Date of Graduation

12-2022

Document Type

Thesis

Degree Name

Master of Science in Plant Pathology (MS)

Degree Level

Graduate

Department

Entomology and Plant Pathology

Advisor/Mentor

Rojas, Alejandro

Committee Member

Correll, James C.

Second Committee Member

Rojas, Clemencia M.

Third Committee Member

Rupe, John C.

Keywords

Biological control; Burkholderia; Plant disease; Pseudomonas; Rice; Seed treatment

Abstract

Rice is the primary staple for more than half of the global population and is the second most important cereal worldwide. In the US, rice is primarily grown in the southern states, with Arkansas leading production and responsible for 47% of the total rice production in the country. Diseases cause significant yield losses in rice. Sheath blight, rice blast and bacterial panicle blight are the main diseases in rice and cause significant yield losses. Sheath blight alone could cause up 50% yield loss in heavily damaged fields with highly susceptible cultivars. Additionally, rice seed and seedling diseases primarily caused by Pythium species and Rhizoctonia solani result in reduced germination, poor seedling development or seedling damping off, reducing plant stand. The research conducted focused on a two-prong approach, by evaluating biological control and chemical control to manage seed and seedling diseases on rice, with the aim of providing different solutions for control of fungal pathogens. First, two Pseudomonas and two Burkholderia spp. were evaluated as potential biological control against three isolates of Rhizoctonia solani and one isolate of Fusarium graminearum using dual culture plate and as seed treatments in controlled environments. Results obtained 48- and 96-hours post-inoculation show both P. fluorescens and B. cepacia caused significant reductions in the mycelial growth of the R. solani and F. graminearum isolates. Further evaluation of these bacteria in seed plate assay indicated that all four bacterial have varying degrees of antagonism against R. solani and F. graminearum. Both P. fluorescens and B. cepacia remained active improving emergence as seed treatments. Further studies are needed to investigate the mechanisms through which the bacteria inhibit fungal growth and their effectiveness of foliar fungal diseases. The second approach evaluated eight different chemical seed treatments containing azoxystrobin, fludioxonil and sedaxane and the combinations of these active ingredients. These seed treatments were evaluated against R. solani and Pythium spp. using seed plate and seedling cup assays in controlled environments with the rice cultivar ‘Diamond’. To determine the efficacy and impact on plant health, emergence at 7-days post inoculation and planting. Plant stand, total plant weight and root weight were measured. Statistical analysis of the results showed a seed treatment of sedaxane or fludioxonil alone was as effective as two or three-way combinations of these active ingredients in improving emergence, plant stand, total plant weight and root weight. A single application of azoxystrobin improved the above parameters but it was significantly less effective than fludioxonil or sedaxane. Despite the effectiveness of most seed treatments, it is necessary to assess the reduced efficacy of single application of azoxystrobin by determining fungicide resistance and the impact on disease management.

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