• When seedlings are transplanted, they establish by producing nodal roots.
• Top leaves contribute more to ear growth and almost half of the pre-anthesis weight of the ear is from the flag leaf.
• In wheat and barley, most of the contribution to grain is from flag leaves.
• Contribution of stored carbohydrates in stem to grain filling is 10 to 20%.
• During moisture stress, when the normal photosynthesis is affected, stem contribution may exceed 20% of final grain weight.
• Primordial differentiation stage is called as panicle initiation stage in cereals and millets, squaring in cotton, flower bud initiation in sunflower etc.
• With the start of primordial differentiation stage, plants enter reproductive phase.
• Primordial differentiation stage is more sensitive to moisture and solar radiation in cereals.
• Crop is said to be at 50% flowering when 50% of plants put forth flowers.
• Opening of flowers and shedding of pollen is called anthesis.
• Blooming also indicates opening of flowers.
• Flowering stage is very sensitive to moisture stress.
• Total area of leaves per unit area of the land surface is leaf area index (LAI).
• Optimum LAI for crops with horizontally oriented leaves is 3-4.
• Optimum LAI for crops with upright leaves is 6-9.
• The proportion of incident light that is intercepted by the crop canopy does not depend on LAI alone but also on the architecture of the plant community.
• Extinction coefficient (K) is a measure of the light intercepting efficiency of the leaf area.
• The maximum temperature above which no germination occurs is usually within the range of 35-45 °C.
• Most of the crop seeds germinate well within the moisture regime of field capacity to 50% available soil moisture.
• Soil crust is the main hurdle for the emergence of crops like foxtail millet, pearl millet etc. as the seeds are small.
• Oxygen content, light and dormancy influence germination and emergence.
• Germination may be affected due to lack of oxygen by waterlogging if rains follow immediately after sowing.
• Seeds of stylo and subabul need treatment prior to soaking to break dormancy.
• Leaf expansion is normal if the relative water content (water content of leaves compared to water content at saturation) is 90-100%.
• Leaf expansion stops when RWC is below 70-75%.
• Relative water content of leaves is more in young leaves compared to old leaves.
• Cell expansion is more affected by moisture stress than cell division.
PLANT GROWTH SUBSTANCES
• Plant growth substances are biochemicals produced in plants (endogenous) or synthetic substances applied to plants externally (exogenous) which cause modifications in plant growth and development.
• There are 5 major groups of endogenous growth substances present in plants Ex: auxins, cytokinins, gibberellins, abscisic acid and ethylene
• Plant growth substances produced by the plant are called phytohormones.
• Plant growth substances are classified into-
1) Growth promoters : auxins, cytokinins and gibberellins
2) Growth retardants : abscisic acid, ethylene
• Growth promoters exist in multiple forms.
• Growth retardants (abscisic acid and ethylene) exist in single form.
• Auxins stimulate elongation of cells of stems and coleoptiles.
• Endogenous auxins are Indoleacetic acid (IAA) and Phenylacetic acid.
• Synthetic auxins are Naphthalene acetic acid (NAA), Indole-3 acetic acid, Indole-3-propionic acid and 2,4-D.
• Auxins promote cell enlargement resulting in elongation of coleoptiles, stem etc.
• Presence of auxins in apical bud suppresses the axillary buds and results in apical dominance.
• Cell division and root formation are important functions of auxins.
• Plant organ development in tissue culture affected by balance of auxins to cytokinins.
• Due to high concentration of auxins and cytokinins, cells grow amorphously without differentiation.
• High ratio of auxin to cytokinin – induction of roots in callus cells.
• High ratio of cytokinin to auxin – formation of shoots.
• Auxins are used to enhance fruit set
• Auxins are used as herbicides at higher doses. Ex: 2,4-D and 2,4,5-T.
• NAA induces flowering in Pineapple.
• IBA is used for inducing rooting of cuttings.
• Cytokinins stimulate cell division.
• Endogenous cytokinins are Kinetin, Zeatin and Isopentenyladenosine.
• Synthetic cytokinin is 6-Benzyladenine.
• Cytokinins promote orderly development of embryos of seed.
• Cytokinins break dormancy of seeds and buds.
• Cytokinins delay senescence.
• Gibberellin is first isolated from the fungus Gibberella fujikuroi.
• Gibberellins increase cell division and cell elongation.
• Gibberellin commonly available is GA3 (gibberellic acid).
• Gibberellins promote cell elongation and increase in size of leaf, flower and fruit.
• Dormancy is broken and flowering is induced by gibberellins.
• Abscisic acid induces leaf and fruit abscission.
• Abscisic acid accumulation induces dormancy.
• Moisture stressed plants produce abscisic acid which facilitates stomatal closure and helps in maintaining cell turgidity.
• Ethylene stimulates the swelling or isodiametric growth of stems and roots.
• Regulation of ethylene can trigger ripening of fruits or delay in ripening process
• Phenolics inhibit cell division, cell enlargement and germination of seed.
• Lucerne leaves contain triacontanol which when applied as foliar spray improves the growth of crops.
• Examples of growth retardants are cycocel (CCC), phosphon-D, maleic hydrazide (MH).
• CCC and MH retard stem elongation and the leaves of the treated plants become thick and dark green.
• Maleic hydrazide is used for sucker control in tobacco and as growth retardant.
Read More-
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- Crop Protection One Liner For Competitive exam
- Seeds and Sowing Point Wise Notes for Competitive exam part-2
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