Suppression of Root Pathogens of Tomato by Rhizobia, Pseudomonas aeruginosa, and Mineral Fertilizers

ABSTRACT

Root diseases caused by root-rotting fungi and root-knot nematodes are a serious problem in tomato (Lycopersicon esculentum Mill.) production throughout the world. Due to constraints in use of synthetic pesticides, alternate methods for disease management including biocontrol and cultural practices are being sought out. The effect of rhizobia (Bradyrhizobium japonicum), Pseudomonas aeruginosa, a plant growth–promoting bacterium (PGPR), and mineral fertilizers (urea and potash) was examined in suppressing the root-rotting fungi and root-knot nematodes. Use of P. aeruginosa and B. japonicum alone or with mineral fertilizers significantly reduced infection of tomato roots by the root-rotting fungi Macrophomina phaseolina, Rhizoctonia solani, and Fusarium solani. Application of PGPR and rhizobia with urea or with both urea and potash resulted in greater suppression of M. phaseolina than when either organism was used alone. Use of P. aeruginosa or B. japonicum alone or with mineral fertilizers suppressed the root-knot nematode Meloidogyne javanica by reducing numbers of galls on roots, nematode establishment in roots, and nematode populations in soil. The tallest plants occurred due to treatment with P. aeruginosa combined with potash and urea. The maximum shoot fresh weight occurred when treatment was P. aeruginosa or B. japonicum used with urea and potash or with urea alone. Application of rhizobia or PGPR has a greater potential to suppress tomato root pathogens when used in conjunction with mineral fertilizers then when used alone.

KEYWORDS:

• Pseudomonas aeruginosa
• mineral fertilizers
• nematode
• rhizobia
• root-rotting fungi
• root knot
• tomato

Financial support provided by the Higher Education Commission, Islamabad, Pakistan is sincerely acknowledged. We thank Dr. Don Ferrin, Department of Plant Pathology, University of California, Riverside, for suggestions on the manuscript.