Chlorophyll fluorescence in vivo has been used to measure the chilling tolerances of three maize
populations and their crosses as males to an inbred Corn Belt Dent tester and to investigate whether
these populations can be chill hardened. In response to chilling at O�C, the logarithm of the maximal
rate of the induced rise of chlorophyll fluorescence (FR) in leaves of the populations of Confite Puneno,
Northern Flint and U.S. Corn Belt Dent and their crosses grown at 20�C day-15�C night decreased
linearly with time. Analysis of variance of the rate of decrease of In FR showed the populations to
possess significantly different levels of chilling tolerance. Confite Puneno, a highland Peruvian maize,
was the most tolerant with a half-fall time for FR of 11 8 h. This compared with 9.4 h for the Northern
Flint population, which is better adapted to cool conditions than the U.S. Corn Belt Dent, and 8 4
h for the US. Corn Belt Dent population. In the crosses, the chilling tolerance character of the paternal
population was retained. Remeasuring plant chilling tolerance using plants grown at 16OC day-6�C
night demonstrated that all three maize populations and their crosses had become markedly chill
hardened in terms of an increase in the half-fall time for FR of leaves kept at O�C. From the results
it is suggested that chlorophyll fluorescence in vivo can be used as a rapid screening test for chilling
tolerance at the varietal level.
