Identifier

etd-04082014-224245

Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Leaf scald, caused by Xanthomonas albilineans, is a major sugarcane disease worldwide that is controlled primarily with host plant resistance. Since visual evaluation of disease resistance can be uncertain due to erratic symptom expression, a more reliable screening method is needed for resistance research. A quantitative polymerase chain reaction (qPCR) assay was developed previously with demonstrated potential for resistance screening. However, only four cultivars with extreme reaction against the disease (two highly susceptible and two highly resistant) were compared. Therefore, additional research was conducted to demonstrate assay specificity, compare bacterial populations in 31 clones with varying levels of susceptibility at different times after inoculation, and evaluate the correlation with the visual rating method currently used for resistance evaluation. SYBR Green and TaqMan qPCRs were tested against DNA from different bacteria and a fungus, and the assays showed high specificity amplifying only X. albilineans isolates. Inhibitors of amplification during PCR were not detected in DNA extracts from four cultivars. Comparison between the bacterial population quantified by qPCR and visual symptom severity ratings showed variable results with the highest correlation between the data at 8 weeks after inoculation (ñ = 0.62, P < 0.0001). In order to measure consistency, the correlation was determined among three different inoculations for data obtained with the same method at different times after inoculation. The qPCR assay was more consistent among the different inoculations (r = 0.77, P < 0.0001) compared with the visual rating system (r = 0.53, P = 0.0026) at 8 weeks after inoculation. Bacterial quantification was more consistent in field inoculations compared to greenhouse inoculation. The high specificity and consistency suggest that qPCR can provide an improved method to evaluate resistance to leaf scald in sugarcane.

Date

2014

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hoy, Jeffrey W.

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