S04 - Session P4 - Understanding wound-responsive mechanisms underlying micrografting success in almond (Prunus dulcis (Mill.) D. A. Webb)

Authors: Ana Pedrosa *, Tércia Lopes, Sandra Caeiro, Liliana Marum , Jorge Canhoto, Sandra Correia

Grafting is a common horticultural technique used to propagate commercially important Prunus spp. fruit crops, including almond tree ( Prunus dulcis (Mill.) D. A. Webb). By combining parts from different varieties, usually a highly adaptable rootstock with a productive scion, major outcomes are achieved regarding plant productivity. In vitro grafting involves grafting a micro-scion onto a micro-rootstock under aseptic conditions bypassing phytosanitary issues reported for field grafting techniques. Besides its important application in crop improvement, it has been also used for studying molecular mechanisms involved in scion-rootstock interactions and long-distance signaling. Researchers have pointed out wound response, preceding vascular reconnection, as a key factor for the successful establishment of a graft union. Many candidate genes that are involved in the plant wound response have been identified. However, their specific but their roles in grafting, particularly in woody species, remains unclear. In this work, wound responsive mechanisms were evaluated in micrografts established from micropropagated shoots of commercially available almond varieties ('Lauranne' and 'Ferraduel') and the rootstocks GF677. Bitter almond micropropagated shoots were also used in the experimental design as rootstocks. In vitro propagation of micro-scions and micro-rootstocks was carried out in a modified MS medium supplemented with 800 µg/L BAP. Heterografts between GF677 and bitter almond rootstocks and scions of 'Lauranne' and 'Ferraduel' varieties were established as well as homografts of bitter almond. Sampling was made before grafting (t0) and one (t1) and three (t3) weeks after grafting, dissecting the micrograft union region for each scion/rootstock combination. Total RNA extraction was performed, and cDNA synthetized from a total of 39 samples in 3 biological replicates. Wound-responsive factors expression ( e.g ., WOUND INDUCED DEDIFFERENTIATION 1,2 ) was evaluated by qPCR, and associated with micrografting success within the different combinations of scions/rootstocks. This study provides deeper mechanistic insights into how wounding responses affect almond micrografting success.