Evaluation of Chitosan Efficacy on Tomato Growth and Control of Early Blight Disease

Tomato (Solanum lycopersicom L.) is one of the world’s most widely cultivated crops. Among the inflicting disease, early blight caused by Alternaria alternata is a major yield-limiting factor in Sudan. Management of the disease has been hampered by use of ineffective fungicides. Chitosan is a natural nontoxic biopolymer derived by deacetylation of chitin. The effects of chitosan at different concentrations against the early blight pathogen A. alternata and growth promotion of tomatoes were evaluated in vitro and under field conditions. Three chitosan concentrations (1, 3 and 5mg/ml) were used in vitro. Chitosan at 3mg/ml and 5mg/ml, was found to have strong antifungal activity against A. alternata, and was selected for further studies. In addition, chitosan at the above concentrations and the commercial fungicide Ortiva ( 250g/l Azoxystrobin) were used in vivo as treatments and distilled water as control. Chitosan at 5mg/ml applied as foliar spray alone, or in combination with seed treatment or seed treatment alone, reduced disease severity by 46%, while fungicide spraying reduced severity by 46% compared to control. In general, regardless of the application method, tomato growth parameters were significantly increased by chitosan treatments compared to control. Application of chitosan at 5mg/ml as foliar spraying combined with 5mg/ml as seed treatment increased plant height and it is fresh and dry weight by 16%, 36%, 24% respectively; and when applied at 5mg/ml as foliar spraying combined with 3mg/ml as seed treatment increased plant height, fresh and dry weight by 16%, 13% , 14%, respectively. This is the first study on the use of chitosan for control of tomato early blight and promotion of growth of tomato plants in Sudan. In conclusion, chitosan shows promise for enhancement of plant growth and control of A. alternata in tomato particularly when applied at 5mg/ml.