Orobanche problems and management in vegetable crops in Khartoum state

One of the major problems of agricultural production is the noxious parasitic weeds. Broomrape (Halouk as the local name), Orohanche spp, is an obligate parasitic flowering plant. It has been recognized as destructive root - parasite on Solanaceous, leguminous and several other broad leaved plants. The studies undertaken included field surveys of Orohanche in the main vegetable producing areas in Khartoum State, interviewing farmers and conducting field and pot experiments to determine the level of infestation and the damage caused by Orobanche to the main vegetable crops, to identify the host range of Orobanche and to develop crop sequence that will reduce the level of infestation. The results of the surveys conducted during this study in major agricultural areas in Khartoum state along the River Nile, White Nile and Blue Nile banks, indicated that within all the locations the species of Orobanche was Orobanche ramosa and no other spccies was found. The major hosts of Orobanche were tomato, potato, eggplant, carrot and pepper. Tomato and potato being the most infected. Along the River Nile, the production system on both sides of the River is characterized by mono-cropping of potato and tomato and this lead to very high level of infestation of Orobanche and yield losses may reach up to 100%. No proper crop sequence is followed and no proper control measure of Orobanche is practiced. However, some farmers practiced hand pulling of Orobanche after flowering, but they leave the pulled Orobanche plants in the fields. Along the White Nile banks, the production system is different; usually farmers raise their crops under residual soil moisture. Eggplant and tomatoes are the major crops. Eggplant represents 70% of the cropped area and the percentage infestation of Orobanche and yield losses due to Orobanche are lower than the other areas. Farmers practiced hand- pulling and addition of fertilizer for Orobanche control. The surveyed locations along the Blue Nile banks included Soba East, Hudeiba, Mahas Kutrang, Nuba Gerrif, Elafoon, Albiotat, Nuba and Mahas Island. The results of the questionnaire at these locations indicated that farmers usually grow different crops but do not follow proper crop sequences. Major crops are: tomato, onion, cucumber, alfalfa, carrot, eggplant and okra. The major hosts of Orobanche were tomato, carrot, eggplant and pepper. The percentage infestation ranged between 60% and 100% and losses in yield ranged between 40 and 80%. The surveyed agricultural schemes included Elsellate, Alban Kuku, Soba- West, Om- Arda, Waha, Elshaab and Gomea. Data indicated that these schemes have different cropping systems. They are characterized by fodder production, mainly Abu-sabeen and alfalfa. Production of vegetable crops includes okra at Gomea Scheme. Since crops produced at these schemes are non- host crops for Orobanche, no infestation of Orobanche in these schemes was found. The results of on- farm experiments conducted in Orobanche naturally infested field of tomato mono- cropped areas along the River Nile in Khartoum State indicated that the damage of tomato caused by Orobanche was so severe to get any yield data from experiment. The level of infestation of Orobanche in tomato crop was very high in all locations (70%- 100%). The mean number of Orobanche plants/ tomato plant and mean number of Orobanche stems/ tomato plant ranged between 6- 40 and 14.3- 287, respectively. Results of on-farm field experiments, conducted at 5 locations in the mam potato producing area in Khartoum state in naturally Orobanche infested fields showed that the percentage infestation of Orobanche on potato crop ranged between 70- 100% and the loss in yield is 100%. The number of Orobanche plants/ potato plant and number of Orobanche stems/ potato plant were 1- 14.7 and 13.7- 146. 7 respectively. Results of field experiments conducted in highly Orobanche infested fields at Shambat Research Station to investigate the effects of crop sequence on Orobanche control and potato crop yield indicated that fixed crop sequence of non-susceptible hosts for three years fo11owed by potato decreased infestation to 10-14% compared to 90-100% in the non- fixed crop sequence of Orobanche susceptible crops. Non- fixed crops sequence of susceptible crop for three years followed by potato decreased potato yield by up to 72%. Fixed crop sequence of non- susceptible hosts for three years fo11owed by potato increased potato yield significantly compared to non- fixed crop sequence of susceptible crops. The increase in yield ranged between 200 and 245%. A crop sequence of onion-onion- Abusabeen- potato effected comparable yield of potato to Orobanche free plots. A crop sequence of alfalfa- alfalfa- onion- potato increased potato yield by 200% compared to non- fixed crop sequence of susceptible crops. The fixed crop sequence of Abusabeen- Abusabeen- Abusabeen- potato resulted in comparable yield to Orobanche tree plots and displayed significantly higher yield than that of non- fixed crop sequence of Orobanche- susceptible crops. Results of pot experiments conducted in the green house at Shambat Research Station showed that tomato, potato, eggplant, carrot, cucumber and fababean were among the host range of Orobanche ramosa. On the other hand sorghum, barely, alfalfa, onion and peas were unable to induce Orobanche seeds germination and are, therefore, not among its hosts. Moreover, parasitism of Orobanche on host crops decreased their fresh and dry weights