Abstract
A survey was initiated to detect Tomato Yellow Leaf Curl virus (TYLCV) and to identify its reservoir hosts in eight locations viz. Gazipur, Ishurdi, Bogra, Narshingdhi, Nawabgonj, Mymensingh, Jessore and Khulna in Bangladesh. Nine plant species viz. Ageratum conyzoidus, Dolichos lablab, Nicotiana phumbaginifolia, Luffa cylindrical, Cucurbita moschata, Benincasa cerifera, Hibiscus esculentus, Capsicum annuum and Vigna radiata were detected as alternate hosts of TYLCV. Altogether 33 different hosts of whitefly, B. tabaci were recorded. The severity of TYLCV varied from 2 - 4 and the mean TYLCV incidence (%) varied from 4.75 to 39.54. Mean incidence of TYLCV were significantly higher in Gazipur region than the rest of the studied regions. Single whitefly has been found capable of transmitting TYLCV. The minimum acquisition feeding period, inoculation feeding period, pre-acquisition starvation period and post-acquisition starvation period required by B. tabaci to transmit the TYLCV were 30 minutes each. The young seedlings up to the age of 20 days were found to be highly vulnerable to the virus. The percentage of TYLCV incidence in different date of planting time (one year from mid October, 2000 to mid September, 2001) of tomato cv. BARI Tomato 4 was evaluated. The highest TYLCV incidence (%) was observed at 75 DAP during the period of March and April, 2001 planting followed by May, 2001 planting, but the lowest TYLCV incidence (%) was found in November, 2000 planting followed by December, 2000 planting. A strong correlation was obtained between the incidence of TYLCV and number of whitefly in tomato plants. Altogether 22 tomato cultivars were screened for their reaction to TYLCV under net house using artificial inoculation method of viruliferous whitefly as well as under field condition in Gazipur, Bangladesh. Out of the materials tested, only three germplasms HTM 008, TM0 1015 and TM 1020 were recorded as highly resistant (HR) to TYLCV and J resulted higher yield during the three consecutive study periods. The percentage of yield loss due to TYLCV at different growth stages of tomato plants was studied. The yield reduction was recorded upto 93.82% when the plants got infection within 30 days of planting, while infection at 45 and 60 days after planting resulted in 70.79 and 55.06% yield loss, respectively. Among the chemicals (Nuvacron, Malathion, Ripcord and Nogos) and botanicals (Jut seed extract, Garlic clove extract, Neem leaf extract and Sharifa leaf extract) tested for controlling TYLCV of BARI tomato 4 in the field, the lowest incidence (24.56%) of TYLCV was observed in Ripcord (0.1%) sprayed plot, while the control treatment resulted the highest incidence (62.77%) of TYLCV at 60 DAP. Maximum number of whitefly (1.10) was found in plots where Sharifa leaf extract was sprayed at 60 DAP and in control plots while lowest number of whitefly (0.32) was recorded in plots that received Ripcord. The highest yield (50.45 t ha1) was obtained applying Ripcord followed by Nuvacron (46.65 t ha1) and Neem leaf extract (45.68 t ha1). The lowest yield (39.28 t ha1) was recorded in the plots that received Sharifa leaf extract. Integrated approach in controlling TYLCV of BARI tomato 4 in the field indicated that the TYLCV incidence (%) varied significantly among the treatments. The TYLCV incidences ranged from 12.07 - 52.85% at 90 DAP. Among the treatments used, the lowest incidence of TYLCV was recorded in T5 i.e. covering the seedlings in seedbed with nylon net and spraying by Ripcord (0.1%) at 30, 45 and 60 DAP, where the highest incidence (%) of TYLCV was recorded in control plot. The highest yield (65.21 t na1) was obtained in T5 and the lowest yield (43.38 t ha1) was recorded in T1 (control) plots. The findings of the present investigations have clearly pointed out the importance of controlling TYLCV in Bangladesh. The epidemiology of TYLCV has been explored and three germplasms have been recorded as highly resistant to TYLCV.