Semester of Graduation

Summer 2026

Degree

Master of Science (MS)

Department

Plant Pathology and Crop Physiology

Document Type

Thesis

Abstract

Louisiana’s Green Industry was valued over $591 million in 2024 and consisted primarily of nursery stocks and commercial and home landscapes. Among other landscape plants, most nursery growers in Louisiana specialize in perennial ornamentals. Over the years, LSU AgCenter’s Plant Diagnostic Center has received samples of azalea, bougainvillea, camellia, fatsia, ligustrum, nandina, rose, sweet olive, sweet viburnum, and yucca exhibiting leaf and stem anthracnose symptoms. Colletotrichum spp. were consistently isolated from these symptomatic hosts. Previous reports of Colletotrichum spp. associated with these host plants are incomplete or lacking. The objectives of this research were to: 1) identify the isolated Colletotrichum spp. using a multi-locus gene approach, and 2) determine the pathogenicity of Colletotrichum spp. to their respective host plants. DNA from each single-spore Colletotrichum sp. isolate was amplified using actin, chitin synthase and internal transcribed spacer gene regions. NCBI Blastn analysis of resulting sequences revealed identification of Colletotrichum spp. representing multiple novel host associations. Colletotrichum siamense was identified from azalea, bougainvillea, camellia, ligustrum, nandina, and sweet viburnum whereas C. nymphaeae and C. liriopes were identified from fatsia and yucca, respectively. Furthermore, the sweet olive isolates were identified as C. theobromicola, which is known to cause boxwood dieback in the US. Pathogenicity tests were conducted on bougainvillea, ligustrum, sweet olive, and viburnum using container grown plants in the greenhouse. Colletotrichum siamense was re-isolated from inoculated bougainvillea, ligustrum and viburnum that exhibited leaf anthracnose symptoms, and C. theobromicola was re-isolated from inoculated symptomatic sweet olive plants. Species identification was confirmed by amplifying all three gene regions as described above. Control plants remained symptom free in all pathogenicity tests. The identification of C. theobromicola on sweet olive prompted further investigation to determine if it can cause dieback on boxwoods. Boxwood dieback has become a major issue in nurseries and despite good agricultural practices, growers are unable to eradicate the pathogen from their production systems. Inoculation of container grown healthy boxwood plants with two isolates of C. theobromicola from sweet olive successfully induced boxwood dieback symptoms. Based on these findings, sweet olive could be a source of primary inoculum of C. theobromicola in nurseries. Previous reports have shown that closely related Colletotrichum spp. not only differ in their sensitivity to fungicides, but their optimal temperature for conidial infection varies considerably. The results from this study will greatly enhance nursery and landscape professionals’ understanding about the importance of accurate identification and disease epidemiology and aid them with implementing best management practices to improve crop production and reduce their losses.

Date

5-18-2026

Committee Chair

Singh, Raghuwinder

LSU Acknowledgement

1

LSU Accessibility Acknowledgment

1

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Available for download on Tuesday, May 18, 2027

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