Dissecting heat stress tolerance in tropical maize (Zea mays L.)

Abstract

The negative effects of heat stress on maize growth and reproduction is often expressed in terms of significant yield penalty. Germplasm selection based on yield potential along with heat stress adaptive secondary traits, and establishing their interaction under stress helps in identifying suitable heat tolerant genotypes. To dissect intricate nature of heat stress tolerance, two field trials were conducted during spring 2014 and 2015 under natural heat stress conditions. Planting was adjusted to expose reproductive and grain filling period to high temperature regimes during May month in Hyderabad, India. Correlation analysis between grain yield under stress and secondary traits observed in two year experiments indicated that the traits such as - leaf firing (LF) (r=−0.34** and 0.06), tassel blast (TB) (r=−0.18 and −0.25), tassel sterility (TS) (r=−0.08 and −0.38*), anthesis-silking interval (ASI) (r=−0.24* and −0.02) and senescence (SEN) (r=−0.27** and −0.34*) were negatively correlated, while pollen shedding duration (PSD) (r=0.33** and 0.4*), seed set percentage (SSP_OP) (r=0.76** and 0.58**) and chlorophyll content (CHL) (r=0.55** and 0.41*) were positively associated with grain yield under stress in 2014 and 2015, respectively. An ASI of 2–4days and PSD of 2–4days were found advantageous to grain yield under heat stress. Stigma receptivity was less affected under heat stress when compared to pollen viability, yet stigma initiation was delayed under heat stress, which resulted in prolonged ASI. Overall effect of heat stress was expressed in terms of SSP_OP, which explained yield variation by 78.5 and 57.8% for experiment 1 and 2, respectively. Thus, traits that are indicative of reproductive success under heat stress (ASI, TB, TS, pollen viability, stigma receptivity and SSP_OP) and other morpho-physiological traits (LF, SEN and CHL) may be used along with grain yield in index selection of suitable germplasm for heat stress tolerance.