THE MODE OF ACTION OF APPLE THINNING AGENTS

Studies on fruit abscission and thinning emphasized mechanism of action of naphthaleneacetic acid (NAA) and 1-naphthyl methyl carbamate (carbaryl) when applied before the "June drop". Auxin sprays (primarily NAA) resulted in the following responses: (a) less reducing sugars per fruit, (b) temporarily stopped or slowed fruit growth, (c) did not affect pedicel capacity to translocate ¹⁴C-IAA or ¹⁴C-sucrose in either direction, (d) reduced ¹⁴C-sucrose movement from foliage to fruit, (e) increased ethylene evolution but not until 24 hours after NAA application, (f) increased water potential of foliage, (g) shading limbs resulted in reduced follar ethylene evolution, (h) shading limbs resulted in reduced fruit retention in the absence of an exogenous ethylene stimulant and (i) reduced number of fruit retained by the tree.
It is suggested that NAA reduces metabolite movement from foliage to fruit which results in the initiation of the fruit abscission process.

Symposium on Growth Regulators in Fruit Production

G.W. Schneider

https://doi.org/10.17660/ActaHortic.1978.80.37