Abstract

Four potato cultivars were grown in plots which, following previous treatments, contained few or many Globodera rostochiensis (Wollenweber) Behrens Rol. Soil moisture content, leaf water potential and percentage ground cover were measured each week, and whole-plant samples (including roots) were taken 6 1 2 and 9 weeks for planting. Leaf areas, fresh and dry weights and inorganic nutrient contents were measured on these samples. Stomatal resistance was measured on one occasion, 13 weeks after planting, and soil samples were taken midway between plants on the same date and roots extracted from them. Yields were measured 30 weeks after planting. In terms of yield Cara, which contains the resistance gene H 1, tolerated nematode attack better than the other cultivars. Of the non-resistant cultivars, Pentland Crown was the most tolerant and Pentland Dell the least; the fact that Maris Peer yielded less than Pentland Dell in heavily infested plots is probably attributable to its early maturity date and lower yield potential. The shoot:root ratio measured 9 weeks after planting was similar for all cultivars following the same previous treatment, but was decreased from 11·9 when the previous crop was Maris Piper to 5·6 when the previous crop was Pentland Crown. Good yields in the presence of nematodes were produced by Cara (and to a lesser extent Pentland Crown) because it produced extra roots in the heavily infested plots; Pentland Dell and Maris Peer produced fewer roots in heavily infested plots. Measuring leaf water potentials and soil water contents was of little value for estimating tolerance but the least tolerant cultivar, Pentland Dell, showed the largest increase in stomatal resistance in heavily infested plots, with Cara showing the smallest. Percentage ground-cover measurements through the growing season gave the best overall picture of the reactions of the four cultivars to nematode infestation, but were time-consuming. Concentrations of potassium in haulm dry matter were decreased and those of calcium increased by nematodes, with the magnitudes of the effects least in Cara and greatest in Pentland Dell. The prospect of developing an assay for tolerance sufficiently convenient for use by plant breeders must depend upon adapting a simple test of this type to a pot scale.

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