Written by Maritha C Manubay
Researchers at PhilRice have determined that the production of hybrid rice seeds is also dependent largely on timing, particularly the flowering stage.
The couple Democrito B. Rebong II and Anna Theresa Isabel O. Rebong, who are both researchers at PhilRice, in their study The flowering behavior of NSIC Rc204H (Mestizo 20) parent line for optimum synchronization and high seed yield, focused on the flowering behavior of Mestiso 20 parent lines to aid in achieving perfect synchrony necessary for high yield seed production.
Rebong II emphasized synchronicity, or the moment when everything seems to come perfectly together, in his study.
“In the production of Mestizo 20, one of only two two-line hybrids in the Philippines, the male and female parent lines should have reached the flowering stage at the same time. Just like in marriage, both male and female should be ready,” he added.
When parent lines S and P (female and male, respectively) have different flowering course, adjust both parents: delay the flowering of the parent which flower earlier and advance the flowering of the parent indicating late flowering.
The female parent head (emergence of top most floret from the flag leaf) flowers seven days earlier than the male parent, but it will take her two days before flowering (opening of florets); while it would only take half a day for the male parent to flower.
Thus, said Rebong II, to attain flowering synchronization, the male parent should be planted just 5 days after the planting of the female parent.
“But timing is not everything, it has to be good,” said Rebong II.
Precision in Synchronization
Even fertilizer application should be in sync with precision.
In the case of Mestizo 20, the flowering duration of the male parent line is longer than the female.
“The flowering duration of the female parent line takes only six days, while the flowering of male parent line is gradual even if it has longer duration of 10 days,” said Rebong II.
In terms of flowering peak, the female parent line, which flowers only in six days, reaches its peak from the third to fifth day. On the other hand, the male parent line reaches its peak from the second to sixth day.
If the female parent line waits too long before it receives pollens from the male parent, then its flowers may close in no time; thus, the parent lines will not produce any seed set.
To help increase receptivity period of stigma, the part of the flower responsible for germination, the researchers recommend GA3 application to female parent line. Gibberelic acid, otherwise known as GA3, is a plant growth hormone which also stimulates cell elongation and advances the panicle exertion of the female line.
Male parent line also needs double dose of GA3 to be taller than the female parent line.
“It is necessary for a male parent line to be taller than female so that when it is time for supplementary pollination, the male parent will be able to give pollens to all female parent line,” said Rebong II.
Supplementary pollination is a method of shaking the male parent at the time of flowering peak, so as to disperse pollen grains and to increase the seed set on the female parent.
As observed by the researchers, the peak of floret opening for both parents is at 10:00 in the morning.
“So as early as 8 am, farmers should start supplementary pollination using 1-centimeter diameter rope along the two columns of P-line enough to supplement pollens to the 8-column S-line,” the researchers suggested.
It is also advisable that before doing supplementary pollination, dew in the P-line should be removed to increase the temperature of the panicle and promote early opening of the floret. This is because spikelet of P-lines observed to flower one hour later than the S-lines.
Supplementary pollination is done everyday within the flowering period.
Synchronization as a Tool
“Understanding that synchronized flowering of parental lines is very crucial, seed growers can learn to use it as a tool to increase the level of hybrid rice seed yield,” said Rebong II.
For the researchers, synchronized flowering requires a lot of prediction, instinct, and adjustments. Failure to get good synchronization may result in yield losses. Thus in every timing, the synchronization should always be made good.