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in the laboratory two ca. 5 mm thick cross-sectional discs were cut 20 cm inside each end of the section. The
he_._wo_>d-+sapwood border and blue-stained areas were marked out on these two discs. Two separate measuren_ents for
fung_t sc_ccess were used: (I) percent of the sapwood which had become blue-stained, and (2) percent of the disc circurn ferer_ce
where the cambial area had been killed. For both measurements, the disc having the most ft._ngal proliferation was used
t(_ represen_ the tree.
Above the lower of these thin discs a thicker one was cut. This ca. 3 cm disc was used for re-isolation of' fungi from
Ihe wood. Three small wood chips were taken along one radius of the disc where staining occurred, one at the front of the
advancing blue=s'tain, one near the carnbium, and one in between.
The data were analyzed using the Minitab statistical system (Ryan et al. 1992).
RESUUFS
Dt.Jrin_4the period late October 1992 to late June 1993 precipitation at As amounted to ca. 400 ram, and a further 200
mm f:cll fron_ late June (inoculation) till inid-September (felling). Although small quantities of water must have leaked
{hrot_gh the ground cover and later the roof, the experimental trees were still deprived of most of this precipitation. The
spring of 1993 was drier than normal; only 124 mm felt during the period 1 March - 30 June, as opposed to a normal of 2 t 5
mm_ Normal annual precipitation is ca. 800 ram.
Measurement of pre-dawn xylem water potentials in late June demonstrated significant differences between stressed
and control trees in both clones (Fig. 1). In Clone 194 the WP values of stressed trees ranged between 0.75 and 0.95 MPa as
compared to 0.35..o0.50 MPa in the control trees. No stressed tree had as high a WP as any of the controls. Clone 582
exhibited les_ difference in WP between the two categories of trees, and one sheltered tree (#6) was no more stressed than
three of the control trees. Trees of the same clones at the top and bottorn of the slope showed no clear differences in WP
(rest_It nol shown).
On 29 June measurements indicated that stressed trees of Clone 194 yielded less constitutive resin in 24 hours than
controls (p=0.0()2), but on 6 July no difference could be detected. In Clone 582 such differences vere absent on both occa-
sions. Subjective estimates of surfTxce exudation of resin from the points of inoculation gave a rating that was about three
lime higher in stressed trees of both clones than in corresponding controls (p=0,0(X)).
LIpon felling on 14 September, no tree had lost its foliage. Several trees of Clone 194 had a yellow tint to their
fi_liage, but this occurred both in stressed and control trees.
The cross-sectional discs showed sapwood blue-staining varying from 0 to 100 percent (Fig. 2). Staining was much
more pronounced in controls than in drought stressed trees of Clone 194. The stressed tree that had the most fungal invasion
had mucf_ tess s{ain than the least affected control (p=O.000). In Clone 582, on the other hand, there was no difference
between stressed and control trees. This measure of fungal success coincided with percentage of the disc periphery where the
cambial area had been killed (Fig, 2). There was no overlap between stressed trees and controls in Clone 194 (p=0.()0()). [n
Chine 582 conm_t _rees proved to be somewhat more affected than the stressed ones (p=0.033).
O. poloruc_m was reisolated from 10 of the 12 trees of Clone 194 and 8 out of 12 in Clone 582. Because almost 12
weeks elapsed from i_oculation to felling, other fungi had also invaded the wood (cf. Solheim 1992). These were mainly
Nectria spp. (f:o_.md in 14 trees), but another Ophiostoma species, O. piceae (Mtinch) H. and R Syd., occurred together wiih
O. I;,o!