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et al., 2011). Rainfall of 70 mm received in 20 days during May-June may
be sufficient for triggering off flushing and flowering process in the plant,
but once the process is set off there should be continuous shower until fruit
ripening. Any dry spell even for a few days within this critical period of 16
weeks (flowering to fruit ripening) will result in low yield. Rainfall after
stress induced profuse flowering (Pillay et al., 1988; Ridley, 1912). Heavy
rains during flowering reduce the rate of pollination and continuous heavy
rainfall promotes vegetative development and limits flowering (Pillay et
al., 1988). Growth of fruit bearing lateral shoots (plagiotropes) and photo-
synthetic rate were maximum during peak monsoon (June-July) in India
(Mathai, 1983). A relative humidity of 60-95% is conducive for optimum
growth at various stages of growth.
Rainfall beyond normal during initial period of annual cycle (i.e., 5-11
March to 25 June-1 July) was harmful or would reduce the yield in major
black pepper growing regions of India (Kandiannan et al., 2011a). Rain-
fall of 244.5 mm received in 26 days during March-April and 144.1 mm
in 14 days during May resulted in very low yield, whereas, no rainfall in
January-February and 40 mm in March and good rainfall from third week
of April-August resulted in good yield (Kannan et al., 1988). Increased
rainfall during December and January tend to decrease productivity while
rains during premonsoon season (March-May) increase the productivity.
A study on 140 years of climatic data of Kerala indicated cyclical rainfall
pattern with a declining trend of annual as well assouthwest monsoon in
the last 60 years and an increasing trend in post monsoon rains (Rao et
al., 2009). Climatic data of two decades (1984-2004) revealed a declining
trend in rainfall and rainy days in major black pepper growing areas of
the country (Krishnamurthy et al., 2011). The impact of climate change in
the form of climate variability like floods and droughts adversely affected
food and plantation crops to a large extent (Rao et al., 2009). In Idukki (a
predominant black pepper growing region), the change in rainfall pattern
during 1999-2000 crop season affected the flowering and yield (John et
al., 1999). Suparman (1998) reported similar observation in Bangka, In-
donesia. Increasing trend in rainfall during summer months was observed
in black pepper growing regions of India (Parthasarathy et al., 2010 and
Kandiannan et al., 2011b) that could affect the flowering pattern. Tem-
poral and spatial variation in rainfall is also noticed (Kandiannan et al.,
2008). Comparison of the rainfall pattern and pepper yields during two
extremely adverse years (1980-1981 and 1986-1987) with that of a fa-
