Whitefly Biotypes |
|
The economic importance of whiteflies on Egyptian agriculture has been recognized since 1930s, but viruliferous whiteflies have become a considerable problem in recent years. The largest and most economically significant group of plant viruses transmitted by whiteflies are the geminiviruses. The tomato yellow leaf curl virus (TYLCV), a geminivirus transmitted by whiteflies, has been recorded in most eastern Mediterranean countries. In Egypt, TYLCV causes about 65% of yield losses in tomato. For many years, bioassays have been the only tool available to describe the characteristics of viral transmission by vectors. With the development of polymerase chain reaction (PCR) and molecular hybridization techniques, it is now possible to detect viral molecules in plants and in individual insects. Knowledge of the mode of transmission of viruses from plant to plant by insect vectors is essential for understanding viral epidomology and for the development of pest management strategies. In Egypt, 20 species
of whiteflies have been recorded. Two of them, B. tabaci and B. argentifolii,
are considered very important pests for their ability to transmit geminiviruses. The heavy
infestation of the castor bean whitefly Trialeurodes ricini (Misra) all over Egypt,
had drawn our attention. Indeed, the castor bean whitefly (CBW) has characteristics that
contribute to severe pest potential. The rapid reproduction which occurs continuously
during summer and its distribution all over the Egyptian governorates in huge numbers
indicate that T. ricini may possess climatic tolerances that permit its survival in
many geographical and cropping zones. This species is recorded here for the first time in
Egypt. OBJECTIVES • Identification of different populations of viruliferous whitefly species in tomato using conventional taxonomical methods. • Identification of viruliferous whitefly biotypes using protein polymorphism and molecular markers. • To study the efficiency of geminiviruses transmission by different whitefly species and their biotypes. |
|
• During our continuous search for producing TYLCV resistant transgenic tomato lines, a heavy infestation with T. ricini, was recognized in tomato fields. It was associated with a high percentage of tomato plants showing TYLCV typical symptoms. In this study we report for the first time that T. ricini is the third whitefly species transmitting geminiviruses. • Based on esterase patterns, five biotypes of the castor bean whitefly which are morphologically indistinguishable, have been differentiated. PCR data revealed that the castor bean whitefly biotypes acquired geminiviruses. • Experimentally, T. ricini behaved as an oligophagous whitefly. The CBW mainly attacks castor bean plants, but the immature stages as well as adults were also collected from other hosts such as cabbage, tomato and wild weeds. The efficiency of TYLCV-Eg transmission by T. ricini was examined by using both traditional bioassays and molecular techniques. The double antibody sandwich (DAS) indirect enzyme linked immunosorbent assays (ELISA) detected TYLCV-Eg in the adults of T. ricini that were allowed an access on infected TYLCV-Eg tomato plants. Polymerase chain reaction was also used to detect the virus in the in the castor bean whitefly extracts. The PCR products indicated that T. ricini acquired the virus. • T. ricini adults need a long time to acquire the
virus than Bemisia tabaci does. The host plant preference could be the factor that
caused a prolongation of the acquisition access period required for T. ricini adults
to acquire TYLCV-Eg. |
|
