This article is an extention of our previous article written by Dr. Vivek Kumar Singh. We suggest you to read the previous two article to understand this knowledge piece in a better form.
This article will talk about the proper management of paddy after the seeds are transplanted.
Weed management
Use of chemical herbicides within 3 to 4 days after transplanting the male lines is recommended.
Optimum fertilizer management
Application of farmyard manure (FYM) at a rate of least 10 t/ha and a fertilizer dose of 120: 60: 40 kg/ha NPK is recommended in the main field. In order to achieve optimum fertilizer-use efficiency, it is recommended that the fertilizer be placed in the root zone with split application: one basal and two top dressing, at tillering and at panicle initiation. In general, split application of N will prolong the pollen supply of the male line and increase tillering capacity. One heavy N application results in a leafy crop, whereas controlled N levels during middle and late crop growth stages prevent excessive growth of flag leaf and provide good aeration and sunshine, which is good for pollen spread.
Rice crop normally suffers from zinc deficiency; application of zinc sulphate at a rate of 50 kg/ha provides the necessary supplement.
Water management
Following transplanting, the main field should be irrigated or drained based on the growth stage of the crop:
Up to the third stage of panicle development: shallow (2-3 cm).
From the third stage of panicle development to heading: about 5 cm.
From heading to grain filling: no shortage of water.
One week before harvesting: water drained out.
Ideal synchronization
For optimum synchronization of flowering, the female parent should flower 2-3 days earlier than the male parent.
If A and R lines have the same growth duration, the A line should flower 1-2 days earlier than the R line in all panicle developmental stages.
If the A line has shorter duration than the R line, the R line should be one stage earlier than the A line during the first three panicle development stages.
If the A line is longer than the R line in growth duration, the A line should be 2-3 days earlier than the R line during the first three panicle development stages.
Adjustment of flowering
If the difference in predicted flowering is more than 3 days between the parental lines, measures should be taken to synchronize flowering. The application of quick-releasing N fertilizers on an early-developing parent in the early panicle development stages tends to delay flowering. Similarly, spraying phosphatic solution (1%) on the later-flowering parent tends to enhance flowering by 2-3 days. If the pollen parent (R line) reveals a tendency towards heading earlier than the seed parent (A line) after the third stage of panicle initiation, root zone placement of N fertilizer is helpful in delaying panicle development.
Leaf clipping
Leaf clipping of A and R lines is helpful for better out-pollination and seed set. Long and erect flag leaf may obstruct pollen dispersal from the R to the A line and affects the out crossing rate. Flag leaves should be clipped off in such cases, when the main culms are still in the boot leaf stage. Flag leaf clipping gives uniform distribution of the pollen over A line plants. However, it is not advisable to perform leaf clipping in areas where diseases such as bacterial leaf blight, sheath blight and bacterial leaf streak prevail, as they may spread further and reduce seed yield.
Use of GA3
GA3 is used to enhance panicle exertion. Female lines with WA cytoplasm have poor or incomplete panicle exertion. Spraying GA3 not only helps exert the panicle but also increases the duration of floret opening, improves stigma exertion and stigma receptivity, and widens the flag leaf angle. Spraying GA3 increases plant height by 10-15 cm and it can also be used to adjust the plant height, in particular of R line in relation to A line. In India, a dose of 50 g GA3/ha has been found to be optimum (30 g GA3 sprayed at 5-10% heading and another 20 g GA3 1 day later, i.e. a 1-day gap between the two sprayings). If the male line is no higher than the female line, it is advisable to give one extra dose of GA3 to the R line to increase its plant height. GA3 should preferably be sprayed in the evening (15.00-18.00 hours) and on sunny days.
Supplementary pollination
Rice is basically a self-pollinated crop. Supplementary pollination serves to enhance the outcrossing rate in order to increase seed set. Supplementary pollination should be done by shaking the pollen parent with the help of ropes or sticks so that the pollen is shed effectively on A line plants. Supplementary pollination needs to be done 3-4 times at 20- to 30-minute intervals and should be continued for 10-12 days during flowering. With improved management of parents and effective supplementary pollination, hybrid seed yield can be increased significantly.
Purity of the hybrid seed is top priority for the production of quality seed. Roguing of off-types and voluntary plants at several stages is essential for obtaining physical and genetic purity. Roguing is the removal of undesirable rice plants from both parents (male and female). Undesirable plants include off-types (eg. maintainer or B-type plants in A line). Off-type plants can be identified by their morphological characters (eg. height, leaf size, leaf shape and colour, panicle shape, panicle size and pigmentation) in the late vegetative/early flowering period. B line plants with similar morphological features to A line plants can be identified by their plumpy anthers, completely exerted panicle and 3-4 days earlier flowering compared to the A line. These plants in the A line row must be uprooted as soon as they are identified. Roguing at an appropriate time (flowering initiation) ensures good seed quality. Roguing is normally done from the vegetative to the flowering stage.
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