"Foolish seedling disease or Bakanad disease" is associated with gibberellin. Th̃is disease is caused by fungus-Gibberella fujikuroi (Fusarium moniliforme) in rice. Gibberellins are weakly acidic plant growth hormones which possess a gibbane ring strutucture and are able to bring about cell elongation of both leaves and stem in general and internodal growth of genetically dwarf plant. Gibberellins were first extracted by Yabuta and Sumiki.
Auxins were first collected by Went (1928) from coleoptile tip of Avena. Auxirs are mildly acidic growth hormones having an unsaturated ring structure and capable of promoting cell elongation, especially shoot segmentai:
Cytokinins are mildly basic growth hormones, which are usually amino-purine derivative and promote cell division in plants. The first cytokinin was discovered by Miller et al, in herring sperm DNA and was named as Kinetin (synthetic). The naturally occurring cytokinin is zeatin, which was discovered by Letham et al, in maize kernel.
Abscisic Acid is also known as stress hormone or dormin. This hormone was discovered by Addicott et al (1963). It counteracts the influence of growth hormone. It is also known as antigibberellic hormone.