RESUMO
In Mexico, there are 29 native species of the genus Hymenocallis, where H. glauca is one of the most cultivated bulbous plants. It holds economic importance as it is commercialized as a potted plant and cut flower (Leszczyñska and Borys, 2001). In October 2023, field sampling was conducted in the Research Center in Horticulture and Native Plants (18°55'55" N, 98°24'02.8"W) of UPAEP University. H. glauca diseased plants were found in an area of 0.4 ha, with an incidence of 35% and an estimated severity of 45% on infected plants in vegetative stage. The symptoms included chlorosis of foliage, necrosis at the base of the stem, and soft rot with abundant white to gray mycelium and abundant production of black, irregular sclerotia of approximately 3.5 mm diameter. Finally, the plants wilted and died. The fungus was isolated from 40 symptomatic plants. Sclerotia were collected, disinfested with 3% NaOCl for one minute, rinsed with sterile distilled water (SDW), and plated on Petri dishes containing potato dextrose agar (PDA) with sterile forceps. Subsequently, a sterile dissecting needle was used to place fragments of mycelium directly on Petri dishes with PDA. Plates were incubated at 23 °C in dark for 7 days. One isolate was obtained from each diseased plant by the hyphal-tip method (20 isolates from sclerotia and 20 from mycelium). After 7 days, colonies had fast-growing, dense, and cottony-white aerial mycelium forming irregular sclerotia of 3.57 ± 0.59 mm (mean ± standard deviation, n=100). In each Petri dish there were produced 21.5 ± 7.9 sclerotia (mean ± standard deviation, n=40), after 11 days; these were initially white and gradually turned black. The isolates were tentatively identified as Sclerotinia sclerotiorum based on morphological characteristics (Saharan and Mehta 2008). Two representative isolates were chosen for molecular identification and genomic DNA was extracted by the CTAB protocol. The ITS region and the glyceraldehyde 3-phosphate dehydrogenase (G3PDH) gene were amplified and sequenced (Staats et al. 2005; White et al. 1990). The sequences of a representative isolate (SsHg3) were deposited in GenBank (ITS- PP094578; G3PDH- PP101843). BLAST analysis of the partial sequences ITS (519 bp), and G3PDH (950 bp) showed 100% similarity to S. sclerotiorum isolates (GenBank: MG249967, MW082601). Pathogenicity was confirmed by inoculating 30 H. glauca plants in vegetative stage grown in pots with sterile soil. Ten sclerotia were deposited at the base of the stem, 10 mm below the soil surface. As control treatment, SDW was applied to 10 plants. The plants were placed in a greenhouse at 23 °C and 90% relative humidity. After 17 days, all inoculated plants displayed symptoms similar to those observed in the field, while no symptoms were observed on the controls. The fungus was re-isolated from the inoculated plants as described above, fulfilling Koch's postulates. The pathogenicity tests were repeated three times. S. sclerotiorum has been reported causing white mold on other bulbous plants, like fennel (Foeniculum vulgare) in Korea (Choi et al. 2015). To our knowledge, this is the first report of S. sclerotiorum causing white mold on H. glauca in Mexico. Information about diseases affecting this plant is very limited, so this research is essential for developing integrated management strategies and preventing spread to other production areas.
RESUMO
Echeveria gigantea, native of Mexico (Reyes et al. 2011), holds economic importance as it is marketed as a potted plant and cut flower due to its drought-tolerant capabilities and aesthetic appeal. In September 2023, a field sampling was conducted at the Research Center in Horticulture and Native Plants (18°55'56.6" N, 98°24'01.5" W) of UPAEP University. Echeveria gigantea cv. Quilpalli plants with white mold symptoms were found in an area of 0.5 ha, with an incidence of 40% and severity of 50% on severely affected stems. The symptoms included chlorosis of older foliage, necrosis at the base of the stem, and soft rot with abundant white to gray mycelium and abundant production of irregular sclerotia resulting in wilted plants. The fungus was isolated from 30 symptomatic plants. Sclerotia were collected, sterilized in 3% NaOCl, rinsed with sterile distilled water (SDW), and plated on Potato Dextrose Agar (PDA) with sterile forceps. Subsequently, a dissecting needle was used to place fragments of mycelium directly on PDA. Plates were incubated at 23 °C in darkness. A total of 30 isolates were obtained using the hyphal-tip method, one from each diseased plant (15 isolates from sclerotia and 15 from mycelium). After 6 days, colonies had fast-growing, dense, cottony-white aerial mycelium forming irregular sclerotia of 3.67 ± 1.13 mm (n=100). Each Petri dish produced 32.47 ± 7.5 sclerotia (n=30), after 12 days. The sclerotia were initially white and gradually turned black. The isolates were tentatively identified as Sclerotinia sclerotiorum based on morphological characteristics (Saharan and Mehta 2008). Two isolates were selected for molecular identification. Genomic DNA was extracted using the CTAB protocol. The ITS region and the glyceraldehyde 3-phosphate dehydrogenase (G3PDH) gene were sequenced for two randomly selected isolates (White et al. 1990; Staats et al. 2005). The ITS and G3PDH sequences of the SsEg9 isolate were deposited in GenBank (ITS-OR816006; G3PDH-OR879212). BLAST analysis of the partial ITS (510 bp) and G3PDH (915 bp) sequences showed 100% and 99.78% similarity to S. sclerotiorum isolates (GenBank: MT101751 and MW082601). Pathogenicity was confirmed by inoculating 30 120-day-old E. gigantea cv. Quilpalli plants grown in pots with sterile soil. Ten sclerotia were deposited at the base of the stem, 10 mm below the soil surface. As control treatment, SDW was applied to 10 plants. The plants were placed in a greenhouse at 23 °C and 90% relative humidity. After 16 days, all inoculated plants displayed symptoms similar to those observed in the field. Control plants did not display any symptoms. The fungus was reisolated from the inoculated stems, fulfilling Koch's postulates. The pathogenicity tests were repeated three times. Recently S. sclerotiorum has been reported causing white mold on cabbage in the state of Puebla, Mexico (Terrones-Salgado et al. 2023). To the best of our knowledge, this is the first report of S. sclerotiorum causing white mold on E. gigantea in Mexico. Information about diseases affecting this plant is very limited, so this research is crucial for designing integrated management strategies and preventing spread to other production areas.