Northern wild rice, Zizinia palustris, is a crucial annual grain crop of the Great Lakes region, providing American Indian families and commercial Caucasian growers economic and agricultural sustenance. The populations of this grain are annually inconsistant in natural settings (rivers, shallow lakes, and Great Lakes estuaries). One of two primary population limitors is the Ascomycete fungal pathogen, Claviceps zizaniae, a smut related to ergot, which infects the individual grains of wild rice after infection through the female stigma (taking the same floral pathway as pollen grains into the ovary). This study examined why the populations significantly affected by fungal smut were the larger intact wild rice populations including upper Hamlin Lake and Lac Vieux Desert in Michigan. The critical dimension investigated was how large wild rice populations with substantial fungal infection rates were able to remain resiliant, producing wild rice harvests that filled the human and ecosytem needs for energy and nutrition.
Results/Conclusions
The results showed that Claviceps zizaniae is limited by its transmission and infection mode. As an aerial born ascomycete fungus, rice smut ascospores must become airborne during the flowering period and reach the fertile female flowers within 48 hours of flower receptivity, because once wild rice pollen grains pollinate the stigma, they inhibit fungal spores from using the style to infect the ovary of the grain. Thus, the battle between plant and fungal spores during peak female receptivity is determined by spore load in the air above and surrounding wild rice plants. As Zizinia palustris populations increase to monoculture levels in natural or paddy settings, the pollen load overwhealms the fungal smut load, ensuring a majority of the flowers on any one wild rice plants will be successfully fertilized, producing a viable rice grain. Studies in the lab have demonstrated the warm, moist conditions necessary for fungal sclerotia to produce capitula containing ascospores. We are working to produce pure cultures that can be utilized in greenhouse experiments to better understand the lifecyle of this pathogen and its population effects on wild rice.
