ABSTRACT
During 1992, a multivirus epidemic reduced tomato production by as much as 25% in the major tomato-growing region of Alabama. Estimated yield losses of 100% resulted from the epidemic in over 250 ha in two counties of North Alabama. Cucumber mosaic cucumovirus (CMV), alone or in combination with potato potyvirus Y (PVY) and/or tobacco etch potyvirus (TEV), was responsible for the crop failure. CMV was detected alone or in combination with PVY and/or TEV in over 70% of the samples tested and was present in 90% of the fields surveyed. In 1993, 21 tomato fields were monitored weekly from transplanting through harvest for CMV, PVY, TEV, tobacco mosaic tobamovirus, and tomato spotted wilt tospovirus. All 5 viruses were detected, with CMV occurring most frequently. Incidence of CMV at the 61% level or higher was found in 16 of the 21 fields surveyed. Tomatoes transplanted in April and May were least effected and had relatively low virus incidence until late in their development. Tomatoes transplanted in June and July were infected at an earlier age, had the highest virus incidence, were the most severely affected, and suffered the greatest loss in yield. In 1994,Aphis gossypii, the cotton aphid, was the most common virus vector found during an aphid monitoring/virus spread study. Populations of A. gossypii peaked in late June, immediately preceding a period of rapid CMV incidence and spread.
ABSTRACT
The quantitative relationship between yield of spring oat cvs. Ogle and Noble and incidence of barley yellow dwarf (BYD) disease caused by barley yellow dwarf virus (BYDV-PAV-IL) was studied. Field plots were infested with Rhopalosiphum padi vectoring BYDV-PAV-IL. A linear critical point regression model was developed that related percentage of maximum yield to BYD incidence, assessed by estimating the percentage of plants with BYD symptoms at Feekes growth stage 10.5 in each plot. The model y = 96.9 - 0.45x (r2 = 0.53) best explained the relationship. Test weight was unaffected by BYD. Although Noble consistently sustained higher disease incidence than Ogle, covariate analysis indicated that the effect of BYD on yield was similar for both cultivars. Studies of random versus focus inoculation of Noble oat, designed to determine the importance of compensation in reducing yield loss associated with BYD, indicated that compensation did not play an important role.
