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The silverleaf whitefly (SLW), Bemisia tabaci biotype B, is considered oneof the most serious pests in cotton worldwide. Its control is based on theuse of pesticides, which are well-known for their harmful effects on non-target organisms and the environment. Here, we examined resistance ofseveral cotton genotypes in terms of antixenosis and antibiosis againstSLW. We also investigated the mechanisms of cotton genotypes involvedin antixenosis against SLW by correlating with leaf trichome density andleaf colour parameters. In choice tests, we selected resistant cotton geno-types, Gossypium hirsutum palmeri, Aubum 56-7, G. hirsutum morrilli,Moco, Nu-16 (B2 B3 B6)- 78/658, Paymaster 53-816 and ‘IAC 23’, basedon SLW oviposition and host preference. No-choice tests with these geno-types confirmed antixenosis effect on SLW; however, no antibiosisresistance was detected in terms of developmental period and adultemergence rate. We found SLW oviposition preference was positively cor-related with trichome density in the abaxial leaf surface, while adult hostpreference was mostly explained by high levels of green intensity ofadaxial surface. Nevertheless, both SLW oviposition and host preferencewere negatively correlated with the lightness level of adaxial leaf surface.Probably, the underlying mechanism of cotton resistance is based on morethan just these two parameters, but our study will contribute to selectingresistant cotton genotypes and helps to understand the mechanismsinvolved in cotton resistance against SLW. To our best knowledge, this isthe first work showing that cotton leaf colour parameters are related toresistance against SLW.IntroductionMany crops in tropical and subtropical regions areseverely damaged by the whitefly Bemisia tabaci(Genn.) (Hemiptera: Aleyrodidae). In the past,whiteflies were considered a secondary pest, but asinfestations have caused high yield losses due to directdamage and the transmission of more than 200 plantviruses, whitefly is currently regarded one of the mostimportant pests in both field and greenhouse cropsworldwide (Brown 1994; De Barro et al. 2011; Navas-Castillo et al. 2011).In Brazil, B. tabaci was first recorded in 1923(Bondar 1928) and biotype A populations were likelythe only ones present until the 1990s. Invasion bybiotype B (silverleaf whitefly or SLW) occurred in theearly 1990s in crops of S~ao Paulo state. This whiteflybiotype likely originated from imported plant material(Lourenc ~ao and Nagai 1994) and rapidly spread acrossthe country. Recent molecular studies showed thatbiotype B is predominant in many crops in differentparts of Brazil, such as cotton, potato, tomato, pump-kin, cabbage and soya beans (Fontes et al. 2010;Rocha et al. 2011; Valle et al. 2011). Even though |
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