Effect of drought and rain in mid-summer on the development and hatching of eggs, emergence of larvae from egg-masses, and survival of larvae of Meloidogyne incognita

Abstract

Soil samples taken from a sweet potato field on August 20, after a period of drought lasting approximately one month when weeds were wilting in the daytime, and on Aug. 28, 8 days after the beginning of rain, were divided into two parts, ie. fine soil and aggregated soil (more than 5 mm in diameter), by sifting with a 5 mm aperture sieve. Root fragments caught on the sieve were also collected to obtain egg-masses. Nematodes were extracted from the two soils by the double-layer centrifugal-flotation method and a combination of this method and Baermann funnel method. Nearly twice as many eggs and ten times more hatched larvae per egg-mass as well as a significantly higher proportion of second-larval-stage eggs were observed within the egg-masses collected on Aug. 20 as compared to those collected on Aug. 28. Approximately 3, 000 living larvae per 100 ml of soil, most of which were physiologically young in terms of their food reserves, were extracted on Aug. 20, while the number of larvae on Aug. 28 (after the rain) showed a drastic increase (about 6, 000). Both the increasing rate of larvae caused by the rain and the proportion of living larvae in the fine soil were higher than in the aggregated soil. These results indicate that hatching of eggs and emergence of larvae from egg-masses are remarkably suppressed by drought which ordinarily occurs in summer in Kyushu, and larvae in soil can well withstand such conditions. Drought is considered to affect the pattern of seasonal population changes of this nematode.