Grafting to address grand challenges
The discovery and implementation of grafting (watermelon onto pumpkin to alleviate soil pathogen pressure on crop productivity) at the beginning of the 20th century can be considered as a small belowground revolution, with benefits still occurring today. Indeed, alleviating soilborne diseases and extending early or late yields through rootstock-mediated vigor have been the main driving-forces for the rapid implementation of this technique, mostly in intensive high-value solanaceous and cucurbitaceous crops. Although the percentage of grafting is nearly 100% in some particular crops and in some areas, it is very low in many other species and, particularly, in developing countries. Moreover, the main agronomic traits of interest remain mostly the same, linked to the narrow genetic variability underlying the existing commercial rootstocks. Hence, the potential of using grafting in vegetables worldwide is still enormous, but further development will certainly depend on its capacity to address grand societal challenges: i) securing food production for the increasing population; ii) tackling malnutrition beyond feeding people; iii) conserving natural resources (aboveground and belowground biodiversity, water and soil); and iv) mitigation of, and adaption to, the climate change. Nevertheless, contributing to those societal challenges through grafting requires addressing some scientific and technical challenges: i) identifying agronomic/societal/environmental problems that can be alleviated by changing the root system of elite crop varieties (e.g., specific soilborne or airborne diseases, abiotic stress factors, alone or in combination, use of water and fertilizers, postharvest and/or nutritional properties of the fruits, association with beneficial microorganisms in the rhizosphere, etc.); ii) establishing publicly accessible collections and databases of the germplasm available in different graftable crop species; iii) developing adequate protocols for germplasm phenotyping and selection as a whole plant and as rootstocks according to the target goal or environment; iv) identifying physiological and genetic determinants of the traits of interest for conventional or biotechnological rootstock breeding; v) on-farm demonstration of rootstock impacts and benefit/cost ratio; vi) optimisation of management practices and well-established protocols; vii) rootstock × scion × environment interaction database supporting farmer decisions; and viii) developing high throughput grafting services providing high quality and affordable transplants at the right timing. For example, developing a rootstock conferring tolerance to the parasitic broomrapes for the industry cultivars, and providing cheap transplants to the farmers, could lead to another grafting-mediated belowground revolution with huge socio-economic and environmental impact in some developing countries.
Pérez-Alfocea, F. (2021). Grafting to address grand challenges. Acta Hortic. 1302, 9-20
biodiversity, food security, natural resources, resource use efficiency, rootstock breeding, rootstock × scion × environment, sustainable development goals