Botany and Improvement 17
Nakasone 1967; Storey 1969; Allan et al. 1987). Floral induction is also correlated
with number of leaves produced. Under favourable conditions, a short-statured vari-
ety like ‘Betty’ produces its first inflorescence at the 24th node and a tall-statured
variety such as ‘Solo’ not until the 48th node. The number of nodes and internodes
often determine the height at which the first flowers appear. For variety ‘Betty’ it is
about 40 cm and for ‘Solo’ about 140 cm (Storey 1986).
After papaya plants begin to flower, a flowering peduncle is produced in each leaf
axis. Each peduncle produces several flowers of which one is terminal and two to five
or more are in lateral positions. In female trees, it appears almost certain that only
the terminal flower will set fruit with laterals dropping within a week after anthesis.
Therefore, only one fruit per leaf axis is produced. On bisexual trees, it is also com-
mon for the terminal flower to set fruit with laterals dropping, thus, producing one
fruit per panicle. However, one or two lateral flowers of some cultivars under favour-
able nutritional and moisture conditions tend to set fruits. In most instances, fruits of
lateral flowers do not persist beyond two or three weeks.
2.2.3 Floral Biology and Pollination
For breeding purposes, terminal flowers are selected and tagged. They are emascu-
lated before anthesis. While the peak time of anthesis is from 5.00 to 8.00 a.m. in
all types of flowers, anther dehiscence begins about 6 h ahead of anthesis (Sharma
and Bajpai 1969). Though no correlation has so far been reported between tempera-
ture and the rate of anthesis, the dehiscence, however, is increased markedly with
rise in temperature and decline in the relative humidity. The pollens of hermaphro-
dite flowers obtained at the beginning of the flowering season show higher fertility
(Sharma and Bajpai 1969). Five per cent sucrose solution gives best pollen germina-
tion under artificial conditions. Papaya pollens stored at room temperature in des-
iccators containing 64.8% H 2 SO 4 and 10% relative humidity retain 50% viability
up to 10 days. When stored in desiccators (63.15% H 2 SO 4 and 10% RH) at lower
temperature (0–4°C), the viability is 52.57% after 3 months of storage (Prakash and
Dikshit 1963). The stigma becomes receptive 48 h before anthesis and continues to
be receptive up to 72 h after anthesis. Usually for crossing, the flowers about to open
are emasculated in the evening and bagged. They are pollinated in the morning next
day with freshly collected or stored pollens and bagged again. Anthesis reaches a
peak between 5.00 and 6.00 a.m. in flowers of all species studied, except pistillate
flowers of C. Cauliflora (7.00–8.00 a.m.) and the staminate flowers of C. Goudotina
(6.00–7.00 a.m.). Anthesis is sex dependent and stigma receptivity is maximum on
the day of anthesis (Subramanyam and Iyer 1986).
It has often been observed that when flowers on female trees are pollinated with
pollens obtained from the flowers of bisexual trees, they set maximum number of
fruits. Plant breeders may encounter pollination problems with bisexual flowers due
to their morphological differences. In most cultivars or breeding lines, the anthers
extend directly over the stigmatic rays, which ensure automatic self-pollination.
Flowers of this type may be bagged with assurance of self-pollination. In some
lines and cultivars the position of the anthers, by virtue of having short filaments
or adnation of the filaments at a flower position on the neck of the corolla tube,