Table
1: Analysis of variance for pollination time Vs
cut and uncut treatments
Table
2: Per cent seed set in cut and uncut (palea and lemma) treatments of CHA male
sterilized WH 542
A
chemical hybridizing agent, CH 9832 was used to induce male sterility in WH 542
during Rabi 98-99 on female fertility
and extent of cross-fertilization. Starting from 24th
day after CHA spray,
6 spikes with and without cutting of palea and lemma were pollinated for 13 days
in a sequence. Seed set pattern indicated that florets of male sterile wheat
open twice to facilitate cross-fertilization. Maximum seed set of 95.4% was
obtained and this clearly indicated that CHA was not interfering with female
fertility especially stigma receptivity. Reasonable amount of seed set in uncut
treatment showed non-hindrance of palea and lemma in out crossing. Relatively
good seed set obtained upto six days indicate that there was extended stigma
receptivity.
Key
words: chemical hybridizing
agent, palea and lemma, seed set, stigma receptivity, wheat (Triticum
aestivum)
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Introduction
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The needed targets of 110mt of
wheat production by 2020AD can be attained via new innovative techniques like
exploitation of heterosis through hybrid wheat. The cost of hybrid seed
production will play a crucial role in commercial viability of hybrid wheat
technology. In this context, to optimize the hybrid wheat technology, better
understanding about floral biology of chemically induced male sterile wheat is
essential. The information on process of floret opening and length of stigma
receptivity will throw some light on male–female time of sowing for parental
synchrony and need of supplemental pollination. Very little information is
available world wide on this aspect. Earlier studies on floret opening indicated
the importance of lodicules, which collapsed and allowed the carpels of sterile
florets continue to grow, forcing the lemma and palea apart resulting in floret
opening which lasts for 2 days or more (Hoshikawa 1960, De Vries 1971). The
objective of the present investigation was i) to study floret behaviour in CHA
induced male sterile WH 542 and; ii) to study the effect of CH 9832 on female
fertility.
Material
and Methods
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Fifteen
plots of two-meter length of WH 542 were sown on Dec.5th 1998. Male
sterility was induced by spraying chemical hybridizing agent CH 9832 at 10-12mm
spike length stage coinciding with stage 23 (Zadoks et al, 1974). At pre-emergence of spike from the boot leaf (stage
51), 20 spikes in each plot were bagged. Later from stage 53 onwards six
different spikes were pollinated everyday for 13 days till stigma lost its
receptivity. Among the six spikes pollinated, the palea and lemma were cut in
three spikes and pollinated while the remaining spikes were pollinated without
cutting. Observations were recorded for number of seeds set in cut and uncut
florets as well as in untreated carefully hand emasculated cut florets as check.
The data was computed for analysis of variance after Arc Sine transformation.
The
analysis of variance revealed that significant differences were found in
treatments (cut and uncut) with respect to seed set over a period of 13 days
(Table 1). In cut treatments, cutting of palea and lemma ensured floret opening
artificially by means of expoxure of stigma and style to incoming pollen. The
amount of seed set formation without cutting of palea and lemma in uncut
treatment mimics natural floret opening and indicates about longevity of stigma
receptivity.
The
per cent seed set in cut and uncut treatments vis-a-vis pollination time (day of
pollination) differ significantly. The maximum seed set of 95.4% was observed in
cut treatment at Zadoks decimal growth stage 63 (Table 2). And
reasonably good seed set was observed between Zadoks decimal growth stages
62–67. In uncut treatment maximum seed set (75.8%) was observed during Zadoks
decimal growth stage 65 (29 day after CHA spray). Seed set pattern in
uncut treatments indicating that male sterile wheat florets open twice. It was
found that first cycle of floret opening continues only for shorter period
because of which seed set per cent of 33.4 was observed on Zadoks decimal growth
stage 62, followed by close of florets for about one day. Correspondingly, high
seed set on 27 day after CHA spray in cut treatment indicates that stigma was
receptive even the florets were closed (Table 2).
In
our experiments, the second cycle of floret opening continues for about 6 days
(64 - 67 Zadoks decimal growth stages) with seed set ranges from 24.2% to 75.8%
which was normally sufficient for cross-fertilization to takes place. The second
cycle of floret opening process starts after an interval of 2 days or more from
first floret opening (Hoshikawa 1960). This second opening lasts for a period of
several days (De Vries 1971) and is normally sufficient for cross-fertilization
to take place provided viable pollen is available. Hence the results of the
present investigation where CHA was used to generate male sterility was in
conformity with works of Hoshikawa (1960) and De Vries (1971). Analysis of
variance showed that cutting of palea and lemma was not going to make any
difference in seed set in comparison to uncut treatment (Table 1). Second cycle
of floret opening, in search of pollen promotes cross-fertilization. Hence, it
can be inferred that palea and lemma are not a hindrance to cross-fertilization
in male sterile wheat. Further, synchrony problem between male and female
parents can be avoided by adjusting planting of male and female in such a way
that male may reach anthesis little latter than female in order to coincide
pollen shedding with the second cycle of floret opening. Seed set of about 95.4%
in this CHA sprayed WH 542 indicates that CHA was not interfering with female
fertility and stigma receptivity.
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ACKNOWLEDGEMENT
We
thank Indian Council of Agricultural Research for funding under A P CESS fund
project on “Development of Hybrid Wheat” under grant no.2(11)/96-FCI
dt.5-1-98 and acknowledge the help rendered by Sh Vineet Kumar and Sh Manoj
Srivastav, Research associates at various levels.
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De
Vries A Ph 1971. Flowering biology of wheat, particularly in view of hybrid seed
production - a review. Euphytica 20:152
-70.
Hoshikawa
K 1960 Studies on the reopened floret in wheat. Proceedings
of crop science society of Japan 29:103-6.
Zadoks.J
C, Chang T T and Konzak C F 1974. A
decimal code for the growth stages of cereals. Weed
research.14:415-21.
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