Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/10/1998
Publication Date: N/A
Interpretive Summary: Phomopsis seed decay, pod and stem blight, and stem canker are three soybean diseases caused by fungi belonging to a complex. The fungi in this complex are endemic to soybean production areas throughout the world and can cause reductions in stands, yield, and seed quality. The specific identification of the fungi in the complex (Diaporthe/Phomopsis) is based on morphological characteristics like color and colony appearance. Because characteristics like color and colony appearance often are too variable or conflicting, identification is difficult. In this study, the specific makeup of the complex was determined based on molecular methods. Combination of morphological plus molecular characterization was used to define the complex as a composition of one distinct species, a second species with two varieties, and a third species which either has several varieties or sub-species or may even be several distinct species. This research is important since it differentiates the fungal species involved in the complex. These results may impact other researchers working on this fungal complex and provides information on genetic differences of the fungi causing three diseases in soybean.
Technical Abstract: Diaporthe phaseolorum (DP) and Phomopsis longicolla (PL) isolates from soybean were examined using traditional mycological approaches and compared to molecular groupings. Cultural characteristics including types of fruiting bodies and conidia were assessed for isolates collected from soybean stems and seeds. Cultures were identified as PL, Diaporthe phaseolorum var. caulivora (DPC), D. p. var. meridionalis (DPM), and D. p. var. sojae (DPS). Molecular markers for these groups were developed by polymerase chain reaction-restriction fragment length polymorphisms (PCR-RFLP). After DNA digestion with five restriction enzymes, isolates within each DPM and PL had uniform banding patterns. Isolates of DPC had two kinds of banding patterns using only Hha I. Banding patterns from isolates of DPC were distinguished clearly from DPM after digestion with Alu I. All isolates within each of PL, DPC and DPM had distinct banding patterns from each other with the only one exception when DNA was digested with Alu I in combination with Rsa I or ScrF I. Isolates of DPS were divided into 13 PCR-RFLP groups.