Identification of tomato varieties resistant to Tomato Curl Stunt Virus in Mozambique

The importance of tomato (Lycopersicon esculentum) as source of food and income generation in Mozambique is threatened by proliferation of a viral disease called Tomato Curly Stunt virus (ToCSV) which belongs to the Geminiviridae Family (Begomovirus genera) transmitted by whiteflies (Bemisia tabacci). The occurrence of ToCSV in areas of tomato production causes yield losses of up to 100 % hence negatively impacting on crop productivity and the communities’ livelihood. Studies based on collaborative efforts between Agricultural Research Institute of Mozambique (IIAM) and University of Eduardo Mondlane (UEM) have not been conclusive. This research project was carried out to identify resistant and adapted varieties among the promising ones that are known to be resistant to Begomoviruses. Promising varieties from AVRDC-Taiwan, Favi-Israel and from Mozambique were evaluated from August to December 2011 in potential endemic locations in a randomized complete block design experiment with four replications in two sites namely Chokwe and Umbeluzi Research Stations. Virus incidence and severity were scored where 1= healthy; 2 = suspected plant; 3 = first stage of the diseased plant with clear symptoms; 4 = curling and beginning of stunting and 5 = severely attacked plant. Fruit set, fruit weight and yield were also measured. Between the two sites at which the study was conducted, higher white fly population density was observed at Chokwe Research Station (46 insects per plant) compared to Umbeluzi Research Station (14 insects per plant. Tomato lines under this study fell into three categories, namely: resistant varieties (TT 369 and TT 304), because no single diseased plant was observed under field conditions; tolerant varieties (AVT0 1130, AVTO 1133, AVTO 1004, AVTO 1007; TT 305, TT 307 and Maximum), where some diseased plants were observed but the disease severity ranged from 1.1 to 2.9; and susceptible varieties (HTX-14 the check, Domingo, Rodade, UC82B and Cuba) whose severity scores were higher than 3. Data on yield showed that the tomato varieties performed better at Umbeluzi with an average yield per variety of 46 tons/ha. Maximum variety recorded the highest yield (69.3 tons/ha) while HTX-14 recorded the lowest yield (22.7 tons/ha). However, in Chokwe all varieties performed poorly with an average of only 7 tons/ha. These differences in yield can be attributed to the high virus incidence, severity and pest population pressure which was relatively higher at Chokwe than Umbeluzi. All resistant (TT 304 and TT 369), intermediate resistant (TT 305, TT 307 AVTO 1002, AVTO 1007, AVTO 1130, AVTO 1133 and Maximum) and stable varieties should be used in breeding programmes.