Hatching induced by root diffusate, obtained from various potato genotypes, and by standard potato root diffusate, was determined in uitro. The used potato genotypes differed considerably in tolerance to Globodera pallidu. A three parameter logistic model was used to describe the numbers of hatched juveniles in relation to time of exposure to root diffusate. Clear differences in hatching characteristics between genotypes were found. Some tolerant genotypes induced hatching of G. pallida juveniles relatively slowly, compared to intolerant genotypes. Other tolerant genotypes, however, induced hatching as fast as intolerant genotypes, and no significant correlation between hatching parameters and tolerance was found.

Roots of eighteen potato genotypes, differing in tolerance of G. pallida, were grown from tuberpieces on agar in Petri dishes. Juveniles of G. pallida were inoculated directly onto root tips. Root length was measured at various times after inoculation. Inoculation reduced root growth within one day. At later stages, genotypes differed strongly in growth of inoculated roots. Between four and seven days after inoculation, growth of inoculated roots was not significantly correlated with growth of untreated roots, and was only poorly correlated with tolerance assessed in the greenhouse or in the field. However, multiple regression analysis revealed that the tolerance of the tested genotypes was associated with both the rate at which they induced hatching and the growth of roots after inoculation. The combination of these two variables accounted for high percentages explained variance.

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One- or 2-year-old Golden Delicious apple trees on M.IX were grown either in a clay loam (in 60-1 containers) or in nutrient solution and the effects were studied of several aeration regimes. With the soil-grown trees these comprised flooding to various soil depths and for different times. With the trees grown in nutrient solution the aeration regimes compared were nutrient solution without aeration, tap water with or without aeration, and aerated nutrient solution (control). Shoot growth was depressed by high water tables, and that of trees receiving non-aerated nutrient solution or tap water (whether aerated or not) ceased after about 2 weeks. The root growth of trees receiving non-aerated nutrient solution or tap water was similarly depressed, but, by contrast, aerated tap water enhanced root growth. Details are given of treatment effects on the Ca, K, N and soluble sugar contents of the young and old leaves and of the young roots. The uptake of all mineral elements was similarly affected by lack of aeration, suggesting that the relationship between low Ca content and increased bitter pit incidence is not associated with differential absorption but rather with differential Ca distribution. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Results are summarized of a 12-year experiment with Cox's Orange Pippin and Golden Delicious on M9 rootstock. A 5-ha field of calcareous clay soil recently reclaimed from the sea was laid out to give 2 replicates of each of 11 drainage/subirrigation regimes. Three levels of N application were superimposed. The results are discussed in terms of changes in soil physical properties (structure, subsidence and compaction), root and shoot growth, and fruit yields and quality. Maximum vegetative growth occurred at groundwater levels of 70 to 130 cm in combination with adequate N application (75-150 kg N ha-1 year-1). The adverse effects of high groundwater levels on vegetative growth increased at higher N levels. Differences in fruit yields due to groundwater level were