Papaya Biology, Cultivation, Production and Uses

16 Papaya

B Pistillate
♀

: Borne on a raceme, corymb, sub-sessile, bracteolate

Calyx : Petals 5, gamosepalous, light green

Corolla : Petals 5, linear, deciduous, polypetalous, twisted aestivation

Androecium : Absent

Gynoecium : Sessile, style very short, stigma 5, dilated or linear, simple or

lobed, ovary–superior, monocarpellary, parietal placentation,

many seeded

Fruit : Berry (pulpy in nature)

Seeds : Blackish to brownish in colour, straight embryo, fleshy

endosperm, cotyledons oblong and flat

Floral formula : % ♀ K (5) C 5 A0 G1

C Normal hermaphrodite
⚥

: Long fruited type plants, flowers similar to pistillate type but the

inflorescence is multi-flowered (5–6 flower corymb), corolla gamo,

stamens 10 (5 + 5), sessile at base of petals, ovary usually functional

Floral formula : % ♀ K (5) C (5) A 5 + 5 G1

D Elongata hermaphrodite
⚥

: Deformed/catface fruits, flowers similar to hermaphrodite type but

five stamens (fused with carpels), sessile at base of petals, ovary

usually functional

Floral formula : % ♀ K (5) C (5) A 5 G1

The quality and quantity of pollen from three types of flowers, elongata, reduced elon-
gata and staminate from the commercialised Thai papaya cultivar ‘KhakNual’, were
determined using pollen morphology, pollen physical characters and pollen develop-
ment processes. Pollen development progressed at the same pace in all three types of
pollen-producing flowers and was consistent with pollen development in many angio-
sperms. Pollen morphology showed that papaya pollen grains are tricolporate, with
three apertures, and there is no significant difference in diameter (25.18–25.72 μm) and
weight (11.76–15.45 ng) among pollen sources. The staminate flower shows the lowest
amount of pollen, with 12,368 pollen per anther, but higher viability and germination
rates of 95.53% and 53.64%, respectively. In contrast, the elongata type shows the high-
est amount of pollen grains with 14,884 pollen per anther and the lowest viability and
germination rates, 93.06% and 46.33%, respectively. The physical characteristics of
pollen grains from reduced elongate and elongate flowers are similar. Reduced elon-
gate flower type can donate pollen without self-pollinating (Phuangrat et al. 2013).

2.2.2 Flower Induction

Neither photoperiod nor temperature induces flowering in papaya. Each plant com-
mences flowering only after a genetically determined number of nodes have devel-
oped following a short period of juvenility (Storey 1986). However, photoperiodic
changes are responsible for sex reversals in certain phenotypically unstable forms
of hermaphrodite and male trees. The reversal occurs at times closely related to
the equinoxes and solstices (Storey 1986). Floral composition of sex reverting types
may be influenced by temperature, water availability and other factors (Lange 1961;