الملخص الإنجليزي
Tomato yellow leaf curl (TYLC) is a complex of begomovirus species which are transmitted exclusively by whitefly (Bemisia tabaci). Typical symptoms of this disease yellowing, upward leaf curling and severe stunting of the whole plant. A survey was conducted for collecting whiteflies from 2-3 farms per Wilayat from different crops. Total nucleic acid isolated from single whitefly was used as template to amplify a fragment of 220 bp from the B biotype and 400 bp for the Q biotype of the mtCOI gene of whitefly using the primers Bem23F/Bem23R. All the samples showed fragment of 200 bp indicating the presence of B biotype. Six primer pairs were used RbF/RbR (900bp), 92F/HbR (700bp), Ars23S-1/Ars23R-2 (580bp), Wol16SF/Wol16SR (650bp), CFBF/CFBR (500bp) and U23F/23SIGR (600bp) to determine the the secondary symbionts associated with whitefly Bemisia tabaci. Only a fragment of 710 bp was amplified in all the screened samples indicating the presence of Hamiltonella species. Agryl cover was used in field experiments in two successive years to evaluate the optimum period for covering the tomato plants against whitefly transmitted begomoviruses. The covering period of 6-7 weeks proved to be the best for getting the highest yield (3kg/plant) with less TYLCV infection. Tomato crops showing begomovirus-like symptoms were collected from three commercial farms at Barka, cloned and sequenced. The results showed the presence of a new begomovirus species which was named Tomato leaf curl Barka virus (TOLCBrV). Fourteen tomato inbred lines carrying Ty begomovirus resistant genes have brought from the Agricultural Vegetable Research and Development Center (AVRDC) and screened against begomoviruses under field conditions in two successive years and also under controlled conditions. Twelve out of fourteen tomato inbred lines showed high resistance against different begomoviruses under field conditions 3 months post transplanting. Six begomovirus species were cloned from different tomato inbred lines Tomato yellow leaf curl virus (TYLCV), Chilli leaf curl virus (ChLCV), Tomato leaf curl Al Batinah virus (TOLCABV), Tomato leaf curl Oman virus (TOLCOMV), Tomato leaf curl Barka virus (ToLCBrV) and Cotton leaf curl Gezira virus (CLCuGeV). An agroinfectious clone of TYLCV was constructed and used to inoculate 14 tomato inbred-lines to see their susceptibility toward TYLCV under controlled conditions. Twelve inbredlines were found resistant against TYLCV. The tomato inbred lines with Ty genes did not develop disease symptoms up to 85 days post inoculation (DPI). Three techniques were used to detect the virus in the plants: southern hybridization, polymerase chain reaction (PCR) and real time PCR (qPCR) at the periods 5, 35 and 85 (DPI). The virus was detected clearly at 5 (DPI) by all techniques, at 35 (DPI) by PCR and qPCR and at 85 (DPI) by qPCR which indicate largely to the restriction of the virus to the inoculated leaf. However, susceptible line 3022E and GS 12 develop severe symptoms yellowing and curling and virus titer was increased from one period to next in comparison to resistant lines where the virus titer decreased from one period to next. These tomato lines are promising and can be used under Oman conditions and offer alternative option to the local susceptible varieties that have been used in Oman, leading to savings in money, time and labor.
