PHYSIOLOGY OF SHOOT GALL FORMATION AND ITS RELATIONSHIP WITH JUVENILITY AND FLOWERING IN MANGO

Shoot gall is a major mango malady in many countries of the world. Studies conducted for several years indicate zero gall formation on young grafted and seedling plants prior to flowering stage. Insect caged on such plants laid no eggs. Chemicals secreted by nymphs in saliva were responsible for conversion of axillary and apical buds into galls. These were associated with chemicals responsible for flowering in mango and were ineffective in their absence.

Endogenous auxin level increased in affected over healthy shoots by 0.047 μg/g as assessed by Oat coleoptile test. Total phenols, on the other hand, decreased by 0.70 mg/g in affected with 5.70 mg/g as against 6.4 mg/g in healthy shoots. While tyrosine and tryptophan content decreased to 0.089 and 0.0128 mg/g at maximum feeding stage of nymphs in affected as against 0.0928 and 0.0150 mg/g in healthy shoots respectively. Use of gibberellic acid (GA), naphthalene acetic acid (NAA), maleic hydrazide (MH), CCC, abscisic acid, alar did not affect gall formation except 2,4-D and 2,4,5-T (100 mg/kg and above) which gave rise to abnormal galls with open scales and elongated axis.