Growth and Development of Horticultural Crops (1+1)

Source & Sink relationship

• The photosynthetic source cells produce the sugars, which can move symplastically to sieve tubes.
• Phloem loading increase sugar concentration to sieve tubes above apoplast
• Sink carbohydrates are utilized
• The build up of sugars in source &removal in sink establish a hydrostatic pressure which moves water &sugars
• Increase of photosynthetic rate-increase in Hydrostatic pressure & Translocation rate
• Sink have the ability to utilize more assimilate.
• If unable to increase in production of assimilate – accumulate and reduce photosynthesis
Hormonal action

• The effect of hormones on sink cell have an effect on partitioning
• IAA, Cytokinin, Ethylene, GA
• They influence –initiation, development, abortion of flowers and seeds.
• Significant effects on source sink relationship in crops.
Assimilate partitioning during vegetative phase

• Leaves, green tissues- original sources
• Some remains in green tissues-cell maintenance
• If slow –converted to starch or some storage materials
• Rest transported to vegetative sinks –roots stem leaves.
The proportion of assimilates partitioned to these 3 organs can influence plant growth & productivity depends upon the nature of crop either root, stem or leaf forms the main economic portion of the crop.

• Young leaves –matured leaves
• Self sufficient export 60-80% -to other parts &to older leaves
During reproductive phase

• Reproductive growth primary part of plant
• Fruits, seeds, flowers, tubers resultant products of larger partitioning of assimilate from vegetative (source) to sink
• In determinant species leaf &stem growth cease at flowering
• Indeterminate species – both vegetative reproductive occur simultaneously
• If much vegetative growth during reproductive phase, yield reduces
• As size of source increase photosynthesis increases
Harvest index

• Two useful terms used to describe partitioning of dry matter by the plant are
• Economic yield is used to refer to the volume or weight of those plant organs that constitute the product of economic value.
• Biological yield proposed by Niche poroviah in 1960 to represent the total dry matter accumulation of a plant’s system.
• The proportion of biological yield represented by economic yield – harvest index
HI = EY/BY*100

• Crop yield can be increased either by increasing the total dry matter produced or by increasing the proportion of economic yield or both.
  
• More partitioning leads to increase of HI, increase of crop yield.
Yield component

• Grain yield –product of a no of sub fractions called yield component.
Y=Nr Ng Wg

Nr-No of reproductive units
Ng-No of grains/ reproductive units
Wg-Avg,wt./grain

• Yield components are affected by management, genotype & environment.
Remobilization

• The movement of compounds from an area where they were once deposited to an area where they can be reutilized – Remobilization
• It occurs in organic & inorganic components
• During leaf senescence carbohydrate, nitrogenous compounds, metabolic nutrients are remobilized.
Grain filling
For the development of grain photosynthate come from 3 sources:

• Current leaf photosynthesis
• From non-leaf parts
• Remobilization deposited in other plant organ.
• During drought grain yield reduces.