| Information on the thermal-time relationships of plant-parasitic nematodes is necessary to predict geographical distributions, nematode population dynamics and resulting crop yield losses. Our objectives were to determine the thermal-time requirements for development of Meloidogyne arenaria race 1, M. javanica, and M. incognita race 4, at constant temperature and field conditions. The base temperature (T b) for development, and heat units expressed as degree-days (DD) required for nematode development from second-stage juveniles (J2) to egg-laying females were determined at constant temperatures ranging from 12 to 35°C. Freshly hatched J2 of the three species were inoculated on okra (Abelmoschus esculentus) and placed in chambers. Data were subjected to regression analysis to estimate the base temperature for each species. The shortest time and average degree-days (DD) above base temperatures 10.3, 9.8, and 10.6°C for development were 19 days and 316 DD, 15 days and 300 DD, and 17 days and 334 DD, for M. arenaria, M. incognita, and M. javanica, respectively. Development under field conditions was determined on four squash (Cucurbita pepo) crops grown on black and aluminized UV-reflective polyethylene mulched (spring and autumn seasons, respectively) or nonmulched drip irrigated beds in 2003. Six thousand nematode eggs and juveniles were pipetted into each plant-hole before squash was seeded for the first crop. A second crop immediately followed. Plots were arranged in a split-plot design with three replicates. Soil temperature was recorded at five depths using a temperature logger. Mulched beds had higher mean soil temperatures, and the number of days required for egg laying was decreased compared to nonmulched beds. The shortest time and lowest degree days (DD) for development to egg-laying females in mulched beds were ca. 19 days and 278 DD, 17 days and 297 DD, and 19 days and 311 DD for M. arenaria, M. incognita, and M. javanica, respectively. Development of egg-laying females was delayed ca. 2 days on nonmulched soil compared with mulched soil for all nematode species. This information will be useful for predicting developmental cycles of the three species under different climatic conditions, and also for estimating the number of generations each species may complete on vegetable crops grown in Florida. |
