Concept of plant ideotype : Concept of plant ideotype A.K. Chhabra and
All copyrights of the figures used in the present presentation lie with the original developers, The information has been gathered here for educational purpose and not for sale. Introduction : Introduction The term ideotype was introduced by Donald (1968).
Acc. to him ideotype: a biological model, which is expected to perform or behave in a predictable manner within a defined environment.
This term has the following synonyms:
Model plant type
Ideal model plant type
Ideal plant type Types of ideotype : Types of ideotype Isolation ideotype
Crop ideotype Slide 4: Isolation ideotypes: it is the model plant type that perform best when the plants are space-planted.
Competition ideotype: this ideotype perform well in genetically heterogeneous population. In case of cereals, this ideotype is tall, leafy, free-tillering plant that is able to shade its less aggressive neighbours. Contd. : Contd. In case of annual seed crops, such an ideotype will include the following features: annual habit, tallness, leafy canopy, tillering or branching, seed size, speed of gerimination and root characters. Slide 6: Crop ideotype: this ideotype perform best at commercial crop densities because it is a poor competitor.
In case of cereals, a crop ideotype is erect, sparsely-tillered plant, with small erect leaves. Several other ideotypes are: : Several other ideotypes are: Market ideotype: includes traits like seed colour, seed size, cooking and baking quality, etc.
Climatic ideotype: includes traits important in climatic adaptation such as heat and cold resistance, maturity duration, drought resistance etc. Contd. : Contd. Edaphic ideotype: Includes salinity tolerance, mineral toxicity/ deficiency tolerance etc.
Stress ideotype: shows resistance to both biotic and abiotic stress. Slide 9: Disease/pest resistance ideotype Slide 10: Other main traits of the ideotype should be:
Satisfactory levels of production (both quantitative and qualitative)
a deep root system,
being able to establish
symbiotic relationships with soil
micro-organisms Slide 11: Moreover it should
compete with weeds
Exploiting genetic varia-
bility for competitiveness. Main features of ideotype breeding : Main features of ideotype breeding Emphasis on individual trait : emphasis is given on individual morphological and physiological trait which enhances the yield.
Includes yield enhancing traits: characters which exhibit positive association with yield are included in the model.
Exploits physiological variation: ideotye breeding makes use of genetically controlled physiological variation in increasing crop yields. …Contd. : …Contd. Slow progress
Designing of model : the phenotype of new variety to be developed is specified in terms of morphological and physiological traits in advance
A continuous process Differences between traditional and ideotype breeding : Differences between traditional and ideotype breeding In case of ideotype breeding values for individual traits are specified whereas such values are not fixed in case of traditional breeding. In other words, first a conceptional plant model is fixed and then efforts are made to achieve such model. In traditional breeding such models are not developed before initiation of breeding program. Wheat ideotype : Wheat ideotype Donald Features of wheat ideotype : Features of wheat ideotype A short strong stem
Few small leaves
Larger and an erect ear
Presence of awns Awns Awns Contd. : Contd. The improved wheat lines developed at CIMMYT, Maxico have some features in common such as:
Photoperiod insensitivity due to Ppd1 or Ppd2
Durable rust resistance Rice ideotype : Rice ideotype In 1964, Jennings introduced ideal plant of rice jennings Features : Features Erect, short and thick leaves
Semi- dwarf stature
High tillering capacity
High harvest index Contd. : Contd. Examples of semidwarf
varieties of rice are IR 8,
IR 20, TN 1 etc. Maize ideotype : In 1975, Mock and Pearce proposed
Ideal plant type of maize
Small tassel size
Angled leaves for good light interception Maize ideotype Cotton ideotype : Cotton ideotype Cotton ideotype proposed by Singh and coworkers in (1974)
for irrigated cultivation and by Singh and Narayanan in (1993) for rainfed cultivation Ideotype for rainfed conditions : Ideotype for rainfed conditions Short stature
Medium to big boll size(3.5 to 4 g)
High degree of resistance to insects and diseases
Few smaller and thick leaves with sparse hairiness Contd. : Contd. Ideotypes for irrigated cultivation:
Responsive to high fertilizer dose
High degree of resistance to insect pests and diseases
Boll size (3.5 to 4g) Steps in ideotype breeding : Steps in ideotype breeding Development of conceptual model: the values of various morphological and physiological traits specified to develop a conceptual theoretical model.
Selection of base material: genotypes for plant stature, maturity duration, leaf size and angle are selected from the global gene pool of the concerned crop species. Contd. : Contd. Incorporation of desirable traits: knowledge of the association between various characters is essential before starting hybridization programme.
Selection of ideal plant type: plants with desirable traits are selected in segregating population and intermated to achieve the desired plant type. Factors affecting ideotypes : Factors affecting ideotypes Crop species: in monocots, tillering is more important but in dicots branching is important.
Cultivation: the features of irrigated crops differ from that of rainfed crop.
Socio-economic condition of farmers: e.g.; dwarf Sorghum is deal for mechanical harvesting in USA, but it is not suitable for the farmers of Africa.
Economic use. Slide 28: Merits: it exploits both morphological and physiological variation. It provides solution to several problems at a time and it is an efficient method of developing cultivars for specific situation or environment.Genes for specific traits are introgressed from unimproved into the elite gene pool. Unimproved gene pool Elite gene pool Genes for specific traits Slide 29: Demerits: ideotype breeding is a slow method of cultivar development. It has not been possible to identify individual traits that enhance yield universally or in a limited genetic and environmental situations. Slide 30: Thank you