EVALUATING PHYSIOLOGICAL TRAITS TO COMPLEMENT EMPIRICAL SELECTION FORWHEAT IN WARM ENVIRONMENTS (REPRINTED FROM WHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998)
Mp. Reynolds et al., EVALUATING PHYSIOLOGICAL TRAITS TO COMPLEMENT EMPIRICAL SELECTION FORWHEAT IN WARM ENVIRONMENTS (REPRINTED FROM WHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998), Euphytica, 100(1-3), 1998, pp. 85-94
The response of spring wheat to heat stress has been determined in sev
eral hot wheat growing environments worldwide on different types of ge
rmplasm. Physiological data has been collected to identify potential t
raits to assist in the empirical breeding for heat tolerance. Initial
studies focused on 10 established varieties to determine genetic diver
sity for heat tolerance, identify association between heat tolerance a
nd traits measured, and evaluate genotype by environment interaction (
G x E). Yields from over 40 hot environments were analysed for G x E,
and relative humidity (RH) was identified as the major factor determin
ing relative genotype ranking. Further analysis focused on 16 environm
ents: those with low RH and relatively high yields, i.e., over 2.5 t h
a(-1). For these environments, mean yield of lines correlated with a n
umber of physiological traits measured in Mexico, including canopy tem
perature depression (CTD), membrane thermostability, leaf conductance
and photosynthetic rate at heading, chlorophyll content during grainfi
lling, leaf internal CO2 concentration, and dark respiration. Morpholo
gical traits were measured in all environments and the following showe
d associations with yield: above ground biomass at maturity, days from
emergence to anthesis and to maturity, grain number m(-2), and ground
cover estimated visually after heading. Subsequent studies focused on
breeding material, namely recombinant inbred lines derived from cross
es between parents of contrasting heat tolerance, and 60 advanced bree
ding lines selected for performance under heat stress. The genetic bas
is for association between heat tolerance and CTD was established by d
emonstrating a correlation between the two traits in RILs (recombinant
inbred lines). Data from RILs, as well as from the 60 advanced lines
grown at several international locations, indicated CTD to be a powerf
ul and robust selection criterion for heat tolerance.