Influence of Plant-gleaned Compounds on the Initiation and Development of Fungal Diseases of Onion (Allium cepa L.) in the Field

Abstract

A study on the control of fungal diseases of onion (Allium cepa L.)  plant; was carried out in the Research and Training (R&T) Farm; of the Michael Okpara University of Agriculture, Umudike, Nigeria. The experiment was a 2 x 3 factorial, laid out in a randomized complete block design (RCBD) with 5 replicates. The treatments comprised of 2 leaf extracts from Azadirachta indica and Dennettia tripetala; sterile water (control); and 2 periods of application of the test plant-derived compounds: 4 weeks after transplanting (4 WAT) and 6 weeks after transplanting (6 WAT). The fungal diseases identified on the naturally infected onion farm were anthracnose (Colletotrichum gloeosporioides), black mold (Aspergillus niger), bulb rot (Rhizopus stolonifer) and leaf spot (Alternaria porri; Curvularia sp). Plots treated with Dennettia tripetala and Azadirachta indica were significantly (p=0.05) superior to the control plot in the reduction of incidence and severity of these fungal diseases. All the plants treated at 4 WAT with the test extracts performed better in their growth parameters, and yield than those spray-treated at 6 WAT. Plants sprayed at 4 WAT with D. tripetala gave  the highest mean yield of 11,984.30kg/ha, while those sprayed with sterile water gave the lowest yield of 7,000.56 kg/ha. Therefore, extracts from Azadirachta indica and Dennettia tripetala should be applied as prophylactics at or before disease initiation (4 WAT) for management of soil and thrash-borne fungal diseases of the onion crop in integrated diseases management programmes in sub-Saharan Africa (SSA) for improved onion production.