Genetic Basis of Variation in Root Aerenchyma Formation in Maize.

Aerenchyma formation results from the programmed death of root cortical cells in maize, and has long been associated with hypoxic stress during soil waterlogging. Other soil stress factors have been shown to increase aerenchyma formation, which is accompanied by decreased root respiration. Reductions in root respiratory burden allow increased root growth into new soil domains, suggesting that aerenchyma may be a strategic mechanism for dealing with nutrient and water deficiency. Recombinant inbred lines from three families (B73xMo17, Oh43xW64a, NY821xH99) were grown to four weeks in a greenhouse, and to eight weeks in a clay loam soil at Penn State's agricultural research station. Tissue segments were collected from the basal portion of a second whorl crown root for free hand sectioning. Images of root cross-sections were analyzed for various root anatomical traits using a program developed in Matlab to calculate area, perform object counting and identify the location of root cortical aerenchyma. Quantitative trait loci were identified for several traits, and will be presented. Correlations between the two developmental stages suggest an opportunity for phenotypic screening of the aerenchyma trait early in seedling growth by breeders. Significant genetic variation was observed for aerenchyma, indicating the potential to modify this trait by breeding to develop more stress-tolerant maize varieties.