Growth Response of Bacterial Antagonists in a Mix of Composted Wood Fibre Waste and Millet Seed under Sterile and Non-sterile Conditions

Abstract: The potential use of composted wood fibre waste (WFW) for the cultivation of bacterial antagonists of Sclerotinia minor was examined with the result that a mix of millet seed (20% w/w) and WFW, suitably amended with nutrients, proved to be an ideal matrix for the growth of some of these bacteria. Densities in terms of cfu’s ranged from 8.5 log10 cfu/g dw to 10.5 log10 cfu/g dw under sterile conditions after 14 days incubation. Lower population densities of the antagonists were achieved under non-sterile conditions in the compost: millet mix of between 7.9-9.3 log10 cfu/g dw at the same period. However, when applied in a pot (glasshouse) trial to protect against S. minor, the millet seed appeared to stimulate the growth of this pathogen resulting in a high incidence of attack of lettuce plants after 2-3 weeks. Although the percentage of healthy seedlings increased following application of compost mix grown antagonists (at a rate of 5% v/v) when compared to the control treatment, these values were not statistically significant (p>0.05) in most cases. Therefore, the use of millet seeds cannot be recommended as a nutrient supplement for the bacterial antagonist cultivation, if to be subsequently used to control fungal pathogens in the field. Key words: Sclerotinia minor, Pseudomonas corrugata, Lysobacter antibioticus, wood fibre waste, compost, bacterial antagonists.