THE INFLUENCE OF CYST NEMATODES AND DROUGHT ON POTATO GROWTH .1. EFFECTS ON PLANT-GROWTH UNDER SEMI-CONTROLLED CONDITIONS

Potatoes were grown under a permanent rain shelter in mobile containers in soil with or without potato cyst nematodes (Globodera pallida). The plants were subjected to an early drought stress period starting at planting until 43 days after planting, to a late drought stress period starting at 43 days until senescence at 92 days and to a drought control. Dry matter weight and characteristics of leaves, stems, stolons and roots were determined at periodic harvests. The early drought stress and nematode infection affected many plant organ characteristics in similar ways. Numbers of leaves, specific leaf area, plant height, specific stem weight, leaf area ratio, mean tuber weight and harvest index were reduced by both stress factors at early stages of growth. Later on, interactions between both stress factors which influence the development rate of the plants led to more diverse plant reactions. Plants of all treatments rapidly senesced at about 90 days after planting. Uninfected plants had then depleted the soil nutrient supply whereas the plants grown in the inoculated soil senesced as a result of the potato cyst nematode infection.