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Biology and Control of Lemon Tree Wood Rot DiseasesBrown heartwood rot is commonly found in mature lemon groves in southwestern Arizona. Two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila, have been isolated from symptomatic trees. A major difference between the two pathogens is that Antrodia forms spore-producing fruiting bodies on infected wood within lemon groves, whereas fruiting on lemon wood infected by Coniophora has not been observed. A third fungus, a species of Nodulisporium, recently was recovered from small dead lemon tree branches with an internal white wood rot. Experiments were conducted to compare the severity of wood rot caused by each of these pathogens. The highest rates of wood decay for each pathogen occurred from May through October, when the mean length of wood decay columns for Antrodia, Coniophora and Nodulisporium was 183, 94 and 146 mm, respectively, and the mean air temperature was 29°C. In comparison, the mean length of wood decay columns from November through April for the same pathogens was 35, 18 and 38 mm, respectively, with a mean air temperature of 17°C. When inoculated with Antrodia, Coniophora or Nodulisporium, the length of wood decay columns on 40- mm-diameter branches was 26, 38 and 24% larger, respectively, compared to wood decay on 10-mm-diameter branches. The length of wood decay columns on inoculated Lisbon lemon was always numerically greater than that on tested orange, grapefruit and tangelo trees. Compared to lemon, wood decay columns ranged from 45 (on grapefruit) to 62 %( on orange) shorter when inoculated with Antrodia, 52 (on orange) to 59% (on tangelo) for Coniophora and 20 (on tangelo) to 51% (on grapefruit) for Nodulisporium. Compared to non-treated branches, suppression of wood decay in the presence of a test fungicide ranged from 28 to 79% for Antrodia, 77 to 91% for Coniophora and 71 to 92% for Nodulisporium. For each pathogen, the lowest numerical degree of wood rot suppression occurred in the presence of trifloxystrobin (Flint), whereas the highest level of suppression was observed with propiconazole (Break). On greasewood, mesquite, Palo Verde and salt cedar, the length of wood decay columns ranged from 20 to 60 mm when inoculated with Antrodia, 1 to 63 mm for Coniophora and 24 to 90 mm for Nodulisporium. For all three wood-rotting fungi, resultant wood decay columns were always much greater on lemon compared to tested desert-dwelling plants. Current disease management strategies include minimizing branch fractures and other non-pruning wounds as well as periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.
Studies of the Biology and Control of Brown Heartwood Rot on Lemon Trees in 2000Brown heartwood rot is commonly found in mature lemon groves in southwestern Arizona. Two basidiomycete fungi, Antrodia sinuosa and Coniophora eremophila, have been isolated from symptomatic trees. Similarities between the two pathogens include the following: each fungus grows optimally at 30 to 35°C, neither organism produces a fleshy fruiting body, they colonize lemon trees primarily through branch fractures and other non-pruning wounds, and both cause a brown wood rot in infected trees. A major difference between the two pathogens is that Antrodia forms spore-producing fruiting bodies on infected wood within lemon groves, whereas fruiting on lemon wood infected by Coniophora has not been observed. The rate of wood decay in lemon branches inoculated with Antrodia is at least three times greater than that caused by Coniophora. Wood decay columns produced by either fungus from late spring to early autumn were at least three times larger than those that developed from late autumn to early spring. When inoculated with either pathogen, the length of wood decay columns on branches 10 mm in diameter was numerically smaller than those on branches 20 and 40 mm in diameter. Wood decay on Lisbon lemon branches inoculated with either Antrodia or Coniophora was significantly greater than that on Marsh grapefruit, Orlando tangelo, and Valencia orange. Treatment of lemon branch inoculation sites with azoxystrobin or propiconazole at 20 g of active ingredient per liter of solution reduced the resultant length of wood decay columns by 61 and 77%, respectively, for Antrodia, and 92 and 85%, respectively, for Coniophora. When selected desert plants were inoculated, Antrodia produced wood decay columns on Palo Verde, salt cedar, greasewood, and mesquite branches that were much shorter than those recorded on Lisbon lemon branches. On the other hand, Coniophora produced longer wood decay columns on salt cedar and mesquite than on Lisbon lemon, whereas wood rot on lemon was greater than that on Palo Verde and greasewood. Current disease management strategies include minimizing branch fractures and other non-pruning wounds, and periodic inspection of trees and removal of infected branches, including physical removal of all wood infected with Antrodia from the grove site.