Spinach Viruses in Southwest Texas. Mark C. Black, Department of Plant Pathology & Microbiology, Texas A&M University, Uvalde, TX 78802-1849

Viruses diseases have occurred annually in commercial spinach in the Texas Winter Garden. Yield and quality losses have varied. Significant losses in the 1987-88 and 1988-89 seasons were mostly attributed to Beet western yellows virus (BWYV), but Tomato spotted wilt virus (TSWV) was also detected at a high incidence in those seasons. This peak of TSWV incidence followed 1987 and 1988 spotted wilt epidemics in area peanut fields. In the 1998-99 season, Beet curly top virus (BCTV) caused the greatest loss. Overall, Cucumber mosaic virus (CMV) occurs most consistently. Tobacco ringspot virus (TobRSV) occurs sporadically at very low levels.

CMV (Cucumovirus) is non-persistent in >60 aphid vector species (primarily Myzus persicae and Aphis fabae), explaining a clustered disease distribution, usually at the field edge. Cultivars have a level of resistance to severe CMV strains. Seed transmission has been reported in spinach and other plants. A common symptom is yellowing of lower leaves, stunting, and dark green rugose new leaves. Host range is extensive (800 species, monocots and dicots) including pepper, tomato, cucurbits, celery, and numerous weeds. Control suggestions are use of resistant cultivars, broadleaf weed control near fields before and after planting, high plant populations, and good growing conditions for rapid plant growth.

BCTV (Geminivirus) in Southwest Texas spinach may represent a fourth BCTV group (Drake Stenger, Univ. Nebraska, personal communication). BCTV is persistent in the vector, beet leafhopper (Circulifer tennelus), which may fly >100 km. Incidence is often higher near the field edge. Resistance could probably be developed in spinach. Early fall seeding has higher incidence than late fall or early winter seeding. Risk is higher with low plant populations. Prolonged summer drought may indicate greater risk. Symptoms are yellow older leaves with asymmetrical younger leaves dwarfed, crinkled, and rolled upward and inward. Host range is moderate (>300 species in 44 families) including pepper, tomato, sugar beet, table beet, cucurbits, broadleaf weeds, and native shrubs. Control suggestions are high plant populations, broadleaf weed control near fields before and after planting and delayed fall planting dates.

BWYV (Luteovirus) is persistent in >eight aphid vector species (primarily Myzus persicae). Incidence is nearly uniform across fields. Resistance could probably be developed in spinach. High light intensity after several days of cloudy weather may trigger rapid symptom development and rapid quality loss. Symptoms are mild chlorotic spotting on interveinal areas, most often on the leaf tips of older and middle-aged leaves. From a distance, the canopy may have a bronze cast. Alternaria invades yellowed leaf tissue, resulting in black lesions with red-orange halos. Host range is moderate (>146 species in 23 families) including spinach, table beet, sugar beet, lettuce, crucifers, and broadleaf weeds. Control suggestions are to avoid high aphid populations, broadleaf weed control near fields before and after planting, and early harvest when symptoms develop.

TSWV (Tospovirus) is persistent in two thrips vectors (tobacco thrips, Frankliniella fusca and western flower thrips, F. occidentalis). Resistance may be difficult to develop. Symptoms are not known. Spinach may be a significant TSWV winter reservoir for spring and summer crops. Host range is extensive (>600 species, monocots and dicots) including peanut, tomato, pepper, tobacco, numerous ornamentals, and tobacco. Control suggestions are high plant populations and avoiding early fall plantings near mature infected peanuts.

TobRSV (Nepovirus) is vectored by dagger nematodes (Xiphinema americanum) and close relatives and apparently at low rates by several insects. TobRSV is seedborne in several plants. Resistance may be difficult to develop. Symptoms include chlorotic mottling and mosaic and tan necrotic lesions. Host range is moderate (many species in 20 families) including cucurbits, tobacco, pepper, bean, tomato, pea, apple, blackberry, blueberry, grape, ornamentals, and broadleaf weeds. Control suggestions are crop weed control and avoid planting after weedy fallow.