Model Plant Type

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Presentation Transcript

Concept of Plant Ideotype : 

Concept of Plant Ideotype DISCLAIMER 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). A biological model, which is expected to perform or behave in a predictable manner within a defined environment. This term has the following synonyms:

Types of ideotype : 

Types of ideotype Isolation ideotype Competition ideotype Crop ideotype

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Isolation ideotypes: it is the model plant type that perform best when the plants are space-planted.

Competition ideotype : 

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.

Competition ideotype : 

Competition ideotype 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.

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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.

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Disease/pest resistance ideotype

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Satisfactory levels of production (both quantitative and qualitative) a deep root system being able to establish symbiotic relationships with soil micro-organisms Other main traits of the ideotype should be:

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Moreover it should compete with weeds exploiting genetic varia- bility for competitiveness. Superweeds infest a corn field

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 Selection Designing of model : the phenotype of new variety to be developed is specified in terms of morphological and physiological traits in advance Interdisciplinary approach 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 Erect leaves Few small leaves Larger and an erect ear Presence of awns

Contd. : 

Contd. The improved wheat lines developed at CIMMYT, Maxico have some features in common such as: Reduced height 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 More panicles High harvest index

Contd. : 

Contd. Examples of semidwarf varieties of rice are IR 8, IR 20, TN 1 etc.

Maize ideotype : 

Maize ideotype In 1975, Mock and Pearce proposed Ideal plant type of maize Small tassel size Low tillers Large cobs Angled leaves for good light interception

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 of cotton for rainfed conditions : 

Ideotype of cotton 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: Short stature(90-120cm) Short duration(150-165days) 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: eg., dwarf Sorghum is ideal for mechanical harvesting in USA, but it is not suitable for the farmers of Africa. Economic use

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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

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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.

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Thank you