Master of Science (MS)


Plant Pathology and Crop Physiology

Document Type



Brown rust, caused by Puccinia melanocephala, is an important disease of sugarcane. Breeding for host plant resistance is the primary control measure. Screening for resistance has relied on rating the severity of symptoms caused by natural infection; however, erratic results make this method problematic. A method accomplishing both infection and disease expression under controlled conditions could avoid the problems associated with resistance evaluations under natural infection. Inoculation of seedlings was evaluated to determine whether it could provide accurate resistance ratings in cross appraisal, and inoculation under controlled conditions was evaluated for the potential to accurately determine resistance reactions in clones with known and unknown reactions in comparison to field reactions. Seedlings from crosses between parents with different levels of resistance were inoculated with urediniospores at concentrations ranging from 1 x 103 to 1 x 106 spores per ml. Disease severity was visually assessed at 1 and 2 weeks after inoculation, and resistance ratings were assigned on a modified 1 to 9 scale. Inoculum concentration strongly affected severity and the frequency of resistant progeny in crosses. Brown rust resistance is a heritable trait; however, parental reaction was not a consistent determinant of progeny distribution across resistance rating categories. These results suggest that seedling inoculation may not be suitable for the evaluation of brown rust resistance. Clones were inoculated with 1 x106 spores per ml, and severity was determined as percentage of leaf area occupied by rust lesions by image analysis. Resistance reactions could not be reliably determined for susceptible clones in single inoculations. Controlled conditions inoculation and natural infection results were not correlated. Multiple inoculations under controlled conditions accurately identified resistant and susceptible clones with severe infection resulting from any single inoculation indicating susceptibility. Therefore, controlled conditions inoculation has the potential to be useful in limited studies to characterize parents in a recurrent selection program and for basic studies of resistance to brown rust.



Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Hoy, Jeffrey W.