http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Evaluation of Aerial Blight Caused by Phytophthora on Cora XDR and Ornamentals
Vinca plants such as Cora XDR are known to have high levels of resistance to Phytophthora aerial blight, and the results of this work show variable susceptibility to Phytophthora nicotianae in varieties and cultivars of vincas. The main objectives of this research project are the following: (i) characterize Phytophthora sp. 2238-2019 at the morphological and molecular level and differentiate this strain from other cultures isolated from ornamentals in Texas, (ii) conduct pathogenicity testing of Phytophthora isolates on Titan, Valiant and Cora XDR varieties, (iii) assess commonly applied fungicides to determine if recommended fungicide applications might be able to control Phytophthora sp. 2238-2019, and (iv) conduct a host plant range study. The overarching objective of this study was to characterize Phytophthora sp. 2238-2019 and observe its virulence on different varieties of vinca, as this isolate was shown to be pathogenic to a Cora XDR. In this study, six suspected Phytophthora species were obtained from the Texas Plant Disease Diagnostic Lab that had been previously isolated from Antirrhinum majus, Catharanthus roseus (2007), Catharanthus roseus (Cora XDR), Dianthus caryophyllus, Catharanthus roseus (2004) and Viola tricolor hortensis. Oomycete and fungal DNA was extracted from the isolates and amplified using PCR with ITS6-4 and FMPH-8 and FMPHy-10b primers. The obtained sequences were placed in NCBI BLASTn search. The resulting identity was compared to observed morphological characteristics to make identifications. Isolates were found to be unique P. nicotianae, with the exception of one isolate, Phytophthora sp. LP-2004. Pathogenicity testing on vinca showed Cora XDR vinca had a lower disease severity compared to other varieties when infected with Phytophthora sp. 2238, with the exception of Cora XDR 'Light Pink.' Fungicide efficacy testing revealed StatureTM (0.5x-4x), Subdue MaxxTM (0.5x-4x), and HeritageTM (4x) were found to restrict Phytophthora sp. 2238- 2019 colony to less than one half the diameter compared to the control plate of Phytophthora sp. 2238-2019. Lastly, it was found that English Lavender (Lavandula angustifolia), "Cora XDR Magenta Halo," and "Cora XDR Magenta," vincas were susceptible to Phytophthora sp. 2238-2019. Characterizing these Phytophthora isolates is important to diagnosticians and plant breeders of vinca for rapid and accurate diagnoses. The electronic version of this dissertation is accessible from https://hdl.handle.net/1969.1/198656
Master of Science Texas A&M University 2022 https://hdl.handle.net/1969.1/198656