Effect of Individual, Concomitant and Sequential Inoculations of Rhizobium, Rotylenchulus Reniformis, Meloidogyne Incognita and Rhizoctonia Solani on Cowpea Plant Growth, Disease Development and Nematode Multiplication

Individually, Rhizoctonia solani was the most aggressive pathogen followed by Meloidogyne incognita and Rotylenchulus reniformis. While concomitance of nematode and fungus was more damaging than the association of both nematode species but the association of R. solani with M. incognita caused distinctly greater plant growth reduction than its association with R. reniformis. Irrespective of the pathogen inoculated, unbacterized plants suffered greater damage than the bacterized ones. Inoculation of Rhizobium 15 days prior to any test pathogen, both singly or in various combinations, resulted in significantly reduced plant growth, poor nematode multiplication, low root-knot index and improved nodulation as compared with its inoculation 15 days after the test pathogen/pathogens. There was no significant difference in plant growth reduction of bacterized plants whether simultaneously inoculated with either nematode species and the fungus or when the nematode inoculation preceded fungus but, on the other hand, there was significantly less reduction in plant growth when fungus preceded nematode inoculation.

In sequential inoculations interactions were time dependent i. e. prior establishment of one nematode species was invariably antagonistic to the multiplication of the other subsequently inoculated species. Rhizoctonia solani, whether inoculated simultaneously or sequentially, reduced the rate of multiplication of both the nematode species as compared to their rate of multiplication when present alone.