Agriculture Reference
In-Depth Information
specialized operators or personnel (i.e. hospital radiol-
ogists, etc.) usually carry out the actual exposure to the
radiation.
To use chemical mutagenic agents safely requires a
number of safety features, spelt out in many countries
(and by most suppliers in safety/hazard assessments)
by specific safety protocols. Staff using these chem-
icals should be aware of the advised risks and safety
procedures. Minimum safety will likely require suitable
gloves, protective clothing and safety glasses combined
with '
Good Laboratory Management Practice
'. It is also
important that procedures and equipment are in place
to deal with appropriate disposal of chemicals, and to
contain and clean up any accidental spills of mutagenic
chemicals.
Semi-dwarf rice derived from mutation breeding has
been cultivated over millions of hectares. The barley
cultivar 'Diamant', developed as a gamma ray mutant
of 'Valticky', was selected to have the
ert
dwarfing
gene. It has been estimated that over 150 cultivars
have been released in Europe that have Diamant in
their pedigree. In addition the Scottish barley cultivar
'Golden Promise' also has this mutant dwarfing gene,
is arguably the best cultivar ever released in the country
and has been a major contributor to the Scottish brew-
ing industry. Similarly, mutant durum wheat occupied
over 25% of the Italian wheat acreage in the mid-1980s.
Finally, health concerns about '
trans
fats' in our diets has
prompted many food processors and others in the food
industry to use non-hydrogenated vegetable fats which
are low in polyunsaturated fats. The first canola cultivar
with low linolenic acid, 'Stellar', inherited the fatty acid
desyntheses gene from a German EMS-induced mutant
line coded as M47. Other low linoleic acid mutants
have subsequently been developed using microspore
mutagenesis and now ultra-low polyunsaturated canola
oil cultivars with highly elevated oleic acid content are
commercially available.
Impact of mutation breeding
Mutation derived cultivars have been released as a direct
result of mutagenesis or have used mutant genotypes
as parents in traditional breeding programmes. Since
the inception of mutation breeding over 2250 culti-
vars have been released world wide (FAO/IAEA [Food
and Agricultural Organization/International Atomic
Energy Agency] Mutant Varieties Database). It should
be noted, however that a high proportion of mutation-
derived cultivars released were ornamental plants and
flowers rather than agricultural crops. Over 70% of
these cultivar releases were developed directly from
mutant breeding lines. Most of these cultivars were
developed and released in Asia with 27% being devel-
oped in China and 11% developed in India. Mutation-
induced cultivars are not quite as common in other
countries although over 125 mutant induced cultivars
have been released in the US and 32 in the UK (31 of
which were barley cultivars) in the past 70 years.
Highest mutant cultivar releases were in rice (433),
followed by barley (269), wheat (220), soybean (89),
groundnut (47), maize (32), pea (32), cotton (24) and
millet (24). Only 46 mutant fruit cultivars were released
over this period. Mutant genes were developed mainly
for dwarf stature, improved disease resistance, stress
resistance, herbicide resistance, and improved grain or
oil quality.
Although many have argued that these released cul-
tivars have made little impact on our agricultural
crops, some major positive impacts cannot be denied.
Practical applications
Having decided which mutagenic agent to use and a
suitable mutagenic treatment strategy (i.e. rate and time,
and which plant part to treat) in reality, the physical
treatment of plant cells by a mutagenic agent to induce
mutation is in fact the easy part of mutation breeding.
By far the most difficult aspect of mutation breeding
relates to selecting desirable mutants while avoiding the
subsequent detrimental effects of mutagenesis.
Mutagens are indiscriminating agents and inevitably
produce a complex mixture of mutations. Mutants
selected as having the trait of interest may have also
undergone a range of chromosome structure changes
and non-genetic (or at least non-nuclear) aberrations.
It is also rare that selected mutants have been geneti-
cally altered for the single gene of interest, and there
may be multiple mutation events, most of which have
a negative impact on the normal growth of the plant.
In seed-propagated crops sterile segregants need to be
sorted out and discarded in the first round of selection.
Therefore selected mutants will have been altered in
number of different ways - most of them bad!
