THE INFLUENCE OF DROUGHT AND CYST NEMATODES ON POTATO GROWTH .4. EFFECTS ON CROP GROWTH UNDER FIELD CONDITIONS OF 4 CULTIVARS DIFFERING IN TOLERANCE

In field experiments carried out in 3 years with and without fumigation and irrigation 4 cultivars of potato differed in their tolerance of cyst nematodes (Globodera pallida). Ground cover, tuber and foliage fresh and dry yields were determined at regular intervals. From these measurements, intercepted radiation, radiation use efficiency for production of total and tuber dry matter and the apparent amount of intercepted radiation at tuber initiation were calculated and compared for all the treatments. The results indicate that cultivars which best maintained ground cover in the absence of nematodes also maintain it best in the presence of nematodes. Such cultivars gave the highest yields at all levels of nematode infestation because the radiation use efficiencies were far less affected by nematodes than was intercepted radiation. The similarity of the responses to nematode infection and to drought and the absence of interaction between these two stress factors facilitated crop simulation modelling. The relationships found here may well be wider used, though they will have to be validated for other cultivars and growing conditions.