Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2003
Publication Date: 1/1/2004
Citation: Anikster, Y., Szabo, L.J., Eilam, T., Manisterski, J., Koike, S.T., Bushnell, W.R. 2004. Morphology, life-cycle biology and DNA analysis of rust on garlic and chives from California. Phytopathology. 94:569-577. Interpretive Summary: Historically, rust has not been a major disease on cultivated garlic and chive in California. However, in 1998 a major outbreak of rust devastated the garlic crop in central California. Continuing rust epidemics in 1999 and 2000 led to the reduction of garlic production in California by almost 90%. In addition, rust was found on chive near the Pacific coast, and one field was so heavily damaged that the entire crop was plowed under. In order to better understand the fungal pathogen that caused this epidemic, collections of rust from California and Oregon were compared with collections from the Middle East. Several differences were found between the rust samples from U.S. (California and Oregon) and the Middle East (Israel and Turkey) which included spore size, life cycle, and DNA sequences. The U.S. samples had a shortened life cycle (three spore stages), which made the rust fungus self-fertile in contrast with the samples from the Middle East, which had a complete life-cycle (five spore stages) and normal sexual stage. Examination of the nuclear condition of the spores in the sexual stages of the fungus elucidated the mechanism for the shortened life cycle of the garlic and chive rust collected from the U.S. This study provides strong evidence that the rust fungus, which caused the epidemic in garlic and chive fields in California, is different from the samples collected from leek and garlic in the Middle East and should be considered a different species. This information will be used by scientists working on rusts disease of garlic, chive, and leek and will help clarify the taxonomy of these rust fungi, which has been in flux for a century.
Technical Abstract: In the late 1990's, commercial garlic fields in California (CA) were devastated by an outbreak of rust caused by Puccinia allii. The disease also was destructive in some CA fields of chive. We compared collections of the pathogen from garlic (Allium sativum) and chive (A. schoenoprasum) in central CA and Oregon (OR) to collections of P. allii from garlic, cultivated leek (A. porrum), and wild leek (A. ampeloprasum) in the Middle East. Teliospores from the CA and OR collections were smaller in length, width, and cross-sectional area compared to collections from the Middle East. On the other hand, basidiospores were larger in length and area. Furthermore, CA/OR collections had a shortened life cycle, producing teliospores, basidiospores, and urediniospores, but not pycnia or aecia. Germinating telisopores produced a two-celled promycelium resulting in two basdiospores, each initially with two nuclei. In contrast, Middle Eastern collections were full-cycled, producing five spore types. Germinating teliospores produced a four-celled promycelium resulting in four basiospores, each initially with one nucleus. In addition, the CA/OR collections produced two-celled, fusiform substomatal vesicles in contrast to bulbous, single-celled vesicles produced by collections from the Middle East. In phylogenetic analysis based on DNA sequence of the internal non-transcribed spacer region of nuclear rDNA, garlic and chive collections from CA and OR formed a distinct cluster separate from the cluster formed by garlic, leek, and wild leek collections from the Middle East and Europe. These results suggest that the fungus causing rust on garlic and chive in California and Oregon is a different species than the rust fungus on garlic and leek in the Middle East and Europe.