Influence of Organic and Conventional Management Systems on Carrot Performance and Implications for Organic Plant Breeding

In this study, 36 carrot breeding lines and cultivars widely used for organic production were grown for 4 years in two locations under organic and conventionally managed trials. Highly significant genotypic main effects and genotype 3 year and, to a lesser extent, genotype 3 location interactions were observed for all traits, including harvest root and top weight as well as top height and width measured at early season, midseason, and the time of harvest. In contrast, management systems and most management system interactions were not significant. Broad sense heritability (repeatability) for most responses was relatively high ($0.75), suggesting a high potential for genetic gains through selection, although early-season top height and width heritability were somewhat lower. High rank correlations were found for all traits when comparing genotypes grown under organic and conventional management in both locations when evaluated across all years for each location (P 0.001) or with few exceptions when evaluated by individual years (P 0.05). An analysis of F1 hybrid cultivars and comparison of the performance of production systems showed no rank correlations for most traits and years. In contrast to the results observed for F1 hybrid cultivars, open-pollinated breeding lines presented more instances of correlation between management systems in given locations and years. The stability analysis provided insights into the relative stability or adaptability of 36 carrot genotypes (cultivars) across environments. Considering all traits evaluated, several open-pollinated and hybrid cultivars demonstrated consistent performance along the environmental index, whereas other cultivars and the more inbred breeding lines did not. An additive main effects and multiplicative interactions analysis did not present any clear patterns for management system or location, but it did reflect the highly significant effect of year in genotype 3 environment interactions. The first and second principal components explain a range of total variance from 41.8% for early top height to 55.2% for harvest top weight. The results of the current study contribute to the body of knowledge regarding genotype X management system interactions and provide insights into implications for organic crop improvement in carrot. The results further aid in understanding the influence of organic management in horticultural crops, which may differ with the results of grain crops.