Breeding of Vegetable, Spice and Tuber Crops

Procedure of mutation breeding

Step1. 1. Choice of material

• The best adapted variety of a crop should be chosen.
• Only one or two features of such variety have to be altered through mutagenesis depending upon the objectives.
• Suppose a variety is high yielding, but susceptible to a particular disease, the objectives of mutation breeding would be to induce resistance to that particular disease in the variety.

Step: 2.Choice of mutagen

• It depends upon the plant parts to be treated. Generally, chemical mutagens are more preferred for seed treatment and radiations for the treatment of vegetative parts.
• The penetration of chemical mutagens can be enhanced dissolving the mutagen in solvents like dimethyl sulphoxide.

Step: 3. Mutagenic treatment

• Plant species- Seeds, Pollens, Buds, Cuttings or Suckers.
• Dose of mutagen –LD 50 refers to a dose of mutagen that kills 50% of the treated individuals
• Duration of treatment- depends on the intensity of radiations or concentration.The seeds are water soaked before treatment. After treatment the seeds or cuttings are immediately planted and pollens are used for pollination. Plants obtained from treated seeds or cuttings are called M1 plants.

Step: 4 Handling of Treated Material

Seed propagated species

• M1 Generation

• Several hundred (500 or more)treated seeds are space planted. All the M1populations are grown using wider spacings for easy identification. Generally the mutants are recessive. All the plants will be chimeras for the mutation present in heterozygous state. About 20 seeds from each M1 plant are harvested separately

• M2 Generation

• About 2000 progeny rows are grown using wider spacings. Oligogenic mutants with distinct features are identified and selected. Only 1-3% of M2 rows may be expected to have beneficial mutations

• M3 generation

• Progeny rows form individual selected plants. Inferior mutant rows are eliminated. If the mutant progenies are homozygous, two or more M3 progenies containing the same mutation. Mutant M3 rows are harvested in bulk

• M4 generation

• A preliminary yield trial is conducted with a promising mutant lines are selected for replicated multilocation trials

• M5-M8 generation

• Selected lines are tested in coordinated Multilocation trials.
• The best performing line is released as a variety
• In case of polygenic traits, identification of character is not possible through visual observations.
  
• The material is tested in replicated trial and screening is done for the character under improvement using appropriate statistical methods
• Inferior plants are rejected in M3 and M4generation based on screening tests and superior plants are bulked to raise next generation.
  
• The homozygous progeny are tested in coordinated trial from M5 to M9 and the best line is released as a variety.