Studies on parental synchronization in flowering for hybrid seed production in onion
(Allium cepa L.)

K. Padmini, R.Veere Gowda1 and  L. B. Naik
Section  of  Seed Science  and Technology
Indian Institute of Horticultural Research

Hessaraghatta Lake Post, Bangalore-560 089, India
E-mail: kpadmini@iihr.ernet.in

ABSTRACT

An experiment was conducted  at the Indian Institute of Horticultural Research, Bangalore, in Rabi season
during 2001-2002 and 2002-2003 to study the flowering of Cytoplasmic Male Sterile Lines CMS (A) and pollinator
lines (C) of onion cv. Arka Lalima for working out effective synchrony in hybrid seed production. Results
indicated that  days to 100% flowering and days to complete flowering in a plant  varied significantly in the
parental lines and C line was  found to be earlier than A line  by 12 days and 25 days, respectively. The duration
of flowering in a plant was also less in C line (23 days) than in A line (29 days). Due to lack of floral synchrony
between parental lines, pollen availability becomes a limiting factor in hybrid seed production in cv. Arka
Lalima. Delay in planting  of C lines   by a week after planting A lines resulted in  synchronised flowering of
parental lines at peak flowering stage. This also resulted in higher fruit set (80%) and hybrid seed yield (15g/
plant) as against planting of A and C lines  simultaneously (29.54% and 0.38g, respectively).

Key words: Cytoplasmic male sterility, flowering, hybrid seed production, onion, synchronization

INTRODUCTION

Onion is one of the important vegetable crops
grown in India under 42 million hectares with a production
of 4.21 million tonnes and productivity of 9.9 million tons/
hectare (National Horticulture Database, 2003). Onion is
one of the pioneering crops in which heterosis was
commercially exploited since early 1930’s (Jones and
Emsweller,1933). In India, Cytoplasmic   Male   Sterile
(CMS)  based  hybrids  were developed in onion.
Synchronisation of flowering of parental lines is absolutely
essential in onion hybrid seed production for effecting
natural crossing in CMS lines (A line ) by pollinators from
pollinator lines (C line) ( Peters,1990). In any hybrid seed
production system using CMS hybrids, supply of adequate
amount of pollen and its continuous  supply  by the pollen
parent until  male sterile lines are in bloom, is important
(Peters,1990). Lack of synchrony in flowering in parental
lines of  onion hybrids has been reported even under
simultaneous planting and identical storage conditions
(Currah,1981). Flowering of onion is initiated by
environmental factors (Pike,1986). In the light of the above,
the present study was undertaken to obtain  information on

the extent of  synchronization possible in respect of various
floral traits of male sterile  and  pollinator lines in hybrid
seed production  of  CMS-based onion hybrid Arka  Lalima.

MATERIAL AND METHODS

A field experiment was conducted to study
flowering behavior in parental lines of onion hybrid Arka
Lalima during the Rabi Season (December) at the
experimental farm of Indian Institute of Horticultural
Research, Bangalore, in  2001-2002. The  seed parent of
hybrid Arka Lalima, namely, CMS line (A line) ms-48  and
pollinator line (C line), Sel-14-1-1 were  raised  for  the
study. A  bulb-to-seed method of seed production  by annual
method  was followed (Yawalkar, 1989). Three plots of
twenty plants each were maintained in both the parents.
Onion bulbs weighing 10-20 g and equatorial diameter of
2.5 to 3.5 cm were cut transversely at the top to one third
to expose the inner scales for early and uniform flowering.
Cut bulbs were smeared with copper oxychloride  to avoid
microbial infection. Cut bulbs of both the parental lines
were planted simultaneously   in  4:1 ratio   such that four
rows of A line alternated  with one row of  C line
(Swarup,1991). Closer planting of 30x30 cm between rows

J. Hort. Sci.
Vol. 2 (1): 47-49, 2007



and plants was adopted as recommended for medium sized
onion bulbs.

Observations were recorded on the number of days
taken for first flowering, days to 50% and 100% flowering
(to start flowering).  For observations on days to complete
flowering, duration of flowering in a plant and the number
of scapes/plant, twenty  plants in each of the parents were
selected  at random. Five umbels from both the parents were
randomly selected to record within an umbel, on   number
of flowers/umbel, duration of flowering in an umbel, days
to 5%, 30%, 50%, 80%, and 100% flowering.

In addition to this, an experiment was conducted
on manipulating date of planting  of parental bulbs  for
effecting  floral synchrony (Atkin and Davis,1954).The
methods employed were: T1- simultaneous planting of
parental bulbs, and, T2- delayed planting of C line by one
week after planting A line. Three plots of twenty plants
each were maintained in each parent. Observations on per
cent plants in flowering  (with opened flowers to effect
natural  crossing of A lines from  pollen  of C line) at the
same time, per cent fruit-set / umbel and hybrid seed yield
/ plant were recorded. Recommended  package of practices
was followed to raise the seed crop.  Statistical analysis
using a  ‘student-t’ test was performed to test the
significance between the parental lines of onion hybrid and
between the two planting dates of parental bulbs.

RESULTS AND DISCUSSION

Flowering behaviour

Pooled data on flowering behavior of parental lines
of onion hybrid Arka Lalima (on simultaneous planting of
A and C lines) in a population and plant is presented in
Table 1.  Perusal of  results revealed that there were no
significant differences between A and C lines up to 50%
flowering from planting. There were also no significant
differences in respect of number of scapes / plant and

number of flowers / umbel between the parents. However,
days to 100% flowering and in the days to complete
flowering in a plant varied significantly between the
parental lines, which has led to problems in synchronized
flowering. The duration of flowering in a plant was also
less in C line (23 days)  compared to A line (29 days).

Data on flowering in an umbel in the parental lines
of onion are presented in Table 2. Differences  between A
and C lines for duration of flowering in an umbel were
significant.  Hence, it is concluded that lack of floral
synchrony between parental lines of onion hybrid Arka
Lalima observed at peak flowering stages of A line limited
natural crossing in A lines in a situation where onion
parental bulbs were planted simultaneously.

Effect of date of planting of parental bulbs  on
synchronisation in  flowering and hybrid seed yield

The effect of planting dates of parental bulbs on
synchronisation of flowering and hybrid seed yield has been
presented in Tables 3 and 4, respectively. Synchronisation
of flowering  at peak flowering was observed in T2: delayed
planting of C bulbs by one week after planting A bulbs
compared to T1: simultaneous planting of parental bulbs.

Table 1. Flowering behavior of CMS and male fertile parental lines in Onion cv. Arka Lalima  for  hybrid seed production

Character 2001-2002 2002-2003 Pooled mean Difference t-test value
A C A C A C between

A and C
Days to first flowering  ** 64 64 69 84 66.50 74.00 7.50 NS
Days to 50%flowering  **  92 87 80 86 86.00 86.50 0.50 NS
Days to 100%  flowering ** 140 136 111 88 126 114 12.00 11.03*
Days to complete  flowering in the plant 140 96.54 122 116 131 106 24.73 5.91*
Duration of flowering in the plant 19.11 21.80 39.06 24.14 29.09 22.97 6.12 3.03*
Number of scapes/plant 4.50 2.86 2.84 2.55 3.67 2.71 0.96 NS
Number of flowers/umbel 166 133 314 265 240 199 41 NS
**  from planting of bulbs (simultaneously)                                                    * P<0.05                                                        NS= Non Significant

Table 2.  Flowering pattern  in onion umbel

Character A line C line Difference t-test value
Days to 5% 5 3 2 2.66*
 flowering
Days to 30% 7 5 2 NS
 flowering
Days to 50% 9 7 2 NS
 flowering
Days to 80% 14 11 3 NS
 flowering
Days to 100% 17 14 3 NS
 flowering
Duration of 20 25 5 3.47*
 flowering in
the umbel(days)
* P <0.05

Padmini et al

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Percentage of plants with open flowers  was 100 in both A
and C lines at 108 days from planting of A line( peak
flowering of both  the parental lines) in delayed planting of
C bulbs by one week after planting A bulbs.

 Thus, there was lack of flowering synchrony in
simultaneous planting of parental bulbs to effect natural
cross pollination. Similar observation of poor co-ordination
of flowering time in synchronous planted bulbs was also

Table 3. Effect of date of planting of parental bulbs  on
synchronisation of  flowering in onion

Days Percentage of plants flowering (with open flowers)
from   at the same time
planting Simultaneous planting of Delayed planting of

parental bulbs C bulbs by one week
after planting A bulbs

A line C line A line C line
73 23.08 18.18 6.67 0
81 7.69 0 63.33 0
88 7.69 36.36 73.33 0
95 30.76 18.18 81.25 100
108 0 0 100* 100*
115 0 0 62.5 100
122 0 0 0 57.14
129 0 0 0 28.6
136 15.39 9.09 0 28.6
140 15.39 18.18 0 0
* perfect synchronization  of flowering in A and C lines

Table 4. Effect of date of planting of parental bulbs on hybrid seed
yield  in onion

          Planting date  Fruit set/ Hybrid seed yield/
umbel (%) plant (g)

T1- Simultaneous planting 29.54 0.38
of parental bulbs
T2- Delayed planting of 80.00 15.00
C bulbs by one week
after planting A bulbs
t  - test value 6.25* 11.12*
* p <0.05

reported by Currah (1981).

With regard to fruit-set per umbel, higher fruit-set
was observed in delayed planting of C lines by one week
after planting A lines (80%) as against simultaneous planting
of parental bulbs (29.54%). Hybrid seed yield per plant
was also highest in   delayed planting of C lines by one
week after planting A lines (15g) as against simultaneous
planting of parental bulbs (0.38g).

The superiority of delayed planting of C lines by
one week after planting A lines results in higher fruit-set
and seed yield per plant and calls for planned dates of
planting and flowering of parental lines for ensuring
synchrony at  peak flowering time.

REFERENCES

 Atkin, J. D. and Davis, G. N. 1954. Altering onion flowering
dates to facilitate hybrid seed production. Bull. Calif.
Agril. Exptl. Stn., 746:16

Currah, L. 1981. Onion flowering and hybrid seed
production. Scientific Horticulture, 32: 26-46.

Jones, H. A . and Emsweller, S. L. 1933. Methods of
breeding onions. Hilgardia,7: 625-642.

National Horticulture Database, 2003. www. hortibizindia.
org

Peters, R. 1990. Seed production in onions  and other Allium
species. In: Onions & Allied  crops. Vol. I. Botany,
Physiology & Genetics, pp162-174.

Pike, L. M. 1986. Onion Breeding. In M.J. Bassett (ed).
Breeding vegetable crops, AVI publishing Co. Inc.
West port, Connecticut, pp 357-394.

Swarup, V. 1991. Breeding procedures for cross-pollinated
vegetable crops. ICAR, New Delhi, India, p118.

Yawalkar, K. S. 1989. Bulb vegetables. In: Vegetable crops
of India, Second Edition, Agri. Hort. Publ.  House,
Nagpur, India, p 370.

(MS Received 24 November 2006, Revised 25 April 2007)

Hybrid seed production in onion

49J. Hort. Sci.
Vol. 2 (1): 47-49, 2007