List flve main groups of natural plant growth regulators. Write a note on discovery, physiological functions and agricultural/ horticultural applications of any one of them.
The five main groups of natural growth regulators are (a) auxins (b) gibberellins (c) cytokinins (d) ethylene (e) abscisic acid Gibberellins Discovery: – They are another kind of promotory PGR. There are more than 100 gibberellins reported from different organisms such as fungi and higher plants. They are denoted as GA1, GA2, GA3. E. Kurosawa reported the symptoms of the disease r in infected rice seedings when they were treated with filtrates of the fungus. Gibberalla fujikuroi caused, bakane’ (foolish seedling) a disease of rice seedlings. The active substances were later identified as gibberellic acid. Physiological functions (i) They cause an increase in length of axis is used to increase the length of grapes stalk. (ii) Gibberellins cause fruit like apple to elongate and improve its shape. (iii) They also delay senescence. Thus the fruits can be left on the tree longer so as to extend the market period. Agricultural Applications (i) Spraying sugarcane crop with gibberellins increases the length of stem. Thus increasing the yield as much as 20 tonnes per acre. (ii) Spraying juvenile conifers with GAs hastens the maturity period, thus leading to early seed production. (iii) Gibberellins also promotes bolting (internode elongation just prior to flowering) in beet, cabbages and many plants with rosette habit.
