J. Bolanos et Go. Edmeades, THE IMPORTANCE OF THE ANTHESIS-SILKING INTERVAL IN BREEDING FOR DROUGHT TOLERANCE IN TROPICAL MAIZE, Field crops research, 48(1), 1996, pp. 65-80
Selection for improved performance under drought based on grain yield
alone has often been considered inefficient, but the use of secondary
traits of adaptive value whose genetic variability increases under dro
ught can increase selection efficiency. In the course of recurrent sel
ection for drought tolerance in six tropical maize (Zea mays L.) popul
ations, a total of 3509 inbred progenies (S-1 to S-3 level) were evalu
ated in 50 separate yield trials under two or three water regimes duri
ng the dry winter seasons of 1986-1990 at Tlaltizapan, Mexico. In over
90% of the trials, ears plant(-1), kernels plant(-1), weight kernel(-
1), anthesis-silking interval (ASI), tassel branch number and visual s
cores for leaf angle, leaf rolling and leaf senescence were determined
, Low scores indicated erect, unrolled or green leaves. Canopy tempera
ture, leaf chlorophyll concentration and stem-leaf extension rate were
measured in 20-50% of the trials. Across all trials, Linear phenotypi
c correlations (P < 0.01) between grain yield under drought and these
traits, in order listed, were 0.77, 0.90, 0.46, -0.53, -0.16, 0.06(NS)
, -0.18, -0.11, -0.27, 0.17 and 0.10. Genetic correlations were genera
lly similar in size and sign. None of physiological or morphological t
raits indicative of improved water status correlated with grain yield
under drought, although some had relatively high heritabilities. Genet
ic variances for grain yield, kernels ear(-1), kernels plant(-1) and w
eight kernel(-1) decreased with increasing drought, but those for ASI
and ears plant(-1) increased, Broad-sense heritability for grain yield
averaged around 0.6, but fell to values near 0.4 at very low grain yi
eld levels, Genetic correlations between grain yield and ASI or ears p
lant(-1) were weak under well-watered conditions, but approached -0.6
and 0.9, respectively, under severe moisture stress. These results sho
w that secondary traits are not lacking genetic variability within eli
te maize populations. Their low correlation with grain yield may indic
ate that variation in grain yield under moisture stress is dominated b
y variation in ear-setting processes related to biomass partitioning a
t flowering, and much less by factors putatively linked to crop water
status. Field-based selection programs for drought tolerance should co
nsider these results.