Preventive and Curative Effects of Treatments to Manage Strawberry Root and Crown Rot Caused by Neopestalotiopsis rosae.

Strawberry root and crown rot caused by the fungus Neopestalotiopsis rosae is an emerging disease that has caused yield losses reaching 70% in Mexico and other regions worldwide. This research evaluated the effects of biological and chemical fungicides applied as preventive and curative applications for controlling root and crown rot caused by N. rosae in strawberries under greenhouse conditions. Treatments included these chemical fungicides: prochloraz, prochloraz+thiram, cyprodinil+fludioxonil, difenoconazole+azoxystrobin, iprodione, captan, thiram, pydiflumetofen+fludioxonil, fluxapyroxad+pyraclostrobin, and hymexazol; each applied at commercial doses. Also tested were biological treatments based on Trichoderma koningiopsis, Trichoderma asperellum, Streptomyces sp., and Bacillus amyloliquefaciens strain D747 (B. velezensis). Disease incidence, severity, plant mortality, root length, and dry weight were determined. Results showed that overall, preventive applications of the fungicides pydiflumetofen+fludioxonil, cyprodinil+fludioxonil, and prochloraz resulted in the smallest area under the disease progress curve, and lowest final disease incidence, severity, and plant mortality. An intermediate group of effective treatments entailed hymexazol, iprodione, T. asperellum, and T. koningiopsis (50-75% efficacy). Treatments with greater efficacy (99 to 100%), prochloraz pydiflumetofen+fludioxonil, cyprodinil+fludioxonil, and prochloraz, also had maximal total plant biomass vis-à-vis the untreated control. In contrast, each treatment's efficacy was significantly reduced when applied curatively (0 to 37% treatment efficacy). These results suggest that certain treatments are useful for controlling strawberry root and crown rot caused by N. rosae, when applied preventively (as root dipping). These results will contribute to design more effective management programs of root rot and crown rot caused by N. rosae on strawberry.

Comparative Performance of Fungicides and Biocontrol Products in the Management of Fusarium Wilt of Blackberry.

Fusarium wilt of blackberry (FWB) is an emerging disease caused by a Fusarium oxysporum species complex. More than 3,000 ha of blackberry (Rubus spp.) crops have been lost in Mexico since 2011. The objectives of this research were: to evaluate the sensitivity of pathogenic F. oxysporum isolates recovered from symptomatic blackberry plants to fungicides with different modes of action; to assess the potential of these fungicides and plant resistance inducers against FWB in the greenhouse; and to determine the effects of commercial biofungicides and two indigenous strains of Trichoderma spp. on the incidence of FWB. The EC50 values of the fungicides prochloraz, thiabendazole, azoxystrobin, thiophanate-methyl, difenoconazole, triflumizole, and potassium phosphite for six pathogenic F. oxysporum isolates were determined. In a separate experiment, the fungicides acibenzolar-s-methyl (ASM), potassium phosphite, and commercial biofungicides, as well as two soil microbial inoculants and two indigenous Trichoderma strains, were tested for protection against wilt development in blackberry plants in the greenhouse. Prochloraz showed an average sensitivity for EC50 of 0.01 µg ml-1 for the tested F. oxysporum isolates, followed by difenoconazole and thiabendazole. Prochloraz and ASM proved to be the most effective treatments in the greenhouse. In contrast, potassium phosphite was ineffective in both the in vitro and in vivo experiments. The soil bioinoculants MicroSoil, Baktillis, T. koningiopsis, and T. asperellum significantly reduced the incidence of disease in the greenhouse. These results provide evidence for the potential of the various tools as useful components of integrated FWB management in the field.

An Emerging Strawberry Fungal Disease Associated with Root Rot, Crown Rot and Leaf Spot Caused by Neopestalotiopsis rosae in Mexico.

In the 2017 strawberry season, several transplant losses reaching 50% were observed in Zamora, Michoacán Valley, Mexico, due to a new fungal disease associated with root rot, crown rot, and leaf spot. In this year the disease appeared consistently and increased in the following seasons, becoming a concern among strawberry growers. Thus, the aim of this research was to determine the etiology of the disease and to determine the in vitro effect of fungicides on mycelial growth of the pathogen. Fungal isolates were obtained from symptomatic strawberry plants of the cultivars 'Albion' and 'Festival' and were processed to obtain monoconidial isolates. Detailed morphological analysis was conducted. Concatenated phylogenetic reconstruction was conducted by amplifying and sequencing the translation elongation factor 1 α, ß-tubulin partial gene, and the internal transcribed spacer region of rDNA. Pathogenicity tests involving inoculation of leaves and crowns reproduced the same symptoms as those observed in the field, fulfilling Koch's postulates. Morphology and phylogenetic reconstruction indicated that the causal agent of the described symptoms was Neopestalotiopsis rosae, marking the first report anywhere in the world of this species infecting strawberry. N. rosae was sensitive to cyprodinil + fludioxonil, captan, iprodione, difenoconazole, and prochloraz.