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Climate and Soil
3.1 Temperature
Papaya is a tropical plant and very sensitive to frost, limited to the region between
32° north and 32° south of the Equator. It is grown up to an elevation of 1200 m
above the mean sea level. It needs plentiful rainfall or irrigation, but must have good
drainage. Flooding for 48 h is fatal to it. Brief exposure to 32°F is damaging; pro-
longed cold without overhead sprinkling can kill the plant (DAIS 2009). Although a
mature papaya tree can withstand a temperature of −2°C, production is only recom-
mended in areas where the average daily minimum temperature during mid-winter
never drops below 5°C. Ideally, night temperatures should not drop below 12°C. The
optimum temperature range for papayas is between 25°C and 30°C. Temperatures
higher than 36°C and lower than 16°C for extended periods can adversely affect the
growth of the trees. It grows well in regions where summer temperature ranges from
35°C to 38°C. It requires 23°C average daily temperature and 6 months for flowering
to fruit maturity. Although papayas are considered sun-loving plants, morphological
plasticity in the shade is high and involves changes in many characteristics such as
leaf mass per area, chlorophyll a and b ratio, stomata density, internode length and
degree of blade lobbing (Buisson and Lee 1993). This plasticity is evidenced by the
morphology adopted by papayas growing in multi-storied agro-ecosystems and in
high-density orchards as well (Iyer and Kurian 2006). The lower the temperature,
the longer the time it will take for fruit maturity with round fruit shape. After the
winter, trees are in a recovering stage and produce few flowers. In subtropical con-
ditions, however, growth and flower production cease when the night temperature
drops below 12°C.
Papaya plants exhibit C3 type photosynthesis systems (Campostrini and Glenn
2007). Optimum temperature for growth is 21–33°C, under which papayas can pro-
duce two leaves per week and 8–16 fruits per month. Temperatures below 10°C are
not well-tolerated (Allan 2005). Light compensation point for leaf-level photosyn-
thesis is Ca. 35 μmol m−^2 s−^1 , and saturation is reached at Ca. 2000 μmol m−^2 s−^1 of
photosynthetic photon flux density (PPFD) (Campostrini and Glenn 2007). High
photosynthetic rates of 25–30 μmol CO 2 m−^2 s−^1 alternate with pronounced (mid-
day) gas exchange depressions, apparently caused by direct stomatal and cuticular
responses to air humidity (Marler and Mickelbart 1998). This process may reduce
productivity by 35%–50% (Campostrini and Glenn 2007).
3.2 Wind Velocity
Papaya does not like strong, cool, hot and dry winds. In open and high-lying areas,
plants are exposed to strong winds or storm. Papaya seedlings and adults are very