The Effects of Light, Rehilling, and Mulching on Greenshoulder and Internal Greening in Carrots

Abstract

Greenshoulder (GS) and Internal greening (IG) in carrots (Daucus carota var. sativus) affect root appearance and can lead to significant economic loss. Experiments were conducted to quantify the critical light intensity that may trigger greening by exposing carrot hypocotyls to different light intensities. Chlorophyll a, b, and total chlorophyll were measured. The effects of rehilling on GS and IG were measured in a 2-yr field study with eight treatments imposed at various stages of growth. Another experiment to confirm the effects of rehilling by etiolating various genotypes was also conducted. Leaf area index, internal and external greening, and IG length were measured. Increasing light intensity enhanced chlorophyll a and b linearly and significantly. The highest amount of chlorophyll a, b, and total chlorophyll accumulation in hypocotyl occurred at the highest light intensity tested (320 μmol m -2 s -1 ). Rehilling reduced GS and IG significantly. However, the response varied significantly between seasons. In 2002, rehilling once at the early vegetative stage, initial bulking stage, or active bulking stage was effective in reducing GS and IG. In the 2003 field study, rehilling once at each of the three stages reduced GS and IG. Compared with the control, rehilling reduced GS by 10 to 21% and IG by 13 to 20%. Among the cultivars tested, mulching reduced GS only for Magno. The results suggest that GS and IG are induced at the hypoctoyl stage and that rehilling could reduce GS and IG considerably; however, the etiolation response appears to be genotype specific.