WSU CAHNRS

College of Agricultural, Human, and Natural Resource Sciences

Department of Plant Pathology

December in the News

Congratulations to our Winter Graduates!

Jennifer Niem successfully defended her MS dissertation research and was awarded an MS degree in Plant Pathology. Jennifer’s supervisory committee included Drs. Debra Inglis (chair), Dennis Johnson, and Tim Paulitz (Dr. Axel Elling as a substitute). Jennifer’s dissertation research focused on soilborne potato pathogens. These pathogens respond differently to soil flooding. Jennifer investigated the survival of the sclerotia and microsclerotia of two potato pathogens, Sclerotinia and Verticillium, under greenhouse and field conditions and demonstrated that flooding as a disease management strategy is promising for Sclerotinia but not for Verticillium. Under greenhouse conditions, exposing sclerotia of S. sclerotiorum to constant flooding for three weeks resulted in reduction in germination, ranging from 15 to 88%, although the sclerotia remained intact. At three months, the sclerotia disintegrated but 0 to 18% of the sclerotial fragments retained their viability. No sclerotia were recovered after six months and they completely decomposed. In contrast, V. dahliae appeared to be more resistant to flooding when initial inoculum density was >7 CFU/g of soil. V. dahliae was recovered from the soil even after six months flooding. This result was also reflected in field microplot experiment where V. dahliae and total population estimates of Verticillium species were higher in flooded compared to fallowed microplots after 12 months. One year after planting potatoes into microplots either previously flooded or fallowed, progress of early dying symptoms as measured by AUDPC, final percent foliar wilt, recovery of V. dahliae from sampled potato stems, and potato tuber yield were not significantly different between flooded and fallowed microplots. Jennifer’s research showed that flooding to eliminate S. sclerotiorum is a promising method of controlling the primary inoculum of white mold in potato fields of western Washington but not for fields with high incidence of Verticillium wilt. Flooding is a potential management practice that not only addresses agronomic, but ecological issues as well by creating habitat for shorebirds and other wetland dependent species as a viable rotation option for farmland.

Christian Aguilar successfully defended her MS and was awarded an MS degree in Plant Pathology. Her committee included Drs. Tobin Peever (chair), Martin Chilvers (Michigan State), Tim Murray, and George Vandemark. Her dissertation was onAssessment of chickpea seed disinfestation procedures and detection of Ascochyta rabiei in chickpea seed using quantitative polymerase chain reaction. Ascochyta blight is a devastating disease of chickpea caused by the fungal pathogen Ascochyta rabiei (teleomorph; Didymella rabiei). Attempts at limiting the dispersal and destructive potential of A. rabiei have focused on early detection of this pathogen in seed through routine testing and seed certification programs. The absence of internationally accepted standards for assaying chickpea seed has made it difficult to predict Ascochyta blight epidemics based on seed infection/infestation rates. Additionally, disinfestant treatments used in screening chickpea seed for the presence of A. rabiei vary, affecting pathogen recovery rates detected by conventional assays. Christian developed a quantitative polymerase chain reaction assay incorporating TaqMan-MGB fluorescent chemistries for the rapid detection of A. rabiei in chickpea seed. A. rabiei-specific primers and a complimentary fluorescent probe were developed using sequence data from the intergenic spacer (IGS) region of the 28s-18s rDNA genes. The specificity of this molecular assay was demonstrated in PCR and qPCR reactions using purified genomic DNA of A. rabiei, Ascochyta relatives and other fungi isolated from chickpea seed. This assay was shown to be sensitive enough to detect 1 pg to 100 fg of purified A. rabiei DNA, with PCR efficiency of 93%. Refinement of the conventional seed plating assay and development of a quantitative PCR assay will provide additional insight into the epidemiological implications associated with seed-borne transmission of A. rabiei, and will improve the management of Ascochyta blight. Christian will continue pursuing PhD studies with Mark Mazzola/Chang-Lin Xiao.

Faculty Featured in WSU Today

Dr. Naidu Rayapati‘s research on cassava was featured in the December 16, 2011, issue of WSU Today.

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