Whole Plant Research

Can Spiroplasma be used to develop crops that are resistant to plant-parasitic nematodes?
Nematodes (roundworms) are the most common destructive macroparasite of crop plants. These pests are a particular problem in Africa, where the (environmentally hazardous) nematicides are too expensive for a small-scale farmer.


John Jaenike and colleagues have recently discovered that the heritable Spiroplasma of Drosophila neotestacea (sDn) provide the fly with complete resistance to their nematode parasite (Jaenike et al 2010). Incubation of parasitic nematodes with flies carrying sDn eradicated the entire population of nematodes (Jaenike & Brekke 2011). Transfer of sDn from Drosophila neotestacea to Drosophila putrida conferred nematode resistance on that species as well, despite the fact that different species of nematodes parasitize those two fly species. We hypothesize that dSn are able kill parasitic nematodes directly, rather than mediating some change in fly biology that allows the fly to clear the parasite. This characteristic appears to be unique to sDn, as similar experiments with other strains of Spiroplasma had no effect on nematode parasitism .


The nematodes that parasitize Drosophila and plants belong to the same order (Tylenchida) and thus are quite closely related. In addition, sDn is closely related to species of Spiroplasma that naturally infect plants. The fundamental question that this research will address is whether sDn can be used to give plants resistance to parasitic nematodes.


Current experiments
The question we're asking in our first set of experiments is whether any of several common African crop plants can be successfully infected with dSn. Eleven African (and worldwide) crop plants are being grown under standard greenhouse conditions. Plants of various ages will be exposed to solutions with varying amounts of dSn. Growth and morphology of infected plants will be compared to that of uninfected plants. After a period of time (which varies depending up on the plant species), plants will be analyzed for the presence of dSn. We are looking not only to see whether dSn is present, but whether the population has grown, which would imply a successful infection.


Future experiments
If we are successful in infecting any of the crop plants with dSn, the infected plants' ability to resist nematode parasitism will be compared to that of uninfected plants. We will also determine whether dSn is present in seeds, which would allow it to easily be passed from one generation to the next.


J. Jaenike, R. Unckless, S. N. Cockburn, L. M. Boelio, S. J. Perlman "Adaptation via symbiosis: recent spread of a Drosophila defensive symbiont" (2010) Science 329 212-215

J. Jaenike, and T. D. Brekke (2011) "Defensive endosymbionts: a cryptic trophic level in community ecology" Ecology Letters 14, 150-155