Growth and Development of Horticultural Crops (1+1)

Growth correlations

• Plants acquire a characteristic shape or form by correlated growth of component parts. Favorable environment can enhance growth quantitatively, but the geometry of the parts and the whole plant is relatively constant. The relationship between the growth rate of individual parts of an organ or organism is called as allometry.
• The relationship between two variants (X and Y) may be expressed as
Y = bx^k



Where

X and Y are physical parameters
b and k are constant. K, being the allometric constant.

• The quantity of K can be calculated from the equation log Y = log b + k log 2 or by linear regression analysis of the data set Y and X. For eg. If length and breadth of a leaf expand at the same rate, the slope of the regression line (the coefficient of allometry or K) is 1.0 (one). Similarly the harvest index (proportion of seed weight to whole plant weight) has a relatively high coefficient of allometry. Actually allometry deals with the correlation of physiological process, specifically with reference to growth analysis of crops.
Shoot-root ratio

• It is a type of allometric growth that reflects one type of tolerance to drought stress. Though the shoot root ratio is under genetic control, it can be modified by the environment. For example, under high nitrogen regime approximately 90per cent of the photosynthate is partitioned into shoot compared to 50 per cent to the shoot under low N. Similarly the water deficits significantly affect the shoot growth.
Apical and lateral growth

• Plants assume a characteristic form or geometry mainly due to apical and lateral buds growth.
Vegetative and reproductive growth

• In annuals, vegetative growth is generally terminated by reproduction. Leaves, stems and other vegetative parts not only fail to compete for current assimilate during ripening of fruits but also sacrifice previously accumulated carbon and minerals through mobilization and redistribution.
• Perennials make only partial commitment to reproduction, and shoot that bear fruits may remain healthy and new vegetative shoots are generated from axillary buds.
Growth and differentiation

• Plant development is a combination of complex processes of growth and differentiation that leads to an accumulation of dry matter.
• While growth is the increment in weight or volume due to cell division and cell enlargement, differentiation is the formation of specialized cells like xylem and phloem and formation of different plant parts like root, stem, leaves, etc.
• Differentiation processes have three requisites
1. Available assimilates in excess of most metabolic uses
2. A favourable temperature
3. Proper enzyme system for cell wall thickening, secondary product accumulation (eg. alkaloids and starches) and protoplasm hardening may occur which result in changes in anatomy and morphology.