Recent evidence suggests peanut (Arachis hypogaea L.) may be sensitive
to relatively mild night temperature in terms of both dry matter accu
mulation and yield. The objective of this research was to quantify the
effects of a range of night temperatures (9-20 degrees C) on leaf CO2
exchange rate (CER) of unhardened plants and to study the mechanisms
involved in the contrasting response of peanut cultivars to differing
night temperature. Four peanut cultivars (Ontario Agricultural College
[OAC] Ruby, OAC Garroy, Chico, and Early Bunch) were grown in either
controlled-environment cabinets or outdoors during August and Septembe
r at Guelph, Ontario. Results of the outdoor study indicated a linear
decline in CER as ambient night temperature fell from 20 to 13 degrees
C for all cultivars except OAC Garroy, with OAC Ruby less sensitive t
o low night temperature than Chico or Early Bunch. Limitations to CER
after chilling at 10 degrees C in the dark were greater for Chico and
Early Bunch (CER reduced by approximate to 35%) than for OAC Ruby and
OAC Garroy (CER reduced by approximate to 15%). All cultivars showed t
he ability to recover CER within 24 to 48 h of alleviation of chilling
conditions. Cultivars grown indoors showed differing responses to one
or two successive chilling nights (Chico was more affected than all o
thers), but after four successive chilling nights, all cultivars showe
d a similar linear response to night temperature (i.e., CER = 0.693 x
Tmin + 11.8; r(2) = 0.90). An analysis of the relative contribution of
stomatal and mesophyll constraints to CER in indoor studies (chilled
at 9 degrees C) indicated significant limitations due to each componen
t, with the relative importance dependent on cultivar and chilling per
iod duration. Results suggest that night temperatures may be an import
ant factor in determining relative cultivar performance in cool produc
tion environments.