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Science Update
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| More Genetic Diversity for
Onions
Onion breeders have developed a new source of cytoplasmic male sterility (CMS).
A CMS line is used as the female parent to produce commercial onion hybrids.
Most hybrid onion seed is produced using a single source of CMS called S
cytoplasm, which traces back to a single plant identified in Davis, California,
in 1925.
Since 1940, commercial onion breeders have relied on the
ARS source of CMS to produce onion
hybrids. But reliance on a single source of hybrid onion seed could lead to a
disastrous scenario in onions similar to the epidemic of southern corn leaf
blight on corn in 1970. The new source of CMS may help diversify male-sterile
cytoplasms, reducing the genetic vulnerability of onions and providing more
stable production of bulb and seed onions at stable costs.
Since the ARS onion breeding program began in 1936, agency breeders have
released more than 40 hybrids and 70 inbred lines of onions to public and
private breeders. They presented the new CMS source at the 1999 National Onion
Research Conference in December.
Michael J. Havey, USDA-ARS
Vegetable Crops Research
Laboratory, Madison, Wisconsin; phone (608) 262-1830. |
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Daily Feedings Boost Catfish Production
Catfish growers who feed their fish each day—rather than every other
day—can increase production. Researchers raised production 30 percent by
feeding 30 percent more feed and offering it daily. This regimen increased
fingerlings' weight by 70 percent. Fingerling growth accounted for the overall
30-percent increases in ponds where young and old fish were raised together.
Weight gains of larger fish were neither helped nor hindered by feeding
frequency.
Until now, some catfish farmers have fed mixed sizes of catfish every other day
when water temperature has risen to 90 °F. That was because daily feedings
in hot weather can deplete oxygen in ponds, creating an unhealthy situation for
the fish. But the installation of highly efficient mechanical aeration can take
care of that problem.
In this 30-week study, researchers stocked 9 ponds at a per-acre rate of 2,000
large fish and 6,000 fingerlings. They supplied as much feed as the fish would
eat either daily or every other day. While fingerlings gained much more by
being fed every day, larger fish gained the same amount under either regimen.
The larger fish apparently made up for not having daily meals by snacking on
the fingerlings, since about 14 percent fewer fingerlings survived in ponds
supplied with feed every other day.
Donald L. Freeman, USDA-ARS
Aquaculture Systems Research
Unit, Pine Bluff, Arkansas; phone (870) 543-8128.
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| Fruit Coatings Forestall
Postharvest Decay
New biocontrol coatings for fruit are being made of reformulated shellac and
sucrose ester, a compound derived by combining sugar with a fatty acid. These
coatings help maintain quality by promoting the growth of beneficial bacteria
and yeasts naturally present on the fruit surface.
Beneficial microbial populations outcompete decay-causing microbes for
nutrients at a critical early stage in the pathogens' development—in
effect, starving them. The chemicals normally used to preserve fruit on its way
to market have been found to kill such beneficials.
Scientists and cooperators with Mantrose Haeuser Co., Inc., of Westport,
Connecticut, have tested both reformulated shellac and sucrose ester coatings
for their ability to reduce development of off-flavors caused by the buildup of
ethanol naturally released by the fruit. Preliminary results from tests on
grapefruit indicate that both coatings allow for a better exchange of oxygen
and carbon dioxide than commercial chemicals permit, with sucrose ester
outperforming reformulated shellac in these tests.
Raymond G. McGuire, USDA-ARS
Subtropical
Horticulture Research Station, Miami, Florida; phone (305) 254-3641.
Plants That Summon Their Own Defenders
When tobacco budworm (Heliothis virescens) and corn earworm
(Heliocoverpa zea) caterpillars chew on certain plants, chemical cues in
their saliva cause the plants to send out defensive signals. Small wasps that
are natural enemies of the caterpillars then follow the signals to find and
sting these pests that are a major problem in cotton, corn, soybean, sorghum,
sunflower, tobacco, and peanuts.
This research builds on previous findings that beet armyworm caterpillars
elicit a chemical SOS response in plants. Interestingly, the budworms and
earworms have been found to produce the same compounds found in the saliva of
beet armyworms. And it seems that plants are able to distinguish which insects
are nibbling on their leaves and give off the proper distress signal to attract
that insect's natural enemy. By studying plant-insect interactions, it may be
possible to develop plant varieties with more powerful chemical defenses
against insect pests.
Consuelo De Moraes,
USDA-ARS Center for
Medical, Agricultural, and Veterinary Entomology, Gainesville, Florida;
phone (352) 374-5912. |
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"Science Update" was published in the
July 2000
issue of Agricultural Research magazine.
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