Influence of water deficit and canopy senescence pattern on Helianthus annuus (L.) root functionality during the grain-filling phase

Abstract Root system size and functionality during the grain-filling phase are critical for water uptake and grain yield realization. In spite of its potential importance, root system functionality during this phase has received little attention. The study reported here aimed at documenting root system functionality dynamics between anthesis and physiological maturity, and its responses to water deficit, in two sunflower ( Helianthus annuus L.) hybrids of contrasting intrinsic patterns of canopy senescence. In experiments repeated in two separate years, crops of the hybrids Aguara 6 (stay green [SG]) and CF 101 (fast dry down [FDD]) were exposed to two levels of soil water availability (irrigation and drought) during grain filling, and the temporal dynamics of root and crop system variables (live root length density [LRLD], root respiration, sap flow rate, green leaf area index [GLAI] and the percentage of live roots [LR%]) were followed. The highest values for all variables were observed close to anthesis, and these differed little or not at all between hybrids within water regimes; but decreased thereafter at rates that differed between hybrids, water supply treatment and response variable. Drought hastened the beginning of root and leaf senescence in of both hybrids. The start of the decline in GLAI in the SG hybrid was significantly ( p p p p p