Assessing cold tolerance heterosis at corn seedling stage using some physiological traits

Corn susceptibility to cold stress during early autotrophic growth is an important limitation for its cultivation in the cold areas. To identify the physiological basis of cold tolerance heterosis in maize seedlings, the changes of some physiological traits were studied in maize cold tolerant and susceptible inbred lines and hybrids at seedling stage in University of Zanjan, Iran, in 2017. The results showed that the effect of cold treatment onchlorophyll fluorescence, relative water content, electrolyte leakage,chlorophyll acontent, chlorophyll bcontent, carotenoids, root volume, root area androot dry weight were significant. The better-parent heterosis was detected in chlorophyll b content, root area, root volume and electrolyte leakage in most hybrids. Performance of MO17×EP80 hybrid was better than other hybrids for all physiological traits under stress conditions. EP42×MO17 and A661×MO17 hybrids also had better root growth and extension under cold stress conditions.The significant correlation was only observed between heterosis values of some traits that had a common genetic, physiological and developmental basis, such as root dry weight and relative water content or chlorophyll b content and electrolyte leakage. However, the correlation between heterosis values of the other traits was generally poor, indicatingthat the genetic basis of heterosis is trait dependent and probably not controlled by a single mechanism. The significant differences among genotypes in all traits, provide a new opportunitto improve cold stress tolerance in a tropical plant using plant breeding.