DIAGNOSIS AND MANAGEMENT OF ‘DANZAZZALAU’ DISEASE OF ONION (ALLIUM CEPA L.) IN KEBBI STATE, NORTHWEST NIGERIA
Onion is an important vegetable crop in Nigeria grown in both wet and dry seasons though it fetches higher profit when cultivated in the dry season. The crop yield is limited by some production constraints, notable of which is the „Danzazzalau‟ disease in Kebbi State. Fungi isolated from infected pseudostem and roots of onion were Fusarium sp. and Thielavia sp. Pathogenicity test was conducted using these fungi and Fusarium sp. proved to be pathogenic on 6-week old onion seedlings. Fusarium sp. was identified as a Fusarium species belonging to biological group clade V. by Centre for Agriculture and Bioscience International (CABI), Egham, Surrey, United Kingdom. Trials were carried out in the screenhouse and field during 2015 dry season at Samaru, Zaria to study the effects of water regimes, manure rates and mulch treatments for the management of „Danzazzalau‟ disease of onion crop. The treatments consisted of three water regimes (3, 10 and 21-day), three manure rates (0 Kg/plot, 40 Kg/plot, and 80 Kg/plot) and three mulch types (polyethylene sheet, rice straw and no mulch) laid out in a Split Plot Design (SPD) with three replications. Water regime was the main plot while manure rates and mulch types were the sub- plots. Incidence and severity of the disease and its effect on onion growth and yield were determined. Lowest disease incidence (36.02 %) and severity (32.93 %) were obtained at the 21-day water regime. The 21-day water regime and rice straw mulch at
1.2 mt/ha produced highest bulb yield of 4.67 t/ha and 4.80 t/ha respectively which were significantly (P≤ 0.05) higher than the other treatments. The efficacy of aqueous and methanol crude extracts obtained from Jatropha curcas, Moringa oleifera and Eucalyptus globulus leaves at 5, 7.5 and 10 g/ml on growth and development of Fusarium clade V. was tested in vitro. Aqueous extract of Moringa at 10 g/ml (5 % w/v) when used to amend culture media led to decrease in number of conidia
produced by 91.53 %, however when Jatropha and Eucalyptus extracts at 10 g/ml (5
% w/v) were used conidial numbers were reduced by 42.3 % and 19.04 % respectively. Conidial dimensions were reduced (6.32 %, 6.05 % and 0.64 %) when 5 g/ml (2.5 % w/v) aqueous extract of Jatropha, Eucalyptus and Moringa were used to amend the culture media respectively. Methanolic extract of Eucalyptus at 10 g/ml (5
% w/v) when used to amend culture media conidial number was reduced by 88.3 % followed by 64.5 % and 20.10 % reduction when Moringa and Jatropha extracts were used respectively. Conidial dimensions were reduced by 5.31 %, 3.20 % and 1.28 % when 5 g/ml (2.5 % w/v) methanolic extract of Eucalyptus, Jatropha and Moringa
were used to amend the culture media respectively. Methanolic extract of Eucalyptus evaluated in vitro at 10 g/ml (5 % w/v) was found to be effective in reducing the
number of conidia produced and conidial dimensions of Fusarium clade V tested. A combination of 21-day water regime and rice straw mulch at 1.2 mt/ha were found to be effective in the management of „Danzazzalau‟ disease of onion and may thus be a good component of an integrated disease management (IDM) programme for irrigated onion production.
Onion (Allium cepa L.) belongs to the family Alliaceae, it is a monocotyledonous, cross-pollinated crop cultivated mainly as a cool season vegetable (Jilani and Ghafoor, 2003). The crop is grown in most regions of the world, with China, India and United States of America being the largest producers (FAOSTAT, 2014). In Nigeria, 1.32 x 106 mt are produced on 42,000 hectares of land which makes it ranks fourth after Egypt, Algeria and Morocco in Africa (FAOSTAT, 2014). Profitable production of onions is favoured by the inclement conditions obtained around the northwestern region of Nigeria. Reports of the National Agricultural Extension and Rural Liaison Services and Federal Department of Agricultural Extension (FDAE) in 2015 showed that the rich alluvial deposits along the River Niger provide suitable soil for its cultivation. The 119.10 x 103 and 109.90 x 103 mt estimates at Sokoto and Kebbi States respectively in 2014 are highest throughout the country.
World Food Programme reported global usage of onions as food and condiment. Its unique flavour and odour makes it indispensible in preparation of many traditional dishes. The numerous ways in which it is prepared from boiling, frying, stewing, baking, pickling, to eating raw make it a versatile food source (WFP, 2014).
Production of onion as a crop is however, constrained by numerous abiotic and biotic factors. In Nigeria, abiotic factors include nutrient deficient soil, shortage of supplementary irrigation facilities, inadequate inputs and poorly defined post-harvest storage and value addition strategies (Ibrahim, 2014). Pests and diseases have been reported to reduce yield and quality of produce (Currah and Felicity, 1990). Major insect pests include onion thrips, cutworms, leaf miners, onion maggot (Hylemya antique Meig.) and several species of mites decimate the crop. Economic diseases of
the crop induced by bacteria, nematodes, viruses, parasitic flowering plants and fungi in the northwestern Nigeria agro-ecology have been listed by Emechebe et al. (1980). Some of these diseases include bacterial soft rot, Iris Yellow Spot Virus disease transmitted by thrips (Thrips tabaci Lind); root knot nematode disease caused by Meloidogyne spp. Colletotrichum gleoesporioides causes the onion twister disease which is very prevalent in northwest Nigeria, Alternaria porri causes purple blotch; Peronospora destructor causes downy mildew disease and neck rot disease caused by Botrytis allii are other fungal diseases of this crop. These pathogens cause yield reductions of 50-70 % which discourage production by the farmers.
A relatively new disease of onion was reported by the Kebbi State Agricultural and Rural Development Authority (KARDA) during the 2009 Annual Cropping Scheme Meeting of the Institute for Agricultural Research, Ahmadu Bello University, Zaria. Symptoms ascribed to the disease were rapid protrusion and clock-wise curl of main leaf, die-back and eventual wilting of the whole plant. The plant can be infected at all stages of growth leading to 100 % loss of the crop as reported by the farmers and it discouraged them from continued production. Adopted strategies to manage the disease by farmers have not been successful. The local name „Danzazzalau‟ given to the condition reflects the sudden protrusion and curling of main leaf that the farmers observed (IAR Cropping Scheme Report, 2009).
Onion is a highly valued vegetable crop possessing culinary and medicinal values. Major constraints to sustainable production of the crop include high incidence of pests and diseases, nutrient deficient soils; inadequate irrigation facilities, expensive inputs and marketing that gives marginal returns to the farmers. Kebbi State produces 135,000 mt of onion with an average yield of 20-35 mt/ha annually, thus making
Kebbi State the second largest onion farming community in Nigeria after Sokoto State (Usman, 2013). Onion production in Nigeria has been declining due to pests infestation (NAERLS and FDAE, 2015) and Kebbi State particularly has had onion yield stagnated at 109 x 103 mt from 2012 to 2014 due to the incidence of a devastating disease locally called „Danzazzalau‟. Total loss especially at seedling stage has been claimed by farmers and all measures to alleviate the menace have proved abortive. When infected stand was uprooted, basal stem plate was rotted and central crown sloughed off. The disease was said to be severe where crop suffers environmental stress and all stages of onion are affected. The need to determine main cause and condition(s) that favour the disease is very important. In view of this, a study to identify the causal organism(s) inducing the disease and proffer management strategies against the disease was carried out.
The objectives of this research are to:
- isolate and identify fungi associated with the „Danzazzalau‟ disease;
- assess the incidence and severity and evaluate some production strategies for the management of the disease;
evaluate in vitro the efficacy of aqueous and methanolic crude extracts of some plant materials on the pathogen development