Agriculture Reference
In-Depth Information
Consider the following example of using mutation
breeding techniques in yellow mustard (
Sinapis alba
).
The aim of the breeding programme was to screen a
large number of mutants (derived by chemical muta-
genesis using EMS) that produce lines that were low
in seed meal glucosinolate content. After screening
several thousand lines over a four year period (using
glucose sensitive test tape) eight lines were identified
which showed lower glucosinolates compared to the
non-mutated parent genotype ('Tilney').
However when these eight lines were grown in repli-
cated field trials it was found that all mutant lines
were considerably lower in yield, produced smaller and
less vigorous plants and matured later than the par-
ent genotype (Table 8.1). So exposure to the mutagen
had produced mutations that had affected glucosinolate
content in the manner hoped for. However, it had also
affected other aspects of the genotype so that the selected
lines all appeared to have mutated for other impor-
tant traits. Further crossing and selection was clearly
necessary before an adapted cultivar was developed.
It has to be pointed out that experience suggests that
apart from loss of function alleles, it is usually easier to
find
a new allele than to
create
one. It may be signif-
icant to note that several years of intense mutagenesis
breeding effort to develop yellow mustard lines with
very low glucosinolate content in the seed meal failed
to achieve this objective. Interestingly, the year after the
mutagenesis program was stopped, a gene which almost
eliminated seed glucosinolates in yellow mustard was
identified within a wild
Sinapis alba
population from
Poland!
Initially many plant breeders believed that mutation
breeding would have a revolutionary effect on cultivar
development. Although there are multiple examples,
like those above, of success in mutation breeding, for
many this revolution has not happened and is unlikely to
now do so. Indeed, many believe that mutation breed-
ing is too unpredictable and should only be considered
as a
last resort technique
when all other avenues have
closed. Whether one is a mutagenasist or not, it is appar-
ent that mutagenesis as a plant breeding technique has
its limitations.
The question must therefore be asked as to what are
the circumstances in which mutation techniques can be
useful? To address this question the following points
should be considered.
Mutagenesis is an indiscriminate breeding approach
and generates large numbers of undesirable variants
along with those that are wanted.
•
•
Most successful mutant cultivars and mutation
derived cultivars have resulted in selection for char-
acters controlled by single (or at best a few) genes.
Quantitatively inherited traits are more challenging
in mutation breeding and will require large efforts to
achieve success. If indeed success is ever achieved.
Table 8.1
Seed yield, oil content, ground cover, days from planting to flowering and days
from planting to flower ending of the yellow mustard cultivar 'Tilney', and eight EMS mutants
selected from Tilney with modified seed quality.
Identifier
Seed yield
(kg/plot)
Oil content
(%)
Percentage
ground
cover
1-9 scale
Days to
flowering
(days)
Days to
flower end
(days)
Tilney
27.33
30.1
8.7
54
80
Til.M3.A
7.00
30.5
3.0
59
86
Til.M3.B
22.67
29.2
4.7
58
85
Til.M3.C
12.67
30.4
2.0
60
86
Til.M3.I
17.00
29.7
4.7
59
86
Til.M3.II
15.67
29.7
3.0
60
87
Til.M3.III
9.67
30.1
2.3
59
86
Til.M3.IV
18.67
31.0
3.3
58
86
Til.M3.V
15.33
31.0
5.0
58
86
