Integration of Cultural Practices to Contain and Control (.Orobanche crenata Forsk in Vicia faba (L

Abstract

The root parasitic weeds Orobanche spp. pose a genuine threat to agriculture and food security across many parts of the world. The weeds, at present, are almost uncontrollable. They attack economically important crops and severely reduce yield and quality. Production of faba bean, the most important cool season leguminous crop in the Northern and River Nile States of the Sudan, is constrained by the recently introduced O. crenata. Afield survey was conducted to ascertain spread of the parasite at two sites, Hagar ElAssal and Wad Hamid, in the River Nile State in season 2006/2007. Laboratory experiments were undertaken at the College of Agricultural Studies (CAS), Sudan University of Science and Technology (SUST) at Shambat to study the effects of temperature, conditioning period, urea and treatments with sodium hypochlorite (NaOCl) and gibberellic acid (GA3) on O. crenata germination. A series of green house experiments was conducted during the period 2005 to 2009 at the Gezira Research Station and CAS. The green house experiments focused on influence of selected cultural practices comprising of irrigation frequency, fertilizers, intercropping and trap cropping on reactions of faba bean to O. crenata. Further studies were also conducted on faba bean genotypes reactions to the parasite, influence of genotypes on O. crenata infestation and development and the influence of O. crenata seed placement in soil on incidence of the parasite. The field survey showed wide distributions of the O. crenata in the surveyed areas as over 90% of the fields were infested. A large proportion of farmers in Hagar ElAssal (88.9%) got their seeds from external sources, while in Wad Hamid 80% of the farmers used seeds from their own farms. A small proportion of farmers (6.7%) in the two sites use organic manure. Furthermore, no strict crop rotation was adopted at both sites. In Hagar ElAssal 11.1% of the participating farmers abandoned planting faba bean. Most of the farmers in Wad Hamid abandoned planting of faba bean and shifted to onion and potato. Hand-pulling was the main method of control and was practiced by 35.6% and 73.3% of the iv responding farmers in Hagar ElAssal and Wad Hamid, respectively. Chemical control of the parasite was practiced by 17.8 % in Hagar ElAssal while the rest of the farmers adopted no control measures. Subsequent to hand-pulling the majority of the farmers, in the two sites, piled O. crenata spikes in the fields. The rest of the farmers pulled and burned the parasite spikes or threw them onto adjoining roads. Following harvest most of the farms were grazed by animals. Laboratory experiments showed that the response of O. crenata seeds to the synthetic germination stimulant, GR24 varied with temperature, the conditioning period and concentration of the stimulant. Seeds conditioned and germinated at 200C were less responsive to GR24 than those similarly treated at 150C. Germination, invariably, increased with GR24 concentration. Germination increased with conditioning time, reached a peak at 14 days and then declined on further extension of the conditioning period. O. crenata seeds conditioned in urea showed decreased germination in response to subsequent treatments with GR24. Urea at a low concentration (0.1 mM) did not reduce O. crenata germination. However, urea at 0.2 to 2 mM reduced germination significantly. O. crenata seeds, soaked in NaOCl solution for different periods of time (1 - 60 min) and subsequently conditioned in water or GA3 solution showed variations in germination. O. crenata germination increased (18 to 85%) with increasing time of soaking in NaOCl from 1 to 12 min and then declined. O. crenata seeds, soaked in NaOCl for 1 to 24 min and conditioned in water showed no germination when treated with GR24 at 0.1 ppm. Seeds soaked for 48 min exhibited 21% germination while those soaked for 60 min displayed no germination. GR24 at 10 ppm applied to O. crenata seeds previously soaked in NaOCl for 1 to 60 min and conditioned in GA3 induced considerable germination (7 to 85 %). O. crenata infestation and dry weight increased with increasing size of the seed bank from 1 mg to 16 mg/pot. O. crenata infestation and development was influenced by genotype. In general, despite seasonal variability O. crenata attachment and emergence were more rapid on ILB1814 and Hediba 93 than on Giza 4. v Furthermore, O. crenata dry weight, irrespective of genotype, gradually increased with time. O. crenata seeds placement in soil played a major role in determination of infestation. Seeds buried at 5 cm depth resulted in heavy infestation and the highest emergence of the parasite compared to those placed in the surface soil or placed at 10 and 15 cm depth. Seed placed at 10 and 15 cm resulted in considerable attachment, but emergence of the parasite was negligible (0 to 3 O. crenata spikes/pot). O. crenata emergence and dry weight were affected by irrigation frequency and faba bean genotype. Irrigation at wilting significantly reduced O. crenata emergence in all genotypes. However, regular and daily irrigations increased emergence and dry weight significantly. On daily irrigation Orobanche emergence and dry weight were high on Hediba 93, but were significantly low on Saliem and Shbah. Intercropping of faba bean with selected legumes (Vigna spp.) reduced Orobanche emergence by 27 to 83% and Orobanche dry weight by 26 to 89%. O. crenata on faba bean, planted in pots previously sown to trap crops, showed reduced emergence and dry weight. O. crenata infestation in faba bean planted subsequent to phillipsara, cowpea, green gram and forage sorghum was significantly reduced. However, on faba bean grown subsequent to barley and wheat O. crenata displayed reduced emergence, albeit not significantly. Effects of nitrogen, added or fixed, on O. crenata emergence, capsule production and dry weight displayed seasonal variability. In the first season (2005/2006) faba bean inoculated with R. leguminosurm, irrespective of genotype sustained comparable Orobanche emergence, while in the second season (2006/2007) Orobanche emergence was highest on ILB1814 (38 plant/pot) and lowest on Hediba 93 and Giza 4 (16 and 19 plant/pot). In general, in absence of added or fixed nitrogen, Orobanche emergence was highest on ILB1814 (28 to 43plants/pot), moderate on Hediba 93 (21 to 23 plants/pot) and lowest on Giza 4 (9 to 10 plants/pot). Nitrogen as urea reduced Orobanche emergence and dry weight. Nitrogen at 2N and 3N applied as urea reduced O. crenata emergence by 54 to 81% and 18 to 67%, seed capsules production by 37 to 64% and 55 to 77%, dry weight by 57 to vi 72% and 32 to 78% on ILB1814 and Hediba 93. However, nitrogen effects on O. crenata on Giza 4 were not significant.