Yellow rust infection of wheat: How the quantity of light received by wheat seedlings before inoculation affects infection efficiency

Many factors are known to influence infection by cereal rusts, including environmental variables such at light, humidity and temperature, the topography of the leaf surface, as well as plant volatiles. However, few studies have aimed to link these factors. Previously, the quantity of light received by wheat seedlings prior to inoculation with Puccinia striiformis f. sp. tritici (Pst) urediniospores was shown to influence yellow rust infection efficiency. In this study we show that germination and the ability of germlings (germinated urediniospores) to enter stomata is enhanced on wheat seedlings subjected to high quantities of light pre-inoculation with Ps urediniospores, while on seedlings exposed to a long dark period germination and infection were compromised. Using headspace collections and GC-MS analysis thereof, we link this effect of high light quantity to quantitative changes in the profile of volatile organic compounds (VOC). We show that the VOC within headspace collections from wheat seedlings exposed to high quantities of light were able to support greater levels of Pst urediniospore germination than the headspace collections from wheat seedlings exposed to a period of dark. In vitro analysis of individual VOC identified compounds that enhanced Pst urediniospore germination. These VOC included the sesquiterpene caryophyllene, the monoterpene α-pinene, the fatty acid α 39 linolenic acid, the organic alcohols 1-hexanol, 3-hexen-1-ol and 5-hexen-1-ol, the aldehyde cis-3-hexenal and the ester hexyl-acetate.