-fields), and 35% of 12,973 samples. TriMV was detected in 32, 6, and 6% of s-counties, s-fields, and samples, respectively. HPV was detected in 34, 15, and 4% of s-counties, s-fields, and samples, respectively. TriMV was detected in all four states. In all, 91% of TriMV-positive samples were co-infected with WSMV, whereas WSMV and HPV were mainly detected as single infections. The results from this study indicate that TriMV occurs in winter wheat predominantly as a double infection with WSMV, which will complicate breeding for resistance to WCM-transmitted viruses.

Generation means analysis of wheat streak mosaic virus resistance in winter wheat

Wheat streak mosaic virus (WSMV; Family: potyviridae; Genus: Tritimovirus) is a major threat to winter wheat (Triticum aestivum L. em. Thell) production worldwide, yet little is known about the genetic control of resistance. Our objective was to determine the mode of inheritance and type of gene action of WSMV resistance in two winter wheat crosses involving a resistant line, ‘OK65C93-8’, and two susceptible cultivars, ‘Tandem’ and ‘Vista’. For each cross, parents, F1, F2, and backcross plants were inoculated and evaluated for WSMV resistance in two replicated greenhouse experiments. Generation means analysis indicated that additive, dominance, and epistatic effects were all involved in the inheritance of WSMV resistance. Broad-sense heritability estimates for visual symptom rating and ELISA values were high for both crosses (0.84–0.91). Narrow-sense heritability estimates were low in the Tandem/OK65C93-8 cross (0.43–0.45) and moderate in the Vista/OK65C93-8 cross (0.71–0.74). Due to the presence of greater non-additive gene effects combined with low narrow-sense heritability in the Tandem/OK65C93-8 cross, selecting for WSMV resistance in this cross would be complex if using conventional methods. On the other hand, the significant contribution of additive gene effects combined with moderate narrow-sense heritability in the Vista/OK65C93-8 cross suggested that it could be exploited to select for WSMV resistance. Progress from selection for WSMV resistance in early generations of winter wheat may vary among populations as indicated in this study. Therefore, evaluating genetic control of parental combinations may be warranted prior to selecting for WSMV resistance from this source.

Development and characterization of wheat–sea wheatgrass (Thinopyrum junceiforme) amphiploids for biotic stress resistance and abiotic stress tolerance

Key messageDevelopment of a complete wheat–Thinopyrum junceiforme amphiploid facilitated identification of resistance to multiple pests and abiotic stress derived from the wild species and shed new light on its genome composition.AbstractWheat production is facing numerous challenges from biotic and abiotic stresses. Alien gene transfer has been an effective approach for wheat germplasm enhancement. Thinopyrum junceiforme, also known as sea wheatgrass (SWG), is a distant relative of wheat and a relatively untapped source for wheat improvement. In the present study, we developed a complete amphiploid, 13G819, between emmer wheat and SWG for the first time. Analysis of the chromosome constitution of the wheat–SWG amphiploid by multiple-color genomic in situ hybridization indicated that SWG is an allotetraploid with its J1 genome closely related to Th. bessarabicum and Th. elongatum, and its J2 genome was derived from an unknown source. Two SWG-derived perennial wheat lines, 14F3516 and 14F3536, are partial amphiploids and carry 13 SWG chromosomes of mixed J1 and J2 genome composition, suggesting cytological instability. We challenged the amphiploid 13G819 with various abiotic and biotic stress treatments together with its emmer wheat parent. Compared to its emmer wheat parent, the amphiploid showed high tolerance to waterlogging, manganese toxicity and salinity, low nitrogen and possibly to heat as well. The amphiploid 13G819 is also highly resistant to the wheat streak mosaic virus (temperature insensitive) and Fusarium head blight. All three amphiploids had solid stems, which confer resistance to wheat stem sawflies. All these traits make SWG an excellent source for improving wheat resistance to diseases and insects and tolerance to abiotic stress.

Biological properties of isolates of Triticum mosaic virus from the Great Plains states of the USA

Abstract Triticum mosaic virus (TriMV) is a recently discovered virus infecting wheat. A total of 170 isolates of TriMV, collected in 2010 and 2011 from wheat (Triticum aestivum L) or jointed goatgrass (Aegilops cylindrica Host) from Colorado, Kansas, Nebraska and South Dakota, were compared with the 06-123 Kansas isolate. These isolates were compared for the percentage of infected plants in N28Ht maize, ‘Gallatin’ barley and ‘Mace’ wheat (with temperature-sensitive resistance to Wheat streak mosaic virus (WSMV). The isolates were also compared for the effect of inoculum virus titre on the percentage of infected plants in WSMV-susceptible ‘Tomahawk’ wheat by mechanically inoculating the cultivar using 1:10 w/v, 1:300 v/v or 1:600 v/v dilutions of extracts. None of the isolates infected N28Ht maize but all isolates infected ‘Gallatin’ barley, ‘Mace’ and ‘Tomahawk’ wheat. Some isolates from Colorado, Kansas and Nebraska had low relative titre in wheat compared with the 06-123 isolate. This information is important in critical selection of TriMV isolates for use in greenhouse and field studies and in resistance screening protocols.

Disease and Insect Resistance in Plants

Disease and Insect Resistance in Plants provides a rich overview of host plant resistance and its application to crop and pest systems. It emphasizes conventional approaches, but it also covers modern techniques in assessing plant resistance, including cell and tissue culture andmolecular genetics (mainly inChapter 7). The book has a strong conceptual base that presents an excellent review of classical theories of hostÐ parasite interaction, the gene-for-gene hypothesis, and vertical and horizontal resistance. Disease and Insect Resistance in Plants is also practical in its discussion of laboratory and Þeld methods for identifying and developing resistant crop plants and in its attention to evaluation and eventual deployment of resistant plants. Thebookdraws concepts and examples fromawide range of crops and pests, but it focuses on certain Þeld and vegetable crops, particularly rice, wheat, oat, potato, and tomato. Consequently, crop pests and pathogens such as brown planthopper, Hessian sy, greenbug, rusts, late blight, and powdery mildew often receive detailed discussion spanning several paragraphs or a few pages at a time. These examples recur frequently throughout the book. Treatment of other cropÐpest examples is brief, sometimes limited to a single sentence. Disease and Insect Resistance in Plants is one of a few textbooks that covers resistance to both diseases and invertebrate pests. Several chapters effectively blend discussion of disease and invertebrate examples, especially in relation to the value of resistance (Chapter 1), resistance sources and testing methods (Chapter 5), conventional breeding methods (Chapter 6), and the stability and vulnerability of resistance (Chapter 8). However, discussion of disease versus invertebrate resistance is unevenly partitioned in other parts of the book. Chapters 2 (disease concepts) and 4 (genetics of hostÐparasite interaction) collectively devote 126 pages to discussion of disease resistance in plants, whereas Chapter 3 allots roughly 45 pages to plant resistance against arthropods and compiles examples of resistance to nematodes 5 pages that make up Table 3.12. Chapter 7 (unconventional breeding methods) devotes 11 pages to plant pathogens, but only 2 pages to nematodes and 1 page to arthropods. In separating discussion of disease versus invertebrate resistance,Disease and Insect Resistance in Plants fails to link common threads of these subjects. For example, the gene-for-gene concept, originally developed to describe the relationship between virulence genes of fungal pathogens and disease-resistance genes in plants, has proven applicable in explaining interactions of host plants with other pathogens and with arthropod and nematode pests. The book could have pointed out that this concept applies to pathogen races and toarthropodbiotypes.Forexample,Chapter 3 covers plant resistance in relation to virulence of arthropod biotypes, and Chapter 4 covers the genefor-gene concept in the traditional manner with regard to virulence of plant pathogens. Unfortunately, the gene-for-gene concept is notmentioned explicitly in Chapter 3, except for a brief remark of studies that discount a “gene-for-gene relationship” between rice and the brown planthopper. Additionally, strict adherence tonarrowinterpretationsof thegene-for-geneconcept and its corollaries leave the reader with limited guidance on application of these principles to pathogens such as viroids or to plant defense systems based on structuralmodiÞcationssuchas leaf trichomes inrelation to arthropod resistance. The book also missed a clear opportunity to discuss plant pathogenÐvectorÐhost interactions in relation to resistance breeding, and the strategies of developing resistance to vectors versus the pathogens they transmit.More discussion and examples ofmanaging pathogenÐvector systems by host plant resistance (e.g., resistance in wheat to the wheat curl mite for limiting Wheat streak mosaic virus) would have enhanced the book. The abundant examples presented in Disease and Insect Resistance in Plants are supported by extensive references with a bibliography making up more than one sixth of the book. The authors fulÞll their objective to revise and enlarge their 1986 book entitled Breeding for Resistance to Diseases and Insect Pests by emphasizing newer and recent techniques and by citing 500 new references. Nevertheless, older references and examples are retained; thus, the book supplies both classic and modern examples of resistance topathogensandpests.Unfortunately, newreferences are not evenly distributed, but rather clustered among subject areas, as with Chapter 7Os 88 post-1986 references. Despite these updates, this chapter still cites some references from the 1970s or early 1980s as “recent” examples. Sometimes new references are compiled in lengthy tables rather than being integrated into text, e.g., Table 3.12 and especially Table 4.1, which spans 40 pages in updating the inheritance of resistance to pathogens in various plant species since 1990. Some chapters (e.g., Chapter 6) contain sections devoid of updated references. The book generally reads well, but editorial deÞciencies are apparent. The text contains many punctuation errors and misspellings. Intermittent use of oneor two-sentence paragraphs produces staccato text and a catalog-like list of examples of pathogen and invertebrate pests. Some lengthy paragraphs lack topic sentences, and there is occasionally poor transition between paragraphs. Sections and especially chapters have abrupt endings that lack bridging to material that follows. Text could have been tightened to improve readability. The font is small and straining to read. Many areas would have beneÞted from pictures, drawings, or other illustrations.