Australian macadamias experience outbreaks of Botryosphaeria branch dieback. Extreme environmental conditions are thought to be responsible for the episodic outbreaks of diseases caused by Botryosphaeriaceae species in horticultural ecosystems. However, studies on the interactive effects of biotic and abiotic stresses in macadamia are unknown. Knowledge of management practices that contribute to the severity of the disease would assist in decisions for Botryosphaeria branch dieback control in commercial macadamia orchards. Using an stem wound inoculation assay with , we investigated the association of soil moisture conditions as a factor of plant stress with the severity of Botryosphaeriaceae infection in macadamia. Sap flow rate and soil water potential were monitored in 72 macadamia potted cv. HAES 344 plants (18-month-old and 12-month-old grown in pine bark-sand mixture) that were kept under three watering treatments, based on the amount of water used per day () at the start of the trial, at , ½ of and ¼ of for 14 weeks. A significant differential effect of the watering regimes was observed on disease severity, revealing a strong ( > 0.87) negative linear relationship between disease severity and sap flow rates. Necrotic lesions were significantly ( < 0.001) longer in the lowest and highest watering regimes. The average sap flow rate of 0.4 kg h was recorded in the plants under moderately watered conditions, ½ regime, whereas 50% and 75% reductions in sap flow rates were recorded at the lowest and highest watering treatments, respectively. Our results indicate that maintaining optimal soil water potential between −50 and −80 kPa through irrigation practices may reduce the risk of Botryosphaeria branch dieback outbreaks in macadamia orchards.

中文翻译：

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土壤湿度条件对伊朗毛二孢菌引起的葡萄球菌枝条顶枯严重程度的影响及对澳洲坚果植物生长的影响

澳大利亚澳洲坚果经历了葡萄球菌分支枯萎病的爆发。极端环境条件被认为是园艺生态系统中葡萄孢科物种引起的疾病间歇性爆发的原因。然而，关于澳洲坚果中生物和非生物胁迫相互作用影响的研究尚不清楚。了解导致疾病严重程度的管理实践将有助于商业澳洲坚果园中葡萄球菌分支枯萎病控制的决策。使用茎伤口接种测定，我们研究了土壤湿度条件作为植物胁迫因素与澳洲坚果中葡萄球菌感染严重程度之间的关系。对 72 个澳洲坚果盆栽品种的液流速率和土壤水势进行了监测。 HAES 344 株植物（18 个月大和 12 个月大的松树皮沙混合物中生长）根据试验开始时每天的用水量 () 进行三种浇水处理，在、 1/2 和 14 周，持续 14 周。观察到浇水方式对疾病严重程度的显着差异影响，揭示疾病严重程度和液流速率之间存在很强的（> 0.87）负线性关系。在最低和最高浇水方式下，坏死病灶的时间显着延长（<0.001）。在适度浇水条件（1/2）下，植物的平均树液流量为 0.4 kg·h，而在最低和最高浇水处理下，树液流量分别减少了 50% 和 75%。我们的结果表明，通过灌溉措施将最佳土壤水势保持在-50至-80 kPa之间，可以降低澳洲坚果果园中葡萄球菌枝条顶枯病爆发的风险。