maintainance of genetic purity methods of genetic purity testing

what is genetic purity ? need of genetic purity. maintenance of genetic purity. Seed classes, advantages of genetic purity. conclusion.

1. . . Welcome

2. CONTENT

3. What is Genetic Purity ? Genotypic purity is simply defined as true to type plants / seeds conforming to the characteristics of the variety as described by the breeders. Principle Genetic purity or genuiness of the cultivar is tested by means of heritable characters (morphological, physiological or chemical) of seeds, seedlings or plants.

4. Need of Genetic purity Testing

5. Minimum standards for genetic purity for different class of seeds CLASS OF SEEDS Breeder Seeds Foundation seeds Foundation seeds Hybrids PURITY % 100 % 99 % 98 % 95 %

6. Factors responsible for Genetic purity Loss (kadam ., 1942)

7. Developmental Variation: Seed crop is grown in difficult environmental Conditions For several consecutive generations the developmental variations may arise as differential growth response. To avoid or minimize such developmental variations the variety should always be grown in adaptable area

8. 2. Mechanical Mixture: It would be necessary to rogue the seed fields at different stages of crop growth

9. 3. Mutations: It is not of much importance as the occurrence of spontaneous mutations is very low i.e. 10-7. If any visible mutations are observed they should be removed by rouging.

10. 4. Natural Crossing: It is an important source of contamination in sexually propagated crops due to introgression of genes from unrelated stocks/genotypes. The extent of contamination depends upon the amount of natural cross-fertilization natural crossing is main source of contamination in cross-fertilized or often cross-fertilized crops. The extent of genetic contamination depends on breeding system of the species, isolation distance, varietal mass and pollinating agent. To overcome the problem of natural crossing isolation distance has to be maintained.

11. 5. Genetic drift: When seed is multiplied in large areas only small quantities of seed is taken and preserved for the next years sowing. Because of such sub-sampling all the genotypes will not be represented in the next generation and leads to change in genetic composition. This is called as genetic drift.

12. 6. Selective influence of Disease: In case of foliar diseases the size of the seed gets affected due to poor supply of carbohydrates from infected photosynthetic tissue. In case of seed and soil borne diseases like downy mildew and ergot of Jowar , smut of bajra and bunt of wheat, it is dangerous to use seeds for commercial purpose once the crop gets infected. New crop varieties may often become susceptible to new races of diseases and that leads to these varieties may become out of seed production programms . (Proper plant protection - major pests and diseases)

13. 7. Techniques of the Breeder Instability may occur in a variety due to genetic irregularities if it is not properly assessed at the time of release. Premature release of a variety, which has been breed for particular disease, leads to the production of resistant and susceptible plants which may be an important cause of deterioration. When sonalika and kalyan sona wheat varieties were released in India for commercial cultivation the genetic variability in both the varieties was still in flowing stage and several secondary selections were made by the breeders .

14. 7. Breakdown of male sterility: Generally in hybrid seed production if there is any breakdown of male sterility in may lead to a mixture of F1 hybrids 8. Improper Seed Certification It is not a factor that deteriorates the crops varieties, but if there is any lacuna in any of the above factors and if it has not been checked it may lead to deterioration of crop varieties.

15. Maintenance of Genetic Purity during seed Production Horne (1953) had suggested the following methods for maintenance of genetic purity;

16. Maintenance of Genetic Purity during seed Production Steps suggested by Hartman and Kestar (1968) for maintaining genetic purity

17. Methods to assess genetic purity

18. 1. Morphological test In laboratory Examination features of seeds such as length, width, thickness, shape, weight, colour , seed coat colour etc. and comparing them with those of authentic sample. Which are examined with naked eye / with magnified hand lens / with the help of scanning electron microscope

19. Traditional approach to purity testing Morphological traits

20. Morphological test In field The seed sample is sown in the controlled condition with the authentic sample Genetic purity is determined on the basis of observation made on the plant morphological characters with reference to authentic sample. Genetic purity is always expressed in percentage Grow out test

21. CONTENT

22. Limitations of morphological methods Environmental stress conditions often mask specific morphological traits. Large amount of land required. Laborious Time consuming Unfavourable condition, i.e. disease and insect infestation may limit GOT in field Morphological markers are becoming limited in relation to rapid increase in number of varieties, hybrids and transgenics.

23. 2. Chemical tests 1. Phenol test 2. Modified phenol test 3. Potassium hydroxide – 4. Ferrous sulphate test 5. NaOH test

24. Advantages of chemical tests They are quick. They require virtually no technical expertise or training. Relatively inexpensive to conduct. No sophisticated equipments are required. The test permits detection of percentage admixture of other type. Its results are usually distinct and easily interpretable.

25. 3. Biochemical methods Electrophoresis Migration of a charged particle through a medium (agarose, polyacrylamide, starch) under the influence of an electrical field. it is usually carried out in aqueous solution •A mixture of molecules of various sizes will migrate at different velocities and will be separated. The varieties are verified on the basis of banding pattern. 1. By measuring Rm of bands 2. Total number of bands 3. Presence or absence of specific band 4. Intensity of band

26. 4. Molecular Marker A  genetic marker  is a gene or DNA sequence with a known location on a chromosome that can be used to identify individuals or species. Restriction Fragment Length Polymorphism RFLP Random Amplified Polymorphic DNA RAPD Amplified Fragment Length Polymorphism AFLP Variable Number Tandem Repeat VNTR Oligonucleotide Polymorphism OP Single Nucleotide Polymorphism SNP Allele Specific Associated Primers ASAP Inverse Sequence-tagged Repeats ISTR Inter-retrotransposon Amplified Polymorphism IRAP

27. General methodology for molecular markers

28. Advantages and limitations of molecular techniques It has very large number of polymorphism development as compared to the bio-chemical markers. Residual heterozygosity can be detected. It is reliable to all crops. Very fast method. Sophisticated instruments required. Very costly.

29. Advantages of genetic purity 1. It is helpful in plant variety protection, registration, certification and patents 2. to detect the even the minute genetic differences between cultivars visa-a-versa for existence of novelty among essentially derived varieties 3. Assurance of genetic purity for ensuring better agronomic performance and predicted expectations 4. Prevention of misappropriation and willful admixture of seed/ cultivars at commercial or farmers level

30. Conclusion Combination of different methods make them accurate. Chemical test creates very less polymorphism and are crop specific. Hybrid purity testing is possible before the sowing of crop . Genetic purity analysis is the important Factor for quality seed For farmer – No loss because of poor seeds + Higher returns For

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