No abstract

Grain yield loss caused by bird cherry‐oat aphid (Rhopalosiphum padi L.) infestation and barley yellow dwarf virus (BYDV) infection may result from direct damage to the winter wheat (Triticum aestivum L.) crop as well as from reduced crop tolerance to stress environments. This greenhouse study measured the effects of R. padi infestation, BYDV infection, or a combination of R. padi plus BYDV on plant height, date of anthesis, yield, and yield components of four winter wheat varieties (‘Roughrider’, ‘Norstar’, ‘TAM 107’, and ‘Vona’) in the absence of additional environmental stresses. Treatments were applied at the two‐leaf growth stage. Early in the pre‐vernalization growth period, R. padi treatment (alone or in combination with BYDV) reduced plant height to about 55 to 60% of the control plant height while BYDY treated plants were about 90% of control. During the post‐vernalization growth period, plant heights attained about 90% of control in the R. padi treatment, to about 80% of control in the BYDV treatment and to about 70% of control in the R. padi+ BYDV treatment. Dates of anthesis were later in the R. padi+BYDV treatments than in the R. padi treatments for Norstar, Roughrider, and Vona but not for TAM 107. Individual kernel weights in the BYDV and R. padi+BYDV treatments were less than control or R. padi treatments for Norstar, TAM 107, and Vona but not for Roughrider. Control or R. padi‐treated plants had a greater number of fertile heads than plants given the BYDV or R. padi+BYDV treatments. Grain yield was strongly associated with kernel number per plant. The number of kernels per plant was reduced 19% by the R. padi treatment, 36% by the BYDV treatment, and 50% by the R. padi+BYDV treatment. Grain yield was reduced 21% by the R. padi treatment, 46% by the BYDV treatment, and 58% by the R. padi+BYDV treatment. With the exception of date of anthesis and individual kernel weight, there were no significant treatment by variety interactions for plant height, grain yield, and yield components. We conclude that R. padi infestation and BYDV infection caused significant yield reductions and that the varieties tested had little difference in their responses to these treatments in the absence of additional environmental stress.

on the extent of the insect infestation (Kieckhefer et al., 1995), the timing of the infestation during the growing There is little information available that describes the effects of season (Kieckhefer and Gellner, 1988), the growth stage bird cherry-oat aphids (Rhopalosiphum padi L.) and Barley yellow of the plant at infestation (Pike and Schaffner, 1985), dwarf virus (BYDV) on cereal plant root systems. This 2-yr field experiment was conducted to determine how spring wheat (Triticum and whether the R. padi transmit BYDV to the crop aestivum L.) root characteristics, shoot characteristics, and grain yield (McPherson et al., 1986). BYDV is a phloem-restricted respond to R. padi infestation, BYDV infection, or a combination of Luteovirus obligately vectored by several species of R. padi plus BYDV. Treatments were applied at the 2-to 3-leaf stage.aphids (Kolb et al., 1991). Symptoms of BYDV infection When measured at anthesis, plants that received R. padi treatments include leaf discoloration (yellow or red), leaf necrosis, (300 aphid days) had about a 30% greater total root length (as meastunting, and delay or lack of heading (Comeau, 1987; sured with a minirhizotron) than control plants. Plants that received Hewings and D'Arcy, 1986; Riedell et al., 1999). BYDV BYDV as well as those that received R. padi plus BYDV had about is considered to be one of the most economically impora 40% decrease in total root length when compared with the control.

Existing crop monitoring programs determine the incidence and distribution of plant diseases and pathogens and assess the damage caused within a crop production region. These programs have traditionally used observed or predicted disease and pathogen data and environmental information to prescribe management practices that minimize crop loss. Monitoring programs are especially important for crops with broad geographic distribution or for diseases that can cause rapid and great economic losses. Successful monitoring programs have been developed for several plant diseases, including downy mildew of cucurbits, Fusarium head blight of wheat, potato late blight, and rusts of cereal crops. A recent example of a successful disease-monitoring program for an economically important crop is the soybean rust (SBR) monitoring effort within North America. SBR, caused by the fungus Phakopsora pachyrhizi, was first identified in the continental United States in November 2004. SBR causes moderate to severe yield losses globally. The fungus produces foliar lesions on soybean (Glycine max) and other legume hosts. P. pachyrhizi diverts nutrients from the host to its own growth and reproduction. The lesions also reduce photosynthetic area. Uredinia rupture the host epidermis and diminish stomatal regulation of transpiration to cause tissue desiccation and premature defoliation. Severe soybean yield losses can occur if plants defoliate during the mid-reproductive growth stages. The rapid response to the threat of SBR in North America resulted in an unprecedented amount of information dissemination and the development of a real-time, publicly available monitoring and prediction system known as the Soybean Rust-Pest Information Platform for Extension and Education (SBR-PIPE). The objectives of this article are (i) to highlight the successful response effort to SBR in North America, and (ii) to introduce researchers to the quantity and type of data generated by SBR-PIPE. Data from this system may now be used to answer questions about the biology, ecology, and epidemiology of an important pathogen and disease of soybean.

No abstract

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.

No abstract

No abstract