What is it?Potatoes will sustain losses during their post-harvest life as they are living organisms with an active metabolism. Depending on storage conditions potato tubers will -to a lesser or greater extent -respire and transpire and thus lose fresh weight. Maintenance and metabolic processes require energy, and potato tubers use part of their dry matter (mainly starch) for necessary energy supply resulting in dry matter loss. Tubers therefore always show a weight loss due to transpiration (water loss) and respiration (dry matter loss). Moreover, potato tubers show changes in their chemical position during the period of storage. Finally, total weight losses can be increased substantially by storage diseases and pests. Nevertheless potato is a commodity that can be stored successfully for up to 10 months provided the right initial product is loaded, the right storage conditions are created and the right treatments are applied.Two types of storage losses can be distinguished: weight losses and losses in quality. The major factors causing weight and quality losses are:

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ObjectiveTo determine, by means of official tests, the resistance to foliage blight under field conditions of advanced clones and new potato cultivars which may be included on a National List or The Common Catalogue of Varieties of Agricultural Plant Species. Experimental conditions Seed productionWhere possible, all seed tubers used in the trials should be produced at the same location and should receive the same post-harvest and storage treatments. Selection and number of cultivarsWhere the trial site is uniform and individual clones or cultivars are compared only with the control cultivars, the total number of cultivars per trial is not critical. Seed treatmentsWhere a pre-planting treatment is deemed necessary, all cultivars should receive the same treatment. Number of sitesMultiple trial sites are the most desirable, but it will usually not be practical to have more than one site, Number of trial yearsIrrespective of the number of trial sites used the cultivars should be tested over a minimum of two years.

Genotype by environment interaction was investigated for yield data from the official Dutch Variety List trials for potato . The data set included 64 genotypes by 26 environments, where environments consisted of year by soil type combinations . Factorial regression models incorporating genotypic and environmental covariates in the interaction were used to analyse the data . The merits of factorial regression models were compared with those of biadditive models . Factorial regression models and biadditive models described comparable amounts of interaction, but factorial regression models provided a better basis for biological interpretation of the interaction .

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