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Results and
Discussion
The onset of pollen germination was variable among the cross
combinations (Table
1). There was
only one cross which showed germination of pollen grains after 5min,
whereas pollen in six crosses started germination after 30min, and in
the other five after 60min. There was no correlation between pollen
germination and seed set. Some crosses with comparatively high pollen
germination showed a poor seed set, while others in which pollen
germination were poor showed a high seed set. Therefore, a good
pollen germination may not ensure a good seed set.
The emergence of pollen tubes on the bifurcated hairy stigma and
style could be observed at different timings in different crosses.
When pollen tube grew faster, there was a good seed set and
vice-versa, except in common wheat x barley, ie, UP 2121 x Karan 265,
UP 2121 x Karan 4 and UP 2121 x UP 2121 (Table
1). Pollen tube
growth was very slow (99 micro-m at 30min after pollination) in durum
wheat x barley and the seed set was also very poor (4%). When common
wheat was crossed with barley, no such correlation was observed. In
this case less seed set may be due to comparatively higher abnormal
pollen tubes. Sudha (1991) reported a highly significant and positive
correlation between pollen tube growth and seed set in wheat x barley
crosses.
A study was made on the development of pollen tubes in different
crosses to find out whether the disturbance of pollen tube growth was
due to the abnormal development of pollen tubes. A striking
aberration was swelling of pollen tube tips filled with densely
stained cytoplasm. The degree of the swellings was variable. Other
aberrations observed were wrong direction of pollen tubes/growth,
swelling of the pollen tube tips and coiling of pollen tubes. The
ratios of the abnormalities recorded after 24h of pollination were
much higher in intergeneric crosses than in selfings
(Table
1). There was no
direct correlation between pollen tube abnormalities and seed set.
Pollen tube inflation and bursting have also been shown in
incompatible hybridizations of wheat x rye (Tozu 1966 Zeven and
Heemert 1970, Lange and Wojciechowska 1976, Jalani and Moss 1980,
Singh and Khanna 1988) and barley x wheat (Fedak and
Jui 1982, Sudha 1991).
Within the selfings, barley showed high seed set. Since wheat
selfings were made at the 'end of the crossing programme when the
temperature was getting high, a low seed set of wheat may be
attributed to that. A good seed set was recorded in barley
x wheat
crosses (53.7-74.9 per cent) while it was poor in the reciprocal
crosses (2- 6.7 per cent). These results were also reported by Fedak
(1980), Islam et al (1981) and Sudha (1991).
An increased seed set was observed after application of three
hormones (GA3, IAA and KIN) in all the crosses except
Karan 4 x PBW 34 and Karan 265 x UP 2121 (Table
2). Kinetin
seemed to be more effective as it increased seed set over control in
eight out of the twelve crosses. This was followed by GA3
(seven out of the twelve crosses) whereas IAA was the least effective
(four out of the twelve crosses). IAA may not be useful in
wheat-barley crosses as it increased seed set over control in only
wheat x barley, ie, UP 2121
x Karan 265 where
GA3 gave a still higher seed set.
In wheat x barley crosses where seed set in the control is quite low
as compared to the reciprocal cross, GA3 increased seed
set over the control in 3 out of 4 crosses whereas KIN increased it
in only 1 out of 4 crosses.
In barley x wheat crosses enough seeds were obtained in the control
so the utilization of hormones may not be so important as in the
reciprocal cross. In this cross KIN increased seed set over control
in 3 out of 4 crosses as compared to 1 out of 4 with GA3.
It is suggested that spray of GA3 would be more useful
while making wheat x barley crosses whereas KIN may be effective in
the reciprocal crosses to get more seed. Kaltsikes and Gustafson
(1986) reported that dousing the floret after pollination with an
aqueous solution of 50 ppm GA3 every day for 4 days helps
increase seed set in triticale.
In the present study, it seems that pollen tube length is more
related to per cent seed set than the other parameters studied.
Embryo rescue technique was applied by using Murashige and Skoog's
(1962) medium and hybrid plants were obtained, since the seeds have
no endosperms and are filled with liquids.The hybrid 'seeds' cannot
germinate to produce the F1 plants, hence the use of
embryo rescue technique would be useful for transferring desirable
characters from barley to wheat. Further investigations would be
necessary to increase the possibility for obtaining the hybrid plants
by this technique.
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