AVOCADO FRUIT GROWTH: PHYSIOLOGICAL PROCESSES AFFILIATED WITH THE OCCURRENCE OF PHENOTYPICALLY SMALL ‘HASS’ FRUIT

Under warm, low rainfall subtropical climates Persea americana Mill. cv.
Hass produces a significant number of phenotypically small fruit which are of minor market value.
The problem develops in the early stages of fruit ontogeny, and is characterized by early seed coat senescence followed by seed coat death and slowing of growth.
Injection of Mevastatin, an inhibitor of the key enzyme of isoprenoid biosynthesis 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), into the pedicel of healthy, rapidly growing fruit reduced growth significantly.
Furthermore Mevastatin inhibited activity of mesocarp HMGR. Injection of abscisic acid (ABA) affected fruit growth and development similarly and inhibited HMGR activity.
In contrast the cytokinin dimethylallylamino purine (iP), although stimulating fruit growth slightly, had little or no effect on HMGR activity.
However, when iP was co-injected with either Mevastatin or ABA the inhibitory effect of these growth regulators was negated.
Since cytokinins (e.g. iP) are purportedly synthesized by a mechanism involving isoprenylation of purine, it is hypothesized that early seed coat senescence and appearance of the small fruit phenotype arises due to a change in endogenous cytokinin:ABA ratio which is exacerbated by unfavourable environmental conditions during the early stage of ‘Hass’ fruit growth and development.

VIII International Symposium on Plant Bioregulation in Fruit Production

I. Bertling, A.K. Cowan, C.S. Moore-Gordon

HMGR, isoprenoid pathway, cytokinins, ABA

https://doi.org/10.17660/ActaHortic.1998.463.26