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Brown heartwood rot, which often is found in branches within lemon groves in southwestern Arizona, is caused by two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila. Another fungus, a species of Nodulisporium, has been recovered from small, dying lemon tree branches with an internal white wood rot. Studies were conducted from 1999 through 2002 to compare the extent of wood decay caused by these fungi (i) on lemon tree branches at different times of the year, (ii) on different types of citrus, (iii) on some desert woody perennial plants, and (iv) on lemon tree branches treated with selected fungicides. The mean length of wood decay columns recorded in lemon tree branches inoculated with A. sinuosa, C. eremophila, and the Nodulisporium sp. during the time periods of November to January, February to April, May to July, and August to October was 2.9, 4.7, 13.3, and 15.2 cm, respectively. There was a significant linear correlation between the length of wood decay columns and air temperature for all three pathogens. The mean length of wood decay columns for all time periods in branches inoculated with A. sinuosa, C. eremophila, and the Nodulisporium sp. was 11.8, 5.8, and 9.6 cm, respectively. In two trials, wood decay columns were significantly greater on Lisbon lemon tree branches inoculated with A. sinuosa compared with those on Marsh grapefruit and Valencia orange trees inoculated with the same pathogen. Wood decay in the presence of the Nodulisporium sp. was greater on branches of lemon compared with grapefruit trees in two trials and on lemon compared with orange trees in one of two trials. With the exception of C. eremophila on creosote bush, each of the three wood rot pathogens caused some wood decay in branches of velvet mesquite, salt cedar, Mexican palo verde, and creosote bush, four common desert perennials found in southwestern Arizona. Compared with nontreated but inoculated lemon trees, the length of wood decay columns in branches inoculated with A. sinuosa, C. eremophila, and the Nodulisporium sp. in the presence of propiconazole was reduced by 79, 94, and 92%, respectively, and, in the presence of azoxystrobin, was suppressed by 71, 80, and 89%, respectively. Current management guidelines focus on minimizing branch fractures and other nonpruning wounds in conjunction with early detection and removal of infected branches before the onset of the increased wood decay development period extending from May to October. |
