Estimating Yield Losses Due to Barley Yellow Dwarf on Winter Wheat in Kansas Using Disease Phenotypic Data

Gaunce, G. M., and Bockus, W. W. 2015. Estimating yield losses due to Barley yellow dwarf on winter wheat in Kansas using disease phenotypic data. Plant Health Progress doi:10.1094/PHP-RS-14-0039 Barley yellow dwarf (BYD) is one of the most important wheat diseases in the state of Kansas. Despite the development of cultivars with improved resistance to BYD, little is known about the impact that this resistance has on yield loss from the disease. The intent of this research was to estimate yield loss in winter wheat cultivars in Kansas due to BYD and quantify the reduction in losses associated with resistant cultivars. During seven years, BYD incidence was visually assessed on numerous winter wheat cultivars in replicated field nurseries. When grain yields were regressed against BYD incidence scores, negative linear relationships significantly fit the data for each year and for the combined dataset covering all seven years. The models showed that, depending upon the year, 19–48% (average 33%) of the relative yields was explained by BYD incidence. For the combined dataset, 29% of the relative yield was explained by BYD incidence. The models indicated that cultivars showing the highest disease incidence that year had 25–86% (average 49%) lower yield than a hypothetical cultivar that showed zero incidence. Using the models, the moderate level of resistance in the cultivar Everest was calculated to reduce yield loss from BYD by about 73%. Therefore, utilizing visual BYD symptom evaluations in Kansas coupled with grain yields is useful to estimate yield loss from the disease. SIGNIFICANCE OF BARLEY YELLOW DWARF Barley yellow dwarf (BYD, Fig. 1) is caused by strains of the Barley yellow dwarf virus (BYDV) and Cereal yellow dwarf virus (CYDV) of the Luteoviridae family. The disease is capable of producing significant yield losses in several different crop species including wheat (Triticum aestivum L.) (Bockus et al. 2010). It is considered one of the most economically important virus diseases of cereal crops in the world (Burnett 1984, Lister and Ranieri 1995, Plumb 1983). In the state of Kansas, it is the fourth most important wheat disease in terms of average estimated yield losses (Appel et al. 2013). The virus particles have an icosahedral shape and encase a single-stranded, positive RNA genome. The virus is phloem limited within the host plant and it cannot be transmitted without the aid of its hemipteran vector (Gildow 1987, Jensen and D’Arcy 1995). The serotype most common to Kansas agronomic cereal crops is PAV, although the closely related RPV strain of CYDV is also common (Bockus, unpublished data). Both of these species are transmitted by either the bird cherry-oat aphid (Rhopalosiphum padi) or the greenbug (Schizaphis graminum) (Power and Gray 1995). BYD symptoms can vary depending on the host; however, even within a host such as wheat, symptoms can differ widely among cultivars. Visual foliar symptoms can vary between yellow leaf discolorations (Fig. 1) to oranges, reds, and purples. They begin at the leaf tip and spread toward the leaf base, particularly on the flag leaves (McKirdy and Jones 1996). Stunting and a decrease in kernel size and kernel number per head can occur, leading to an overall decrease in yield in the infected plants (Herbert et al. 1999, Hoffman and Kolb 1998, Weisz et al. 2005). The stunting symptom is usually associated with early infections of the wheat plant by the pathogen. BYDV is thought to over-season in native perennial grasses and volunteer host plants which are considered to be the main viral/vector reservoir (Jones et al. 1990, McKirdy and Jones 1993). The virus is often spread in the fall when viruliferous aphid species fly or are blown from the reservoirs into winter wheat fields at emergence (McKirdy and Jones 1996). Infection