Abstract
Tomatoes (Solanum lycopersicum L.) have been bred to exude higher amounts or different types of the specialized plant metabolites, acylsugars, from type IV trichomes. Acylsugars are known to deter several herbivorous insect pests, including the western flower thrips (WFT), Frankliniella occidentalis (Pergande); however, all previous studies investigated the effect of acylsugars on leaves, or acylsugar extracts obtained from leaves. In spite of the WFT predilection for flowers, there is a gap in knowledge about flower defenses against thrips damage. This is especially important in light of their capacity to acquire and inoculate viruses in the genus Orthotospovirus, such as Tomato spotted wilt orthotospovirus (TSWV), in flowers. Therefore, we turned our attention to assessing thrips oviposition differences on flowers of 14 entries, including 8 interspecific hybrids, 5 tomato lines bred for specific acylsugar-related characteristics (type IV trichome densities, acylsugar amount, sugar moiety and fatty acid profile), and a fresh market tomato hybrid, Mt. Spring, which only produces trace amounts of acylsugars. Our results show that the density of the acylsugar droplet bearing type IV trichomes is greatest on sepals, relative to other flower structures, and accordingly, WFT avoids oviposition on sepals in favor of trichome-sparse petals. In concordance with past studies, acylsugar amount was the most important acylsugar-related characteristic suppressing WFT oviposition. Certain acylsugar fatty acids, specifically i-C5, i-C9 and i-C11, were also significantly associated with changes in WFT oviposition. These results support continued breeding efforts to increase acylsugar amounts and explore modifications of fatty acid profile and their roles in deterring thrips oviposition. The finding that acylsugar production occurs and reduces thrips oviposition in tomato flowers will be important in efforts to use acylsugar-mediated resistance to reduce incidence of orthotospoviruses such as TSWV in tomato by deterring virus transmission and development of thrips vector populations in the crop.
Highlights
The western flower thrips (WFT), Frankliniella occidentalis (Pergande), has a host range exceeding 1200 plant species [1] and is a very significant pest of agricultural and horticultural crops worldwide [2, 3], inflicting damage to plants by sucking out contents of individual cells and transmitting viruses in the genus Orthotospovirus [1, 4,5,6,7,8]
WFT oviposition on flowers was suppressed by increasing acylsugar amount, and at least three fatty acid components were associated with changes in WFT oviposition preferences, one of which was associated with suppression of oviposition
The importance of acylsugar amount and fatty acid profile in suppressing thrips oviposition on flowers is consistent with earlier work in which effects of purified acylsugars from leaves on WFT oviposition were shown to be concentration dependent and vary depending on acylsugar type [39]
Summary
The western flower thrips (WFT), Frankliniella occidentalis (Pergande), has a host range exceeding 1200 plant species [1] and is a very significant pest of agricultural and horticultural crops worldwide [2, 3], inflicting damage to plants by sucking out contents of individual cells and transmitting viruses in the genus Orthotospovirus (family Tospoviridae) [1, 4,5,6,7,8]. Orthotospoviruses have an extensive host range of over 1,090 plant species [3, 7, 8] and the type member, Tomato spotted wilt orthotospovirus (TSWV), is estimated to cause annual worldwide losses of over $1 billion [9]. The importance of WFT as a global pest on tomatoes and other commercial crops has driven efforts to find sustainable and effective management strategies, including host plant resistance [14]
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