Abstract
Leaf spot or Tikka (Cercospora arachidicola and Cercosporidium personatum) of groundnut (Arachis hypogaea L) is an economically important foliar disease and major yield reducing factor all over Bangladesh. The disease also reduces the quality of the pods of groundnut. A survey on the incidence and prevalence of leaf spot of groundnut in major groundnut growing areas in Bangladesh was carried out during 2008-2009. The survey was done at farmers' fields as well as research plots of different research organizations viz. Bangladesh Agricultural Research Institute (BARI) and Bangladesh Institute of Nuclear Agriculture (BINA) and different regional agricultural research stations of BARI and BINA. Altogether 262 germplasms/lines/varieties were evaluated, where none was found free from the disease. The disease incidence and severity were found to vary from location to location, variety to variety and growth stage of plants, where leaf damage, disease severity and disease score ranged from 9-80%, 20-90% and 4-9, respectively. The highest leaf damage, disease severity and disease score were recorded from research fields of BARI, Hathazari, Chittagong followed by Experimental farm, Department of Plant Pathology, Bangladesh Agricultural University (BAU), Mymensingh; but the lowest count was made in research fields of Bangladesh Institute of Nuclear Agriculture (BINA), Ishwardi, Pabna. The highest leaf damage, disease severity and disease score were recorded in groundnut variety Dhaka-1 and DG-2 and the lowest in BARIchinabadam-7 and BARIchinabadam-8. The conidial length and breadth of C. arachidicola ranged from 36.2 168.95um and 2.59 10.30μm, respectively having septation 4-12. The conidial length and breadth of C. personatum varied from 19.31 - 38.80μm and 5.86 10.60μm, respectively and septation of the conidia ranged between 2 - 6. Pathogenicity of collected isolates differed significantly. Twenty three botanicals, BAU-Biofungicide and Bavistin were evaluated, where extracts of tomato leaf, neem leaf, datura leaf (black), marigold leaf, lemongrass, debdaru leaf, garlic clove, onion bulb and BAU- Biofungicide were found promising in controlling leaf spot and increasing yield of groundnut. These selected botanicals and BAU-Biofungicide were evaluated for their effect on germination and seedling vigour of groundnut, where maximum vigour was recorded for seed treatment with BAU-Biofungicide followed by tomato leaf extracts. BAU-Biofungicide treatment showed 46.07% higher vigour over the untreated control. Seed treatment with BAU-Biofungicide followed by tomato leaf extracts was resulted 18.49% higher germination over untreated control. Pod yield was increased by spraying extract of neem leaf (39.36%), BAU-Biofungicide (24.93%), extracts of debdaru leaf (24.49%) and datura leaf (black) (21.59%), respectively over untreated control in fields experiment, but seed treated with BAU-Biofungicide increased germination, number of nodules and seedling vigour by 20.96%, 113.33% and 31.67%, respectively over untreated control. Moreover, BAU-Biofungicide as seed treatment plus spray and extract of neem leaf increased pod yield (50.95%) and (39.23%), respectively over untreated control. The BCR of using BAU-Biofungicide (seed treatment + spray) was found 1:3.28, extract of neem leaf was 1:2.86 and BAU-Biofungicide only spray was 1:2.83. The oil and protein content increased by 49.25% and 31.50%, respectively in BAU-Biofungicide treatment followed by extract of neem leaf by 48.89% and 30.80%, respectively as compared to untreated control.