Altaf Hussain | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES PhD Final Exam Seminar by Altaf Hussain. This seminar is open to the general public to attend.
Thesis Topic:  Spatial characteristics of volatile communication and the role of soil resources in pine defenses.

PhD with Dr. Nadir Erbilgin.

Seminar Abstract:  The recent unprecedented climate change has increased the frequency and severity of tree-killing Dendroctonus bark beetles (Coleoptera: Curculionidae, Scolytinae). Understanding factors and mechanisms influencing host plant-bark beetle interactions at landscape level such as plant defenses, edaphic conditions, plant nutrients, and plant-plant interactions will be important for determining the impact of bark beetle outbreaks and tracking their invasion success. I studied the range expansion of mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB) into the novel host jack pine (Pinus banksiana Lamb.) in the boreal forest of western Canada. I investigated the effect of soil moisture on the existence of gradients in the chemical defenses along jack pine stems by using a MPB associated phytopathogenic fungus, Grosmannia clavigera. I further tested whether soil moisture gradients can affect non-structural carbohydrate (NSC) production and allocation to two main classes of chemical defenses in jack pine, monoterpenes and diterpene resin acids. I found that constitutive NSC production increased with stem height, diterpene resin acid concentrations decreased, and monoterpene concentrations did not vary. With increasing soil moisture, NSC production decreased, monoterpene concentrations increased, and diterpene resin acid concentrations did not vary. At induced level, trees on the sites with higher soil moisture developed smaller necrotic lesions and had higher monoterpene concentrations by mobilizing local NSC reserves. Diterpene resin acid concentrations did not vary with soil moisture but differed at each stem height. I also compared MPB host acceptance and brood production in jack pine cut bolts from trees on sites with different soil moisture, and nutrient concentrations. Host acceptance and brood production were greater in bolts from the site with lower soil moisture and higher phloem nitrogen concentration.

Finally, I tested whether pines interact and cooperate by using the volatile defense compounds, and whether such interactions correlate with the spatial characteristics of sites, and tree attributes. I studied the constitutive and induced responses in non-attacked lodgepole pines within 30 m radii of pines attacked by MPB. I found that pines interacted with chemotypically related trees only. These results suggest that pines discriminate between volatile cues from kin and strangers, and the emitters likely aid only chemotypically related pines by emitting specific blends of volatiles that can only be deciphered by the receiving kin.