Steps in Ideotype Breeding
Ideotype breeding consists of four important steps, viz:
1) Development of conceptual theoretical model,
2) Selection of base material,
3) Incorporation of desirable characters into single genotype, and
4) Selection of ideal or model plant type. These steps are briefly discussed below:
1. Development of Conceptual Model:
Ideotype consists of various morphological and physiological traits. The values of various morphological and physiological traits are specified to develop a conceptual theoretical model. For Example, value for plant height, maturity duration, leaf size. Leaf number, angle of leaf, photosynthetic rate etc. are specified. Then efforts are made to achieve this model.
2. Selection of Base Material:
Selection of base material is an important step after development of conceptual model of Ideotype. Genotype to be used in devising a model plant type should have broad genetic base and wider adaptability (Blixt and Vose. 1984) so that the new plant type can be successfully grown over a wide range of environmental condition with stable yield. Genotypes for plant stature, maturity duration, leaf size, and angles are selected from the global gene pool of the concerned crop species. Genotypes resistant or tolerant to drought, soil salinity, alkalinity, disease and insects are selected from the gene pool with the cooperation of physiologist, soil scientist, pathologist and entomologist.
3. Incorporation of Desirable Traits:
The next important step is combining of various morphological and physiological traits from different selected genotypes into single genotype. Knowledge of the association between various characters is essential before starting hybridization programme, because it help in combining of various characters. Linkage between procedures, viz single cross, three way cross, multiple cross, backcross, composite crossing. E.g. Mutation breeding, heterosis breeding, etc. are used for the development of ideal plant types in majority of field crops. Backcross technique is commonly used for transfer of oligogenic traits from selected germplasm lines into the background of an adapted genotype.
4. Selection of Ideal Plant Type:
Plant combining desirable morphological and physiological traits are selected in segregating population and intermated to achieve the desired plant type. Morphological features are judged through visual observation and physiological parameters are recorded with the help of sophisticated instruments. Screening for resistance to drought, soil salinity, alkalinity, disease and insects is done under controlled conditions. This task is completed with the help of scientist from the disciplines of physiology, soil science, pathology and entomology. Finally, genotypes combining traits specified in the conceptual model are selected, multiplied, tested over several locations, and released for commercial cultivation.