EVALUATION OF SOME ENVIRONMENTALLY SAFE CHEMICALS AND BIOAGENTS AGAINST Fusarium solani AND Sclerotium rolfsii INFECTED COWPEA PLANTS

Abstract

Incidence of root rot and damping-off caused by Fusarium solani and Sclerotium rolfsii on cowpea plants was successfully controlled by some plant extracts, essential oils, bioagents, systemic resistance-chemical inducers and seed dressing fungicides which tested under laboratory, greenhouse and field conditions in two successive seasons (2008 and 2009). All tested plant extracts; Artemisia absinthium, Ocimum basilicum and Mentha longifolia; significantly reduced the linear growth of F. solani and S. rolfsii. The maximum inhibition in fungal radial growth was induced by Ocimum basilicum and Artemisia absinthium with averages of 81.29 and 61.99%, respectively. All the tested essential oils reduced the fungal growth of S. rolfsii, the most effective oils were Syzygium aromaticum and Eucalyptus globulus with averages of 87.70 and 81.10 %, respectively. On the other hand, using culture filtrates of Trichoderma harzianum, T. viride and Bacillus subtilis significantly reduced the linear growth of F. solani and S. rolfsii with the average of 75.28, 69.62, and 54.36%, respectively. Results of chemical inducers revealed that salicylic acid have the highest inhibition effect on the mycelial growth of F. solani and S. rolfsii with the average of 20.00 and 29.63 %, respectively. Under greenhouse conditions, all treatments caused significant decrease of disease incidence and increase of survival plants, as compared to the untreated plants. Soaking seeds in Ocimum basilicum extract and S. aromaticum oil decreased damping-off and had the highest percentage of healthy survival cowpea plants. Soaking cowpea seeds in Vitavax-captan or in the suspension of T. harzianum, (however, had the best effect) for decreasing damping-off and increasing survival plants. The disease could be controlled also by salicylic acid and ascorbic acid (4mM) which decreased damping-off and root-rot incidence and increased survival plants. On the other hand, there is a correlation between induced resistance and some biochemical changes in leaf tissues of cowpea healthy plants such as increasing the activity of peroxidase and Polyphenol oxidase enzymes. T. harzianum, salicylic acid and S. aromaticum produced the highest level of peroxidase and Polyphenol oxidase enzymes activity. Under field conditions, Vitavax-captan, bioagents T. harzianum, plant extract; Ocimum basilicum, essential oil; S. aromaticum and resistance-inducing chemical salicylic acid significantly reduced disease incidence and increased seed yield production.