PARENT SESSION
Contributed Oral Session 102: Herbivory: Effects of Photosynthesis; Nutrients
Wednesday, August 10, 1:30 PM - 5:00 PM, Meeting Room 520 B, Level 5, Palais des congrès de Montréal

Comparison between artificial defoliation, herbivory and fungal infection on leaf gas exchange of Senecio vulgaris.

Cachu, Yolanda ^*,1, Paul, Nigel ¹, ¹ Lancaster University, Lancaster, United Kingdom

ABSTRACT- There is increasing evidence that different patterns of defoliation cause contrasting effects on photosynthesis, transpiration, and ultimately on growth and fitness. However, broader comparisons of foliar damage including fungal infection as well as herbivory have not been made. Also the hypothesis that removal of infected leaf tissue by herbivores is beneficial to the host by eliminating a net sink for photosynthate has not been tested. To test this hypothesis and compare the effects of different types of leaf damage we examined the consequences of herbivory, artificial defoliation, infection by a rust fungus and their interactions on leaf gas exchanges in the annual composite Senecio vulgaris. S. vulgaris plants were grown in controlled environment conditions. The treatments consisted of control (no infection or leaf area removed), defoliation (25% of leaf area removed by holes), herbivory by Tyria jacobaeae larvae, inoculation with the foliar pathogen Puccinia lagenophorae (rust), rust + herbivory and rust + defoliation. Leaf gas exchange was measured daily with an infra-red gas analyser for 10 days after damage. Neither herbivory nor defoliation significantly affected photosynthesis or dark respiration in remaining tissues of damaged leaves. By contrast rust infection significantly reduced photosynthesis and increased respiration after sporulation had occurred. Transpiration rates both in the light and in the dark were not significantly changed by rust, herbivory or defoliation, but the combination of rust and defoliation caused significant increases. Removal of rust pustules transiently increased photosynthetic rates during the first 4 days following defoliation. T. jacobaeae larvae showed no preference between healthy or infected tissue. We conclude i) that compared with herbivory and defoliation rust infection is more damaging than expected from the leaf area affected and ii) that selective removal of rusted tissue can benefit the host plant.

Key words: defoliation, herbivory, senecio vulgaris, rust fungus