Selecting tolerant strawberry germplasm to the fungus Macrophomina phaseolina

S. Youssef, A.A. Shalaby, B. Pickel, M. Maymon, M. Borenstein, N. Dai, R. Cohen, S. Freeman
Macrophomina phaseolina is a soilborne fungal pathogen causing crown and root rot in strawberry worldwide. M. phaseolina is one of the most destructive soilborne pathogens of strawberry in the Mediterranean region. M. phaseolina was isolated from different cultivars of strawberry showing crown rot, foliage wilting, charcoal rot and plant mortality, cultivated in Qualubia, El Behera and Ismailia governorates in Egypt, and other regions in Israel. The most effective approach for managing the disease relies on resistant germplasm selected using reliable techniques. Pathogenicity tests using M. phaseolina isolates were conducted for virulence and viability using various methods. Various cultivars of strawberry were inoculated by inserting M. phaseolina microsclerotia-colonized toothpicks into crowns of the plants, compared to plantings into a potted soil mix containing 2.5×103 sclerotia mL‑1. All inoculated plants were grown at 30°C under greenhouse conditions. Disease symptoms were observed 4 days after inoculation with plant mortality of all the cultivars occurring approximately 20 days post-inoculation, using the toothpick method. In contrast, the microsclerotia inoculation method appeared to be more accurate in distinguishing susceptibility/ tolerance of the tested strawberry cultivars, with initial disease symptoms appearing 2 weeks after inoculation. Using the microsclerotia method, disease symptoms progressed faster in the cultivar 'Festival' that was more susceptible to the pathogen, while the 'Florida 90' cultivar showed an intermediate level of disease, with 'Fortuna' showing the least disease progress over time. Additional cultivars were tested in a screenhouse using the microsclerotia method. A differential mortality rate was observed. Thus, disease screening of resistant germplasm to M. phaseolina should rely on an accurate and reliable inoculation technique.
Youssef, S., Shalaby, A.A., Pickel, B., Maymon, M., Borenstein, M., Dai, N., Cohen, R. and Freeman, S. (2021). Selecting tolerant strawberry germplasm to the fungus Macrophomina phaseolina. Acta Hortic. 1309, 751-758
DOI: 10.17660/ActaHortic.2021.1309.107
charcoal rot, inoculation techniques, Macrophomina phaseolina, soilborne pathogens, strawberry wilt

Acta Horticulturae