Daucus carota var. sativus

Traits evaluated: ANTHOCYANIN ROOT COLOR (ANTHRTCOL); HYPOCOTYL PIGMENTATION (HYPOPIG); MAXIMUM CORE SIZE (MAXCORESIZ); MAXIMUM STORAGE ROOT LENGTH (MAXSTRTLEN); MAXIMUM STORAGE ROOT WEIGHT (MAXSTRTWGT); MEAN CORE SIZE (MEANCORESZ); MEAN STORAGE ROOT LENGTH (MEANSRTLEN); MEAN STORAGE ROOT WEIGHT (MEANSRTWGT); MINIMUM CORE SIZE (MINCORESIZ); MINIMUM STORAGE ROOT LENGTH (MINSTRTLEN); MINIMUM STORAGE ROOT WEIGHT (MINSTRTWGT); ROOT GREENING (ROOTGREEN); ROOT PHLOEM CAROTENOID COLOR (ROOTPHLOEM); ROOT SKIN PIGMENTATION / COLOR (RTSKINPIG); ROOT XYLEM CAROTENOID COLOR (RTXYLEMCOL); NATURE OF STORAGE ORGAN (STORORGAN); STORAGE ROOT DIAMETER (STORRTDIAM); STORAGE ROOT SHAPE (STORRTSHP); STORAGE ROOT SURFACE (STORRTSURF); STORAGE ROOT TIP SHAPE (STRRTTPSHP)

Evaluation location: Iowa, United States. Method: Daucus direct seeded into two 4-foot rows 8 inches apart in NCRPIS Farm Greenhouse-3 sandbox measuring 8 ft. x 4 ft. x 2 ft (l x w x h) and filled to 20-inch depth with sand. Sandbox was watered as needed and seedlings fertilized with a liquid fertilizer twice weekly. Seedlings were thinned to 2 to 3 -inch spacing. Roots were carefully dug from the sand for notes/images after two to four months (or sooner if plants began to bolt). Root characterization notes/images were recorded on plants between 50 and 130 days after planting (DAP); average was 92 DAP. Notes/images recorded on 10 roots per accession.

Accessions were planted in a randomized complete block design with two replications at the Hancock Research Station in Hancock, WI, in the summer of 2016 and 2017. One hundred seeds of each accession were planted in each 1-m plots. Canopy height was measured just before harvest with three measurements taken per plot. Harsh flavor was evaluated on a scale of 1 to 5 (with 5 being the least harsh, and 1 being the harshest) on at least three individual roots per plot after harvest in fall 2016.

The objectives of this study were to evaluate the response of diverse carrot germplasm to heat stress, identify heat-tolerant germplasm that may be used by plant breeders, and define the appropriate temperature for assessing heat tolerance in germinating carrot seed.

This study is the first field-based, multi-year experiment to evaluate shoot-growth trait variation over a 100-day growing season in a carrot diversity panel (N=695) that includes genetically diverse carrot accessions from the United States Department of Agriculture National Plant Germplasm System. This study provides the first broad-sense heritability estimates for early-season seedling vigor and early-season canopy coverage on a diverse collection. We also develop a method for characterizing flowering to identify accessions that are predominantly biennial, which could be incorporated into biennial breeding programs without substantially increasing the risk of annual growth habits.