Exploring Solanum rootstock biodiversity for improving nutrient use efficiency in tomato

Agricultural productivity must increase by 60% to feed the expected population of 9.6 billion people in 2050, and this increment needs to be achieved in parallel to the socio-environmental sustainability of the natural resources. In other words, it is necessary to produce more with less or more with the same. In general, the crop efficiency in the use of fertilizers is estimated to be below 50%, therefore there is a huge scope for reducing the inputs without compromising yield. While nutrient-related traits have been rarely targeted in breeding programmes, the belowground root traits can offer an interesting opportunity for this purpose. Indeed, the root system serves as the interface between the soil, where the nutrients are located, and the shoot, where the nutrients are transported and converted into (normally) harvestable biomass. Consequently, the root has a significant role in the nutrient use efficiency of the crop by affecting both the nutrient capture efficiency from the soil (through changes in root system architecture and nutrient-transport components) and the nutrient use efficiency in the shoot (through influencing shoot growth and physiology and their control by nutrient availability). Using rootstocks additionally offers the possibility of straight enhancement of root traits without altering the major properties of the elite scion cultivars (Albacete et al., 2015). Here we present some preliminary data on the genetic variability of Solanum spp. in response to nutrient (N, P, K) deficiency in order to select genotypes as a basis for developing nutrient-efficient tomato rootstocks. A total of 96 genotypes, including the cultivated tomato Solanum lycopersicum, the wild species S. pennellii, S. habrochaites, S. pimpinellifolium, and S. neorickii, and the introgression lines derived from crosses between the domestic tomato and some of its wild relatives, have been evaluated during the vegetative development stage under low N, P, and K fertilization. Under N-, P-, and K-deficiency conditions, variation in plant biomass was 4.2-, 2.4-, and 2.3-fold, respectively. Based on both above-and belowground productivity, 10 genotypes with specific or broad resilience under the different individual nutrient deficiencies were selected for further evaluation as rootstocks of an elite commercial tomato cultivar.