Reciprocal Grafting Reveals Differential Metabolic Responses Between Robusta Clones with Contrasting Tolerances to Drought

Faced with global warming, the surface area of coffee cultivation regions is expected to diminish significantly in the near future. As a result, new varieties or agronomical practices improving drought tolerance need to be found. The aim of this work is to characterize drought tolerance of Coffea canephora genotypes and their reciprocal grafted plants with physiological tools and biochemical analyses. Under greenhouse conditions, control plants (sensitive or tolerant) and reciprocal grafted plants submitted to 14 days of water deprivation show variations of the monitored parameters, such as soil and leaf water potential, stomatal conductance, and osmoprotectant compounds (sugars, polyols, amino acids). The variations observed confirm the differences between the phenotypes defined as drought-tolerant and drought-sensitive. Reciprocal grafting shows enhanced and contrasting situations. A sensitive clone grafted onto tolerant rootstock presents higher tolerance to drought and physiological or biochemical parameters similar to a drought-tolerant clone. The opposite is observed for tolerant clones grafted onto a sensitive one. More contrasted results are obtained with glucose, fructose, proline, and mannitol content which could be used as indicators for drought tolerance. Our finding shows strong variability for drought tolerance in our Robusta clones and demonstrates the impact of grafting on physiological and biochemical parameters linked to drought tolerance. The use of drought-tolerant rootstock leads to better regulation of water management and biochemical composition of the scion in drought-sensitive clones. This could be an approach to improving drought tolerance of Coffea canephora genotypes and to limiting the impact of global warming on coffee farming.