Effect of soil environment on infection of subterranean clover by Meloidogyne arenaria

Abstract

The effect of environmental factors on Meloidogyne arenaria and its infectivity on subterranean clover were investigated both in a naturally infested subterranean clover pasture and under controlled conditions in a pot experiment. In the field, the nematode population was altered by seasonal changes during the sampling periods in 1987 and 1988. The hatching of M. arenaria was determined by the germination of subterranean clover brought about by the opening seasonal rains in April or May. The first generation of M. arenaria in subterranean clover roots appeared to develop and reproduce more rapidly while the soil temperature was still relatively high (>15¦C) in May-June and the second generation developed as soil temperature increased between September and November. These findings were consistent with observations from the pot experiment, where M. arenaria gall production and its development and reproduction in both the tap and lateral roots were greater at 20/15¦C and 25/20¦C than at 15/10¦C. In 1987, egg masses of M. arenaria were first observed approximately 6 weeks after the commencement of the growing season, while in 1988 they appeared only after about 15 weeks. This may be attributed to a delay in the opening seasonal rains in 1988 compared with 1987, as well as cooler soil temperatures in 1988. The pF values in the field soils sampled in this study ranged from non-inhibitive to inhibitive suction, with values from 1.8 to 4.8. Greater nematode infection in the tap roots at moisture levels of pF 1.28 and 0.97, but not at 0.71, may be related to better nematode mobility at the higher soil moisture content and its preference for tap roots under more favourable conditions.