Impacts of Crop Variety and Time of Inoculation on the Susceptibility and Tolerance of Winter Wheat to Wheat streak mosaic virus

Abstract

Miller, Z., Menalled, F., Ito, D., Moffet, M., and Burrows, M. 2014. Impacts of crop variety and time of inoculation on the susceptibility and tolerance of winter wheat to Wheat streak mosaic virus. Plant Dis. 98:1060-1065.Plant genotype, age, size, and environmental factors can modify susceptibility and tolerance to disease. Understanding the individual and combined impacts of these factors is needed to define improved disease management strategies. In the case of Wheat streak mosaic virus (WSMV) in winter wheat, yield losses and plant susceptibility have been found to be greatest when the crop is exposed to the virus in the fall in the central and southern Great Plains. However, the seasonal dynamics of disease risk may be different in the northern Great Plains, a region characterized by a relatively cooler fall conditions, because temperature is known to modify plant-virus interactions. In a 2-year field study conducted in south-central Montana, we compared the impact of fall and spring WSMV inoculations on the susceptibility, tolerance, yield, and grain quality of 10 winter wheat varieties. Contrary to previous studies, resistance and yields were lower in the spring than in the fall inoculation. In all, 5 to 7% of fall-inoculated wheat plants were infected with WSMV and yields were often similar to uninoculated controls. Spring inoculation resulted in 45 to 57% infection and yields that were 15 to 32% lower than controls. Although all varieties were similarly susceptible to WSMV, variations in tolerance (i.e., yield losses following exposure to the virus) were observed. These results support observations that disease risk and impacts differ across the Great Plains. Possible mechanisms include variation in climate and in the genetic composition of winter wheat and WSMV across the region.

Impact of Timing and Method of Virus Inoculation on the Severity of Wheat Streak Mosaic Disease

“…Laboratory experiments revealed a higher incidence of WSMV in barley plants inoculated using WCM compared with mechanical inoculation in the field (Ito et al 2012;Lehnhoff et al 2015), indicating that the method of inoculation can influence disease severity. A similar study by Miller et al (2014) revealed severe symptoms and yield loss in wheat plants mechanically inoculated with WSMV in the spring but not those inoculated during the fall. They attributed this phenomenon to postinoculation temperatures being warmer in the spring and cooler in the fall in Montana.…”

“…In Oklahoma, Hunger et al (1992) reported that samples from winter wheat plants mechanically inoculated in the fall consistently tested positive for WSMV, whereas test results for plants inoculated in the spring were inconsistent. However, in Montana, Miller et al (2014) reported WSMV incidence of 5 to 7% and 45 to 57% in fall and spring, respectively, in mechanically inoculated winter wheat. As observed in this study, some of these differences could be attributed to unfavorable temperatures following inoculation, because fall temperatures in the southern and central Great Plains are warmer than those in the northern region (Miller et al 2014).…”

“…However, in Montana, Miller et al (2014) reported WSMV incidence of 5 to 7% and 45 to 57% in fall and spring, respectively, in mechanically inoculated winter wheat. As observed in this study, some of these differences could be attributed to unfavorable temperatures following inoculation, because fall temperatures in the southern and central Great Plains are warmer than those in the northern region (Miller et al 2014). Despite Miller et al (2014) reporting higher WSMV incidence in spring compared with fall inoculation, the infection rate was comparable with what was observed in this study in the spring mite inoculation, although much higher compared with the mechanical inoculation.…”

“…Another factor possibly influencing this is the more advanced growth stage of the plants in the spring. Therefore, mechanical inoculation is not an adequate method when temperatures are not ideal and, thus, too variable for seasonal studies like this one that use field inoculation to investigate cultivar resistance and the impact of WSMV on yield (Byamukama et al 2014;Hunger et al 1992;Miller et al 2014).…”

“…Hunger et al (1992) reported yield losses of up to 87% in susceptible cultivars when infected with WSMV during the fall season, whereas spring inoculations did not consistently show symptoms. In the northern Great Plains of the United States, spring inoculation of WSMV in winter wheat resulted in 45 to 57% yield reduction, compared with only 5 to 7% in fall inoculations (Miller et al 2014). Knowledge of the effects of time of infection (early fall, late fall, or spring) of winter wheat by WSMV on disease intensity and yield will enable development and deployment of improved management tactics.…”