No abstract

Confidor, an imidacloprid insecticide, was used in two applications at four rates (47.6, 71.4, 95.2, and 119 g a.i./ha) for indirectly controlling Tomato yellow leaf curl virus (TYLCV) in field plantings of tomato. This spray regimen was compared with standard applications of cypermethrins at 10- to 15-day intervals throughout the growing season. In three field trials, a combination of integrated pest management (IPM) practices and two applications of Confidor at the two highest rates immediately after planting and 6 weeks later, protected tomato plants against the disease until 12 weeks after sowing. All rates of Confidor reduced disease incidence compared with standard chemical control applied in an integrated strategy, and quantitative efficacy increased with increase of insecticide rate. In the three seasons, the mean incidence of TYLCV 12 weeks after sowing was 42.7% in plots not adopting IPM compared with 15.7% in those that did. Disease incidence was reduced by Confidor treatments to 2.2 to 17%. Confidor-treated plots consistently had higher yields than control plots, and the yields decreased with the decrease in the rate of Confidor application. Confidor offers several advantages over standard applications of cypermethrins to control TYLCV. When applied immediately after planting, its long-lasting systemic activity protected the crop against the disease during early stages of growth. In addition, it reduced the number of sprays and increased tomato yield.

An isolate of Fusarium solani (Sud 96) obtained from infected Striga plants in Sudan and six other isolates from Japan were evaluated for their effects on Striga germination. Among all the isolates, only the one from Sudan demonstrated high inhibitory activity. Aqueous and organic solvent culture extracts, as well as fungus suspension, when mixed with GR24, a synthetic analog of the natural germination stimulant strigol, inhibited germination of conditioned Striga seeds. Fusarium solani (Sud 96) filtrates, from cultures grown on autoclaved rice, sorghum grains, and potato dextrose agar (PDA), were more effective in reducing Striga germination than those from cultures grown on wheat straw. A significant difference between rice compared to sorghum and PDA cultures only occurred at high dilutions (40-fold). Complete inhibition of germination occurred when F. solani (Sud 96) culture filtrates and GR24 were applied simultaneously. Filtrate treatments made 2, 4 and 6 h subsequent to treatment with GR24 were less inhibitory. Filtrate treatments applied 8 h or more following GR24 had negligible effects on germination. Chromatographic separation on a silica gel column indicated the presence of several compounds with high inhibitory activity.

Fusarium wilt caused by Fusarium oxysporum f.sp. ciceris (Foc) is the most important soilborne disease of chickpea in the Sudan and many other countries. A total of 76 Foc isolates from six different chickpea‐growing states in the Sudan have been collected in this study to investigate the genetic diversity of Sudanese Foc isolates. Additional 14 Foc isolates from Syria and Lebanon were included in this study. All isolates were characterized using four random amplified polymorphic DNA (RAPD), three simple sequence repeats (SSR), five sequence‐characterized amplified region (SCAR) primers and three specific Foc genome primers. Based on the similarity coefficient, the results indicated two major clusters included seven subclusters. The isolates from the Sudan were grouped as identified as races 0, 2 and unknown races. The isolates from Syria and Lebanon were grouped together as they identified as races 1B/C and 6, respectively. This study identified a new race Foc (race 0) in the Sudan. The results of this study will be useful for breeders to design effective resistance breeding program in chickpea in the Sudan.

Metabolites of the fungus Fusarium solani (Sud 96) inhibited Striga hermonthica germination induced by the germination stimulant GR24. The active principles were identified as trichothecenes acuminatin, neosolaniol, 8-acetylneosolaniol, and tetraacetoxy T-2 tetraol (neosolaniol diacetate) on the basis of their chromatographic behavior and nuclear magnetic resonance and mass spectra. Inhibitory activity of the four trichothecenes against Striga germination increased with acetylation of the hydroxyl moieties. The most abundant inhibitor produced by the fungus, 8-acetylneosolaniol, completely inhibited Striga germination at 24 μM. The fungal toxin did not affect the germination of sorghum, a host crop, but retarded root and shoot elongation of the seedlings by 60 and 30%, respectively, at the same concentration.