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The two-spotted spider mite, Tetranychus urticae, is a serious global pest of eggplants and other vegetables in the tropics and subtropics. The scarlet (Solanum aethiopicum L.) and gboma (Solanum macrocarpon L.) are two cultivated eggplants indigenous to sub-Saharan Africa. In this study, 120 accessions of S. aethiopicum and five accessions of S. macrocarpon from the World Vegetable Center’s genebank collection were evaluated for spidermite resistance based on leaf damage scores and trichome types and densities. The highest levels of resistance were detected in S. macrocarpon accessions VI050393 and VI050444. In addition, two accessions of S. aethiopicum, VI042749 and VI042753, were moderately resistant. All other S. aethiopicum accessions were susceptible or highly susceptible. Spider mite resistance was significantly associated with the presence of type VII glandular trichome, but nonglandular stellate trichomes were not associated with resistance. The resistant S. macrocarpon accessions can be directly used as resistant cultivars or in prebreeding programs aimed at breeding resistant lines of the most commonly cultivated eggplant (S. melogena). The scarlet (Solanum aethiopicum L.) and gboma (Solanum macrocarpon L.) are two eggplant species commonly grown as vegetables in tropical Africa and elsewhere as minor crops (Daunay and Hazra, 2012; Plazas et al., 2014a; Schippers, 2000; Sunseri et al., 2010). According to the Global Biodiversity Information Facility (GBIF; 2017), the main clusters of S. aethiopicum and S. macrocarpon are inWest Africa (Taher et al., 2017). Both S. aethiopicum and S. macrocarpon belong to the Leptostemonum clade (Knapp et al., 2013), which are native to the Old World and were domesticated from Solanum anguivi (Lester and Niakan, 1986) and S. dasyphyllum, respectively (Bukenya and Carasco, 1994). In many African countries, their leaves and roots are used as traditional medicines for the treatment of several ailments; for example, they are used to help heal wounds and to treat high blood pressure, diabetes, and inflammatory tumors (Oboh et al., 2005). These species are therapeutically valuable because of their high content of phenolic acid and chlorogenic acid (Plazas et al., 2014b; San Jos e et al., 2013). Globally, S. aethiopicum is the second most important cultivated eggplant after S. melongena L., which is a well-known eggplant (Plazas et al., 2014a). Depending on the utilization type, S. aethiopicum can be classified into four main cultivar groups (Gilo, Kumba, Shum, and Aculeatum) (Lester, 1986). The Gilo group is cultivated for its fruits, the Kumba group is cultivated for its fruits and leaves, the Shum group is cultivated for its leaves, and the Aculeatum group is cultivated as an ornamental (Lester and Daunay, 2003; Prohens et al., 2012; Taher et al., 2017). S. macrocarpon is cultivated for its leaves and its fruits (Maundu et al., 2009; Plazas et al., 2014a). The use of its leaves, which are consumed similar to spinach, is common in the eastern and central parts of Africa (Nyadanu and Lowor, 2015; San Jos e et al., 2016). Few studies have examined the diversity of S. macrocarpon (Polignano et al., 2010); however, in general, it is less morphologically diverse than S. melongena and S. aethiopicum (Plazas et al., 2014a; Taher et al., 2017). The two-spotted spider mite [Tetranychus urticae Koch (Acari: Tetranychidae)] is one of the most damaging agricultural pests worldwide. This insect can cause potential damage to more than 1100 plant species, including different eggplant species (Adeniji and Aloyce, 2012; Rakha et al., 2017). High temperatures and dry conditions are suitable for the multiplication of spider mites, which live in colonies mostly on the underside of leaves. Foliar damage occurs because mites suck the chlorophyll, nutrients, andwater from the leaf cells with their piercing and sucking mouthparts. Damage is seen as collections of tiny white or yellow spots and very thin webbing on the underside of leaves. Heavy infestation will result in leaf discoloration, often called bronzing and drop off, and will finally lead to stunting or plant death (Khanamani et al., 2014; Srinivasan, 2009). Chemical control of spider mites is often costly, and the excessive use of pesticides damages the environment and harms human health. Biological control by natural enemies is economical in greenhouses but is not feasible in the field (Bostanian et al., 2003; Khanamani et al., 2014). Therefore, resistant eggplant cultivars are considered an important component to managing the spider mite. The relationship between insect resistance and trichome types and densities has been reported for many plant species (Mitchell et al., 2016; Tian et al., 2012). For the genus Solanum, eight types of trichomes have been identified, of which four (i.e., types I, IV, VI, and VII) are glandular trichomes and four (i.e., types II, III, V, and VIII) are nonglandular (Glas et al., 2012; M argineanu et al., 2014). Trichomes of cultivated eggplants S. melongena and S. aethiopicum are mostly nonglandular-type stellate (Hasanuzzaman et al., 2016; Stephenson et al., 2018). Nonglandular and glandular trichomes may act as a physical barrier that can deter pest movement on plants (Mitchell et al., 2016; Rakha et al., 2017). For instance, in wild tomato, spider mite resistance has been associated with high densities of certain glandular 240 HORTSCIENCE VOL. 54(2) FEBRUARY 2019 trichomes (Rakha et al., 2017). In addition to a physical barrier, glandular trichomes store and secrete secondary metabolites that can prevent an insect attack or their feeding and oviposition on the plant (Glas et al., 2012; Rakha et al., 2017; Schilmiller et al., 2008). The role of trichomes in relation to pest resistance has been investigated, especially in Solanaceous crops such as tomato (Solanum lycopersicum L.) (Rakha et al., 2017) and potato (Solanum tuberosum) (M argineanu et al., 2014). However, to date, only limited data regarding trichome types and their relationship with insect resistance are available for African eggplants like S. aethiopicum and S. macrocarpon. The objectives of the present study were to evaluate S. aethiopicum and S. macrocarpon accessions from the collection of the World Vegetable Center (WorldVeg) and to determine resistance to the spider mite based on leaf damage using choice assays. In addition, trichome type and density were characterized and correlated with mite resistance to study the possible mechanisms of resistance. Materials and Methods Location and seed sources. Experiments were conducted at WorldVeg in Taiwan. Seeds of 120 accessions of S. aethiopicum and five accessions of S. macrocarpon were obtained from the WorldVeg genebank (Table 1). The accession countries of origin were Bangladesh (1), Brazil (41), Burkina Faso (1), Cameroon (5), France (1), Ghana (5), Guinea (1), India (2), Ivory Coast (2), Kenya (2), Madagascar (2), Malaysia (1), Mali (1), Philippines (2), Senegal (1), Taiwan (1), Tanzania (5), Togo (1), Uganda (1), Yugoslavia (1), Zambia (1), and unknown (47). Two accessions (VI040627 and VI042040) Table 1. Mean rating of Tetranychus urticae damage, type, and trichome density scores of Solanum macrocarpon and S. aethiopicum accessions and the two susceptible S. melongena checks.

hortscience

Sources of Resistance for Two-spotted Spider Mite (Tetranychus urticae) in Scarlet (Solanum aethiopicum L.) and Gboma (S. macrocarpon L.) Eggplant Germplasms