Hypersensitive Response in Live Oak: Characterization and Efficacy Against a Host of Specific Gall-Forming Wasp

Campbell, Cristina M.
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The establishment and spread of host-plant-specific pathogens and insect herbivores are fundamentally affected by plant defenses. Hypersensitive response (HR) is a plant defense classically recognized as resulting from a gene-for-gene interaction between pathogens and plants. More recently HR arising from plant-insect herbivore interactions has been documented in select study systems. HR results in localized necrotic plant tissue in response to, and at the site of, attack from pathogens and insect herbivores. It is well established that HR is associated with increased mortality, reduced establishment, and decreased spread of pathogens. However for insect herbivores, most studies of HR lesions in response to insect attack have investigated the mechanics of the process leaving assessment of the effect of HR on natural populations of insect I herbivores relatively unexplored. Herein I examined necrotic lesions that arise in the leaves of Quercus fusiformis (plateau live oak) in response to oviposition by the host specific gall-forming wasp Belonocnema treatae to assess whether apparent HR functions in plateau live oak as a plant defense, and if so, to estimate its importance. To do this I examined the probability of gall establishment in the presence and absence of necrosis within and among individual live oak trees monitored in each of two years. The probability of B. treatae gall formation was significantly reduced by necrotic lesions thus illustrating that lesions act as a plant defense. HR was commonly observed and individual trees varied widely in HR effectiveness both within- and among- years. This study is the first to demonstrate the effectiveness of HR lesions against any of the 1300 species of cynipid wasps. Cynipid diversity is centered on oaks with individual gall- former species typically restricted to individual species of oak. My results make cogent the questions concerning the frequency of HR and the effectiveness of HR defense among oak species against their diverse gall-formmg fauna.
Gall wasps, Live oak, Plant defenses, Texas
Campbell, C. M. (2010). <i>Hypersensitive response in live oak: Characterization and efficacy against a host of specific gall-forming wasp</i> (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.