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Abstract
Ten compounds applied as foliar spray were screened for reducing and delaying bolting in fall-planted carrots (Daucus carota L.). Only butanedioic acid mono-(2,2-dimethylhydrazide) (daminozide) was effective; seedstalk height was reduced and root size was unaffected. Daminozide effectiveness was greatest in weak-bolting cultivars. Two sprays of 5000 ppm, 2 weeks apart at about 4 and 2 weeks prior to natural bolting were most effective, suggesting that daminozide does not interfere in the cold temperature induction process, but rather has a delaying and inhibitory effect on the initial seedstalk elongation. Two sprays of 500 liters/ha of daminozide solution of 5000 ppm gave promising results. Root quality was improved without influencing carrot yield or dry matter content. Although (2-chloroethyl)trimethymammonium chloride (chlormequat) suppressed bolting in some experiments, it was less effective than daminozide at comparable rates and higher rates decreased yield.
The soluble sugar content of mature carrot roots (Daucus carota L. cv. Ti-To, Nantes type) grown in broomrape-infested or noninfested soil was measured. Orobanche aegyptiaca Pers. (Egyptian broomrape) and O. crenata Forssk. (crenate broom-rape) decreased the total sugar content similarly. Sucrose was the primary sugar in noninfected roots and its level was greatly reduced in infected roots. Concentrations of sucrose were higher in the cortex than in the core; broomrape infection reduced sucrose concentration in both portions of the root. Even broomrape-infected roots with a healthy appearance (acceptable size and color) had a greatly reduced sucrose content. These results show that broomrape infection can reduce carrot root quality even when the visual appearance of the root is not affected.