Vigorous Rootstocks Improve Nitrogen Efficiency of Tomato by Inducing Morphological, Physiological and Biochemical Responses

Due to insufficient fertilizer application by small-scale farmers, soil fertility is declining in low-input agriculture while environmental pollution of both air and water is rising in high-input agriculture due to excessive nitrogen (N) fertilizers application. However, the efficiency of N fertilizers is frequently low, since plants take up often less than 50% of the applied N, and thus the not utilized N is left in the soil and/or lost from the plant/soil system. To improve the available N in sustainable agriculture, improved fertilizers as well as soil and crop management practices are necessary. Among these, a way to improve N efficiency and reduce the losses in production caused by low N efficiency in high-yielding genotypes would be to graft them onto rootstocks capable of improving N efficiency of the scion in both agriculture systems. The aim of this study was initially to determine the genotypic differences in N efficiency of some local and hybrid tomato genotypes and further to evaluate whether reciprocal grafting could improve N efficiency of tomato through examining shoot agronomical, root morphological and leaf physio-biochemical responses induced by the rootstocks. Two hydroponic experiments were conducted in a deep water culture (DWC) technique at Plant Physiology Laboratory of Erciyes University. In the first experiment (Exp.1: 12th September 2017), 4 hybrids and 10 local Turkish varieties and 4 local Ghanaian tomato cultivars were screened under 2 N doses (Low N: 0.3 mM and High N: 3.0 mM) in complete randomized block design under 3 replications for six weeks. Based on the results of the first experiments, two tomato genotypes HelenaF1 and ALT (N-efficient) were chosen and used as rootstock by grafting with N‑inefficient; P005 and Karahidir tomato genotypes under 2 N doses in the second experiment (Exp.2: 2nd February 2018). As compared to non-grafted control plants, the grafting increased the shoot dry matter by almost 31.6% and 31.1%, the shoot N uptake by 50.1% and 41.3% and the total leaf area by 29.4% and 67.3% at low and high N rate, respectively. Best performance in nitrogen use efficiency (NUE) was shown by Karahidir/ALT (S1/R2) and Karahidir/Helena (S1/R1) graft combinations. HelenaF1 and ALT genotypes have high rootstock potential which was associated with morphological, physiological, and biochemical response characteristics particularly at low N supply. Therefore, these traits could be useful for the selection and breeding of “N-efficient” tomato rootstocks for sustainable agriculture in the nearby future.