Forest Pathology (2017) 47 (4 - e12345)

X. Gao, X. Zhou, H. Wang, X. Kong, S. Zhang, Z. Wang, W. Wu, Z. Zhang and F. Lieutier (2017)
Influence of severe drought on the resistance of Pinus yunnanensis to a bark beetle-associated fungus
Forest Pathology 47 (4 - e12345)
Abstract: Research on tree response to pest attacks under drought and heat stress is crucial for predicting the effect of climate change on forest pests and tree health. In this work, we studied the influence of severe water stress on the resistance of Pinus yunnanensis to inoculations of Grosmannia yunnanensis, a pathogenic fungus associated with the aggressive bark beetle, Tomicus yunnanensis. Experiments were performed in two plots, one located at the top of a hill and the other at the foot of a hill, in Xiaojiu, Yunnan, China, from May to September 2010 and March to April 2012. Measurements of soil and needle water content and predawn needle water potentials confirmed that severe droughts occurred during these periods. Maximum water stress intensity even occurred in 2010 during the typical rainy season. Following low-density inoculations, the reaction zone length and fungal growth were measured in the phloem. Sapwood blue staining and total sapwood occlusion were quantified following fungal mass inoculations. Our results suggest that severe water stress has a negative impact on a tree's resistance to G. yunnanensis. By comparing our results to previous work performed from 1997 to 1999 on the same tree species, and in the same locality under mild water stress, we concluded that drought had opposite effects on tree resistance above and below a certain threshold of predawn needle water potential. The threshold, corresponded to maximum efficiency for tree defence mechanisms, was visible in our results, and was estimated to be approximately -1.1 MPa to -1.2 MPa for P. yunnanensis under local conditions. We suggest that the existence of such a threshold of water stress intensity may be viable for any conifer undergoing biotic aggressions and, specifically, bark beetle attacks.
(The abstract is excluded from the Creative Commons licence and has been copied with permission by the publisher.)
Link to article at publishers website
Database assignments for author(s): François Lieutier

Research topic(s) for pests/diseases/weeds:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Grosmannia yunnanensis	Pine (Pinus)	China (south)
	Tomicus yunnanensis	Pine (Pinus)