Global status of tospovirus epidemics in diverse cropping systems: successes achieved and challenges ahead.

Spread of Tomato spotted wilt virus (TSWV) and population development of its vector Frankliniella occidentalis were studied on the pepper accessions CPRO-1 and Pikante Reuzen, which are resistant and susceptible to thrips, respectively. Viruliferous thrips were released on plants of each accession (nonchoice tests) or on plants in a 1:1 mixture of both accessions (choice tests) in small cages containing 8 or 16 plants. Significantly fewer CPRO-1 plants became infected in the primary infection phase in both tests. fit the nonchoice test, virus infection of the resistant plants did not increase after the initial infection, but all plants eventually became infected when mixtures of both cultivars were challenged in the secondary infection phase. Secondary spread of TSWV from an infected resistant or susceptible source plant was significantly slower to resistant plants than to susceptible plants, independent of source plant phenotype. The restricted introduction and spread of TSWV in the thrips-resistant cultivar was confirmed in a large-scale greenhouse experiment. The restricted and delayed TSWV spread to plants of the resistant accession in both the cage and the greenhouse experiment was explained by impeded thrips population development. The results obtained indicate that thrips resistance may provide a significant protection to TSWV infection, even when the crop is fully susceptible to the virus.

Restricted Spread of Tomato spotted wilt virus in Thrips-Resistant Pepper.

The effect of two temperature regimes (daytime, 29 ± 2°C, night-time, 24 ± 3°C; and daytime, 23 ± 1°C, night-time, 18 ± 2°C) on the symptoms caused by tomato spotted wilt virus (TSWV), and the accumulation of TSWV virions, was compared in Datura stramonium, Nicotiana tabacum cv. White Burley and Physalis ixocarpa. Tobacco plants were more severely affected by TSWV at the high temperature regime, but the incidence (percent of plants with symptoms) was 100% for both regimes. In P. ixocarpa and D. stramonium the higher temperature caused an increase in both incidence and rate of development of symptoms. At high temperature, all three species showed both local and systemic symptoms; however, at low temperature only P. ixocarpa consistently developed systemic symptoms. In general, virus accumulation in the inoculated leaves (presumably the combined effect of virus replication and local movement) of all plants was higher at the lower temperature. Long distance movement in tobacco, leading to virion accumulation in other plant organs, was favoured by high temperature; but there was relatively little effect in P. ixocarpa and D. stramonium.

https://bsppjournals.onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3059.1998.00249.x

Effect of temperature on symptom expression and accumulation of tomato spotted wilt virus in different host species

In 2009, chlorotic mottle and necrosis were observed on chrysanthemums (cv. Jimba) in Aomori Prefecture, Japan. A virus was isolated from the chrysanthemum plants by serial local-lesion transfer. The symptoms exhibited by the test plants, the particle morphology, the features of the protein and the potential for transmission by thrips were similar to those for Impatiens necrotic spot virus (INSV). The partial nucleotide sequences of the nucleocapsid protein gene and the 3′-untranslated sequence of the S RNA shared 99% identity with that of an INSV isolate. This report is the first of INSV infection of chrysanthemums in Japan.

First report of Impatiens necrotic spot virus infecting chrysanthemum ( Chrysanthemum morifolium ) in Japan

The effects of 21 weeds acting as hosts of tomato spotted wilt virus (TSWV), temperature, thrips population and diversity on disease progress in chrysanthemum cv. Polaris were studied. Under greenhouse conditions, only Taraxacum officinale, Bidens sp., Resedaluteola and Mirabilis jalapa were hosts for TSWV. Of 38 weeds species in the area surrounding a chrysanthemum field, Tithonia tubaeformis and R. luteola had the highest populations of adult and immature thrips. These weeds, as well as M. jalapa, had an extensive seasonal distribution and may play a key role in the disease progress. Seventeen thrips species belonging to the genera Bravothrips, Thrips and Frankliniella were identified on weed flowers, with Frankliniella occidentalis (FOC) representing 9.5% of all thrips identified. Of 123 thrips collected from chrysanthemum inflorescences, 9.75% were FOC, and only 2.5% of them transmitted TSWV. Of all the thrips species collected from chrysanthemum flowers in the field, only FOC was capable of transmitting TSWV. On 120 experimental plots established at two sites, with three transplanting dates (June, July and August), it was estimated that 1.25% of the chrysanthemum cuttings were already infected with TSWV when transplanted. Secondary spread, vectored by FOC, occurred only for the earliest transplanting date and resulted in a further 2.36% disease incidence.

Implications of weed composition and thrips species for the epidemiology of tomato spotted wilt in chrysanthemum (Dendranthema grandiflora)

Under field conditions, impatiens necrotic spot (INSV) and tomato spotted wilt tospoviruses (TSWV) were detected by the dot blot technique in chrysanthemum (Dendranthema grandiflora Tzvelev cv. Polaris) plants having concentric rings and line patterns, from Villa Guerrero and Coatepec de Harinas, State of Mexico. There were 15 species of thrips associated with chrysanthemum in the region, 10 already known and five being described as new species. The known species were: Frankliniella adadusta, F. aurea, F. helianthi, F. inutilis, F. minuta, F. simplex celata, F. occidentalis brunnescens, F. occidentalis dubia, F. occidentalis and Thrips tabaci. From among the aforementioned species, only the last two have been recognized as vectors of tospovirus. Twenty‐six species of weeds were found associated with chrysanthemum, of which, 16 were positive for the TSWV and none for the INSV.

Tospoviruses, weeds and thrips associated with chrysanthemum (Dendranthema grandiflora Tzvelev cv. Polaris)

The use of certified cuttings of chrysanthemum (Dendranthema grandiflora Tzvelev cv. Polaris) had an initial beneficial effect on the incidence of tospovirus infection but had little effect on final incidence. It improved the quantity and quality of production compared with the use of uncertified cuttings. Black polyethylene mulching and floating polypropylene covers provided no protection against the viruses, but polyethylene mulching improved growth. Disease progression was more rapid soon after thrips populations showed greatest abundance. The Gompertz model best explained the virus disease development.

Effect of using certified virus‐free cuttings, mulching and floating covers on chrysanthemum production (Dendranthema grandiflora Tzvelev cv. Polaris) and incidence of tospoviruses

N. R. M. Johansen

Papers

Tospoviruses, weeds and thrips associated with chrysanthemum (Dendranthema grandiflora Tzvelev cv. Polaris)

Effect of using certified virus‐free cuttings, mulching and floating covers on chrysanthemum production (Dendranthema grandiflora Tzvelev cv. Polaris) and incidence of tospoviruses