Resistance to the insect vector Bemisia tabaci enhances the robustness and durability of tomato yellow leaf curl virus resistance conferred by Ty-1.

Tomato yellow leaf curl virus (TYLCV) is a begomovirus (genus Begomovirus, family Geminiviridae) transmitted persistently by the whitefly Bemisia tabaci. It causes tomato yellow leaf curl disease (TYLCD), resulting in significant yield losses worldwide. TYLCD is controlled mainly by using F1 hybrid tomato cultivars harboring the TYLCV resistance gene Ty-1. However, infected Ty-1-bearing tomato plants accumulate viral DNA, which may eventually lead to the emergence of a resistance-breaking TYLCV variant. Recently, a B. tabaci-resistant tomato line derived from the introgression of type IV leaf glandular trichomes and acylsucrose secretion from wild tomato (Solanum pimpinellifolium) was shown to effectively control the spread of TYLCV. In this study, we combined B. tabaci resistance and Ty-1-based TYLCV resistance to increase the robustness and durability of the TYLCD resistance mediated by Ty-1 in tomato plants. Specifically, we characterized and used a Group 2-like isolate of the Israel strain of TYLCV (TYLCV-IL-G2) that contributes to TYLCD epidemics in southeastern Spain. A comparison with isolates of the previously identified TYLCV variant revealed TYLCV-IL-G2 has a similar host range, but it induces a slightly more severe TYLCD in Ty-1-bearing tomato plants. Moreover, we demonstrated that acylsucrose-producing B. tabaci-resistant tomato plants can limit the spread of TYLCV-IL-G2 better than a near-isogenic line lacking type IV trichomes and unable to secrete acylsucrose. Pyramiding Ty-1-based TYLCV resistance and B. tabaci resistance provided by type IV glandular trichomes helped to decrease the effects of TYLCV on Ty-1-bearing tomato plants as well as the likelihood of TYLCV evolution in infected plants.

Seed priming with rutin enhances tomato resistance against the whitefly Bemisia tabaci.

Flavonoids are ubiquitously distributed in plants, showing pleiotropic effects in defense against abiotic and biotic stresses. Although it has been shown that seed priming with flavonoids can enhance plant resistance to abiotic stress, little is known about its potential to enhance plant tolerance to biotic stresses, especially for herbivorous insects. Here, we investigated whether treatment of tomato (Solanum lycopersicum) seeds with rutin improves plant resistance against the whitefly (Bemisia tabaci). Specifically, we measured the effect of rutin seed treatment on tomato seedling vigour, plant growth, feeding behavior and performance of B. tabaci on plants grown from control and rutin-treated seeds, and plant defense responses to B. tabaci attack. We found that seed treatment with different concentrations of rutin (viz 1, 2, 5, 10, and 20 mM) had minimal impact on shoot growth. Furthermore, seed treatment of rutin reduced the developmental rate of nymphs, the fecundity and feeding efficiency of adult females on plants grown from these seeds. The enhanced resistance of tomato against B. tabaci is closely associated with increased flavonoids accumulation, callose deposition and the expression of jasmonic acid (JA)-dependent defense genes. Additionally, callose deposition and expression of JA-dependent genes in tomato plants grown from rutin-treated seeds significantly increased upon B. tabaci infestation. These results suggest that seed treatment with rutin primes tomato resistance against B. tabaci, and are not accompanied by reductions in shoot growth. Defense priming by seed treatments may therefore be suitable for commercial exploitation.

Host Plant Resistance to Bemisia tabaci to Control Damage Caused in Tomato Plants by the Emerging Crinivirus Tomato Chlorosis Virus.

Tomato chlorosis virus (genus Crinivirus, family Closteroviridae) (ToCV) is rapidly emerging, causing increased damage to tomato production worldwide. The virus is transmitted in a semipersistent manner by several whitefly (Hemiptera: Aleyrodidae) species and is expanding its geographical and host ranges associated with the emergence of whiteflies of the Bemisia tabaci complex. Control is based essentially on intensive insecticide applications against the insect vector but is largely ineffective. No virus-resistant or tolerant commercial tomato cultivars are available. Recently, a B. tabaci-resistant tomato line based on the introgression of type IV leaf glandular trichomes and secretion of acylsucroses from the wild tomato Solanum pimpinellifolium was shown to effectively control the spread of tomato yellow leaf curl virus, a begomovirus (genus Begomovirus, family Geminiviridae) persistently transmitted by B. tabaci. As short acquisition and transmission periods are associated to the semipersistent transmission of ToCV, its possible control by means of the B. tabaci-resistant tomato could be compromised. Moreover, if the antixenosis effect of the resistance trait present in those tomato plants results in increased B. tabaci mobility, an increased ToCV spread might even occur. We demonstrated, however, that the use of acylsugar-producing B. tabaci-resistant tomatoes effectively controls ToCV spread compared to a near-isogenic line without type IV trichomes and acylsugar secretion. No increase in the primary ToCV spread is observed, and secondary spread could be reduced significantly decreasing the incidence of this virus. The possible use of host plant resistance to whiteflies to limit spread of ToCV opens up new alternatives for a more effective control of this virus to reduce the damage caused in tomato crops.

An Acylsucrose-Producing Tomato Line Derived from the Wild Species Solanum pimpinellifolium Decreases Fitness of the Whitefly Trialeurodes vaporariorum.

A combination of biological control and host plant resistance would be desirable for optimally controlling the greenhouse whitefly, Trialeurodes vaporariorum in tomato crops. Whitefly settlement preference, oviposition, and survivorship were evaluated on ABL 10-4 and 'Moneymaker', two nearly-isogenic tomato lines with, and without, whitefly-resistance traits based on type IV leaf glandular trichomes derived from the tomato wild species Solanum pimpinellifolium, respectively. Significantly reduced preference of T. vaporariorum adult whiteflies for ABL 10-4 leaves was observed. Moreover, T. vaporariorum altered its abaxial-adaxial settling performance on leaves of ABL 10-4 plants. A significantly lower tendency to settle on abaxial leaf surface was observed in ABL 10-4 compared to Moneymaker plants. Furthermore, T. vaporariorum deposited fewer eggs and exhibited a significantly reduced egg to adult survivorship in ABL 10-4 than in Moneymaker plants. Therefore, reduced fitness and distorted performance were observed for T. vaporariorum on ABL 10-4 tomato plants supporting that type IV leaf glandular trichomes might protect them from this pest and, indirectly, from the viruses it transmits.