The experiment was conducted as a part of PhD research in a farmer`s field at Amtoli Upazilla in Barguna district of Bangladesh during winter 2008-09. The soil of the experimental field was under the Agro Ecological Zone (AEZ) 18 (Young Meghna Estuarine Floodplain) having soil PH 6.1 to 6.8 and silty loam texture.A total of twenty tomato varieties were used in the experiment namely BARI Tomato-1/Manik (BARI-T1), BARI Tomato-2/Ratan (BARI-T2), BARI Tomato-3 (BARI-T3), BARI Tomato-4 (BARI-T4), BARI Tomato-5 (BARI-T5), BARI Tomato-6/Chaity (BARI-T6), BARI Tomato-7/Apurba (BARI-T7), BARI Tomato-8/Shila (BARI-T8), BARI Tomato-9/Lalima (BARI-T9), BARI Tomato-10/Anupoma (BARI-T10), BARI Tomato-11/Jhumka (BARI-T11), BARI Tomato-12 (BARI-T12), BARI Tomato-13 (BARI-T13), BARI Tomato-14 (BARI-T14), Roma VF T-311 (Roma VF, Country of origin, Holland, the Netherlands), Unnayan F1, Udayan F1, Rio Grande (Rio Grande, Country of origin China), Tidy and Digonta. The seeds of these tomato varieties were collected from Bangladesh Agricultural Research Institute (BARI), Joydebpur, Gazipur and from local markets. The experimental field was ploughed and leveled to have a good tilth. Fertilizer dose was used as N-200, P2O5-100, K2O-150, S-20 and B-2 kg ha-1 as suggested by Rahman et al. (1998). Cowdung was applied@ 5 t ha-1. Cowdung and all the fertilizers except urea were applied during final land preparation. Urea was applied in two splits, oneat 21 and other at 35 days after transplanting.Tomato seedlings of the twenty varieties were raised separately in a well-drained nursery bed and 28 days old seedlings were transplanted in the main field on first week of November 2008. Row to row distance 60cm and plant to plant distance 50cm was maintained in the experimental field. Irrigation, staking of the plants and other intercultural operations were done as and when required. Tomato Spotted Wilt Virus (TSWV) was identified on the basis of field symptoms as described by Tisserat (2005), Natalie (2005), Momol and Pernezny (2006) and Swift (2006).Later on it was confirmed by ELISA test. The protocol was according to manufacturer’s recommendations.The data on the prevalence of TSWV and yield of tomato were collected at three stages of the plant growth. Three growth stages of the plants were categorized as early (transplanting to first flowering), mid (first flowering to first fruiting) and late stage (first harvesting to last harvesting). Percent reductions of root depth, fresh root weight, dry root weight plant-1and yield plant-1were calculated following the formula mentioned bellow:
Reduction percentage, P =A-A1/A x100
Where, P = Reduction percentage of root depth, weight or yield plant-1, A = Root (depth or weight plant-1) or yield g plant-1 of healthy plants and A1= Root (depth or weight plant-1) or yield g plant-1 of infected plants.Randomized Complete Block Design (RCBD) was followed with 3 replications. The data were analyzed statistically using the analysis of variance (ANOVA) of MSTATC software for proper interpretation. The mean values were compared by Duncan’s multiple range test (DMRT) at 5% level of significance. The correlation regression between percent reduction of root depth, fresh root weight, dry root weight plant-1 and percent reduction of yield due to TSWV infection were performed by correlation and regression model. To interpret the data bar diagrams and graphs were also used when necessary.