Abstract: Powdery mildew, caused by Blumeria graminis f. sp. tritici (syn. Erysiphe graminis f. sp. tritici), is one of the most important fungal diseases of common wheat (Triticum aestivum L.) worldwide and causes severe yield losses. Wheat germplasm N9436, developed by our research group, is a resistant material to powdery mildew. In the present study, a suppression subtraction hybridization (SSH) cDNA library was constructed with cDNA from N9436 leaf inoculated by Blumeria graminis as the tester and cDNA from N9436 healthy leaf as the driver. A total of 140 positive clones were randomly chosen from the SSH-cDNA library and were amplified with sp6 and t7 primers to examine the insert size. Their sizes ranged from 200 to 1 000 bp with an average of 238 bp. Among the 140 clones, 32.86% showed redundant and repeated sequences by sequence analysis. The most frequent se-quence was glutathione transferase and followed by ribulose-1,5-bisphosphate carboxylase/oxygenase small/large subunit. After screening repeat and redundant sequences, 94 ESTs were acquired. Nucleic acid and protein homology search were performed using the BLAST (Basic Local Alignment Search Tool) program with the default settings at NCBI website (http://www.ncbi. nlm.nih.gov). BlastX results in nr-protein database revealed that 49 ESTs were highly homologous with known proteins involved in disease resistance and defenses, energy metabolism, cell structure, protein synthesis and processing, transport and signal trans-duction. BlastNr results showed that 69 and 20 ESTs had high identities with known Unigene and function-unknown ESTs, re-spectively, and 5 ESTs matched none in the nr-database. Compared with BlastX and BlastNr analysis, 33 ESTs were both in the nucleic acid and protein databases including 22 ESTs associated with powdery mildew resistance, out of which 6 for signal trans- duction, 2 for hypersensitive necrosis reaction (HR) system, and 14 for systemic acquired resistance (SAR) system, respectively.

Key words: Wheat, Powdery mildew, Suppression subtraction hybridization (SSH), Expressed sequence tag (EST)