Greening of carrot roots (Daucus carota L.): Estimates of heritability and correlation

Abstract

Heritability estimates were made by S1 on parent regression, half sib on maternal parent regression, and half sib intra-class correlation. Heritability of greening on the shoulders of carrot roots appeared to be low, less than 25%, when estimated in a population synthesized from diverse cultivars and breeding lines and grown without special attention to cultivation procedures. As shown in a separate trial, expression of greening is much influenced by exposure of the root to sunlight. External greening, defined as the length of visible green extending from the crown toward the root tip, did not seem to be genetically correlated with root weight, length, diameter, or shape index (the length/diameter ratio), but the sampling errors of the correlation estimates were very high. Two cycles of selection for and against eternal greening appeared to result in larger, shorter and thicker roots in the greening population than in the ‘nongreening’ one. The mean differences in greening between the green and nongreen selections grown in 1964 were 11.0 vs. 6.1 mm external green and 14.6 vs. 7.8 mm internal green; in 1965, they were 23.8 vs. 16.6 mm external green, 21.5 vs. 15.2 mm internal green. Internal greening (measured after slicing the root lengthwise) and external greening were phenotypically correlated in three populations, r=0.69, 0.75 and 0.76. Correlated response to selection suggested that they were also genetically correlated. Heritability was moderate (38–56%) for root shape index and was very low for the other root measurements, weight, length, and diameter. The genetic correlation of shape index with length was high and direct; with diameter, high and inverse.