Root-growth Characteristics Contributing to Nitrogen Efficiency of Reciprocally Grafted Potatoes (Solanum tuberosum L.) Under Hyroponic Conditions

To assess whether grafting could improve the nitrogen (N) efficiency of potato cultivars and to determine which physiological and morphological characteristics are predominantly contributing to N efficiency, a hydroponic experiment was conducted. Two contrasting potato cultivars (Agria: N‑efficient and Van Gogh: N‑inefficient) were grafted reciprocally onto each other. Grafted and non-grafted control plants were grown in a growth chamber for 42 days in 8 L pots filled with continuously aerated nutrient solution under two N rates (Low-N : 0.5 mM N and High-N : 3.0 mM N) by using a deep water culture (DWC) technique. The shoot and root fresh (FW) and dry (DW) weights, main stem length, number of leaves, total leaf area, photosynthetic activity of leaves, shoot and root N concentration, total N uptake, total root length and root volume of potato plants were significantly increased with increased N rate. The grafted plants produced significantly higher above ground biomass than non-grafted ones, indicating that N efficiency was significantly improved by the reciprocally grafting under low and high N rates. Non-grafted cv. Agria showed higher numbers of shoot and root FW and DW, total leaf area, intensity of photosynthesis net measurements, compared to non-grafted cv. Van Gogh under both N rates. In reciprocal grafting, the growth performance of cv. Agria slightly increased when it was grafted onto cv. Van Gogh, whereas a significant increase in crop growth performance was recorded when cv. Van Gogh was grafted onto cv. Agria. The N efficiency of non-grafted cv. Agria was closely associated with its vigorous root growth and active root system under both N conditions. Same root morphological characteristic could not be exhibited by the N‑inefficient cv. Van Gogh. Our study suggested that root morphological characteristics are contributing more than shoot characteristics to N efficiency of potatoes. These traits could be useful characters to breed/select N‑efficient potato rootstocks for sustainable agriculture in the future.