Expression of Thinopyrum intermedium-Derived Barley yellow dwarf virus Resistance in Elite Bread Wheat Backgrounds

Applied phenomics and genomics for improving barley yellow dwarf resistance in winter wheat

Barley yellow dwarf is one of the major viral diseases of cereals. Phenotyping barley yellow dwarf in wheat is extremely challenging due to similarities to other biotic and abiotic stresses. Breeding for resistance is additionally challenging as the wheat primary germplasm pool lacks genetic resistance, with most of the few resistance genes named to date originating from a wild relative species. The objectives of this study were to (1) evaluate the use of high-throughput phenotyping to improve barley yellow dwarf assessment; (2) identify genomic regions associated with barley yellow dwarf resistance; and (3) evaluate the ability of genomic selection models to predict barley yellow dwarf resistance. Up to 107 wheat lines were phenotyped during each of 5 field seasons under both insecticide treated and untreated plots. Across all seasons, barley yellow dwarf severity was lower within the insecticide treatment along with increased plant height and grain yield compared with untreated entries. Only 9.2% of the lines were positive for the presence of the translocated segment carrying the resistance gene Bdv2. Despite the low frequency, this region was identified through association mapping. Furthermore, we mapped a potentially novel genomic region for barley yellow dwarf resistance on chromosome 5AS. Given the variable heritability of the trait (0.211–0.806), we obtained a predictive ability for barley yellow dwarf severity ranging between 0.06 and 0.26. Including the presence or absence of Bdv2 as a covariate in the genomic selection models had a large effect for predicting barley yellow dwarf but almost no effect for other observed traits. This study was the first attempt to characterize barley yellow dwarf using field-high-throughput phenotyping and apply genomic selection to predict disease severity. These methods have the potential to improve barley yellow dwarf characterization, additionally identifying new sources of resistance will be crucial for delivering barley yellow dwarf resistant germplasm.

Wheat resistome in response to barley yellow dwarf virus infection

Barley yellow dwarf virus (BYDV) caused one of the most serious virus diseases of wheat (Triticum aestivum) worldwide. The wheat-Thinopyrum intermedium translocation line YW642 carries BYDV resistance gene Bdv2. To explore resistant wheat resistome in response to BYDV infection, we used Affymetrix GeneChip® Wheat Genome Arrays to analyze transcriptomes of YW642 and its susceptible parent Zhong8601 at 12 and 72 h postinoculation with BYDV compared to mock-inoculated controls. Relative to mock-inoculated control, 335 defense-related transcripts were upregulated in BYDV-inoculated YW642, among which 70 were upregulated only in BYDV-inoculated YW642 but not in BYDV-inoculated Zhong8601 through clustering analysis. Additional analysis using BYDV-inoculated Zhong8601 as reference revealed that 59 defense-related transcripts were upregulated in BYDV-inoculated YW642. Comparison of these upregulated defense transcripts obtained via the two analysis ways indicated that 19 overlapped defense-related transcripts were highly expressed in BYDV-inoculated YW642 relative to BYDV-inoculated Zhong8601 and mock-inoculated YW642, which likely are significant factors in Bdv2-mediated defense response to BYDV. High expression of some resistance homologous genes, pathogen-associated molecular pattern-triggered immunity-related genes, ABC transporter genes, pathogenesis-related protein genes, and genes in reactive oxygen species, phospholipid signaling, and jasmonic acid-signaling may contribute to Bdv2-mediated defense response to BYDV.

Yield penalties of disease resistance in crops

Recently, there have been rapid developments in understanding the costs of disease and pest resistance in model plants and their ecological relevance in wild plants. In crop plants, however, much (although not all) of our current understanding of costs of resistance must be inferred from research on model species. To determine the true costs of resistance in crops and the likely benefit of resistance genes in new cultivars, however, other aspects of the plant's phenotype must be studied alongside resistance.

Different Reactions to the Wheat Curl Mite and Wheat streak mosaic virus in Various Wheat-Haynaldia villosa 6V and 6VS Lines

Wheat curl mite (WCM), Aceria tosichella, is the vector of Wheat streak mosaic virus (WSMV), a destructive viral pathogen in wheat (Triticum aestivum). Genetic resistance to WCM colonization can reduce the incidence of wheat streak mosaic. Chromosome 6V in Hay-naldia villosa is a new source of WCM resistance. We compared variation in resistance among different sources of H. villosa chromosome 6V and 6VS lines to WCM and WSMV and their effectiveness in controlling the incidence of WSMV following exposure to viruliferous WCM. WCM resistance varied among the 6V and 6VS lines depending on the H. villosa parent. The 6V substitution lines Yi80928, GN21, and GN22 derived from an accession of H. villosa from China, and the 6VS translocation lines 92R137, 92R178, and Sub6V from an H. villosa accession collected from the United Kingdom were uniformly resistant to WCM colonization. In contrast, the 6V substitution line RW15 and a 6VS translocation line Pm33 developed from an H. villosa collection from the former Union of Soviet Socialist Republics were susceptible to WCM. All 6V and 6VS lines were susceptible to WSMV when manually inoculated. However, symptom expression was delayed in the WCM-resistant 6V and 6VS lines after exposure to viruliferous WCM. The 6V and 6VS lines differed in their ability to control WSMV infection. WCM-susceptible lines RW15 and Pm33 had no effect on controlling the infection by WSMV. Lines GN21 and GN22 were the most effective of the three H. villosa sources in limiting the spread of WSMV. Their high yield potential and protein content, in combination with resistance to stripe rust (Puccinia striiformis f. sp. tritici) and powdery mildew (Erysiphe graminis f. sp. tritici), make GN21 and GN22 promising sources of WCM resistance.

Biological control of postharvest diseases of fruits

Losses from postharvest fruit diseases range from 1 to 20 percent in the United States, depending on the commodity. The application of fungicides to fruits after harvest to reduce decay has been increasingly curtailed by the development of pathogen resistance to many key fungicides, the lack of replacement fungicides, negative public perception regarding the safety of pesticides and consequent restrictions on fungicide use. Biological control of postharvest diseases (BCPD) has emerged as an effective alternative. Because wound-invading necrotrophic pathogens are vulnerable to biocontrol, antagonists can be applied directly to the targeted area (fruit wounds), and a single application using existing delivery systems (drenches, line sprayers, on-line dips) can significantly reduce fruit decays. The pioneering biocontrol products BioSave and Aspire were registered by EPA in 1995 for control of postharvest rots of pome and citrus fruit, respectively, and are commercially available. The limitations of these biocontrol products can be addressed by enhancing biocontrol through manipulation of the environment, using mixtures of beneficial organisms, physiological and genetic enhancement of the biocontrol mechanisms, manipulation of formulations, and integration of biocontrol with other alternative methods that alone do not provide adequate protection but in combination with biocontrol provide additive or synergistic effects.