128 Papaya
process of feminisation of stamen (Hama et al. 2004; Drea et al. 2007). Such type
consists of bisexual flower types with stamen-to-carpel conversions. Hermaphrodite
flowers of Carica tend to be highly variable in the extent of development of sta-
mens and carpels, ranging from flowers with ten stamens and five carpels (elongata
type) (Figure 11.3c) through abnormal flowers with 1–5 stamens fused to different
degrees with the ovary and with some developing stigmatic tissue on the anthers
(Figure 11.3b). The conversion process occurs rapidly upon stamen–carpel contact
and all stamen tissues undergo feminisation (Figure 11.3a and d) due to mutation,
gene alteration or environmental stress. The genetic nature of carpelloidy remains
to be understood, possibly within the framework of the genetic system for sex deter-
mination which rests on five pairs of genes occurring in three sex-determining com-
plexes in the sixth chromosome. The stamen filaments and connective tissues were
the most responsive to feminisation. The Carica results highlight mechanisms that
allow direct resource reallocation (Wright and Meagher 2003) between male and
female organs through (partial) sex conversion once bisexual flowers have evolved.
Imperfect flowers’ occurrence in hermaphrodite plants of papaya tree is related
to genetic causes, which are affected by environmental factors. Longer dry periods,
high temperature, high and low moisture (Manshardt 2012) and imbalanced fertilisa-
tion, may lead to this disorder. High humidity conditions as well as high concentra-
tion of water and nitrogen in the soil tend to change the sex of the hermaphrodite
flowers producing deformed fruits.
The high nitrogen in papaya may be a factor behind low level of some micronu-
trients (especially boron). Any type of stress may also cause the problem as well as
gene alteration through mutation. It was the highest in summer and become worse
FIGURE 11.3 Carpelloid fruits bearing papaya plant (cv., Red Lady) (a), pistilloidy (stamen
feminisation) (b), hermaphroditic flower (c) and different stages of stamen to carpel conver-
sion in complete carpelloid fruit (d).