Agriculture Reference
In-Depth Information
Table 9.2.
Distribution of the three sex types of
fl
owers per panicle of two litchi
cultivars (Limangkura, 1966).
Functional
fl
ower type (%)
Flowers per
panicle
Potential fruiting
fl
owers (%)
Cultivar
I
II
III
Groff
964
14
20
66
20
Hei ye
1042
22
19
59
19
practices or dif erent climatic conditions. An overlap of the types occurs on
one tree since not all panicles open at the same time.
Pollination and fruit set
Natural pollination
Controlled pollination studies have shown the presence of a relatively high
degree of self-sterility in litchi. Limangkura (1966) self-pollinated litchi fl owers
and produced 4.2% set, while cross-pollinated fl owers yielded 6.9% set. Litchi
infl orescences caged to prevent insect visitation had 0.026-0.105% fruit set as
compared to 0.17-11.25% fruit set on infl orescences open to insect visitation
(Pandey and Yadava, 1970). Bees (
Apis
and
Mellifera
spp.) make up 98-99%
of the total insect visitors to the fl owers, mostly during the morning hours,
when nectar secretion occurs. The stigmas of litchi fl owers are receptive to
pollination for 72 h from the time it divides into the two lobes, and the anthers
remain functional up to 1-3 days after anthesis.
Controlled pollination studies in longan have shown the presence of a
relatively high degree of self-incompatibility. Bees (
Apis
and
Mellifera
spp.) are
the major pollinators and comprised 98-99% of the total insect visitors to
the fl owers. The visits occur mostly during the morning hours, when nectar
secretion occurs. Too much rain during anthesis can reduce fl ower opening
and the insect activity needed for pollination. Irrigation after a period of
soil water stress is reported to aid in fl owering, even though the tree fl owers
profusely in areas with high water tables.
Floral induction, fruit set and chemicals
Growth regulators and other horticultural techniques have been tried by many
researchers to overcome the problem of irregular litchi fl owering, to enhance
fruit set and to reduce seed size (Menzel, 1983; Joubert, 1986). Sodium
naphthalene acetate (SNA) at 200 and 400 ppm promoted blossoming in
'Chenzi' only when climatic conditions favoured vegetative growth. The
inhibition of vegetative growth is a requisite for fl oral initiation, and SNA
mimics low temperatures that inhibit growth. There is no increase in fl oral
