88 Wyka et al.: Effects of G. clavigera and L. longiclavatum on Western White Pine Table 1. Evaluation of mortality 120 days after inoculations and injection of Pinus monticola seedlings with respective treatments in Experiment 1. Mortality rates for each treatment are based on 10 seedlings. Study Pathogenicity Treatment G. clavigera L. Longiclavatum Alamo/B.S.x Phytotoxicity Sterile agar TREE-äge Arbotect Alamo UTCw z Vascular discoloration evident. y Treatments within a study with the same letter are not significantly different based on Fisher’s exact test with Bonferroni-adjusted P-values. x Blue-stain (B.S.) both G. clavigera and L. longiclavatum. w Untreated Control (UTC). to compare the differences in foliar browning, circumferential girdling, and axial lesion length. Lesion length was log-transformed prior to anal- ysis to decrease variance heterogeneity. Pairwise comparisons among treatments were carried out with Tukey’s HSD procedure at the 0.05 level of significance using the MIXED procedure in SAS. Experiment #2 Dual inoculation of G. clavigera As before, P. monticola seedlings (mean caliper and height of 0.5 ± 0.02 and 15.0 cm ± 0.4 SE respectively), were purchased from the Univer- sity of Idaho, Franklin H. Pitkin Forest Nursery (Moscow, Idaho, U.S.). In this experiment, G. clavigera and sterile MEA agar, with 10 replicates per treatment were employed. Leptographium longiclavatum was not used in this experiment because it failed to survive cold storage between experiments. Inoculations were made as in Ex- periment 1, but with a second inoculation being made on the opposite side of the stem (180 de- grees to the first) and offset by 1 cm in height. The lesion data from Experiment 1 were used to determine the offset distance between inci- sions in this experiment. Seedlings were kept in a greenhouse under the same environmental conditions as previously stated and destruc- tively autopsied after 40 days. This was suffi- cient time to observe needle browning. Lesion development was not documented, as research- ers were only concerned with tree mortality. Cross sections of stems with fungal inoculations were plated on MEA to recover fungal species. ©2016 International Society of Arboriculture RESULTS no evidence of repression with increasing concen- trations of TREE-äge (from 1 to 10,000 ppm, t31 Fungicide Screening The effect of concentration on repression of G. clavigera growth in vitro (Table 2) was not the same for all fungicides (F8,29 = 17.76, P < 0.001). There was = 0.05, P = 0.962). In contrast, there was significant re- pression observed with increasing concentrations of the fungicide treatments Alamo and Arbotect (t31 15.46, P = < 0.001 and t31 = = 10.28, P = < 0.001, respec- tively). Treatments of Alamo at 1,000 and 100 ppm, showed significantly greater repression than respec- tive concentrations of Arbotect (P < 0.05) (Table 2). However, Alamo at 10 and 1 ppm, and Arbotect at 100, 10, and 1 ppm, were not significantly different in repression than the control (P > 0.05) (Table 2). Experiment #1 Pathogenicity of fungal isolates After inoculations, L. longiclavatum and G. clavigera successfully colonized the sapwood and resulted in mortality of 50 and 90% of seedlings, respectively (Table 1). One seedling in the DI water control group (10% mortality) and two in the sterile agar treatment group (20% mortality) died. As mentioned, these two control groups were pooled (15% mortality) for statistical com- parisons, resulting in a significantly lower mor- tality than that observed with G. clavigera (FET, P < 0.001) but no difference in that observed with L. longiclavatum (P = 0.467) (Table 1). Ten per- cent mortality was observed in seedlings injected Pooled controls [100 μL DI H2 O % Mortality ± SE 90 ± 10.0% ay 50 ± 16.7% ab 10 ± 10.0% b 15 ± 8.0% b 20 ± 13.0% 10 ± 10.0% 0.0 ± 0.0% a 0.0 ± 0.0% a 0.0 ± 0.0% a 10 ± 0.0% a Foliar symptoms desiccated desiccated desiccated desiccated desiccated normal normal normal desiccated Vasc. disc.z yes yes yes no no no no no yes Notes vascular lesions vascular lesions vascular lesions dehydrated dehydrated] n/a n/a n/a unidentified vascular infection
March 2016
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