172 V. G. Kakani et al.
Hence, an interaction between temperature and water stress occurs on plant growth
during the entire 12 h of photo-thermo period, providing a longer period for the
interaction to influence the growth and development of the crop plant under study.
However, under field conditions, increase in day temperature follows a more or less
sinusoidal pattern (Fig. 8.1), and high air temperature effects on plant in field occur
for a short duration of only 3–4 h. Furthermore, the temperature of plant canopy can
be higher than that in controlled environment under similar air temperatures due to
associated radiative heating in semiarid tropic (SAT) regions (Guilioni et al. 2000 ).
Hence, the interaction between the stress events that occur under controlled envi-
ronment might be different from those occurring in the field. If true, this would have
important implications for using controlled environment facilities for screening for
water and temperature stress.
Temperature increase across the treatments, T1 to T4, (Table 8.1) was achieved
by using plastic heat tunnels in the field. Humidity was controlled in these heat
tunnels by opening the heat tunnel doors for brief periods during the day; nonethe-
less, an increase of humidity in these heat tunnels did occur, particularly at sowing
1 (i.e. T2). The normalized WUE values observed in this study were less (1.6–1.3 g
kPa L−1) than recorded by other researchers (e.g. 3.5 g kPa L−1 by Ong et al. 1987 ;
1.9 g kPa L−1 by Mathews et al. 1988 ) due to the higher temperatures to which the
crop was exposed. This experiment was conducted during the hot summer season
of India and warmer temperatures would have caused an increase in evaporation
with less water available for transpiration by the plants. Water stress inhibits leaf
expansion and stem elongation through a reduction of relative turgidity (Slatyer
1955 ; Allen et al. 1976 ; Vivekanandan and Gunasena 1976 ), thus altering both leaf
Table 8.7 Interaction between genotype and temperature treatments for flower number (plant−1)
at 30 DAA, pod number (plant−1), pod yield (g m−2) and harvest index as observed at final harvest
Cultivar Mean temperature treatments (°C) SED
T1(27) T3 (29) T4 (30)
Flower number
TMV 2 35 35 28 4.2
ICGS 11 42 55 50
Pod number
TMV 2 16 10 10 2.4
ICGS 11 15 24 22
Pod yield
TMV 2 140.0 51.0 42.8 15.26
ICGS 11 142.2 103.8 109.4
Harvest index
TMV 2 0.36 0.18 0.14 0.024
ICGS 11 0.34 0.29 0.28
TMV 2 Spanish botanical type, a selection from ‘Gudhiatham Bunch’ and a local variety
, , *** indicate significance at 0.05, 0.01 and 0.001 levels of probability, respectively
SED Standard Error of Difference of Means