Root system architecture in a barley RIL population: Agronomic effects of seedling and adult root traits

Drought tolerance has always been one of the main breeding targets of breeding programs for dryland agriculture in the Mediterranean region. This target has become even more urgent, given the current trends of decline and unpredictability of rainfall in the region. Historically overlooked, focus on roots has recently become a critical component in plant research aimed at improving drought tolerance. Recent advancements in root phenotyping methods have enabled more comprehensive investigations. The objective of this study was to assess the genetic control of root system architecture (RSA) of barley evaluated at an early stage, and its potential as a predictor of adult RSA and agronomic performance. We evaluated the RSA in seedlings of an elite recombinant inbred line population, Orria x Plaisant, using rhizoslides, and found genetic diversity and QTL for most traits. The extreme lines for root opening angle (RoA) were further tested for adult root structure under field conditions, through a shovelomics approach. A multifactorial analysis combining previously available agronomic traits with the two root analyses found a negative correlation between RoA at seedling stage and thousand kernel weight (TKW) in all years and locations tested. Some QTL were detected for root traits at seedling stage and some of them co- located with yield or related harvest traits. For adult plants, we found that a narrow RSA, compact, with profuse root growth was advantageous for yield in the field trials that suffered more drought. Overall, we found weak relationships of seedling RSA traits with agronomic performance and adult RSA traits. However, these relationships can still be useful to help selecting plants for good performance under drought in plant breeding programs.