Influence of growth factors on the plant pathogens by select suppression of Pseudomonads
Rhizobacteria were evaluated for their ability to inhibit the growth of damping-off pathogens such as Pythium ultimum, Rhizoctonia solani and common root rot pathogen, Cochliobolus sativus. The level of antagonism by Pseudomonads 63-28, U-14 and Ral-3 was examined on solid growth media under varying conditions of temperature, pH, and sources of C, N, and amino acids. In vitro antibiosis of the pathogens was greatly influenced by environmental and nutritional conditions. Generally, antagonism was greatest at 25-300C and decreased at 400 C. The influence of pH appears to be rhizobacteria and pathogen dependent. For example, optimum inhibition of P. ultimum growth by 63-28 was between pH 4.6-6.0, whereas, optimum inhibition of R. solani growth by U-14 was at 7.6-9.1. Growth inhibition of C. sativus by Ral-3 was pH independent. Mannitol or trehalose strongly enhanced the antifungal activity of 63-28, whereas lactose had a negative effect. Antagonism of 63-28, U-14 and Ral-3 was enhanced by nitrogen sources tested except NaNO2 on U-14. The influence of the amino acids did not effect Ral-3, but, antibiosis by 63-28 was increased by amino acids phenylalanine, arginine, or histidine. U-14's activity was increased with the addition of proline, serine, or arginine. The results from this study clearly show that growth factors have a significant impact on microbial antagonism.
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