School of Biological Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, Australia.
School of Agriculture and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia, Australia.
Tree Physiol. 2019 Jan 1;39(1):6-18. doi: 10.1093/treephys/tpy113.
There is increasing concern about tree mortality around the world due to climatic extremes and associated shifts in pest and pathogen dynamics. Yet, empirical studies addressing the interactive effect of biotic and abiotic stress on plants are very rare. Therefore, in this study, we examined the interaction between drought stress and a canker pathogen, Quambalaria coyrecup, on the eucalypt - Corymbia calophylla (marri), which is experiencing increasing drought stress. We hypothesized that drought stress would increase marri's susceptibility to canker disease, and cankers would have the largest negative effect on plants that are already drought stressed before pathogen inoculation. To test the hypotheses, in a glasshouse, marri saplings were exposed to drought either before or after pathogen inoculation, or were well-watered or droughted throughout the experiment either with or without inoculation. Canker development was greater in well-watered saplings than in droughted saplings, with the fastest development occurring in well-watered saplings that had experienced drought stress before inoculation. Irrespective of water treatments, marri saplings employed phenol-based localized biochemical defence against the pathogen. Drought reduced photosynthesis and growth, however, a negative effect of canker disease on saplings' physiological performance was only observed in well-watered saplings. In well-watered saplings, canker-induced loss of sapwood function contributed to reduced whole-plant hydraulic conductance, photosynthesis and growth. The results provide evidence that timing of drought stress influences host physiology, and host condition influences canker disease susceptibility through differences in induced biochemical defence mechanisms. The observations highlight the importance of explicitly incorporating abiotic and biotic stress, as well as their interactions, in future studies of tree mortality in drought-prone regions worldwide.
由于气候极端和相关的病虫害动态变化，世界各地对树木死亡的担忧日益增加。然而，关于生物和非生物胁迫对植物的相互作用的实证研究非常罕见。因此，在这项研究中，我们研究了干旱胁迫和溃疡病原菌 Quambalaria coyrecup 对桉树 Corymbia calophylla（马利桉）的相互作用，马利桉正经历着越来越多的干旱胁迫。我们假设干旱胁迫会增加马利桉对溃疡病的易感性，而且在接种病原菌之前已经受到干旱胁迫的溃疡病对植物的负面影响最大。为了验证假设，在温室中，马利桉幼苗要么在接种病原菌之前或之后暴露于干旱条件下，要么在整个实验过程中无论是否接种病原菌都保持充分供水或干旱状态。与干旱幼苗相比，充分供水的幼苗的溃疡病发展得更大，而在接种病原菌之前经历干旱胁迫的充分供水幼苗的发展速度最快。无论水分处理如何，马利桉幼苗都采用酚类的局部生化防御机制来抵抗病原菌。干旱减少了光合作用和生长，但只有在充分供水的幼苗中才观察到溃疡病对幼苗生理表现的负面影响。在充分供水的幼苗中，溃疡病导致边材功能丧失，从而降低了整株植物的水力导度、光合作用和生长。结果表明，干旱胁迫的时间会影响宿主的生理机能，而宿主的状况会通过诱导生化防御机制的差异影响溃疡病的易感性。这些观察结果强调了在未来研究干旱地区树木死亡率时，明确纳入非生物和生物胁迫及其相互作用的重要性。
