On the physiology of yield production in carrots. - Implications for breeding towards nutrient efficiency

Summary Mineral nutrition efficiency is an important objective in plant breeding and breeding research to face the economic and ecologic problems of current agriculture and horticulture. Plant nutritioners are therefore suggested to identify selection parameters for genotypes, that are able to achieve yields above average at low supply of soil or fertilizer nutrients. Analysis of nutrient efficiency mechanisms turned out to be difficult, because of a complex regulation and the high number of compounds involved in nutrient efficiency. The present research on the physiology of carrot yield production was performed to identify physiological markers for carrot yield production that may be helpful in future studies on the selection of nutrient efficient genotypes. Investigations on a hybrid system and on different cultivars demonstrate that the extent of cytokinin sensitivity of the storage root cells is a substantial factor in carrot yield production. Cytokinin sensitivity in addition to cytokinin concentration determine yield productivity of carrot genotypes by regulating the limiting sink size of the harvest organ. Cytokinin sensitivity was tested in primary tissue culture experiments and appeared to be developmentally regulated and could be modified by temperature. Implications of the results for breeding strategies towards nutrient efficiency are discussed.