Available online at http://ajol.info/index.php/ijbcs Int. J. Biol. Chem. Sci. 9(2): 603-613, April 2015 ISSN 1997-342X (Online), ISSN 1991-8631 (Print) Original Paper http://indexmedicus.afro.who.int Geographical distribution and prevalence of the main tomato fungal wilt diseases in Benin Rachidatou SIKIROU 1* , Vincent EZIN 2, Feston BEED 2,3 , Sètondji Alban Paterne ETCHIHA AFOHA 1, Félicien Dji-ndé TOSSO 4 and Franck OUESSOU IDRISSOU 1 1Laboratoire de Défense des Cultures, Centre de Recherches Agricoles d’Agonkanmey, Institut National des Recherches Agricoles du Bénin (INRAB), 01 BP 884 Cotonou, Bénin. 2International Institute of Tropical Agriculture, BP 08932, Cotonou, Bénin. 3AVRDC- The World Vegetable Center, 4th Floor, Research & Development Building, Kasetsart University Bangkhen, Bangkok 10900, Thailand; Mailing address: P.O. Box 1010 (Kasetsart), Bangkok 10903, Thailand. 4Laboratory of Applied Ecology, Faculty of Agronomic Sciences, University of Abomey-Calavi, 01 BP 526 Cotonou, Bénin. *Corresponding author, E-mail: [email protected], Tel.: +229 97882620 ABSTRACT Tomato is one of the most economically important vegetable crops in Benin and its production represents more than 51% of the total production of vegetable crops. The ecological peculiarity of its farming exposes it to diseases and pests. Tomato wilt constitutes the major phytosanitary constraint for its production. To identify the causal agents, a survey was carried out across the 12 departments of Benin. Three districts were selected per department and three villages in each district were surveyed. Two farmer’s fields were visited per village where five diseased plants were collected per field. Three pathogens identified from the samples collected in the diseased fields: Sclerotium rolfsii, Fusarium oxysporum f. sp. lycopersici and F. solani . Pathogenicity test conducted for each of the isolated pathogens was positive. The symptoms observed in greenhouse were exactly the same as those recorded in the field. The prévalence of tomato wilting recorded in farmer’s fields varies from 0.1% to 27% for S. rolfsii , from 3% to 20% for F. oxysporum f. sp. lycopersici, and from 1% to 3% for F. solani . The most disseminated and most devastating pathogen was S. rolfsii . F. oxysporum f. sp. lycopersici and F. solani were less disseminated and less devastating pathogens. © 2015 International Formulae Group. All rights reserved. Keywords : Tomato, fungal wilts, incidence, distribution, Bénin. INTRODUCTION and reduce farmers' income. Among these Tomato ( Lycopersicon esculentum ) is problems include diseases caused by soil- the main vegetable crop in Benin and is an borne pathogens which are the most limiting important source of income for farmers factors to tomato production and are the main (Agossou et al., 2001; James et al., 2010). cause of economic losses recorded by farmers Tomato is grown in rain and dry seasons in all (Sikirou et al., 2001). the 12 departments of the country. However, Wilting of tomato reduces or prevents phytosanitary problems limit its production its production in some areas in Benin. For © 2015 International Formulae Group. All rights reserved. DOI : http://dx.doi.org/10.4314/ijbcs.v9i2.3 R. SIKIROU et al. / Int. J. Biol. Chem. Sci. 9(2): 603-613, 2015 instance, in the valley of Ouémé, the Collines, Alibori, Borgou, Atacora and pathogens can jointly cause yield losses up to Donga) (Figure 1) in 2006 and 2007. In each 100% (Sikirou et al., 2001). Tomato wilt is department, three districts were selected and frequently caused by five different pathogens three villages were inspected in each of them. including bacteria such as Ralstonia In each village, two tomato fields were visited solanacearum (Wydra and Dannon, 2006; and in each field, five wilted tomato plants Sikirou et al., 2009) and Clavibacter were sampled and placed in labeled michiganensis (Blancard, 2015) and fungi envelopes. In each field, three density squares such as Fusarium oxysporum f. sp. lycopersici of 50 m 2 (5 m x 10 m) each were delimited to (Osuinde and Ikediugwu, 2002), Sclerotium evaluate the prevalence of wilted tomato rolfsii (Sikirou et al., 2001; Adandonon, plants. According to the cropping system of 2006), and F. solani (Cucuzza and Watterson, regions, the number of plants per density 1991). S. rolfsii and F. oxysporum f. sp. square in the fields varies between 50 and lycopersici are among the most aggressive 200. The prevalence was assessed as the soil-borne fungi causing wilt and rot of tomato number of wilted plants over the total number plants (Khaled et al., 2005). The symptom of of plants in the delimited density square. S. rolfsii is often manifested by yellowing Villages and fields surveyed were randomly accompanied by wilting of plants. At the later selected. The collected samples were carried stage, the fungus develops sclerotia at the to the laboratory of diagnosis of plant diseases collar of the plant. F. oxysporum causes at IITA - Benin. yellowing of the lower leaves on one side of the plant followed by wilting (Smith et al., Isolation of fungi 1988). F. solani attacks more often plant roots Fungi were isolated according to the and cause wilting. These fungi survive in the techniques of Fox (1993). The techniques soil and also in plant debris (Smith et al., consist of washing infested plant parts with 1988). As mentioned above, wilting of running tap water to remove soil surface; and Solanaceae in general and of tomato in to superficially clean them with cotton soaked particular is a major concern for farmers in in 70% diluted ethanol for 3 min. The roots Benin. Apart from the work of Sikirou et al. were cut into sections of 0.5 cm long which (2001, 2009) who reported the presence of S. were then soaked in a solution of 1% sodium rolfsii , F. oxysporum and R. solanacearum as hypochlorite for 5 min and then rinsed with responsible for wilt of tomato in some sterilized distilled water. These sections were localities of Southern parts of Benin, no then dried on sterilized filter papers under the known data is available on their geographical laminar. After drying, the root sections were distribution and prevalence. The objectives of placed on the water agar in Petri dishes (Fox, the present study were to (i) locate fungal 1993). The Petri dishes were then incubated at diseases of wilting of tomato in Benin, and (ii) a temperature of 25 °C for 3 to 5 days. The to evaluate the pathogenicity of the causal mycelium was collected and then cultured on agents of these diseases. PDA medium (prepared as follows: 39 g of PDA were put in 1 liter of distilled water and MATERIALS AND METHODS autoclaved for 30 min at 120 °C). Origin and collection of samples A survey was carried out across the 12 Identification of isolated fungi departments of Benin (Atlantique, Littoral, Fungi were identified on the basis of Mono, Couffo, Plateau, Ouémé, Zou, macroscopic characteristics (color, colony 604 R. SIKIROU et al. / Int. J. Biol. Chem. Sci. 9(2): 603-613, 2015 pigmentation, elevation, mycelium and its 23 F. oxysporum f. sp. lycopersici recorded aspect) and microscopic characteristics (color, isolates, eight were tested with two per shape and size of spores and conidiophores). department. Three of the 5 collected F. solani The identification of fungi was carried out isolates were also tested. Three classes of with the aid of the identification key (Barnett pathogenicity were determined. Isolate was and Hunter, 1987; Samson et al., 1995; Kirk et (1) highly pathogenic when the first al., 2001). symptoms appear before 15 DAI, (2) Fusarium species were identified by a moderately pathogenic when the first serial dilution technique of isolates’ symptoms appear after 15 DAI and (3) non- suspensions (Toussoun and Nelson, 1976). virulent when no symptoms appear until 28 One milliliter of an initial spore suspension DAI. was taken and then diluted four times in a ratio of 1:10. Each level of dilution was used S. rolfsii to inoculate the water agar. After 24 hours, the With the isolates of S. rolfsii , each plant mycelium from a single spore was transferred was inoculated at the collar with 50 sclerotia. on nutrient medium, Potato Dextrose Agar The sclerotia were counted and taken together (PDA) (9 g in 1 L of distilled water and 20 g with the PDA medium on which the fungus of agar) then on Carnation Leaf Agar (CLA) was grown. Five plants were inoculated per (15 g of agar in 1 L of distilled water and then isolate. Control plants were inoculated with autoclaved for 30 min at 120 °C and after uncultured PDA medium. The same classes of cooling at 55 °C add 2 to 3 pieces of carnation pathogenicity as mentioned above were leaf). The latter medium was specific to considered for S. rolfsii species tested. All the identify F. oxysporum f. sp. lycopersici . inoculated plants were kept in the greenhouse and monitored for the appearance of wilting. Pathogenicity test The assessment of wilting disease was carried Fusaria out for 28 days. Out of the 149 recorded The inoculum was prepared by isolates, 23 were selected for the harvesting with sterilized distilled water, pathogenicity test. Fungi were recovered from spores, mycelium and chlamydospores from a symptomatic inoculated plants using the different isolates of Fusarium grown on PDA. previous isolation methods. The resulting suspensions were diluted and filtered using a sieve. For each isolate, the Statistical analysis spore concentration was evaluated using the The analysis of variance (ANOVA) was hemacytometer. performed using the General Linear Model Five 3-weeks-old tomato plants cv. (GLM) procedure of the Statistical Analysis Tounvi, were transplanted into individual System (SAS) Version 8.1 on the prevalence plastic pots (14 cm x 16 cm) containing of wilted tomato in the field. The Student- sterilized field soil.