In Situ Root Growth with Mini-Rhizotrons: Lessons from Elevated CO2 and Genotypic Variability Experiments

Abstract

Root systems are notoriously difficult to study yet are likely largely responsible for performance under various environmental stresses. Better understanding of root systems might help us identify useful traits and/or superior genotypes in crops grown in the Canadian Prairie. Recently, with the development of mini-rhizotrons, i.e. clear acrylic tubes that are installed at an angle in the soil, scientists have been able to observe the development of root systems non-destructively as roots grow around the tube. Preliminary results were presented pertaining to experiments conducted in semi-arid areas: 1) Root growth in two lentil cultivars in response to elevated CO2 in the Australian Grains Free Air CO2 Enrichment (AGFACE) program 2) genotypic variability in root growth and depth with a subset of lines from the field pea and lentil breeding programs at Montana State University (MSU), and 3) root growth and depth in stay-green/low grain protein parents in wheat and barley populations, also at MSU. Preliminary results from AGFACE not only suggested differences between the two cultivars observed, but root depth was shallower with the better adapted cultivar, which was contrary to expectations. Preliminary results with ~20 lines of lentil showed root depth was not necessarily associated with larger biomass or higher harvest index, which suggests such trait might be stacked to improve lentil yields. Finally, early root assays with stay-green parents in the greenhouse were compared to flowering and maturity root growth in the field and suggested these are not good proxies to select for deep rooting in barley and wheat and other methods (such as thermal imagery for example) will be needed if breeders want to select for root growth at depth considering how time consuming the image analysis from mini-rhizotron currently is.