UNITED STATES DEPARTMENT OF AGRICULTURE
AGRICULTURAL RESEARCH SERVICE
WASHINGTON, D.C.  20250

with

THE CALIFORNIA AGRICULTURAL EXPERIMENT STATION
DAVIS, CALIFORNIA  95616

and

THE OREGON AGRICULTURAL EXPERIMENT STATION
CORVALLIS, OREGON  97331

and

THE WISCONSIN AGRICULTURAL EXPERIMENT STATION
MADISON, WISCONSIN  53706

RELEASE OF MOTLEY DWARF RESISTANT CARROT POPULATION

The Agricultural Research Service, United States Department of Agriculture, the California
Agricultural Experiment Station, the Oregon Agricultural Experiment Station, and the
Wisconsin Agricultural Experiment Station, announce the release of a carrot population to be
used as germplasm for developing improved genotypes and producing hybrids with motley
dwarf resistance.

Motley Dwarf Resistant population (MDR) was derived from crosses made in 1981 between
B6439 (a dark orange Imperator-shaped inbred from an open-pollinated synthetic consisting
of 16 fresh market inbreds) and Oregon 6 (a long Danvers-shaped breeding line from
Autumn King and OSU 26-2 with moderate field resistance to motley dwarf). Selection was
made in Corvallis, Oregon, for motley dwarf resistance and for dark orange, long, smooth
root in five subsequent generations. Now at M₆, MDR is the result of six generations of
selection for motley dwarf resistance and acceptable root shape and color. MDR tends to
produce limited amounts of seed.

Roots of MDR are short to medium long (14-18 cm), tapered, and medium orange with large
cores. Root surface is fairly smooth and greening of the root shoulder surface is common. Tops
of MDR are fairly tall and dark green. Carotene content of mature roots is 140 to 160 ppm
(compared to 70 to 100 ppm for older and 120 to 160 ppm for modern fresh market varieties).
Flavor is average. Motley dwarf resistance is excellent in the MDR population. In two years of
field testing and one year of greenhouse testing, this population exhibited a minimal amount of
leaf mottling and root stunting typical of motley dwarf (Table 1). Interestingly, performance of
F₁ hybrids with MDR as one parent had few disease symptoms to suggest resistance to be a
dominant trait. Roots of the MDR population suffered no reduction in seed yield after exposure
to the disease whereas plants of other genetic background produced no seed, even if symptoms
in earlier stages of growth were not severe.

Table 1.

¹Field tested in Corvallis, OR; natural infection. 1=no infection, 5=badly infected
²Greenhouse tested in Davis, CA; infected with inoculated host. 0=no infection,
  5=badly infected.

Breeder's seed of MDR will be prorated upon written requests before April 1, 1994, addressed to
P.W. Simon, USDA, ARS, Department of Horticulture, 1575 Linden Drive, University of
Wisconsin, Madison, WI 53706.

When this germplasm contributes to a new cultivar, it is requested that appropriate recognition
be given to its source.