136 Papaya
12.2.4 Nutrition
Papaya is a heavy-feeder fruit crop. If sufficient amount of balanced fertiliser is
applied to the plants, they fail to produce fruit or give meager fruiting. Mycorrhizal
interactions of male and female papaya plants may differ: females seem more
responsive to changes in soil fertility and readily adjust mycorrhizal colonisation
accordingly (Vega-Frutis and Guevara 2009). Many studies are reported on the posi-
tive effects of arbuscular mycorrhizal fungi on papaya (Sukhada 1992). Judicious
use of organic manures, inorganic and microbial fertilisers is rapidly gaining favour
in fruit crops (Anwar et al. 2005). It is also necessary to strike a balanced (Carbon:
Halogen) ratio for fruiting properly. Besides, some micronutrients also play a vital
role in fruiting. Boron is also essential for pollination and seed production (Gupta
et al. 1985). Other soils are naturally deficient in certain elements, making it neces-
sary to amend them with fertilisers (Nelson 2012a, b). Lack of moisture over a pro-
longed period will slow down the growth and encourage the production of a number
of male or sterile flowers. The result is that fewer fruits are set on the tree resulting
unfruitfulness in papaya. Low moisture levels or low nitrogen can induce female
sterility (Awada and Ikeda 1957). Abiotic stresses like, low temperatures, high soil
moisture and high nitrogen seem to produce carpellodic flowers (da Silva et al. 2007;
Jimenez et al. 2014).
12.2.5 Pollination
Pollination is required for good setting of fruits and seed production. The farm-
ers generally remove all the male plants, considering them to be unproductive, and
because fruiting cannot take place in absence of pollination. For proper fruiting, pol-
lination is essential and for adequate pollination, sufficient pollinisers are required.
In dioecious varieties, 10%–12% male plants in the orchard population are required
for proper pollination (Ram 2005).
Cross-pollination may be common or infrequent, depending upon the papaya
variety, flowering behaviour and the environment. In some instances, male plants
may more effectively pollinate hermaphrodites in adjacent orchards than the her-
maphrodites can self-pollinate. Pollen can be produced year-round. The grains are
relatively large (32–39 μm), and in the subtropics can be larger in local warmer areas
(Sippel and Holtzhausen 1992). Viability of pollen may vary seasonally, being high-
est in the rainy season and spring, while the lowest in winter in subtropical (OGTR
2003). The flowers open in the early night-time (Pares et al. 2002), or the morning
(Azad and Rabbani 2004), and since they are strongly dimorphic or polymorphic,
provide different cues to potential insect pollinators. Staminate flowers may be more
fragrant and open for 24 h, and they produce calcium oxalate crystals in the anthers
and nectar basally, thus being an attractant for insects. The pistillate flower has no
nectar, but a sweet non-sugar exudate seems available on its flared large antler-like
stigmas (Pares et al. 2002). The female flowers may remain open for seven days
(Mabberley 1998).
Although the floral morphology in papaya plants suggests insect pollination, vari-
ous authors have indicated that wind pollination may also be important (da Silva et al.