Short communication: Effect of mycoviruses on growth, spore germination and pathogenicity of the fungus Fusarium circinatum

Abstract

Aim of the study: To assess the impact on two mycoviruses recently described in F. circinatum mitovirus 1 and 2-2 (FcMV1 and FcMV2-2) on i) mycelial growth, ii) spore germination and iii) relative necrosis.Material and methods: Fourteen monosporic strains of F. circinatum (one of each pair infected with mycoviruses and the other without them) of the pathogen with and without viruses were selected for the assay. The statistical analysis, were a linear mixed model of analysis of variance considering one between-subjects factor (isolate) and one within-subjects factor with four levels (1=without viruses, 2=only virus FcMV1, 3=only virus FcMV2-2 and 4=both viruses).Main results: Colony growth rates of F. circinatum isolates were significantly reduced in presence of mycoviruses (p=0.002). The spore germination was also reduced in the F. circinatum isolates containing mycovirus as compared to mycovirus-free isolates (p<0.001). No significant differences in lesion lengths caused by F. circinatum were found in relation to the presence/absence of mycovirus (p<0.61).Research highlights: Reduction of the percentage of spore germination in the isolates of F. circinatum with mycovirus infections, as compared to free isolates, provides indications of reduction of metabolic activity and plant physiology are discussed. The lack of significant differences found in the length of the lesions caused by F. circinatum with respect to the presence/absence of mycovirus, indicates that further studies with a larger number of variables are required Additional keywords: pine pitch canker; hypovirulence; biological control; forest pathology.

Vertical Transmission of Fusarium circinatum Mitoviruses FcMV1 and FcMV2-2 via Microconidia

“…Previous in vitro studies showed contradictory results; total growth of the fungus on PDAS and spore germination was significantly reduced by the presence of mitoviruses FcMV1 and FcMV2-2 [19] whereas mitovirus-infected isolates did not show different extracellular laccase activity or mycelial growth rate (mm 2 /day) on Bavendamm's medium [18]. For in vivo studies, where the mitovirus infected and mitovirus-free isolates were inoculated on young seedlings, there were different results as well.…”

“…For in vivo studies, where the mitovirus infected and mitovirus-free isolates were inoculated on young seedlings, there were different results as well. While Muñoz-Adalia et al [18] observed that FcMV1 led to higher fungal pathogenicity and lower survival of seedlings, Flores-Pacheco et al [19] obtained that there were no significant differences in the necrotic lesions caused by the pathogen irrespective of whether it was infected with the mitoviruses. In view of the above, it can be concluded that to date, the presence of mitoviruses has no clear pattern in the behavior of the Spanish isolates of the pathogen.…”

“…The correlation between additional growth and germination variables, due to the small sample size (n = 7) and non-normal distribution of the data, was explored with a non-parametric correlation matrix of the results of transmission rates and the additional variables of seven Spanish isolates (072, Fc104, 020, 035, 042, FcCa70 and Fc221), as proposed by Muñoz-Adalia et al [18] and Flores-Pacheco et al [19]. The following variables were included in the analysis: (1) spore germination (%); (2) area of fungal colony (mm 2 ), measured by the growth of the fungus on PDAS (potato dextrose agar plus 0.5 mg/L streptomycin) for seven days; (3) mycelial growth on Bavendamm's medium containing tannic acid (mm 2 /day), measured for five days using photographic methods based on pixel colorimetry (image processing with ImageJ 1.48v); (4) relative necrosis length (mm) produced by F. circinatum isolates in P. radiata seedlings; and (5) area under the disease progress curve (AUDPC).…”

“…The main aim of the present study was to investigate how the probability and rate of transmission of these mitoviruses via microconidia vary in relation to the fungal isolate and strain of virus (FcMV1 and FcMV2-2). A further aim of the study was to examine the possible correlation between the transmission rate (%) of the isolates and other phytopathological variables, such as germination and mycelial growth, as previously determined in Muñoz-Adalia et al [18] and Flores-Pacheco et al [19].…”

Environmentally friendly methods for controlling pine pitch canker

“…Fusarium circinatum hosts several species and types of mitoviruses (Martínez‐Álvarez et al ., ; Vainio et al ., ), but the role the viruses play in pathogen virulence is not clear. While virulence of F. circinatum was enhanced on 1‐year‐old P. radiata seedlings (Muñoz‐Adalia et al ., ), mycelial growth of F. circinatum colonies and spore germination were significantly reduced by the virus presence under in vitro conditions (Flores‐Pacheco et al ., ). Current understanding of the occurrence of hypovirulence caused by viruses in F. circinatum remains poor.…”