<I>Rhizoctonia</I> species are important pathogens of all turfgrasses, yet little is known about the structure of populations of these pathogens or the effect of disease control programs on population dynamics. Isolates of <I>Rhizoctonia</I> were obtained from a single creeping bentgrass putting green in 2002 and 2003 and from multiple tall fescue landscapes in 2003. Creeping bentgrass isolates were obtained by placing 5 mm soil cores on alkaline water agar, incubated at ~24 C for 1 to 2 days and the actively growing hyphae were transferred to potato dextrose agar (PDA). Tall fescue isolates were obtained from foliar lesions using the same procedures. Isolates were characterized using morphological characteristics, anastomosis reactions, nuclear staining, and ribosomal DNA (rDNA) sequences. From creeping bentgrass, 21 distinct clones of <I>R. solani</I> AG 2-2 IIIB were present in the sample population in 2002. Seven of these clones were also recovered on multiple sampling dates. Fifteen of the 21 clones from 2002 were recovered in 2003. All seven clones that were isolated in multiple sampling dates in 2002 were also recovered in 2003. There were 29 and 21 isolates of <I>R. zeae</I> collected from the sample population in 2002 and 2003, respectively. All 21 clones exhibited similar EC<sub>50</sub> values to mancozeb, chlorothanlonil and azoxystrobin. Of 224 isolates collected from tall fescue during 2003, 88 were <I>R. solani</I> AG 1, 105 were binucleate <I>Rhizoctonia</I> CAG 1, 14 were <I>R. zeae</I>, two were <I>R. cerealis</I>, and 15 were not identified to species or AG. One hundred and seventy four of the isolates were assayed for sensitivity to the fungicides flutalonil, iprodione, tebuconazole, and trifloxystrobin. Mean EC<sub>50</sub> values varied across fungicides and species, but generally were below 3.3 mg L<sup>-1</sup>. The diversity of <I>Rhizoctonia</I> populations associated with tall fescue, and the range in fungicide sensitivities among species indicates that response to management programs may vary with location and environment. The effects of phosphorous acid on fungal growth, disease incidence and turfgrass quality was evaluated in vitro and in vivo. Mean EC<sub>50</sub> values of azoxystrobin (+SHAM) for <I>R. solani</I> 2-2 IIIB, and AG 1, <I>P. aphanidermatum</I>, and <I>R. zeae</I> were 1.27, 0.04, 0.012, and 0.145 mg L<sup>-1</sup>, respectively. Applications of phosphorous acid to creeping bentgrass and tall fescue did not significantly reduce brown patch incidence or increase turfgrass quality in field or greenhouse experiments. The benefit of phosphorous acid as a fungicide or plant nutrient is questionable.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-07122004-140248 |
| Date | 19 July 2004 |
| Creators | Lee, David Jackson |
| Contributors | Dr.Rick L. Brandenburg, Dr. Lane P. Tredway, Dr. Charles H. Peacock, Dr. H. David Shew |
| Publisher | NCSU |
| Source Sets | North Carolina State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://www.lib.ncsu.edu/theses/available/etd-07122004-140248/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to NC State University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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