Kyle's Abstract

An experimental and mathematical study of M. oryzae spore germination and dispersal in the presence of host and non-host volatiles

Each year, the fungus M. oryzae destroys enough of the world’s rice, barley, and wheat crops to feed more than sixty million people.  In this project we investigate whether or not there are volatiles in host plants that cause M. Oryzae spores to react.  If true, these volatiles may cause the fungus to spread and to spread rapidly.  The first part of this project focuses on germ tube growth.  The spores and volatiles were strategically placed near each other in order to determine the angles the spores’ germ tubes made with the volatile.  The angles were measured using computer software and the date collated in a rose plot, which revealed the distribution of angles. The second part of this project focuses on spore dispersal in a controlled setting.  After placing either volatiles or actual leaves in a dish with the fungus and allowing ten days for the spores to disperse, the distance the spores traveled was measured using computer software.  Our results reveal that the spores tend to germinate in random orientations.  However, data from our second experiement suggests that spores utilize an active dispersal process and that host volatiles may change the vigor with which spores disperse.  The results show that limonene, a volatile of the rice plant, is one such volatile that triggers vigorous active dispersal.

Mandy's Bangin Abstract

Spores Gone Wild

 Magnaporthe oryzea is a fungus capable of infecting rice, wheat, barley and rye. Typically known as the cause of rice blast disease; it is estimated to kill enough rice to feed 60 million people a year. M. oryzea is not only a major threat to the world's food sources, but is also a potential weapon of bio terrorism. The infective fungal structures are the asexual spores. Understanding the mechanisms by which they behave is crucial to developing protection from this fungus.

 The objectives of this project were two-fold. First, we ask: How does M.oryzae spore behavior depend on the presence of volatile compounds released by host plants, such as rice and barley, vs. non-host plants, such as lima bean? Second, we ask: Are the spores released from their stalks by an active or passive method?

 To answer these questions, we examined spore growth under different conditions in petri plates. Germination tubes were measured and compared after exposure to liquid forms of the rice volatile, limonene, and the lima bean volatile, farnesyl acetate. Germ tubes showed slight differences, however no directional growth favoring a specific volatile was established. Evidence for an active dispersal mechanism was determined after measuring distances of spores released from M. oryzea growing on the vertical side of an agar block. Using a mathematical approach, a distribution of these distances compared to a model distribution of particles after diffusion suggested the presence of an active dispersal mechanism.