Streptomyces pactum may control Phelipanche aegyptiaca in tomato

Abstract

Phelipanche aegyptiaca (syn. Orobanche aegyptiaca), achlorophyllous obligate root parasitic weed attacks economically important crops in several plants families including Solanaceae. Of the Solanaceous crops tomato (Solanum lycopersicum) is the most susceptible. Available records showed that an array of microorganisms could give adequate control of the parasite and alleviate its damage in tomato. In the present study 88 actinobacterial strains, associated with antagonistic activity against plant pathogens, were assayed for their effects on germination of P. aegyptiaca seeds. Of the strains Streptomyces pactum Act12 was selected for detailed laboratory, greenhouse and field studies. The results showed that S. pactum Act12 cell-free culture filtrate inhibited seed germination and germ tube elongation of P. aegyptiaca by 93.9% and 97.4%, respectively. In potted plants S. pactum Act12 culture reduced P. aegyptiaca emergence and dry weight by 85.7% and 55.4%, respectively, increased tomato biomass, total number of bacteria and the ratio of bacteria to fungi in tomato rhizosphere by 25.8%, 84.9% and 123.6% over the control, respectively. In the field experiment S. pactum Act12 decreased P. aegyptiaca emergence by 32.3% and increased tomato fruit yield by 57.1%. The results indicate the potential of S. pactum Act12 as a bioagent for P. aegyptiaca control in tomato and suggest that the suppressive effects of S. pactum Act12 on P. aegyptiaca parasitism is an outcome of decreased germination, alteration of composition of rhizospheric microbiota and promotion of host defense mechanisms.