Semester of Graduation

Summer 2021

Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Roseau cane (Phragmites australis) is a wild plant with an extensive root system that is useful in areas vulnerable to soil erosion. In Louisiana, this plant plays an important role protecting the coastal infrastructure of the lower Mississippi River delta (MRD). Currently, P. australis growing in the MRD is being affected by a die-off, which has been associated with several biotic and abiotic factors.

Plant pathogenic fungi is a biotic factor that negatively affect plant growth. Therefore, foliar fungi were isolated from plants growing in one die-off affected area (MRD) and two non-affected areas (Pecan Island and Manchac) of coastal Louisiana. Isolated fungi were identified to the genus level by morphological analyses and partial DNA sequences using PCR reactions with primers that amplified the ITS region of the fungal ribosomal DNA. 1,216 fungal isolates were classified into 20 different taxa. Higher richness of fungal communities was found in the die-off area (MRD) than in the two areas not affected by die-off.

Selected fungal isolates of the genera Bipolaris, Alternaria, Nigrospora, and Fusarium were further identified at the species level, by sequencing the ITS, partial ß-tubulin, RPB2, GAPDH, plasma membrane ATPase, and Calmodulin regions. Multilocus phylogenetic analyses were conducted on these selected isolates. The isolates were identified as A. alternata, B. yamadae, F. sulawense, and N. osmanthi.

Identified fungi was used to inoculate detached leaves of the Delta haplotype of P. australis and whole plants of three haplotypes, Delta, Gulf, and European. All fungal isolates caused necrotic lesions on detached leaves and leaf spot symptoms on whole plants. Regardless of the fungal pathogen used to inoculate whole plants, the European haplotype showed less severe symptoms than the Delta and Gulf haplotypes. This suggests that the European variety may be more tolerant to plant pathogenic fungi than the Delta variety.

The results of this study suggest that the make-up of the foliar fungal communities in P. australis plants of coastal Louisiana is influenced by the die-off problem. Evaluating the fungal composition of the rhizosphere of plants growing in die-off and non-die-off areas may provide further information to complement this study.

Committee Chair

Valverde, Rodrigo A.

Available for download on Thursday, July 07, 2022

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