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Tolerance and growth responses of populus hybrids and their genetically modified varieties to simulated leaf damage and harvest

Axelsson, E. Petter, Hjältén, Joakim
Forest ecology and management 2012 v.276 pp. 217-223
biomass production, branches, buds, correlation, genome, herbivores, hybrids, leaves, line differences, plantations, risk, shoots, stemwood, tree damage, trees
Tolerance is along with resistance the two most basic mechanisms used by trees to mitigate damage by herbivores and together they comprise important traits in plant material used in forestry. Genetic modification of trees has targeted various traits including resistance with promising results. Nevertheless, little is still known of how changes of the plant genome may interact with damage to affect tolerance and productivity of the trees. To address this we tested tolerance and growth responses of two different populus hybrids and their corresponding GM varieties to simulated leaf damage and harvest. Morphological growth responses to leaf damage included a decreased biomass production of the effected shoot (e.g. the main stem) which was partly compensated for increased biomass production in the undamaged branches. This compensation was mainly due to growth responses in already existing branches rather than stimulation of new buds. However, despite growth inductions in branches the net growth response seen over the whole plant was negative, e.g. plants could not fully compensate for lost leaf tissue and thus showed under-compensation for damage. We further show that the ability for post harvest re-growth correlated positively with the biomass of plants at harvest but only for the high damage treatment and not for low to intermediate levels of damage under which this relationship was neutral. Tolerance may thus have intricate influence over the success of short rotation plantation practices under which plants are subjected to repeated harvests while simultaneously being subjected to increased risk of severe leaf damage by herbivores. The ability for tolerance did not differ significantly between the two tested hybrids or among hybrids and their corresponding GM varieties. This was also so for the capacity for re-growth after harvest. The production of stem wood and leaves as well as total biomass was, however, significantly different among lines. These among line differences were both caused by differences between the two Wt hybrids (e.g. Wt-Lignin produced ∼37% more biomass than Wt-Bt) and differences caused by genetic modification (e.g. Wt-Bt produced ∼19% more biomass compared to Bt27). Our results give a strong indication that the growth responses of the GM varieties to leaf damage and harvest were substantially equivalent with their corresponding non-GM varieties. These similarities predict that the effect of damage on production should be alike regardless of if the GM or non-GM products are used.