Varietal response and toxicity of aqueous leaf extracts of Azadirachta Indica to Phytophtora Colocasiae causing Taro leaf blight in Unwana Southeast, Nigeria

Abstract

Taro is one of the major leafy vegetable and tuber staples in the southeast, Nigeria. Production of the crop is, however, seriously constrained by the challenge of taro leaf blight (TLB). Selection of appropriate variety and bio-pesticides are seen as major ways of ameliorating this impediment. This work evaluated the response of 4 varieties of taro to TLB, and effects of 5 levels of Azadirachta indica (0, 50, 100, 150, and 200 g/ha), and 200g/ha of Ageritum conyzoides and Mancozeb (as positive controls) on the disease initiation and development. The experiment was set up as 4 x 7 factorial experiments in RCBD with 3 replicates. The result showed that NCE-003 which had 56.15% and 2.28 and NCE-002 (60.16% and 2.84) for mean disease and severity scores respectively were the least susceptible varieties, while NCE-005 was the most susceptible to the disease with (82.63% and 7.03) for the respective parameters under consideration. About 50-200g/ha of aqueous extract of A. indica inhibited spore germination (77.09-96.02) and radial growth (58.24-68.37) of the fungus compared to (0.00%) obtained from the control experiment. Also these levels of the test extract significantly (P<0.05) minimized the mean incidence and severity of TLB from 82.63% and 7.08 on the control plants by (58.24-65.37%) and (1.84-2.61) respectively in the field. Minimization of the disease and crop tissue damage translated to improved mean taro yield by (5.83t-10.90/ha) and mean corm weight (115.50-147.20g) compared with 4.36 and 91.70% recorded on the untreated control experiment; and general performance (leaf area, number of leaves cormels) of the crop. Therefore, integrating the use of NCE-003 and NCE-002 with 150-200g/ha of A. indica could effectively improve taro corm and leaf yield for sustainable food sufficiency and security in sub-Saharan Africa.