Agriculture Reference
In-Depth Information
Harvest
Flowering
fruit set
Flower bud
development
Vegetative
growth
Root
growth
Fruit
drop
Fruit
drop
May
Jun
Jul
Aug
Sep
Oct
Nov Dec
Month
Jan
Feb
Mar
Apr
May
Jun
Fig. 7.3.
Phenological cycle for bearing cv. 'Fuerte' in Queensland, Australia,
showing the development and interaction between root, shoot,
fl
ower and fruit
growth. The cycle will vary with the cultivar and needs to be determined for each
location (redrawn from Whiley
et al.
, 1988a).
The juvenile period in avocado can be from 5 to 15 years. If girdled in
early autumn 3 years after planting, fl owering and fruit set can be increased
signifi cantly. Since the cultivars 'Pinkerton' and 'Gwen' have precocious
of spring, juvenility is likely to have a genetic basis, which is modifi ed by
environment (Lavi
et al.
,
1992).
In
fl
orescence and
fl
ower
The small, pale green or yellowish-green fl owers are borne on multi-
branched axillary panicles terminating in a shoot bud (Fig. 7.2). One or two
million fl owers may be produced in a single fl owering period, although only
about 200-300 fruit mature (Whiley
et al.
,
1988b). This fl owering leads to
considerable water loss, and the recommendation is to irrigate during this
period. The fl ower is bisexual with nine stamens, six of which form the outer
circle and three in the inner circle. At the base of the inner circle are located a
pair of nectaries, alternating with three staminodes, which also secrete nectar.
Each stamen has four pollen sacs, which release cohesive pollen. The single
pistil contains one carpel and one ovule (Bergh, 1976).
The avocado fl ower has a unique fl owering behaviour (Fig. 7.4), and
all avocado cultivars and seedlings, irrespective of race, fall into one of two
complementary groups, designated 'A' and 'B' (Table 7.3). Flowers of the
