Abstract
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.
Highlights
Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), known as the California strain, cotton strain, A-strain and A biotype (Perring, 1995), has been detected in Brazil since 1928 (Bondar, 1929)
Knowledge of the genetic variation within whitefly populations is necessary for their efficient control and management
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
Summary
Bemisia tabaci (Genn.) (Hemiptera: Aleyrodidae), known as the California strain, cotton strain, A-strain and A biotype (Perring, 1995), has been detected in Brazil since 1928 (Bondar, 1929). The Brazilian B. tabaci population known as the B. tabaci biotype BR (Lima et al, 2000) occurs on several native and cultivated host plants and is thought to be widely distributed in the country This biotype may represent an indigenous biotype of B. tabaci as it does not feed on cassava, contrary to A biotype and is a vector of only three geminiviruses: the bean golden mosaic virus, the bean dwarf mosaic virus and the tomato golden mosaic virus. In the last three decades, a new biotype has colonized the Americas, causing heavy losses in different agroecosystems This new biotype was first detected in poinsettia in Florida (USA) and received the common names of Florida strain or poinsettia strain.
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