RAJA

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SYNTHETIC SEED Submitted to: Dr. H.L.Dhaduk Asst. Res. Scientist College of Agriculture JAU, Junagadh Submitted by: Raja Tomer Roll No. 48 Fourth Semester College of Agriculture AN ASSIGNMENT PRESENTATION ON “BREEDING OF FIELD CROPS(1+1=2)” AG. BOT. 4.4

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INTRODUCTION: Synthetic or artificial seeds have been defined as somatic embryos engineered for use in the commercial propagation of plants. Synthetic varieties is developed by intermating in all possible combinations a number of inbred lines with good combining ability and mixing the seed of F1 crosses in equal quantity is referred to as synthetic variety. Synthetic seeds are single encapsulated somatic embryos. The term, “EMBLING” is used for the plants originated from synthetic seed. The use of synthetic varieties for commercial cultivation was first suggested in Maize (Hays & Garber, 1919). Frequently, Na- alginate is used for the encapsulation of embryo.

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OBJECTIVE: To develop a clonal propagation system that will enable the vegetative propagule to be stored for long periods of time. Enable multiplication of the plant.

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FEATURES OF SYNTHETIC SEED Relevance: These are relevant to cross pollinated crops. E.g. Maize, Pearlmillet, Alfalfa, and many more. Base material: It can be developed from inbreds, clones, open pollinated varieties or end products of recurrent selection. Genetic concept: The basic concept is exploitation of heterosis or hybrid vigour. Such varieties are constituted from good general combining inbreds. Synthetic exploits more of additive gene action. However, synthetic seed utilizes the heterosis partially because some level of inbreeding takes place in later generations.

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Genetic constitution: Synthetic seed consists of several heterozygotes initially but subsequently it is also maintained by open pollination so some degree of selfing occurs resulting in fixation of some genes. As a result, in later generations it consists of heterozygotes and homozygotes. Adaptation: Highly adaptable to environment as constitutes polymorphic and stable population. Disease resistance: Have better resistance to plant disease due to their heterogenous nature and broad genetic base. Yield level: Yield of Synthetic seeds is always higher than the open pollinated parental variety but lower than the yield of single and double cross hybrids.

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PRODUCTION OF SYNTHETIC SEED Isolation of explant: Healthy organ made of diploid cell is selected as explant to initiate the tissue culture. These explants are submerged for 30 minutes in2% sodium hypochlorite for sterilization. After sterilization these explants are rinsed with distilled water for at least 2-3 times and kept in sterilized container after proper drying. Inoculation of explants: In aseptic conditions, with sharp scalpel cut pieces of 1 mm thickness or diameter. Then transfer these pieces in test tube containing MS medium with chemical inducing callus formation and somatic embryogenesis.

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Isolation of somatic embryos: Calli formed from incubated test tubes are observed for embryonic calli. Somatic embryo having torpedo and globular structures are isolated. Encapsulation of somatic embryos: Somatic embryos are immersed in calcium free MS medium containing 2-3% Na aliginate supplemented with 1-3% sacchrose at 5.7 pH. This solution with somatic embryos is drooped in 30-100 mm calcium nitrate solution for encapsulation. It takes 20 minutes for hardening and then these beads like structures are gently rinsed with deionized water for 10 minutes and autoclaved at 121˚c for 20 minutes. Storage of synthetic seed: Hydrated synthetic seeds can be stored as such or may be dehydrated by drying in water soluble plastic resin and hardened wafers to keep only 6% water. Seeds can be stored in dark for 3-7 weeks at 25±1ºc.

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ENCAPSULATION PROCESS

THE MORPHOLOGICAL STAGES OF SOMATIC EMBRYO DEVELOPMENT IN ALFA ALFA (Medicago sativa L.) : 

THE MORPHOLOGICAL STAGES OF SOMATIC EMBRYO DEVELOPMENT IN ALFA ALFA (Medicago sativa L.)

THE ALFA ALFA TISSUE CULTURE SYSTEM USED TO PRODUCED SYNTHETIC SEED : 

THE ALFA ALFA TISSUE CULTURE SYSTEM USED TO PRODUCED SYNTHETIC SEED

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DESICCATION TOLERANCE: Desiccation tolerance is a quantitative characteristic not a qualitative one. It can be induced by a pretreatment with ABA or stress to elicit the desired response. The type of pretreatment used, the duration for which it is applied and the stage of embryo that is treated are critical factors. For 3 days in 20 mm ABA is sufficient to induce tolerance, but chilling requires almost 3 weeks.

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OVERVIEW OF DRY SYNTHETIC SEED PRODUCTION: After pollination, a zygotic embryo of a dicotyledonous species develops through a series of morphological stages termed globular, heart and torpedo. Cotyledons develop and expand as the storage reserves of protein, starch and/or oil are deposited. Before the embryo achieves its maximum weight, it acquires the ability to tolerate drying. Then, the seed's vascular connections to the maternal plant are severed, it stops importing nutrients and it begins to lose water. Once they are hydrated, germination commences culminating in the emergence of a radicle and then the mobilization of the storage reserves by the seedling.

Fig.1 SCHEMATIC REPRESENTATION OF THE MAJOR STAGES IN ZYGOTIC EMBRYO DEVELOPMENT FROM POLLINATION TO GERMINATION : 

Fig.1 SCHEMATIC REPRESENTATION OF THE MAJOR STAGES IN ZYGOTIC EMBRYO DEVELOPMENT FROM POLLINATION TO GERMINATION

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ADVANTAGES (Synthetic seed for Commercial Crop Production) Propagation of variety of crop plants, especially crop for which: True seeds are not used or readily available for multiplication (eg. Potato) or True seeds are expensive (eg. Cucumber) Hybrid plants (eg. Hybrid rice) Vegetatively propagated plants which are more prone to infection (eg. Day lily, Garlic, Potato, Sugarcane, Sweet Potato, Grape, & Mango). Multiplying genetically engineered plants (transgenic plants) somatic and cytoplasmic hybrids (obtained through protoplast fusion techniques) sterile and unstable genotype.

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Besides this; Useful material for presentation of desirable elite genotypes (Cryopreservation). More adaptable to environmental changes than hybrids due to greater variability and broad genetic base. Much cheaper than single or double cross hybrids, so easily affordable. No need to purchase fresh seed every year. Farmer can use their own saved seed for 4-5 years.

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GERMINATION AND SEEDLING VIGOUR: Dry somatic embryos lack the vigour normally associated with seedlings from normal seeds. The reason for this is not obvious. Prehydration of the somatic embryos in a moist atmosphere (100% relative humidity generated in a sealed chamber over water) for 24 h improves the vigour of some but not all batches of somatic embryos. The most probable cause of poor seedling vigour is abnormal apical or plumule development.

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Figure 2. Germination and conversion frequencies (%) of dry alfalfa somatic embryos and seeds. Data from Lai et al. (1995).

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APPLICATIONS: Production of hybrids in alfalfa. In cross pollinating species, this technology might provide an alternative way to store germplasm instead of a field or greenhouse nursery. Store genetically heterozygous plants. By making cuttings of the plant as a means to propagate the plants which are sterile and do not set seed. Enable long-term storage of some tropical species that produce recalcitrant seeds that can not be dried, and long term storage of these species in seed banks is not currently possible. By the short term storage of propagules to enable the synchronized planting of commodities in a greenhouse.

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THANK YOU