THE CONTRIBUTION OF SEED CHARACTERS TO CARROT PLANT AND ROOT SIZE VARIABILITY

Three experiments examined the influence of variation in seed characters in carrot crops grown at densities from 50 to 400 plants m-2 on seedling and root weight variation. Coefficient of variation (CV) of seedling weight 20 days after 50% emergence was positively related to CV of embryo length and spread of seedling emergence and negatively related to the ISTA germination count made after 7 days at 20-degrees-C. At low plant density (50-100 plants m-2), CV of root weight was largely unrelated to CV of embryo length over the range of CV from 18-31% but at high density (300-400 plants m-2) CV of root weight increased from c. 65 to 77% in expt 1 and c. 75 to 90% in expt 3. Seeds with small embryos, however, sometimes failed to produce emerged seedlings and although embryo size is a good absolute measure of potential variation it may have limited agronomic application. An effective measure of potential variability which encompasses variation in both embryo size and the ability of embryos to grow and emerge may be provided by the intermediate count of the official germination tests; close relationships between root weight variability and the intermediate count of the official germination test were found in expt 3.