The study of PCNB-tolerance in Sclerotium rolfsii, and the effect of soil ph on sclerotial germination and pathogenicity /
A pentachloronitrobenzene (PCNB)-tolerant isolate of Sclex-
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| Format: | Thesis Book |
| Language: | English |
| Published: |
[Place of publication not identified] :
[publisher not identified] ;
1996.
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| Subjects: | |
| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739364201&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | A pentachloronitrobenzene (PCNB)-tolerant isolate of Sclex- otium rolfsii was observed from a Texas peanut field in 1985. In this study, Texas peanut fields were surveyed to determine the frequency distribution of PCNB-tolerance among isolates of S. rolfsii. A total of 377 isolates were collected; 306 isolates were collected from five intensively sampled fields in central Texas and the other 71 isolates were obtained from arbitrarily selected locations in Texas. Nineteen of 377 isolates were classified as PCNB-tolerant based on having radial mycelial growth inhibited less than 80% by 10 PCNB/ml of growth medium. The effective dose for 50% growth inhibition (ED5.) of the original PCNB-tolerant isolate found in 1985 was 5.6 times greater than that of sensitive isolates of this study. The ED50 values of 18 newly collected PCNB- tolerant isolates were from 25% to 80% greater than that of PCNB- sensitive isolates tested. However, the ED50 values of 18 PCNB-tolerant isolates were from 23.2% to 33.2% of that of the original PCNB-tolerant isolate. PCNB- tolerance was not increaed or lost after 15 generations in the presence or absence of PCNB on potato dextrose agar (PDA). PCNB-tolerance, expressed as the ED50 value was negatively correlated with pathogenic aggressiveness in greenhouse and microplot tests. However, these negative correlations were due primarily to the weak pathogenic aggressiveness of the original PCNB-tolerant isolate. Sclerotial germination has been reported to be inhibited at pH above 7.0 on agar media. However, stem rot caused by S. rolfsii frequently occurs in Texas peanut fields with soil pH above 7.5. In this study, sclerotial germination was decreased as soil pH increased above 7.0, but sclerotial germination was observed at soil pH 8.7. Similar to sclerotial germination on soil, disease incidence was decreased as soil pH increased above 7.0. However, disease caused by S. rolfsii was incited at soil pH as high as 9.8. |
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| Item Description: | Vita. "Major Subject: Plant Pathology". |
| Physical Description: | xii, 87 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 61-77. |