1Dept of Agronomy, Eastern University of Sri Lanka, Chenkalady, Sri Lanka; 2Dept. of Plant Science, Lincoln University, New Zealand.

Background and objectives
Onion rot caused by Fusarium solani is one of the predominant diseases of onion cultivation in eastern Sri Lanka. Currently control of this pathogen mainly relies on fungicides which are economically and environmentally undesirable and even inadequate as a long term solution to crop protection. It is now recognised that biological control of plant pathogens is a viable alternative and can be successfully exploited in modern agriculture.

The predominant antagonistic fungal spp. found in sandy regosols of eastern Sri Lanka is Trichoderma koningii (IMI number 357117, Report of BC Sutton) [1]. This shares the same niche with the pathogen F. solani, and causes deleterious effects on the pathogen. It is possible, therefore, that it may have value as a biopesticide against F. solani An attempt was made in vitro to study the concentration of locally available strain of T. koningii in the control of F. solani.

Materials and methods
Different concentrations (13x104, 26x104, 39x104 and 52x104 spores/ml) of T. koningii seeded pour plates were prepared (10 cm diameter petri dishes) and a mycelial disc of F. solani (1 cm diameter) was placed on the centre of each of the T. koningii seeded plates. All the treatments were replicated four times and arranged in a completely randomized design, and were incubated at room temperature (30-32C). Radial mycelial growth of F. solani in different concentrations of seeded T. koningii plates were measured for 5 consecutive days and were compared with non-seeded plates.

Results and conclusions
All the T. koningii seeded treatments used in this study have significantly (P<0.0001) reduced the mycelial growth of F. solani over the control. The treatment means were further compared using Duncan's multiple range test [2], and it was found that there were significant differences among different spore concentrations of seeded T. koningii. At 39x104 spores/ml, the mycelial growth of F. solani was found to be the lowest. At high concentration (52x104 spores/ml), the mycelial growth was increased significantly (P<0.05). High F. solani mycelial growth found in high T. koningii spore concentration (52x104 spores/ml) may be due to lack of nutrient sources in the medium for the T. koningii spore germination. The importance of nutrient sources for the germination of T. koningii was explained by several workers. In practice, mass additions of T. koningii to soil with food base produced encouraging results. Success of this biocontrol system can be attributed partially to the fact that the T. koningii is a natural antagonist and can be applied directly to soil to control F. solani. Intensified studies on the optimum concentration of T. koningii spore suspension to control F. solani under natural conditions should be carried out in different biotypes of T. koningii in different soil types and seasons in this region prior to recommendation.

1. Anparasy A, Rabeendran N, Raveendranath S, 1993. Proceedings of the Sri Lanka association for the Advancement of Science 50, 94-95.
2. Gomez KA, Gomez AA, 1981. Stastistical procedure for field experimentation.