Manipulation for Achieving Flowering Synchrony for Hybrid Seed Production
Authors: Rajesh Kumar Sharma1, Mamta Nehra2 and B S Tomar1
1ICAR-Indian Agricultural Research Institute, New Delhi-110012
2GB Pant University of Agriculture and Technology, Pantnagar-263145


Introduction:

In the hybrid seed production, seed yield and its quality attributes can be increased through proper synchronization of flowering of parental lines and optimum female to male parental rows. The hybrid seed is produced generally by planting the parental lines alternating each other at a definite row proportion. This planting proportion of rows decides the amount of hybrid seed produced and is influenced by vigour of the parents (male and female) and especially the pollen production ability of male parent. To get more hybrid seed, one may be tempted to put more number of female rows without taking care to supply adequate pollen to all seed parent rows. The optimum planting ratio worked out for one hybrid may not be the same for another hybrid of a same crop or in different crops. In hybrid seed production the seed parent and pollen parent are planted in a certain row ratio at certain spacing. The row ratio and spacing of pollen parent and seed parent have a distinct effect on the hybrid seed yields. The row ratio or row proportion refers to the number of rows of the male parent (R line) to that of the female parent (A line) in a seed production plot. Suppose if we plant 2 rows of `R' line followed by 8 rows of `A', the row ratio can be taken as 2:8. In hybrid rice seed production plot the recommended male (R) to female (A) row ratio is 2:8. However, the row ratio may vary from region to region, depending on weather, management and parental lines. R and A lines can be planted in several row ratios of 2:8; 2:12; 3:10 etc.

Factors Influencing Row Ratio:

The ratio of pollen parent (R line) to seed parent (A line) is determined by the characteristics of the parental lines.
Plant height of pollinator. Growth and vigour of the pollinator.
Size of the panicles andamount of residual pollen.
Duration and angle of floret openingin CMS lines.
Stigma exsertion of CMS lines

To facilitate out crossing, the rows of male and female in the seed production plot should be perpendicular to the prevailing wind direction expected at flowering time of the parents.
It is simultaneous flowering of male and female parent in seed production is known as synchronization. The synchrony in flowering of male and female parent is termed as nicking. It is essential for commercial large scale production of hybrids in different crops. Synchronization in flowering between the parental lines assumes greater importance as the seed set on female parent depends on the amount of pollen supplied from the male parent during flowering period. Failure to obtain proper synchronization is the most commonly encountered problem in hybrid seed production, resulting in very poor or no seed set at all. The knowledge on flowering behaviour of the parental lines which varies with locations and seasons is very much essential to know the exact difference in days to flowering between the parents. If the flowering gap is more, the problem of non-synchronization could be overcome by staggered sowing of male parent based on the information on days to flowering at each location and season. Some, time in spite of adjusting the sowing date, the parents do not flower at a time because of the differential response of the parents to the change in environmental conditions. Therefore, it is essential to adjust the flowering of parental lines after observing the difference at primordial development stage. If the difference in flowering is marginal, it can be manipulated to some extent by the application of gibberellic acid, urea, phosphorus etc.

Synchronization in Rice

i) Staggered Sowing of Male Parents:
Seedling date is usually determined by leaf age, effective accumulated temperature (EAT), and growth duration.
In general, the period from initial to full heading of a CMS line is 4-6 days longer than for a restorer line.
The first sowing of the male parent establishes the dates for second and third sowing.
The second sowing is done when the leaf emergence on the first sowing is 1:1 the third sowing when the leaf emergence is 2:1.
The second sowing is the main parent.
The planting ratio for sowing at different dates is 1:2:1.

ii) By Fertilizer Application:
Beginning about 30 days before heading.
Young panicle development is compared under magnification. During the first three stages of panicle differentiation, treat the earlier developing parent with quick releasing N fertilizer.
Urea spray @ 2% enhances flowering.
Spray the later developing parent with Potassium dihydrogen phosphate @ 1.5%.
This adjusts development differences of 4-5 days.
Foliar spray of 400 ppm maleic hydrazide (MH) to female parent at panicle initiation delayed the flowering by 3.5 days.

iii) By Water Management:
During later stages of panicle differentiation.
Draining water from the field will delay male parent panicle development.
Higher standing water will speed panicle development.

iv) By GA3 Application:
Spray GA3 @ 75 g/ha with knapsack sprayer in two split doses, i.e. 1st spray on 15-20% earhead emergence and 2nd spray in the next day for enhanced seed set

Synchronization in Sorghum
Adopt Staggered Sowings.
The advancing parent has to be sprayed with 500 mg of maleic hydrazide in 1 litre of water, 45 days after sowing.
1% urea solution can be sprayed on late parent.
One irrigation may be skipped for the advancing parent.
Flowering can be delayed, by spraying CCC (Chloro Chlorine Chloride) @ 300 ppm.

Synchronization in Pearl Millet
Adopt Staggered Sowing of parental line which are early in flowering
1% urea sugar solution can be sprayed on lagging parental line.
Jerking of early parent delay the flowering.
To enhance the growth of lines lagging behind, extra nitrogen fertilization or foliar spray may be used.

Synchronization in Sunflower
Flowering behaviour of parental lines should be ascertained in the hybrid seed production.
There should not be more than 3 to 4 days difference in the flowering to avoid stagger problems.
In case of BSH-1, DRSH-1 and PKVSH-27 hybrid seed production, simultaneous sowing of both parents is recommended.
However, the R line has to be sown 8 days early in case of KBSH-1 and 4 days later in case of APSH-11.



About Author / Additional Info:
I am a PhD student of Seed Science and Technology at IARI New Delhi