Bemisia tabaci (Genn.) was considered a secondary pest in Brazil until 1990, despite being an efficient geminivirus vector in beans and soybean. In 1991, a new biotype, known as B. tabaci B biotype (=B. argentifolii) was detected attacking weed plants and causing phytotoxic problems in Cucurbitaceae. Nowadays, B. tabaci is considered one of the most damaging whitefly pests in agricultural systems worldwide that transmits more than 60 different plant viruses. Little is known about the genetic variability of these populations in Brazil. Knowledge of the genetic variation within whitefly populations is necessary for their efficient control and management. The objectives of the present study were to use RAPD markers (1) to estimate the genetic diversity of B. tabaci populations, (2) to study the genetic relationships among B. tabaci biotypes and two other whitefly species and (3) to discriminate between B. tabaci biotypes. A sample of 109 B. tabaci female individuals obtained from 12 populations in Brazil were analyzed and compared to the A biotype from Arizona (USA) and B biotype from California (USA) and Paraguay. Trialeurodes vaporariorum and Aleurodicus cocois samples were also included. A total of 72 markers were generated by five RAPD primers and used in the analysis. All primers produced RAPD patterns that clearly distinguished the Bemisia biotypes and the two other whitefly species. Results also showed that populations of the B biotype have considerable genetic variability. An average Jaccard similarity of 0.73 was observed among the B biotype individuals analyzed. Cluster analysis demonstrated that, in general, Brazilian biotype B individuals are scattered independently in the localities where samples were collected. Nevertheless, some clusters were evident, joining individuals according to the host plants. AMOVA showed that most of the total genetic variation is found within populations (56.70%), but a significant portion of the variation is found between crops (22.73%). The present study showed that the B biotype is disseminated throughout the sampled areas, infesting several host plants and predominates over the A biotype.
Em 1991, um novo biótipo de Bemisia tabaci denominado de raça B, mosca branca da poinsétia ou mosca da folha prateada foi detectado no Brasil. Esta praga trouxe muitos prejuízos e danos à agricultura nacional, por ser mais agressiva do que a existente anteriormente, conhecida como B. tabaci ou B. tabaci biótipo BR (não B). A relação taxonômica entre B. tabaci e B. tabaci biótipo B não é clara e não existem evidências morfológicas consistentes que possam distinguir esses dois biótipos. RAPD-PCR tem sido utilizada para identificação de biótipos presentes nas populações, utilizando-se, como padrões de referência, adultos de Bemisia tabaci das raças A e B provenientes dos Estados Unidos. As coletas de mosca branca foram feitas em 27 culturas e plantas daninhas em 57 localidades do país. As populações foram então analisadas, observando-se que a população predominante em 20 estados brasileiros é de B. tabaci biótipo B. Os biótipos BR e B foram encontrados coabitando a mesma região, em três diferentes localidades: Jaboticabal, SP; Rondonópolis e Cuiabá, MT e Goiânia, GO.
In 1991, the poinsettia strain, silverleaf whitefly or B biotype of Bemisia tabaci was detected in Brazil. This variant is a far more serious agricultural pest than the previously prevalent non-B (BR) biotype. The correct identification of B. tabaci is problematic since it is highly polymorphic with extreme plasticity in key morphological characters that vary according to the host. RAPD-PCR was used to survey the B biotype and other biotypes of B. tabaci in Brazil. Whiteflies were collected from cultivated plants and weeds from 57 different localities and on 27 distinct crops. RAPD analyses using two selected 10-mer primers reliably identified the BR biotype and the B biotype of B. tabaci and also differentiated other whitefly species. The presence of the B biotype was confirmed in 20 Brazilian states. The BR and B biotypes of B. tabaci were found to coexist in the whitefly populations of three different localities: Jaboticabal, SP; Rondonópolis and Cuiabá, MT, and Goiânia, GO.