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Poster Session: Biology and Disease Management - Chemical Control

283-P

Application of phosphite inhibits growth of plant fungal pathogens and primes plant defense response.
U. GILL (1), K. Mysore (1)
(1) The Samuel Roberts Noble Foundation, Ardmore, OK, U.S.A.

Phosphite (Phi) is used as fertilizer or fungicide specifically against plant diseases caused by oomycetes such as Phytophthora spp. The effect of Phi on fungal pathogens is not known. We therefore studied the effect of Phi on rust pathogens such as Puccinia emaculata and Phakopsora pachyrhizi, the casual agents of switchgrass rust and Asian soybean rust, respectively. Application of Phi at different concentrations inhibited spores germination and germ-tubes growth of P. emaculata and P. pachyrhizi at varying degrees under both in vitro and in vivo conditions. Switchgrass and soybean plants sprayed with Phi exhibited reduced disease symptoms when inoculated with their respective rust pathogens. However, washing off Phi from leaves prior to rust inoculation partially recovered disease susceptibility. Our results indicated roles of Phi in both, priming plant defense and inhibiting fungal growth. A microarray experiment was conducted to understand the molecular mechanism of Phi-induced switchgrass defense. Microarray data revealed a dramatic increase in transcript levels of phenyl propanoid pathway genes, several chitinase encoding genes, and some jasmonic acid induced genes. In addition, reactive oxygen species pathway gene were also induced. We also initiated an RNAseq experiment to identify P. emaculata genes whose expression may be affected by Phi treatment. These results will be presented at the meeting.