Transcriptomic Analysis Reveals the Molecular Defense Mechanisms of <i>Poa pratensis</i> Against Powdery Mildew Fungus <i>Blumeria graminis</i> f. sp. <i>Poae</i>

Kentucky bluegrass (<i>Poa pratensis</i> L.) is a valuable cool-season turfgrass widely utilized for forage, turf, and ecological purposes; however, its productivity and ornamental value are significantly compromised by powdery mildew, caused by <i>Blumeria graminis</i> f. sp. <i>Poae</i>, which negatively affects turf quality. In the present study, we examined the interactions between <i>P. pratensis</i> varieties and <i>B. graminis</i>, focusing on primary haustorium formation at 24 h post-inoculation and the formation of germ tubes at 48 h post-inoculation. We explored the molecular mechanisms underlying the response of different <i>P. pratensis</i> varieties at 48 h post-inoculation via transcriptomic techniques. Our results revealed that the primary haustorium formation rate in ‘Taihang’ at 24 h after <i>B. graminis</i> inoculation was significantly lower than that in ‘Explorer’ and ‘Black Jack’. The conidia of <i>B. graminis</i> could form two to five germ tubes, and the proportion of conidia that formed five germ tubes in ‘Taihang‘ at 48 h post-inoculation was significantly lower than that in the other two varieties. Transcriptome analysis revealed 680,765 transcripts as unigenes. A total of 9983 unigenes were identified as differentially expressed genes in one or more varieties of <i>P. pratensis</i> after inoculation with powdery mildew compared with the control. In total, 6284 differentially expressed genes were upregulated in ‘Taihang’, which was substantially greater than those in ‘Black Jack’ (4530) and ‘Explorer’ (4666). Moreover, 2843 differentially expressed genes were specific to ‘Taihang’, whereas 1644 and 1590 unique differentially expressed genes were specific to ‘Explorer’ and ‘Black Jack’, respectively. The specifically expressed genes play crucial roles in determining the disease resistance of powdery mildew. Notably, the expression of genes encoding chitinase, gamma-glutamyltranspeptidase 1, UDP-arabinopyranose mutase 1, oxalate oxidase 2, mitogen-activated protein kinase kinase 1-like, tryptophan decarboxylase, and aromatic L-amino acid decarboxylase was closely related to powdery mildew resistance in ‘Taihang’, making them promising candidate genes for studying resistance to powdery mildew in <i>P. pratensis</i>. This study identified critical genes involved in powdery mildew resistance in <i>P. pratensis</i>, providing a basis for future gene mining and molecular breeding to increase disease resistance in <i>P. pratensis</i>.