Antagonistic Effects of Bacillus Species in Biocontrol of Tomato Fusarium Wilt

Fusarium solani is the causative organism of Fusarium wilt of tomato (Lycopersicon esculentum Mill). Four Bacillus spp identified as B. amyloliquefaciens, B. cereus, B. pumilus and B. subtilis were tested for biocontrol activities in vitro as zone of inhibition and in vivo as percent disease control and disease incidence. The result from in vitro analysis showed that B. amyloliquefaciens inhibited the growth of F. solani the most by 95.2% while B. cereus had the highest growth of F. solani and inhibition of 55.7%. B pumilus and B. subtilis showed inhibition of 70.46% and 82.1% respectively and were significantly lower (p=0.05) than the control with 100% F. solani growth. In vivo, B. cereus had the least disease incidence and highest percent disease control (18.75% and 81.2%). This was significantly different from the control (100% and 0%), B. amyloliquefaciens (25% and 75%), B. pumilus (37.5% and 62.5%) and B. subtilis (37.5% and 62.5%). Also, growth parameters like shoot and root length from treatment with B. cereus (38 mm ±1.47 and 31 mm ±1.22) were significantly longer (p=0.05) compared to the control. This result shows that these four Bacillus spp are very effective biocontrol agents and should be harnessed for further biocontrol applications. Address for correspondence: Telephone (work): +27 183892568 Fax: +27 183892134 E-mail: [email protected] INTRODUCTION Tomato is one of the most important vegetables because of its health benefits and phytochemical properties. Because of its low calorie and absence of cholesterol, it is one of the recommendations of diets needing low cholesterol. They are quite rich in many important nutrients and vitamins which include phosphorus and potassium and also vitamins B and C. They are also very important against common cancers like breast and prostate cancer. As important as tomato is nutritionally and in being an important cash crop for smallholders and medium-scale commercial farmers in Africa, soil-borne pathogens inflicts a lot of diseases and infections on it (Babalola and Glick 2012). Such diseases include Bacterial wilt, root knot nematodes disease, early blight, late blight and Fusarium wilt. Fusarium wilt is a devastating disease of tomato and causes a lot of loss to farmers worldwide. symptoms begins as gradual yellowing and wilting of the lower leaves (Khan and Khan 2002) which is brought about by the growth of the microconidia inter-cellularly in the xylem of the stem and root. As a result of the failure of the infected xylem of the plant to meet the water requirement of the plant, death of the tomato plant is inevitable (Burgess et al. 2008). Spores from the conidia are released into surrounding tissues as the plant dies. They later form chlamydospores that fall back into the soils (Jones 2000). These spores can remain in the soil for as long as 30 years until favourable conditions are available and they can re-infect plants (Thangavelu et al. 2004). Several microorganisms are being used in the control of tomato pests and diseases. Listed among tomato pest control agents are F. compactum and F. arthrosporioides (Babalola 2010a,b,c). Included in tomato disease control agents are Trichoderma, Pseudomonas and Bacillus species. Bacillus-based biocontrol agents are quite important in the management of pests and plant diseases (Jacobsen et al. 2004). Varieties of Bacillus and Paenibacillus help to promote the health of crops and control diseases by producing antibiotic metabolites, suppressing plant pathogens, others antagonise plant pathogens by competing for nutrients like iron and phosphate, others indirectly fix nitrogen which they make available to the plants and help stimulate plant nutrient uptake (Gardener 2004). This research seeks to elucidate the biocontrol abilities of these four Bacillus spp in order to make use of these abilities for further biocontrol interventions. MATERIAL AND METHODS Bacillus spp Inoculum Preparation The following typed cultures and locally isolated organisms (LIO) from the culture collec© Kamla-Raj 2013 Ethno Med, 7(3): 205-216 (2013)