In plant breeding, the main objective of crop improvement is selection for enhanced yield. When a plant has high yield, it may be due to plant architectural traits such as leaf angle, leaf size, leaf shape, plant canopy, etc. The plant having these model characters makes it more adaptable to the environment for which it was developed and thereby increasing the yield. This takes us to the concept of ‘Ideotype’ proposed by C. M. Donald in 1968.

The term ideotype literally means ‘form denoting an idea’. Ideotype is a biological model that is expected to behave in a predictable manner in a defined environment. There are different types of ideotype based on the breeding objectives viz., crop or communal, isolation, competition, market, edaphic, disease or pest and stress ideotype. A successful ideotype is usually a weak competitor relative to its mass.

Cotton “The king of fiber”, shows difference in yield due to variations in plant architectural traits like size, shape and orientation of shoot characters that effect planting density requirement, resistance to pests and diseases, yield potential and ease of harvest. It also influences physiological characters like photosynthesis, light interception and radiation use efficiency. Various cotton ideotypes have been proposed for different situations like rainfed, irrigated condition, heat and drought stress, climate change, etc.

Leaf shape of cotton is one of the major plant architectural traits used for developing an ideotype. There are four types of leaf shapes in cotton they are, Normal, Sub-ok­ra, Okra and Super-okra. The genetics of this trait is being worked out since 1953. Andres et al. (2016) used orthologous mapping and sequenced D genome of Gossypium raimondii and identified two LATE MERISTEM IDENTITY1 like genes as strong candidate genes for leaf shape in cotton. The super okra and okra leaf shapes conferred resistance to boll rot, earliness to maturity, reduced motes but comparatively boll retention and yield declined.

Nawab et al. (2011) studied the effect of leaf shape on fiber and agronomic traits. They studied 3 crosses involving one common parent. The cross HRVO-1 × Acala 63-74 showed okra leaf shape which had positive significant correlation with fiber elongation and negative significant correlation with number of monopodia. HRVO-1 × CIM-446 showed negative significant correlation with plant height. All three crosses showed positive correlation with sympodial branches.

Patil, et al. (2018) identified promising compact genotypes for rainfed conditions based on ideotype concept. They classified genotypes into compact, super compact, tall compact and highly robust and raised them in 3 different spacing environments. The genotype F-17 was found to be super compact and had better response to High Density Planting.

Ideotypes in cotton are being designed for climate change. A crop model system DSSAT CSM-CROPGRO-Cotton was used to identify best cultivars for Northern Cameroon region for year 2050 under two climatic scenarios RCP-4.5 and RCP-8.5 for low input rainfed conditions. Virtual cultivars (3125) were simulated. The optimized ideotypes were identified for each criterion but none for both. The optimized ideotypes had early anthesis date, longer reproductive duration and maximum photosynthesis rate. Such traits should be considered for identification of suitable cultivars in breeding program for future climate changes (Loison et al., 2017).

Off late the advent of newer technologies like genome editing and functional phenomics have exhibited their ability to reduce the time and effort required for ideotype development. The candidate genes are being identified for trait like leaf shape (CRL and LMI-1) which help in selecting for plant ideotypes for high yield.

The crop design formulated for a plant type may not be perfect but breeding, testing and exploitation of ideotype helps in breaking the yield barrier(s) and move towards enhanced yield. This plant type designing must be pursued with imagination. It lies in finding ways to pick and assemble the genes scattered in diverse genetic resources. Yield not only depends on genes which control yield but also genes for plant architectural traits, both of which have to be incorporated into one individual which is inevitable to achieve the actual fruits of ideotype breeding.

REFERENCE

Andres, R. J., Bowman, D. T., Jones, D. C. and Kuraparthy, V., 2016, Major leaf shapes of cotton: Genetics and agronomic effects in crop production. J. Cotton Sci., 20(4): 330-340.

Donald, C. M., 1968, The breeding of crop ideotypes. Euphytica, 17(3): 385-403.

Nawab, N. N., Saeed, A., Tariq, M. S., Nadeem, K., Mahmood, K., Hassan, M., Shakil, Q., Alam, M. S., Hussain, S. I. and Khan, A. A., 2011, Inheritance of okra leaf type in different genetic backgrounds and its effects on fibre and agronomic traits in cotton. Afr. J. Biotech., 10(73): 16484-16490.

Patil, R. S., Soumya, J., Paloti, M. C. and Roy, U., 2018, Promising compact cotton (Gossypium hirsutum L.) genotypes for rainfed situation based on the Ideotype Concept. Second National Conference on "Genetics and Cytogenetics", UAS, Dharwad.

Romain, L., Audebert, A., Debaeke, P. and Gérardeaux, E., 2017, Design of African rainfed cotton ideotypes using DSSAT CROPGRO-Cotton. Eur. J. Agron., 90: 162-173.

Somashekhargouda, P., Patil, N.S. and Patil, B.C., 2016, Influence of plant architecture on morphological, biophysical parameters and yield of cotton genotypes. Environ. Eco., 34(4): 1808-1812.