Comparative Analysis of Tomato Rootstock Root System Morphology

At its most basic, grafting is the replacement of one root system with another containing more desirable traits. Grafting of tomato (Solanum lycopersicum) onto disease-resistant rootstocks is an increasingly popular alternative to managing economically damaging soil-borne diseases. Certain rootstocks have been shown to confer additional benefits to the scion in the form of improved tolerance to edaphic and other abiotic stresses; however, the mechanisms behind the enhanced stress tolerance are not well understood. Specific traits within root system morphology (RSM), in both field crops and vegetables, have been shown to improve growth under abiotic stress conditions. A greenhouse study was conducted November 2015 – January 2016 to compare the RSM of 17 commercially available tomato rootstocks and one commercial field variety (‘Florida-47’). Plants were grown in containers filled with a mixture of Turface® and pool filter sand (2:1 v/v) and harvested at 2-, 3-, or 4-weeks after emergence. The study was laid out in a RCBD with four blocks and fully factorial (18 cultigens  3 harvest dates) arrangement. At harvest, roots were carefully cleaned and then stained with 0.5 g L^-1 neutral red dye for 24 h. Following staining, roots were scanned and analyzed with WinRhizo. Data collected included total root length (TRL), average root diameter, specific root length (SRL), and relative diameter class. No significant cultigen  harvest interaction was found. The main effect of cultigen was significant (P ≤ 0.05) for all response variables and the main effect of harvest was only significant (P ≤ 0.01) for TRL. ‘Shield RZ’, ‘RST-106’, and ‘TD-2’ had the longest TRL throughout whereas ‘Beaufort’, ‘Kaiser’, and ‘RST-105’ had the shortest. ‘BHN-1088’ had the thickest average root diameter, which was 32% thicker than the thinnest, observed in ‘Beaufort’. SRL in ‘Beaufort’ was 60% larger than ‘BHN-1088’. This study demonstrated that, in the non-grafted state, differences exist in RSM of tomato rootstocks grown and that, grown in a solid porous media, these differences can be quantified quickly and accurately using WinRhizo software. This method has the potential to help serve as a screen to further characterize rootstock quality and selection for growers.