Abstract
The present investigation consisted of two parts. In the
first part an attempt was made to induce seed dormancy in the
non-dormant commercial cultivar of peanut, Dhaka-1 (DA-1) and to
improve the pod and seed size of the same cultivar through
induction of mutation using gamma irradiation and ethyl methane
sulphonate (EMS) treatments. In the second part an investigation
was carried out taking nine peanut genotypes previously developed
in BARI to identify the most stable ones at varied
environments for pod yield, oil and protein content.
Effects of mutagenic treatments were studied in Mi and M2
generations. There was a deleterious effect on germination of the
treated seeds and Mi plant survival. In the severest situation,
over 40% plants died in the field. The root length in the very
young seedlings was slightly reduced consequent to the gamma
irradiation, whereas a stimulatory action was observed as a
result of EMS treatment. However, in both situations the root
length became almost similar to the control by about 4 weeks of
age. Similar situation existed in case of shoot length also.
Flowering was slightly delayed in M1 and M2 generations.
Maturity period decreased by 2-3 days in Mi, and increased by
5-10 days in M2 generations. Up to 50% рollen sterility was
manifested in Mi plants.
Plant height at maturity decreased (by 6.1 - 16.3%) in both
Mi and M2 generations of gamma ray populations, whereas in case
of EMS populations plant height increased in Mi, but decreased in
M2 generation. Number of developep dops/plant decreased (up to
34.6%) in Mi but increased slightly in M2 generation. Pod size
increased slightly in Mi, and a further increase was present in
M2 generation. Pod yield/plant decreased in M (up to 33.9%), but
increased (up to 34.3%) in M2 generation.
On the basis of field and laboratory germination tests, 46
true breeding dormant mutant M4 families were finally selected.
Several agronomically and commercially important characters of
the selected dormant mutants/mutant families were studied in M2,
M3 and M4 generations.
Seeds Of M2, M3 and M4 selected mutants showed a range of
dormancy period, 24-38 days. A longer dormancy period was present
with the progress of growing generation. Pod yield/plant was
slightly higher (by 2-3 g) in most of the selected mutants
compared to the control (17.5 g). All of the selected mutants had
a thicker pod shell and seed coat in a varying degree compared to
the control. In some cases, pod shell thickness increased up to
70% and that of seed coat up to 100% over the control.
Crude wax content in seed coat, water absorption capacity of
the dried pods and, oil and protein content in seeds were
determined in M3 and Ma in a limited samples of the selected
mutant families. Crude wax content in seed coat increased
considerably in majority of the mutant families compared to the
control. All mutants had a reduced water absorption capacity
(51.3-63.1%), against the control having 66.1%. Oil content in
seeds in the mutants was either comparable to or slightly lower
than the control (44.6%). Regarding protein content a few mutants
had a higher protein content (28.4-32.1%) than the control (27.4), others had either similar to or slightly lower protein
content than the control. Along with the selection activities for
dormancy, observation for bold-poddedness and 1arger seed
character were made. Finally a total of 20 bold podded mutant
families were identified. Some commercially important characters
were studied in these selected mutants/mutant families in M2, M3
and M4 generations.
All bold podded mutants had a reduced number of developed
pods/plant than the control. On the other hand, there occurred
considerable increase in pod yield/plant (19.6-24.8 g) in the
mutant families, over the control (17.1g). Pod yield increase
was resulted because of a great increase in pod size and seed
size in the mutants. The range of 100 pod weight of the mutants
was 100.9 to 115.0 g and the control had 80.9 g, and that of 100
seed weight was 41.1-48.0 g in the mutants against the control
having 26.8 g.
Oil and protein content in seeds were determined in 15
mutant families in M3 and M4 generations. Some had a slightly
higher oil and protein content, others had a slightly Iower oil
and protein content than control having 43.1% oil and 27.5%
protein. However, there was no occurrence of increase in both oi
and protein simultaneously in the same mutant family. An inverse
relationship existed with respect to oil and protein content in
the seeds.
In the stability studies part of the present research, pod
yield, oil content in seed and protein content in seed meal were
studied in nine peanut genotypes (G) grown at four locations (L) in three winter cultures (Y). The genotypes differed significantly for these characters in all locations and years. Further,
a significant G-L, G-Y and G-L-Y interactions were present. Mean
yield (x), regression coefficient (b), deviation from regression
coefficient (S2d) and coefficient of determination (R2) for each
character were estimated. These four parameters were used
together to identify the stable genotype(s), following a new
method proposed recently.
With respect to the pod yield in the environments tested, the
genotype G-6 was high yielder with above average stability and
the genotype G-2 was high yielder but with below average
stability. For oil content in seeds, the genotype G-1 had high
oil content with above average stability, and the genotypes G-4
and G-9 both had high oil content but with average and below
average stability, respectively. With respect to protein content
in seed meal the genotype G-7 had high protein content with average stability, and the genotypes G-5 and G-8 had medium protein
content but both with above average stability.