Tomato Spotted Wilt Virus: TSWV in Vegetable Crops: Tospoviruses

Tospoviruses In Solanaceae and Other Crops in The Coastal Plain of Georgia

Management of TSWV

Plant Growth and Yield in Tomato and Pepper as Affected by Tomato Spotted Wilt Virus
Juan Carlos Díaz-Pérez

Effect of TSWV on Plant Development, Fruit Yield and Fruit Quality

Successful tomato production is normally associated with healthy vegetative top growth throughout the growing season. Early plant infection with TSWV typically results in severe symptoms or plant death (Francki and Hatta, 1981; Gitaitis, 1998; Moriones et al., 1998). Diaz-Perez et al. (2003) found that there is an increasing reduction of vegetative top fresh weight, fruit number and fruit yield (total and marketable) with increasingly earlier expression of TSWV symptoms during tomato plant development. Compared to symptomless plants, total fruit yield of symptomatic tomato plants are reduced by 2.3 percent, for each day before harvest that plants first exhibited symptoms of TSWV (Diaz-Perez et al., 2003).

The mechanisms through which TSWV affects tomato plant growth and yield are not fully understood. However, TSWV infections in tobacco have been associated with reductions in leaf chlorophyll content and diminished rates of CO2 assimilation (Goodman et al., 1986). Wilting associated with TSWV is probably an indication of plant water deficits, which may also affect gas exchange and shoot growth. Unpublished data (Diaz-Perez et al.) show that TSWVinfected tomato plants exhibit reduced rates of photosynthesis and transpiration.

In order to obtain high tomato yields, appearance of TSWV symptoms should be delayed as much as possible during the entire season, but particularly during early stages of plant development. Use of TSWV-resistant cultivars and utilization of colored mulches may be helpful in the management of TSWV.

Effect of Plastic Film Mulch, Cultivar and Environment on TSWV

In tomatoes and peppers, losses are significant because the majority of currently available cultivars are susceptible to TSWV. Besides, fruit quality of the resistant cultivars is often lower compared to that of the susceptible cultivars. A list of commercially available tomato and pepper cultivars resistant to TSWV is shown in Table 4. The use of pesticides to control thrips is usually ineffective for management of TSWV (Brown, 1989; Cho et al., 1998), although imidacloprid applications to tomato transplants may offer some protection (Riley and Pappu, 2000). As a complement to chemical control, cultural control measures such as the use of silver reflective mulches may be considered as part of a TSWV management strategy. Plastic film mulches, particularly metallic reflective mulches, have also been found to reduce the populations of thrips and other insect vectors (Csizinszky et al., 1995; Farias-Larios and Orozco-Santos, 1997; Olson et al., 2000).

In a study that included eight plastic film mulches and three cultivars, appearance of first TSWV symptoms was delayed on gray mulch, followed by black-on-silver, silver-on-black and silver-painted mulches (Diaz-Perez et al., 2003). The susceptible cultivars ‘Florida-91’ and ‘Sun Chaser’ showed first symptoms of TSWV 3-4 days earlier than ‘BHN-444.’ Among mulches, TSW incidence was highest for tomato plants grown on white mulch, with incidences on the other mulches and bare soil ranging from 14 percent to 35 percent. Among cultivars, ‘BHN-444’ had the lowest incidence of TSWV (12%) — and highest fruit yield — while ‘Florida-91’ and ‘Sun Chaser’ had incidences that were about three times greater.

Integrated management is probably the most effective method to manage TSWV and delay the expression of symptoms (Cho et al., 1998). Plants grown on silver mulches have fewer thrips compared to plants grown on other mulches or bare soil (Brown et al., 1989; Csizinsky et al., 1995; Olson et al., 2000; Schalk and Robbins, 1987). In a 5-year study in Florida, tomato plants grown on silver reflective mulch had lower thrips numbers

Table 4. List of commercial pepper and tomato cultivars resistant to TSWV.

and TSWV incidence compared to plants grown on black plastic mulch (Olson et al., 2000). Similarly, Riley and Pappu (2000) in Georgia found that silver reflective mulch in combination with intensive insecticide applications and resistant cultivars resulted in reduced thrips populations and TSWV incidence. Reduction in thrips population has been attributed to the mulch color effect on the vector, due to a modification of the light environment around the plant (Csizinszky et al., 1997). However, appearance of TSWV symptoms depends on factors other than the number of thrips.

In addition to light effects on the vector, colored mulches modify root zone temperature (RZT) under the mulch. RZT directly affects tomato plant growth (Díaz-Pérez and Batal, 2002), which may influence plant response to TSWV. Symptoms of TSWV were delayed in tomato plants grown on gray, silver-onblack, black-on-silver, and silver-painted mulches (Díaz-Perez et al., 2003), where the mean RZT for the season approached the optimal RZT (26.1 C) for tomato plant growth and yield. These results suggest that RZT, as modified by plastic mulches, may be related to the appearance of TSWV symptoms. However, environmental factors other than RZT may also influence the impact of TSWV on tomato plants, as suggested by the study of (Díez et al., 1999) who found that growth and yield of tomato plants grown under mesh were higher compared to plants grown in open air conditions.

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