Three root-colonizing fungi, binucleate Rhizoctonia (BNR) isolate BNR621, BNR isolate P9023, and Trichoderma hamatum 382 (T382) were studied for suppression of Botrytis blight in geranium and demonstration of induced systemic resistance (ISR) as a mechanism of biocontrol. Root isolations of the BNR fungi confirmed that BNR621 and P9023 colonized the geranium root system. Root colonization is considered a requirement for biocontrol. Induction of resistance to Botrytis blight was observed in geraniums transplanted into potting mix amended with formulations of P9023 and T382 2 weeks prior to inoculation with B. cinerea when grown under environments either highly or less conducive to disease development. In the less disease-conducive environment, P9023 and T382 provided protection equivalent (P<0.0001) to a weekly rotation of fenhexamid and chlorothalonil fungicides. The effects of cellular and biochemical changes of ISR on germination of conidia of B. cinerea and Botrytis blight lesion area and expansion rates were tested in vitro. No differences in conidia germination were observed between treatments at any sampling time, with a mean germination rate of 80% across all treatments. The size of the leaf lesion area was dependent upon the length of time between topdressing of the geranium plants with the biocontrol agents and detachment of the leaves for inoculation. In geranium leaves detached and inoculated 7 days after topdressing with a Pesta formulation of either BNR621 or P9023, AUDPC calculated from lesion area was reduced (P<0.0001). In contrast, leaves detached and inoculated 14 days after topdressing with a formulation of T382 had a smaller (P<0.0001) AUDPC from lesion area than plants treated with a Pesta formulation of BNR621. Based on the overall suppression of Botrytis blight in geranium and the reduction in lesion size observed in the detached leaf assays, a role for restriction of lesion development is suspected in the control of B. cinerea in geranium. In a comparison study, induction of resistance to Rhizoctonia stem rot in geranium cuttings taken from stock plants treated with formulations of BNR621, P9023, or T382 was evaluated. No consistent control of Rhizoctonia stem rot in geranium cuttings by a biocontrol treatment was observed. However, cuttings taken from geraniums topdressed with a Pesta formulation of BNR621 14 days prior to propagation and inoculation had a greater probability (P=0.03) of rooting and growing out to healthy plants as compared to inoculated cuttings taken from untreated stock plants.
| Identifer | oai:union.ndltd.org:NCSU/oai:NCSU:etd-01192007-123849 |
| Date | 29 January 2007 |
| Creators | Olson, Heather Anne |
| Contributors | C. Y. Warfield, D. M. Benson, M. A. Cubeta |
| 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-01192007-123849/ |
| 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, dis sertation, 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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