Factors influencing the infectivity of plant parasitic nematodes

Abstract

The influence of the host plant (tomato), temperature, pH , suction potential, osmotic potential and soil pore size on the hatch, mobility and invasion of the parasitic nematode Meloidogyne javanica were studied to try to define the conditions for maximum infection and to determine any characteristics of the nematode that increase its chances of invading the host. There are three phases of infection as defined in this paper: hatch, migration to the root, and invasion. The optimum temperature for hatching and for movement was about 25 to 30 °C and for invasion 20 to 30 °C. The optimum soil moisture for hatching, movement and invasion was in the region of field capacity when most of the larger pores have drained of water. The optimum pore size for movement and invasion was about 75 to 120 μm. Pores of this size range occur in coarse-textured soils, e. g. sandy loams. Osmotic potential and pH probably have only a minor influence on infection in soil. In water and sterile soil the rate of hatch was high, whereas in non-sterile soil hatch was inhibited unless tomato plants were present. Hatch, therefore, reached a maximum in soil only in the presence of a host plant, thereby increasing the chances of infection. The conditions for maximum hatch, movement, and invasion are similar, so when an egg does hatch it is in an environment conducive to rapid migration to the root and to quick invasion. Larvae were found to be infective for a limited time, 4 to 8 days, in these experiments. There was a visible depletion in food reserves during this time. It is suggested that as soon as the larva hatches and begins to migrate through the soil its sources of energy (food reserves) are used up, so after a time the nematode is unable to generate sufficient propulsive force to penetrate the root. Percentage infection decreased with nematode density. There was no lack of space for movement around the root but observations and measurements of invasion with single roots on agar indicated that there were at least six possible factors related to nematode density that influenced penetration: (1) multiple invasion, (2) increased attraction to roots following initial penetration, (3) shortage of space at the root tip, (4) destruction of root tissues and inhibition of root growth, (5) loss of attraction to roots when root growth stopped, (6) interference between individuals.