Growing of Pumpkin Lines: The experiment was conducted during November 2010 to April 2011. The test entries consisting of 26 selected pumpkin lines were used in the present experiment. They were collected from Vegetable division, Horticultural Research Centre (HRC), Bangladesh Agricultural Research Institute (BARI), Gazipur. Twenty to twenty eight days old seedlings of the 26 test entries, earlier raised in poly bags, were planted individually in pits of 45 cm x 45 cm x 40 cm sizes in unit plots of 2.0 m and 2.0 m. There were 78 plots with 3 replications and each plot contained 4 pits for each of the test entries. Standard cultural practices and recommended doses of fertilizers were applied. Bait traps were placed in field for controlling fruit flies (Nasiruddin and Karim 1992)
Measured Traits The experiment was laid out in randomized complete block design (RCBD) with three replications. The virus incidence, severity of virus diseases in experimental fields was recorded through frequent investigation. Viruses were identified studying visible symptoms followed by serological test. Numbers of plants in each plot showing virus disease-like symptoms were recorded and the disease incidence, which measures the extent of propagation of a disease within a given field (Agrios 2005), was also estimated by using the following formula:
% Disease incidence = [Number of diseased plant or parts/Total number of plants or parts observed]X 100%
According to Begum and Khan (1996), the lines were graded as different degrees of susceptibility and resistant based on disease incidence viz. highly resistant (HR=0.0% disease incidence) resistant (R=0-25% disease incidence), moderately resistant (MR= 26-50% disease incidence), moderately susceptible (MS= 51-75% disease incidence) and susceptible (S= 76-100% disease incidence). Disease severity was expressed in percent disease index (PDI). The PDI was computed by using a standard formula (Paper et al. 1996) as given below:
PDI= {(ΣDiseasegradex number of plants in grade)/(Total number of plants x highest disease grade)}X 100
The severity of different virus diseases of pumpkin was indexed on a 0-5 scale, where 0 = no visible symptoms, 1 = slightly mosaic on leaves, 2 = mosaic patches and/or necrotic spots on leaves, 3= leaves near apical meristem deformed slightly, yellow, and reduced in size; 4= apical meristem with mosaic and deformation, and 5= extensive mosaic and serious deformation of leaves, or plant dead (Xu et al. 2004). Fully ripen fruits were harvested and data on fruit yield, yield contributing characters, fruit skin color fruit shape were recorded.
Identification of Viruses: Pumpkin plants grown in the experimental field were checked at 55 days after transplanting. The recorded symptoms include mosaic, leaf curling, chlorosis, shoe-sting, leaf distortion, fern leaf and smaller leaflets of plants. Individual plants showing visible symptoms of virus diseases were recorded. Photographs of the symptoms were taken and compared with standard literatures (Zitter et al. 1996). Viruses were identified by serological detection. Samples of virus infected leaves were transported to the lab and detected by DAS-ELISA (Double Antibody Sandwich Enzyme Linked Immunosorbent Assay). Four antisera were used for virus detection namely Papaya ringspot virus (PRSV-W), Zucchini yellow mosaic virus (ZYMV), Watermelon mosaic virus (WMV2) and Cucumber mosaic virus (CMV).