Molecular phylogenetic analysis of Helminthosporium solani and alternative disease management strategies for silver scurf
Olivier, Claudia
Ph.D. Thesis., Cornell University, 1998, 192 pages
1998
บทคัดย่อ
Silver scurf is an economically important postharvest disease of the potato tuber periderm caused by the fungus Helminthosporium solani. Not much is known about the ecology of H. solani, and no effective means for postharvest control of silver scurf are available. The main objectives of this study were to (1) improve our understanding of the phylogeny of H. solani; (2) develop molecular tools for detection of this pathogen; and (3) evaluate control strategies for silver scurf.
Nucleotide sequence analyses of internal transcribed spacer (ITS) regions and ribosomal genes of Helminthosporium spp. revealed that the hyphomycete H. solani is most closely related to the wood saprophyte H. velutinum and to the teleomorph Leptosphaeria bicolor, but not to species formerly grouped in the genus Helminthosporium sensu lato. PCR primers specific for H. solani were developed based on ITS sequences of the fungus, which allowed specific pathogen detection in soil and plant tissue.
Organic and inorganic salts were tested in vitro for growth inhibition of H. solani and as postharvest treatments on potato tubers for suppression of silver scurf lesion development and sporulation on lesions. The food preservative potassium sorbate was most effective against silver scurf. The treatment was fungicidal at 0.2 M in vitro and significantly reduced both lesion formation and sporulation when applied to potato tubers.
Production of the fungitoxic volatile allyl isothiocyanate (AITC) and growth suppression of fungi by plant tissue of 65 Brassica accessions (B. juncea and B. nigra) was quantified by gas chromatography and bioassays, respectively. AITC production varied among Brassica accessions and was correlated with pathogen suppression.
Cultivars of B. juncea (high AITC) and B. napus (no AITC) were tested in the field for suppression of root rot pathogens of pea and bean and for reduction of Verticillium wilt of potatoes, when planted as green manure crops. Disease suppression by both species varied and was a function of biomass and AITC production in B. juncea.
This dissertation makes contributions to our understanding of silver scurf and demonstrates control means for silver scurf reduction in the field and during potato storage.