Module 3: Hybrid Seed Production.wmv

Hybrid rice. Module 3 hybrid seed production. Objectives at the end of this module we will understand. Procedure of cytoplasmic genetic male sterility CMS. Optimum package for hybrid rice seed production and CMS multiplication. Synchronization of parental lines. Roguing. Promotion of exertion of panicle. Application of gibberellic acid. Flag leaf clipping. Supplementary pollination. Harvesting, threshing and processing. Seed drying. Economics of hybrid seed production. Lesson 1. Hybrid seed production and cytoplasmic genetic male sterility CMS procedure. The existing rice hybrids used in commercial production in India are developed by using cytoplasmic genetic male sterility and fertility restoration system CMS system. This system involves three lines namely cytoplasmic genetic male sterile line CMS or A line maintainer B line and restorer R line. Lines for developing rice hybrids. Hybrid seed production using the CMS system involves the following two steps. Production of A line A multiplied by B. Production of hybrid seed A multiplied by R. The B and R lines are multiplied in the same way as inbred varieties. Thus the procedure of hybrid rice seed production in which two different lines including male sterile lines, seed parent and restorer lines, pollen parent are planted alternatively in a certain low ratio in the same field and the outcross seeds are harvested from the male sterile plants. Differs from that of inbred varieties in which only one line is grown and the self-fed seeds are harvested. Therefore in the whole process of hybrid seed production it requires a set of complicated techniques centering on raising the outcrossing rate to obtain a high seed yield. Through extensive trials on different components like suitable locations, seasons, planting time, planting geometry, low ratios, GA3 application and supplementary pollination etc. A package for production of hybrid seed was optimized. A summarized version of the package is given below. The appropriate season for large scale seed production is rubby dry season due to favorable weather conditions such as bright sunshine and absence of continuous rainy days during flowering period and moderate wind velocities to favor cross pollination. The ideal locations for seed production should have well-drained fertile soils with assured irrigation facilities with a mean temperature of 25 to 30 degrees centigrade, relative humidity of 70 to 80 percent and no continuous rainfall during flowering period. Large-scale hybrid seed production in India is concentrated in Karimnagar and Warangal districts of Andhra Pradesh. Synchronization of parental lines. Male and female parental lines of most of the hybrids differ for their days to flowering by a few days to almost 20 to 25 days. This difference in flowering also varies from season to season, location to location and from year to year. Because of this unpredictable variations there are problems in obtaining proper synchronization of flowering of parental lines. To overcome this problem it is necessary to meticulously record data on flowering of parental lines at each locations or seasons in pilot studies and accordingly plan for large-scale seed production. Lesson 2. Roguing exertion of panicle and application of GA. Roguing. Roguing is the removal of undesirable rice plants from the hybrid seed production plots. Undesirable rice plants are those plants either in A or R line rows that differ from plants that are true to type. Roguing helps to prevent the off types from cross pollinating the true to type A line plants and thus enhancing the purity of hybrid seed. The undesirable plants come from many sources. They may be voluntary plants from the previous crop. Contamination due to improper isolation also results in the occurrence of off types. Ad-mixing during the process of harvesting, threshing, packing and handling are also other sources from which the off types occurred. Therefore due care is to be taken to remove the off types during the cropping season. Roguing can be done at any time during the crop stage. Off type rogues can be removed whenever they are identified. Earlier the better. The most important stages for roguing are at maximum tillering, flowering and just before harvesting. Roguing before harvest. Remove plants that have normal seed set in A line rows. Remove off type plants that have difference in grain characters like grain shape and size, glooms colour or the presence or absence of awns. Promotion of exertion of panicle. Most of the male sterile lines based on wild abortive WA cytoplasm have imperfect exertion of panicle with the result as much as 15% spikelets remain enclosed in the flag leaf and are not exposed for out crossing. Through following methods the exertion of the panicles can be promoted to a great extent. Application of gibberellic acid GA3. It is an efficient and effective growth hormone which stimulates the cell elongation. Thus can be used to enhance panicle exertion in CMS line. Besides GA3 has the following favourable effects. Increases the duration of florid opening, increases stigma exertion and receptivity, promotes plant height, influences flowering and hence flowering in parentin lines can be adjusted. Widens the flag leaf angle, promotes exertion and growth rate of secondary and tertiary tillers. In hybrid seed production plots of rice 5 to 10 percent panicle emergence stage is most appropriate for first spring 40 percent and the remaining 60 percent of GA3 should be sprayed on the following day. The ideal time for spraying is from 8 to 10 a.m. and from 4 to 6 p.m. Spraying should be avoided during cloudy weather and when the windy velocity is high. A dose of 45 to 60 grams per hectare of GA3 is optimum. The hormone does not dissolve in water and it should be dissolved in 70 percent alcohol. 1 gram of GA3 in 25 to 40 milliliter of alcohol. Lesson 3 flag leaf clipping and supplementary pollination. Flag leaf clipping. Normally the flag leaves are erect and longer than the panicles and they come in the way of easy pollen dispersal thus affecting the out crossing rate. The clipping of flag leaf helps in free movement and wide dispersal of pollen grains to give higher seed production. The flag leaf should be clipped when the main comes are in booting stage. Only half or two-third portion of flag leaf should be removed. However flag leaf cutting is not advisable in the plots infested with diseases as this operation may spread the disease further. Supplementary pollination. Rice is basically a self pollinated crop and hence there is a need to go for supplementary pollination in order to enhance the extent of out crossing. Supplementary pollination is a technique of shaking the pollen parent so that the pollen is shed and effectively dispersed over the airline plants. Supplementary pollination can be done either by rope pulling or by shaking the pollen parent with the help of two bamboo sticks. Timing and frequency of supplementary pollination is very important. The first supplementary pollination should be done at peak anthesis time that is when 30 to 40 percent of the spikelets are opened. This process is repeated three to four times during the day at an interval of 30 minutes. Supplementary pollination has to be done for 7 to 10 days during the flowering period. Lesson 4- Harvesting, threshing and processing, seed drying and economics. Harvesting, threshing and processing. From the point of view of maintaining high purity extreme care is needed while harvesting, threshing and processing of the hybrid rice plots. Seed drying. Seed drying helps seeds maintain their ability to germinate and their vigor for a longer period. Drying controls mold growth and the activity of the other organisms that reduce the quality of stored grain. Drying reduces seed discoloration. Seeds can be safely stored when they have been dried to a moisture content of less than 13 percent. Economics of hybrid seed production. The hybrid rice seed production is fast becoming a lucrative proposition for entrepreneurial farmers. With the average seed yield of 1.5 to 2.5 ton per hectare at an average procurement price of rupees 30 to 40 per kg. The gross returns are rupees 60,000 to 80,000 per hectare. The cost of seed production is around rupees 25,000 to 30,000 per hectare. Hence the net profit by undertaking hybrid rice seed production works out to be rupees 35,000 to 50,000 per hectare. And hybrid rice growers are benefited substantially. Besides hybrid rice seed production generates additional employment for 60 to 80 percent days per hectare. Particularly for rural women in activities like supplementary pollination, roguing etc.