Sugar Beet, Energy Beet, and Industrial Beet - Industrial Crops: Breeding for BioEnergy and Bioproducts - page 85

warm season bioenergy crops would be grown during the summer, supplemented
with energy beet during the winter. Sugar beets have been grown in all states in the
USA and could be grown profitably with proper varieties (with particular attention
to disease resistance) and husbandry. While these regions do experience freezing
temperatures, progress is being made on winter hardiness and frost tolerance (aka
winter beets) [ 23 ]. Also, beets are being considered for energy production in the
major US sugar beet growing regions as a distinct crop, where the processing
stream of sugar beet for energy would differ from that for sucrose in a few subtle
ways, such as grinding and pressing pulp for juice extraction rather than diffusion
from sliced beets for sucrose recovery [ 24 ].

Genetic Resources

Extensive germplasm resources exist for Beta vulgaris and related species. The
USDA-ARS National Plant Germplasm System (NPGS) collection has seed avail-
able through the Germplasm Resources Information Network ( www.ars-grin.gov/
npgs/ ) , with seed stocks maintained at the Western Regional Plant Introduction
Station in Pullman, WA, and duplicates held in long-term backup storage at the
USDA-ARS National Center for Genetic Resources Preservation in Fort Collins,
CO. Approximately 1,900 accessions are currently available for distribution,
including official USDA-ARS germplasm releases, with another 25 % unavailable
for reasons such as reduced viability and low seed quantities, for which seed
increases occur yearly depending on available space. Another

large, well-

maintained collection is the Dutch-German Beta collection with 2,000 accessions

housed at the Institute of Plant Genetics and Crop Plant Research (IPK),
Gatersleben, Germany. An International Database for Beta is maintained by the
Julius K ¨ hn-Institut, Quedlinburg, Germany ( http://idbb.jki.bund.de/idbb )asan
international repository of global network of Beta germplasm holdings. Each of
these holdings represents a diverse collection of wild species, crop types, landraces,
and USDA-ARS released germplasm. Efforts to characterize this germplasm have
been ongoing for a decade or more, mostly for disease resistance traits [ 25 ]. Core
collections have been defined in collaboration between US and European gene
banks.
Beets are typically outcrossing, enforced by a complex system of self-
incompatibility, and genetic diversity is high within B. vulgaris [ 26 , 27 ]. Allelic
diversity among cultivated species may be ~25 % of that found in wild germplasm
[ 28 , 29 ]. This underutilized diversity is relevant for germplasm enhancement
[ 30 ]. Breeding is typically through population improvement approaches, and selec-
tion has reduced the level of heterozygosity in USDA-ARS germplasm releases
over time [ 31 ]. Relatively few morphological mutants have been described in beets
[ 32 , 33 ], and, unfortunately, genetic stocks for most of these are no longer available.
Newer approaches involving mutagenesis [ 34 ], TILLING [ 35 ], and recombinant
inbred lines [ 36 ] are being used to uncover and tag genetic variation at individual

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