CONICET | Buscador de Institutos y Recursos Humanos

st1:*{behavior:url(#ieooui) }  ABSTRACT The objectives of this study were to identify the anatomical, morphological and mechanical properties of the root system of sunflower plants related to their tolerance to root lodging, and to evaluate the effects of increases in crop population density on these properties. An experiment was carried out using crops of two genotypes of susceptibility to lodging (CF29: tolerant and Zenit: sensitive) sown to achieve densities of 5.6, 10 and 16 plants.m2. At the R6 (end of anthesis) developmental stage plants were artificially lodged and the following response variables assessed: total root biomass in the root plate (hemisphere of roots and soil formed when lodging occurs) and separated by layers (05 and > 5 cm depth), root number (classified in three categories [01 mm; 1.12 mm; >2 mm diameters]), axial tension required to provoke root failure, and the number and cell wall thickness of vascular bundles in root cross-sections. The CF29 genotype had 1.35 fold greater root biomass than Zenit, mainly located in the first layer of soil (05 depth). This higher biomass of CF29 reflected a higher root number than Zenit for all three categories of root diameter. Roots of CF29 exhibited higher axial tension failure thresholds than those of Zenit, and these thresholds increased more sharply with root diameter than for Zenit. In addition, CF29 roots had vascular bundles with thicker cell walls (30% greater) with respect to Zenit. In summary, the better anchorage of CF29 with respect to Zenit arises from several mutually reinforcing characteristics at both root-plate and individual root axis morphology and histology levels. Key words: cell wall thickness - crop population density - root axial tensile strength - root biomass - root lodging - root number