STUDIES ON THE POTENTIAL USE OF PASTEURIA-PENETRANS AS A BIOCONTROL AGENT OF ROOT-KNOT NEMATODES (MELOIDOGYNE SPP)

Some aspects of the interaction of the bacterial parasite Pasteuria pe netrans and the root-knot nematode (Meloidogyne spp.) were investigate d in laboratory and pot experiments. The variable spore attachment on juveniles exposed to water suspensions of the bacterium is probably at tributed to differential susceptibility of biotypes within a heterogen eous Meloidogyne population. The relationship between spore concentrat ion and attachment level is not linear over a range of spore dosages, indicating that even at very high spore concentrations the number of s pores capable of attachment may not be present in excess and it is dif ficult to ensure sufficient numbers of spores to ensure infection will attach to all nematodes. Attempts to apply the bacterium in condition s such as might occur in seedbeds did not suppress nematode multiplica tion after transplanting in nematode-infested soil, indicating that th e only effective application method is a thorough spore distribution i n the planting sites. Two major constraints were revealed: high levels of spore attachment to juveniles does not always guarantee a signific ant reduction of egg laying and this is greatly influenced by the Melo idogyne biotype. Furthermore, the cumulative effect of the parasite in reducing Meloidogyne populations over several crop cycles was less th an expected as the bacterium reduced intra-specific competition far th e food supply and the less damaged root enabled many nematodes to surv ive.