Intolerant Cultivars Research Articles

Differences in the tolerance of potato cultivars to potato cyst nematodes (Globodera rostochiensis and G. pallida) in field trials with and without nematicides

SUMMARYIn field trials Cara, Brio, Maris Piper and Pentland Javelin were consistently more tolerant of damage by Globodera rostochiensis yielding more than Corsair, Pentland Dell, Maris Anchor and Maris Peer, in untreated, heavily infested soil and giving the smallest increases to nematicide treatment. No yield or growth differences were found between plants in untreated and nematicide treated plots at a nematode‐free site.The most tolerant cultivars all had a gene (H1) for resistance to G. rostochiensis derived from Solanum tuberosum ssp. andigena and in soil infested with G. pallida the tolerance of at least one resistant cultivar (Maris Piper) appeared to be lessened. However, some resistant cultivars were comparatively intolerant, even to G. rostochiensis. Early cultivars were generally less tolerant than late maturing cultivars but there were exceptions. Amongst cultivars with resistance derived from Solanum vernei the early cultivar Guardian was more tolerant than the main crop cultivar Corsair.The effect on the yield of several cultivars of a range of densities of G. rostochiensis, produced either by applying different rates of a nematicide or by cropping in the previous year, was examined at two sites. The results indicated that the slope of the regression for yield in relation to nematode density was less for tolerant than intolerant cultivars. At sites infested with G. rostochiensis Maris Piper was found to be consistently more tolerant than Pentland Crown.

Towards a Consistent Laboratory Assay for Resistance to Heterodera avenae1

Causes of variation in numbers of females on a cultivar are examined. These are such that an accurate assessment of resistance in the field is not possible. The method used for a laboratory assay is as follows. Seed is selected for uniformity of size and pre‐germinated before sowing, when the seminal roots are about 1 cm long, in tubes of sandy loam. Tubes are opaque (2.5 cm internal diameter by 13 cm long) and are set on a base of potting compost. Seedlings are inoculated immediately with the required number of larvae in 1 mi water ‐ for oats 50 larvae, wheat 75 larvae and barley 100 larvae. They are inoculated at the same density at 3‐daily intervals on four further occasions. The aim is to produce 50 females on the most susceptible cultivar; densities have been determined from intolerant cultivars. Plants are grown under 10‐h day‐length at 15oC and are harvested 2 months after the last inoculation, at which time they are assessed and the valuable plants can be repotted and grown on for seed production.