MSc

Rice is a staple food for more than half the world’s population. The growth and
productivity of the crop is intimately associated with climatic variants. Among different climatic
factors, temperature and incidence of UV-B radiation are important. The incidence of stress
(Temperature and UV) at different stages of growth determines the productivity of the crop.
Hence the present study was undertaken with the prime objective of evaluating the interactive
effect of UV-B radiation and elevated temperature at different phenophases of Uma rice variety
and its effect on growth and productivity.
The study was carried out at College of Horticulture, Vellanikkara during Jan to May-
2018. The UV-B radiation and atmospheric temperature were maximum during this season. 14
days old Uma seedlings were used as plantingmaterial. It was grown under four different
conditions, namely T1(10C lesser than ambient+ low UV-B), T2 (10 C higher than ambient+ low
UV-B), T3 (20 C higher than ambient+ low UV-B), T4 (Open condition). The plants were kept in
the polyhouses for 30 days during three phenophases of the crop viz, seedling to active tillering
(P1), active tillering to early reproductive (P2) and early reproductive to harvest (P2) and returned
to ambient condition to complete their life cycle. Morphological, biochemical, physiological and
yield parameters were analyzed during the growth period.
Exposure of plants to T1 (10 C below ambient) had least negative influence on growth,
physiology and yield of the crop across different developmental stages. A 10C increase in
temperature above ambient (T2) in phase 1 improved the yield and yield parameter. However the
impact was negative under same condition during phase 2 (P2) and phase 3 (P3). Maximum
deleterious effects were observed in T3 during phase 2 and 3.
Plants grown in open condition had lower plant height and higher number of tillers as
compared to plants grown in polyhouse condition (T1, T2 and T3). Number of days to heading
was less in plants grown under high temperature conditions (T2 and T3). The photosynthetic rate,
stomatal conductance and transpiration rate were maximum in T2 condition in all the three
phases of growth.
Analysis of biochemical parameters showed that the IAA content was 67 percent lesser in
plants grown under open condition as compared to ployhouses during P1. Similar decrease was
also found in the case of gibberellic acid and chlorophyll. Amylose content of the grain were
significantly reduced in the plants grown under T2 and T3 conditions during P2 and P3.
Plants exposed to temperature above ambient level (T2 and T3) during P2 and P3 stages
recorded a reduction in yield. Maximum yield reduction was observed in T3 condition which was
13 percent in P2 and 56 percent in P3. Reduction in spikelets number and pollen viability were
the main reasons. The study indicates that plants were most sensitive to high temperature stress
during the P2 and P3 stages, which can contribute to drastic yield decline while, the early stress
can have a positive influence on yield.