Epidemiology of Tomato Curly Stunt Virus in Mozambique

Tomato (Lycopersicon esculentum) has a great socio-economic importance in Mozambique, since it is one of the sources of income for many families. However, its continuous production throughout the year provides conditions for the overwintering of several diseases, particularly, the viral diseases. The emerging viral disease, Tomato Curl Stunt Virus (ToCSV), transmitted by the white fly (Bemisia tabaci) is negatively impacting on tomato production in some regions of the country. A clear understanding of the epidemiology of this virus disease is a pre-requisite for designing effective control strategies. Two studies aiming at understanding the epidemiology of ToCSV where carried out, namely: (1) disease incidence and impact along the year and (2) a disease survey throughout the country. In the first study, an on station trial using RCBD was conducted in two sites namely Umbeluzi and Chokwe Research Stations from June 2011up to May 2012, where in each month was made a transplant totaling 12 planting dates. In this trial, three tomato varieties, HTX -14, UC 82 - B and AVRDC were evaluated. Variables analyzed included white fly population density, disease incidence and severity based on three observations in each plating date at 15, 35 and 55 days after plating. In the first study, high white fly population density (20,095, 19,313, 22,589, 21.53 in Chókwè 16,783, 16,963, 17,898 and 17,973 in Umbeluzi) and high rate of disease incidence (92,692, 98,584, 97,808 end in Chókwè 100.00 and 92.09, 97 195, 93 496, 90 815 in Umbeluzi) respectively were recorded for the tomato transplanted in November, December of 2011 and January and February of 2012, and consequently low production was recorded due to high percentage of fruit (70,187, 76,988, 77,578 and 78,861 in Chókwè, 51,715, 54,166, 72,769 and 70.362 in Umbeluzi) respectively, attributed mainly to the disease infection. In southern Mozambique, it is recommended to produce tomatoes from May to September, because the density of whitefly is low and incidence and severity of disease, or cultivate in greenhouses. In the second study, surveys were carried out in 18 districts of the country from February 2011 to July 2012. This study was done to record incidence and severity of disease as well as to collect samples to confirm the presence of virus using PCR (Polymerase Chain Reaction). In the second study, incidence and severity of disease was observed in 10 out of the 18 Districts, and the districts of southern Mozambique registered higher rates of infection 90, 70, 68 e 90.2 in Moamba, Namaacha, Boane and Chokwe respectively. Of the 1650 samples collected, 521 (31.58%) tested positive by PCR, and the presence of the virus was confirmed in 6 districts namely: Moamba, Namaacha, Boane, Chókwè, Manica and Angónia. There need to avoid handling of seedlings of these locations to regions still free ToCSV considered.