Characterization and Control of Root Rot and Wilt Fungi of Geranium (Pelargonium graveolens L.) with Special Reference to First Record for Fusarium proliferatum as Wilt Pathogen on Geranium in Egypt

Geranium root rot and wilt are the most destructive geranium diseases, limiting global production. During the present study, yielded fungal isolates belonging to four fungal species were recovered from diseased geranium (Pelargonium graveolens L.) plants showing root rot and wilt symptoms collected from nurseries and fields in Qaliobia and Behera governorates during 2021. Four fungal species were identified as Fusarium proliferatum, Fusarium solani, Macrophomina phaseolina, and Rhizoctonia solani with frequencies of 40.78, 17.48, 22.33, and 19.42, respectively.  Pathogenicity tests showed that all the tested fungi were pathogenic on geranium to different degrees. However, Fusarium proliferatum showed only wilt symptoms recognized with yellowing of leaves, discoloration of the internal vascular tissues, and no rot symptoms were developed on the plants. According to the available literature, the present study suggests that this is the first report of F. proliferatum as a wilt pathogen of geranium in Egypt. Moreover, control studies were performed in vitro and under greenhouse and field conditions to control root rot and wilt fungi of geranium. The in vitro studies showed that the three tested essential oils, i.e., marjoram, peppermint, and thyme, completely (100%) inhibited the growth of the tested fungi in vitro at 4000, 5000, and 4000 ppm, respectively. Also, the greenhouse experiment showed that dipping healthy rooted cuttings in the tested essential oils at the above-mentioned concentrations before planting with another treatment as soil drench at 30 days after planting significantly decreased disease severity percentages (DS%) of root rot and wilt of geranium by 89.68, 71.07, and 92.20%, for the three tested essential oils, respectively. This is compared to 75.37, and 61.61, for the check treatments with Plant Guard (4 mL/l) biocide, Rhizo-N )3 g/l) biocide, and Occidor 50% SC (2g/l) fungicide, respectively, and compared to 89.42% for Occidor 50% SC (2g/l) fungicide. Meanwhile, a similar trend was obtained in fields naturally infested with the root rot and wilt fungi of geranium in Beheira and Qaliobia governorates during 2022/2023 season. Treatments by dipping the rooted cuttings before planting and then treatment at 30 days after planting as soil drench in marjoram, peppermint, and thyme essential oils, significantly, decreased DS% by 49.50, 34.55, and 55.87 %, significantly. This is compared to 43.49, 49.23, and 55.87% for Plant (4 mL/l), and Rhizo-N )3 g/l) and Occidor 50% SC (2g/l) fungicide, respectively. Furthermore, all these essential oils treatments under field conditions showed significant improvement effects in growth characteristics (plant height, number of branches, fresh weight) and the oil productivity of geranium grown in field naturally infested with root rot and wilt fungi.