Agriculture Reference
In-Depth Information
Day 1
Day 2
Type A
Type B
06:00
12:00
18:00
06:00
12:00
18:00
Time
Fig. 7.4.
Protogynous dichogamy pattern of
fl
ower opening involves two types, A
and B, with both types found in the three ecological races. This behaviour enhances
cross-pollination. These patterns may be disrupted by low temperatures and some
overlap occurs.
'A' class open in the morning for 2-3 h, functioning as females with a white
stigma, while the stamens remain closed and are in a horizontal position.
These fl owers close at approximately noon and reopen the following day
during the afternoon hours for 3-4 h, functioning now as males, with stamens
in a vertical position. The stigmas are no longer functional. Flowers of the 'B'
class open in the afternoon as females, the stamens remaining closed. These
fl owers close in the evening and reopen the next morning as male fl owers. This
phenomenon is called protogynous, diurnally synchronous dichogamy (Bergh,
1969). The dichogamy is protogynous, as the pistil matures before the stamens
in both classes and all fl owers of a class are synchronized to be functionally
female at one time of the day and functionally male at another time. Looking
at the whole tree with numerous fl owers opening any day during the fl owering
period, varieties of the 'A' group are in the female stage during the mornings
and in the male stage during the afternoons and those of the 'B' group are
in the female stage in the afternoons and in the male stage in the mornings;
this way they complement each other for fertilization purposes. Temperatures
of 17/12°C and 33/28°C during fl owering time can prevent pollen-tube and
embryo growth, resulting in the production of unfertilized, underdeveloped
fruit. This disruption of fruit set, with endosperm and embryo development
not being observed at low temperatures (17/12°C), is more marked in type
'B' fl owers (cv. 'Fuerte'), where no female fl ower opening occurs (Sedgley and
Grant, 1983). The fl owering cycle is extended by cool temperatures from the
usual 36 and 20 h for types 'A' and 'B', respectively. Growing temperatures of
25-30°C during the day and night temperatures of 15-20°C are considered
optimum (Table 7.2). A much cooler temperature range during winter will
stimulate fl owering (Whiley, 1984). Type 'B' cultivars ('Fuerte') are generally
less productive than type 'A' ('Hass') under cool fl owering conditions.
