Abstract
Grafting provides a tool aimed to increase low-P stress tolerance of crops, however, little is known about the mechanism (s) by which rootstocks can confer resistance to P deprivation. In this study, 4 contrasting groups of rootstocks from different genetic backgrounds (Solanum lycopersicum var. cerasiforme and introgression and recombinant inbred lines derived from the wild relatives S. pennellii and S. pimpinellifolium) were grafted to a commercial F1 hybrid scion and cultivated under control (1 mM, c) and P deficient (0.1 mM, p) conditions for 30 days, to analyze rootstocks-mediated traits that impart low (L, low shoot dry weight, SDW) or high (H, high SDW) vigor. Xylem sap ionic and hormonal anlyses leaf nutritional status suggested that some physiological traits can explain rootstocks impacts on shoot growth. Although xylem P concentration increased with root biomass under both growing conditions, shoot biomass under low-P was explained by neither changes in root growth nor P transport and assimilation. Indeed, decreased root P export only explained the sensitivity of the HcLp rootstocks, while leaf P status was similarly affected in all graft combinations. Interestingly, most of the nutrients analyzed in the xylem sap correlated with root biomass under standard fertilization but only Ca was consistently related to shoot biomass under both control and low-P, suggesting an important role for this nutrient in rootstock-mediated vigor. Moreover, foliar Ca, S, and Mn concentrations were (i) specifically correlated with shoot growth under low-P and (ii) positively and negatively associated to the root-to-shoot transport of the cytokinin trans-zeatin (t-Z) and the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), respectively. Indeed, those hormones seem to play an antagonistic positive (t-Z) and negative (ACC) role in the rootstock-mediated regulation of shoot growth in response to P nutrition. The use of Hp-type rootstocks seems to enhance P use efficiency of a commercial scion variety, therefore could potentially be used for increasing yield and agronomic stability under low P availability.
Highlights
While the low availability of phosphorus in most agricultural soils commonly limits plant growth requiring the application of chemical fertilizers or organic manures, it is considered one of the major contaminants of aquifers following nutrient addition
This study aims at verifying whether the rootstock could induce variation in shoot vigor under low P conditions by altering root export of P and other nutrients/phytohormones that regulate shoot growth and P use efficiency
Boludo F1, Seminis Vegetable Seeds Ibérica S.A., Barcelona, Spain) as scion, which was either self-grafted or grafted onto 144 different rootstocks (Albacete et al, 2015b): a population of 129 recombinant inbred lines (RILs) developed from a salt-sensitive genotype S. lycopersicum var. as female parent and a salt-tolerant line from S. pimpinellifolium as male parent (Monforte et al, 1997) provided by Instituto Valenciano de Investigaciones Agrarias (IVIA); six accessions derived from a cross between S. lycopersicum var. cerasiforme and S. pimpinellifolium, selected for drought tolerance and nine introgression lines from S. lycopersicum × S. pennellii and × S. habrochaites, selected for high root/shoot ratio, salinity, and drought tolerances
Summary
While the low availability of phosphorus in most agricultural soils commonly limits plant growth requiring the application of chemical fertilizers or organic manures, it is considered one of the major contaminants of aquifers following nutrient addition. Grafting is used as an alternative to breeding in horticultural crops since appropriate and compatible rootstocks can enhance plant performance by improving both nutrient acquisition and utilization efficiency (Lee and Oda, 2010; Gregory et al, 2013; Albacete et al, 2015c; Nawaz et al, 2016). Grafting alters concentrations of several macro and micronutrients in the shoot tissues compared to the non-grafted and self-rooted plants (Rouphael et al, 2008), rootstock-mediated physiological effects under nutrient deficit conditions have been rarely studied (Pérez-Alfocea, 2015; Nawaz et al, 2016). Rootstocks can improve P uptake and its transport to the leaves, almost no information is available about the underlying rootstock-mediated physiological mechanisms (Albacete et al, 2015c; Pérez-Alfocea, 2015; Nawaz et al, 2016)
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