Variation Studies in Carrots as an Aid to Breeding. VI. Genotype-Environment Interactions in Contrasting Field Environments

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Abstract
Two series of field trials of carrot cultivars were conducted over the period 1968–73. In one series cultivars were grown at different sites and densities, repeated over years (the between-sites set), whereas in the second series similar cultivars were grown at a single site with different sowing dates, lengths of growing season and densities repeated over years (the within-site set). In each of the characters reported, namely yield, percentage of split roots, percentage of purple-topped roots and root length/diameter (LD) ratio, genotype χ environment (GE) interactions were detected within both environmental sets. An extension of joint regression analysis was used to estimate the relative linear responsiveness to environment of the cultivars and to test the consistency of these estimates over the two environmental sets. Conclusions differed somewhat between characters; for yield the largest interactions were non-linear, but some evidence of small linear interactions consistent over the two sets was obtained. For the two defect characters the interactions were largely linear but some were consistent over sets and others not. For LD ratio the interactions were again largely linear but entirely consistent over sets. It is suggested that carrot breeders requiring to test breeding lines in more than one environment should consider using less costly within-site environmental treatments, such as different sowing dates and low density, when selecting for improvement in the characters reported here.

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