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Bull. Spec. CORESTA Congress, Yokohama, 1996, p. 177, P26

Whitefly-transmitted virus diseases in tobacco in Mexico

NIKOLAEVA V.B.; STOUT J.T.; GARIBAY C.C.
Centro International de Investigation y Capacitacion Agropecuaria (CIICA), Tapachula, Chiapas - Mexico.
Bemisia tabaci (Gennadius) has become an important pest of tobacco in Mexico. We describe the damage this pest causes on tobacco and that the damage may be associated with geminivirus infection transmitted by the whitefly. In the summer of 1995 large acreages of cotton and sesame were infested with very large whitefly populations. After the cotton was defoliated and the sesame harvested, the whiteflies moved to alternate hosts. As a result, infestations on tobacco became higher than normal. Also, symptoms that we have tentatively ascribed to geminivirus infection increased. Preliminary evidence for the presence of geminiviral sequences in DNA from symptomatic tobacco tissues follows. DNA was isolated from tissues of seven symptomatic tobacco plants and used as template in PCR amplification reactions in which the degenerate primers PAL1v1978 and PAR1c496 (Rojas, M.R. et. al., 1993, Plant Disease 77:340-347). After analysis of the PCR reactions on agarose gels, all samples were seen to give a single 1.1 Kb, product characteristic of Western Hemisphere bipartite geminiviruses. The PCR products were cloned into pBluescript II KS+. These cloned fragments will be sequenced in order to further characterize the virus. We are reported the geminiviruses occurrence and the B. tabaci population dynamics during the growing season of three types of tobacco at five planting dates, 15th of September, October, November, December and January. Burley tobacco planted during the months above showed an incidence of WTGV of 2.5-15.4%, Virginia 2.5-17.7%, Dark Tobacco 0.0-10.1%. The population dynamics (average) during this period of growing of tobacco was 2.0 to 30.5 WF/plant in Burley; 1-30.8 WF/plant in Virginia and 2-50 WF/plant in Dark Tobacco. The severity and timing of initial infestations were different in tobacco planted at different dates in the field. All tobacco types planted at 15th of September showed the initial symptoms 55-60 days after planting. Those planted at 15th of October, November, December and January showed the first symptoms occurrence 20-30 days after planting. This represents 20-30 days earlier than the previous date.