Abstract
Environments with short growing seasons and variable climates can have soil temperatures that are suboptimal for chilling-sensitive crops. These conditions can adversely affect root growth and physiological performance thus impairing water and nutrient uptake. Four greenhouse trials and a field study were conducted to investigate if rootstocks can enhance tomato performance under suboptimal soil temperatures (SST). In a controlled greenhouse environment, we exposed four commercial rootstocks (Estamino, Maxifort, RST-04-106-T, and Supernatural) grafted with a common scion (cv. BHN-589) to optimal (mean: 24°C) and SST (mean: 13.5°C) and compared their performance with the non-grafted BHN-589 cultivar. Several root and shoot physiological traits were evaluated: root hydraulic conductivity and conductance, root anatomy, leaf gas exchange, leaf δ13C, shoot C and N, and biomass. Under field conditions, the same five phenotypes were evaluated for canopy growth, normalized difference vegetation index (NDVI), leaf nutrients, biomass, and yield. Under SST, root hydraulic conductivity (Lp) and conductance (KR), stomatal conductance (gs), and plant biomass decreased. Hydrostatic Lp decreased more than osmotic Lp (Lp∗hyd: 39–65%; Lp∗os: 14–40%) and some of the reduced conductivity was explained by the increased cortex area of primary roots observed under SST (67–140%). Under optimal soil temperatures, all rootstocks conferred higher gs than the non-grafted cultivar, but only two rootstocks maintained higher gs under SST. All phenotypes showed greater reductions in shoot biomass than root biomass resulting in greater (∼20%) root-to-shoot ratios. In the field, most grafted phenotypes increased early canopy cover, NDVI, shoot biomass, and fruit yield. Greenhouse results showed that Lp∗os may be less affected by SST than Lp∗hyd and that reductions in Lp may be offset by enhanced root-to-shoot ratios. We show that some commercial rootstocks possess traits that maintained better rates of stomatal conductance and shoot N content, which can contribute toward better plant establishment and improved performance under SST.
Highlights
Tomato (Solanum lycopersicum L.) is a highly nutritious crop produced globally and under a wide array of abiotic and biotic stresses
Suboptimal soil temperatures (SST) only reduced Lp∗os for two phenotypes compared to their optimal soil temperature (OST) counterparts (Figure 1B)
Rootstock vigor is usually referred as the cause of improved cultivar performance, this study shows specific traits associated with grafting that enhanced tomato performance under SST
Summary
Tomato (Solanum lycopersicum L.) is a highly nutritious crop produced globally and under a wide array of abiotic and biotic stresses. For thermophilic crops such as tomato, production is especially challenged in regions where low temperatures are a significant environmental factor determining the cropping season (Schwarz et al, 2010). Air temperatures fluctuate close to the optimal conditions for shoot function, but root physiology is still challenged by SST (Walter et al, 2009). Root performance under SST becomes critical (Schwarz et al, 2010), especially early in the growing season, and the use of rootstocks that are less susceptible to SST could provide desirable traits to overcome some of the limitations for cold-sensitive vegetables in regions where soil warming is slow or farmers consider earlier plantings to avoid extreme heat during the summer
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