NEMATODE PROBLEMS AFFECTING POTATO PRODUCTION IN SUBTROPICAL CLIMATES

Globodera rostochiensis and G. pallida are the principal nematodes aff ecting potato in subtropical regions and are responsible for considera ble yield losses; Meloidogyne spp. and Pratylenchus spp. are of local importance. The tolerance limit of potato to both cyst nematodes is 1. 3-2.1 eggs/g soil and the relative minimum yield at high nematode dens ities ranges from 0 to 40%. Short-cycle potatoes planted in summer and harvested in the fall minimize nematode reproduction and yield loss. Long-cycle potatoes planted in the fall and harvested in spring suffer greater yield loss than short-cycle potatoes and allow a significant proportion of the nematodes to reach the cyst stage. Potato crops sown in spring and harvested in summer suffer the heaviest crop losses and allow maximum reproduction of the cyst nematode (39-65 x). Nematode p opulation buildup is influenced by the number of generations completed per year, the length of the potato growing season, and the soil tempe rature. Thus, appropriate cropping systems can be used to control nema tode populations. Quarantine regulations and crop rotations are major control measures. The use of resistant cultivars is effective if the p athotype of the nematode is known. Soil solarization is effective but costly. The use of chemical nematicides is also expensive and may caus e environmental contamination.