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Characterization of fungi species associated with Ascochyta blight of field peas in Montana

Ayodeji Owati: Montana State University

<div>The production of pea (<em>Pisium sativum</em> L) in the Northern Great Plains of the United States is rapidly increasing. Montana is the leading producer of peas in the US, where 610,000 acres were planted in 2016, accounting for 44% of the total production in the US. Chief among fungal diseases of peas is Ascochyta blight (AB). This disease is caused by a complex of fungal pathogens (<em>Didymella pisi</em>, <span><em>Peyronellaea pinodes</em></span>, and <span><em>Peyronellaea pinodella</em>). <em>D. pisi</em> is predominant in Montana’s fields. </span>Recently, a shift in pathogen composition has been observed in Montana from <em>D. pisi </em>to <em>P. pinodes</em> and <em>P. pinodella</em>. <span>In addition, a <em>Phoma spp. </em>associated with diseased seeds were included in this study.</span> To characterize these pathogens, we evaluated the effects of temperature on their mycelial growth rate and sporulation. Four levels of temperature were used; 15, 20, 25, and 30 <sup>o</sup>C. Mycelial growth on PDA was measured daily and the number of spores quantified after two weeks on 1/3 PDA. The results in all the temperature levels showed that <em>Phoma spp</em> had the highest growth rate (p-value = < 0.001) and produced more spores than the other species (p-value = < 0.001). Pathogenicity assays on pea indicated that <em>P. pinodes</em> caused greater disease severity than the other species when inoculated on pea plants (p-value = < 0.001). These results will be used to understand the changes in predominant species composition causing AB in pea in Montana.</div>