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

Mineral nutrition efficiency is an important objective in plant breeding an d breeding research to face the economic and ecologic problems of current a griculture and horticulture. Plant nutritioners are therefore suggested to identify selection parameters for genotypes, that are able to achieve yield s above average at low supply of soil or fertilizer nutrients. Analysis of nutrient efficiency mechanisms turned out to be difficult, because of a com plex regulation and the high number of compounds involved in nutrient effic iency. The present research on the physiology of carrot yield production wa s performed to identify physiological markers for carrot yield production t hat may be helpful in future studies on the selection of nutrient efficient genotypes. Investigations on a hybrid system and on different cultivars de monstrate that the extent of cytokinin sensitivity of the storage root cell s is a substantial factor in carrot yield production. Cytokinin sensitivity in addition to cytokinin concentration determine yield productivity of car rot genotypes by regulating the limiting sink size of the harvest organ. Cy tokinin sensitivity was tested in primary tissue culture experiments appear ed to be developmentally regulated and could be modified by temperature. Im plications of the results for breeding strategies towards nutrient efficien cy are discussed.