EXAMINATION OF GRAFT FAILURE IN NEW-ZEALAND CHESTNUT (CASTANEA SPP) SELECTIONS

Three experiments were conducted from 1988 to 1996 to evaluate graft f ailure in New Zealand chestnut selections. It was found that graft fai lure was genotype specific. Grafts from the North Island selections (e xcept '1002' and '1007') were most strongly affected. A cross section of the graft union from different selections showed varying forms of g raft failure, although the reasons for the failure were not certain. W hen the rootstock '1005' was chosen, graft failure was categorised int o two forms: early and late graft failures. Early failure started imme diately after grafting up until 19 months after grafting (MAG) with a peak at 9 MAG. Late graft failure started at 32 MAG. Long Bay 1, Long Bay 2, Crewenna 2 and Crewenna 3 selections had both early and late gr aft failures while selections 1005, 1015 and Don Whelan showed a late graft failure. 'Crewenna 1' did not fall into any specific category. A cross section of the graft union of the surviving grafts showed that there were different degrees of graft failure ranging from a healthy g raft with little cracking at the graft union, to a graft about to fail with extensive cracking coupled with black wood and bark within the s tem. The likely reasons for the graft failures recorded in this study are discussed. It is not known at this stage whether the failure is ca used by a specific incompatibility reaction or is a less specific reac tion. (C) 1998 Elsevier Science B.V. All rights reserved.