Maximizing AxR Seed Yield Series: Making Your Parental Lines Flower At The Same Time
Hybrid rice seeds are produced by planting male and female parental lines in rows next to each other and allowing them to cross-pollinate. These are harvested from the female plant, which are then planted for hybrid rice cultivation.
Hybrid rice seed production (HRSP) is a tedious yet rewarding endeavor. Hybrid seeds sell at a minimum of about P60 per kilogram. A one-hectare farm that produces 1,500 kg hybrid seeds will have a gross sales of P90,000 while the same field if planted with commercial rice yielding 5,000 kg will have gross sales of about P65,000 based on the current price of paddy rice. While HRSP is more costly than commercial rice planting, the returns would justify the added cost.
However, not all regions and seasons are favorable for HRSP. It is not recommended for wet season planting. So far, there are only two major provinces/regions in the Philippines identified by PhilRice suitable for HRSP- Davao Oriental in Mindanao and Kalinga in Northern Luzon. In fact, farmer-cooperatives devoted to HRSP are in these regions, notably the Davao Oriental Seed Producers Cooperative (DOSEPCO), Kalinga Hybrid Rice Seed Producers Multi-purpose Cooperative, and the Tabuk Hybrid Rice Seed Producers Multi-purpose Cooperative. These cooperatives are stories of successful implementation of HRSP.
Maximizing returns in HRSP involves diligently practicing the major points discussed by your technical representative from the Department of Agriculture, farmers’ cooperatives, or in Pioneer’s case, the field agronomist. We will have a three-part series on HRSP and we will start with the most critical point synchronization of flowering.
It is absolutely important that the male and female parental lines flower at the same time in the field even though they have different growth durations (Figure 2). This ensures optimum pollination of the females by the males by making pollens available during critical flowering period of the female. Parental lines of different hybrids have different duration of the vegetative stage. Hence, the female parent of PHB71, differs in maturity to the female parent of Mestizo I of IRRI. Their male parents would also differ in days to flowering.
Synchronization of flowering is achieved by differential seeding and adjustments by crop management later in the crop’s growth stage. Planting of more than one set of males can also be done.
Differential seeding is adjustment of seeding dates according to flowering, dates or growth duration of the parental lines, referred to as the “nick.”
For example, if your A-line has growth duration of 110 days and your R-line has growth duration of 120 days, you must seed your R-line 10 days before sowing your A line. The delay in sowing the parent with shorter growth duration will help achieve synchronization of flowering for both parental lines.
Seedlings for HRSP are transplanted in rows perpendicular to the wind direction and in row ratios of 2 males: 8 females, or sometimes 1:8, 2:10, 1:10 or even 1:12.
Proper transplanting ensures that delays in flowering are avoided. Usually, experts recommend transplanting one seedling per hill. Unless the seedling dies, there is no difference in yield of a hill transplanted by one or more seedlings.
Transplant 21-day-old seedlings to ensure timely heading and flowering of parental lines. Transplanting older seedlings delays flowering by about half the number of days by which the seedlings are older than 21 days. For example, transplanting 25-day-old seedlings delays flowering, by 2 days. In contrast, transplanting younger seedlings advances flowering by approximately half the number of days by which the seedlings are younger than 21 days. If transplanting delays cannot be avoided, be sure to delay transplanting of both A and R lines.
SOW MALES IN BATCHES
The principle of differential seeding of males in two or more batches is to ensure pollen availability in the field. This technique is particularly useful for male parental lines with very short periods of pollen shedding.
Differential seeding within males usually ranges from 3-10 days, depending on the male’s ability for dehiscence. Differentially-seeded male plants are transplanted alternately in the male rows. In effect, if you have a male parent with a three-day dehiscence period but differentially seeded in two batches with a three-day gap, you will have a collective male plot dehiscence of six days.
ADJUSTMENT OF FLOWERING IN CULTURAL MANAGEMENT
Observe panicle initiation
Differential seeding is not sufficient to achieve optimum synchronization. Weather fluctuations as well as crop management practices can alter the growth duration of one or both parental lines. It is therefore useful to predict flowering date on the basis of panicle initiation. Remember that all rice cultivars have approximately the same duration of reproductive and ripening stages, but differ in the vegetative stage. Since the reproductive stage starts at panicle initiation, flowering date can be predicted by sampling the panicle primordium.
Here are simple steps in observing developing panicle.
• Select the primary tiller and cut it at the base where the stem and root join.
• Slit the stem lengthwise from the base up to the top of the tiller.
• Open the slit immediately above the nodal portion.
• Observe the developing panicle (preferably with a magnifying lens). It is about 1 mm long.
The young panicle undergoes ten developmental stages before emerging from the leaf sheath. Please refer to http:// www.knowledgebank.irri.org/hybridriceseed/default.htm for a detailed illustration of the developing panicles.
Estimate flowering date by panicle primordium stages
For complete flowering synchronization, the male parent should be one stage earlier than the female parent during stages 1, II, and III of panicle development. Both parents should be in the same stage during stages IV, V, VI, and VII. The seed parent should be slightly earlier than the pollen parent during stages VIII, IX, and X of panicle development.
Spray urea and phosphate fertilizers to adjust flowering date
If the female parent is ahead of the male in estimated flowering date based on panicle primordium sampling, spray quick releasing nitrogen fertilizer. Spraying phosphate fertilizer on the male parent and keeping standing water in the field advances the flowering date of the male parent.
Synchronization of flowering is the primary consideration in hybrid rice seed production. While synchronization can be manipulated by differential seeding, corrective measures in cultural management can be employed to counteract the effects of weather fluctuations and crop management practices.