Genotype x environment interaction of potato chip colour

Ten potato genotypes were tested in replicated trials over three sites in New Brunswick. Five of them were tested in 1991, 1992 and 1993, and another five in 1992 and 1993. Tubers were harvested and put in storage rooms with two temperature regimes: 7 degrees C and 13 degrees C. Prior to testing glucose content and chip colour, a portion of tubers stored in 7 degrees C was sampled and subjected to reconditioning for 2 and 4 wk in a storage room with the temperature regime of 21 degrees C. High relative humidity (>80%) was maintained in all storage rooms. Glucose and colour score of chips were determined during November in each of the three years. Analysis of variance revealed genotype x environment interactions for both traits. Since variation of chip colour is controlled primarily by glucose content in potatoes, this causal relationship was used as a basis to perform path regression analysis for each of the genotypes, based on all available data of the two traits. The regression equation is composed of two terms: an average chip score over environments (mu) and a multiplicative term with a genotypic coefficient (g) and an environmental index (r); mu measures the overall chipping ability, whereas g responds to environment and thus represents chipping stability. The 10 genotypes were different from one another on estimates of both parameters. The estimates of r showed lesser differences between the three test sites than between storage-temperature regimes. Storing potatoes at 13 degrees C and 7 degrees C gave the best and worst chip-colour scores, respectively Reconditioning at 21 degrees C after storing at 7 degrees C improved the colour performance. No clear association was observed between chip colour, specific gravity and marketable yield. Good chipping genotypes tested in the experiment, however, had lower yields than others. The present results indicate that path regression analysis is an effective method for detecting the role of glucose content in the control of the expression of chip colour.