Elimination of a Bud Union Abnormality of Sweet Orange Grafted on Rough Lemon by Shoot-tip Grafting in Vitro

A bud union abnormality of several old line sweet orange varieties grafted on rough lemon rootstock was observed for the first time in Spain in container-grown plants. Shoot-tip grafting in vitro was carried out on these varieties as part of the standard procedure in the Spanish Citrus Variety Improvement Program. Ten propagations from a micrografted source of Cadenera punchosa sweet orange on rough lemon growing in containers under outdoor conditions were found free of symptoms after 6 yr. Ten similar propagations graft-inoculated with the parent source and ten propagations made directly from the parent showed the bud union abnormality after 6 yr. These results indicate that the bud union abnormality observed in several varieties was produced by a graft-transmissible agent and that it could be eliminated by shoot-tip grafting in vitro