A method for long‐term storage of spores of Phakopsora pachyrhizi was optimized. Three methods with different procedures for spore harvest and four different reactivation methods (varying in ...hydration or using heat shock) were analysed for the suitability for long‐term storage at −80°C. All conservation methods as well as all reactivation methods lead to the infection of soybean leaves after 1 year of storage. Regarding efficiency and labour input, the most recommended method is to tap off spores from infected and sporulating leaves with subsequent dehydration before storage at −80°C. Because hydration or heat shock steps did not provide any advantages, spores can be suspended in Tween water directly after storage and used as inoculum.
Zymoseptoria tritici is a dominant pathogen in wheat causing Septoria leaf blotch (SLB), and sterol 14α-demethylation inhibitors fungicides (DMI) are commonly used for control in Northern Europe. In ...14 winter wheat trials carried out in Denmark, Lithuania, and Sweden in the years 2011 to 2013, fungicides containing DMIs were investigated for their efficacy and impact on CYP51 mutations in Z. tritici populations. All fungicide treatments were applied twice – each time using 50 % of the standard rate, applied at GS 37 & 55. The single-agent DMIs, epoxiconazole and prothioconazole and a mixture of difenoconazole + propiconazole gave similar control and crop yields. The best solution varied among localities. Adding prochloraz to prothioconazole as well as using co-formulations of DMIs + SDHIs generally improved control compared with using DMIs alone. Yield responses were significant from all treatments, but co-formulations of DMIs plus SDHIs increased yield the most. Specific CYP51 mutations in Z. tritici were analysed by pyrosequencing and qPCR. Their frequency varied across sites and countries. The amount of I381V was high in all trials whereas the amount of A379G was moderate. Levels of D134G, V136C, and S524T were low to moderate across all sites. DMIs and mixtures of DMIs + SDHI selected differently for CYP51 mutations. Prochloraz increased selection for D134G and V136A and decreased selection for A379G and I381V. The lowest selection pressure towards D134G and V136A/C was recorded in the presence of the mixture difenoconazole and propioconazole. Mixtures of DMIs and SDHI tended to lower the frequency of V136A/C compared to DMIs used alone but had no measurable impact on the frequency of I381V and A379G. No responses were seen in relation to S524T, which only occurred at a very low level.
In Algeria, barley (
Hordeum vulgare
L.) is the second most cultivated cereal after wheat; however, this crop is challenged by several foliar diseases. Net blotch is one of the most common diseases ...of barley in Algeria and is caused by the fungus
Pyrenophora teres
(Died.) Drechsler, which occurs in two forms:
P. teres
f.
teres
(
Ptt
), causing the net form (NFNB), and
P.
teres
f.
maculata
(
Ptm
), causing the spot form (SFNB). Since the two forms are morphologically similar but genetically distinct, several PCR primer sets have been developed for their differentiation in the past. In this study, net blotch symptom types were monitored in 58 fields, through almost all cereal-growing areas in Algeria, then 212
P. teres
mono-spore isolates were analyzed with respect to the occurrence of
Ptt
and
Ptm
by using two type-specific primer pairs. The results indicate that
Ptt
is the dominating type of net blotch in Algeria and was prevalent in almost all provinces surveyed, while
Ptm
was found less frequently. This is the first characterization of the Algerian net blotch population with the aim to distinguish both forms and, therefore, could contribute to a wider knowledge of the epidemics of this important plant pathogen.
The chemopreventive effect of polyphenols from green tea e.g. (-)-epigallocatechin gallate (EGCG) and (-)-epigallocatechin (EGC) against cancer has been demonstrated in several studies. The aim of ...this investigation was to prove whether these compounds modulate the activity of antineoplastic drugs. Therefore, the influence of EGCG and EGC was tested on doxorubicin-resistant murine sarcoma (S180-dox) and human colon carcinoma (SW620-dox) cell lines. Both substances showed a sensitizing effect on the cell lines if they had been treated with doxorubicin. These results suggest that protein kinase C may be inhibited by EGCG and EGC, and this may lead to a reduced expression of some drug resistance related proteins.
Fifty two isolates of Mycosphaerella graminicola from Tunisia were analysed for their sensitivity to pyraclostrobin and epoxiconazole in microtitre tests and for mutations in the target genes of the ...modes of action, cytochrome b and CYP51, respectively. All isolates were highly sensitive to pyraclostrobin, thus no isolate carried the G143A mutation in the cytochrome b gene, the mutation which is the proved mechanism in M. graminicola for QoI resistance. The Tunisian M. graminicola population was more sensitive to epoxiconazole when compared with European populations based on previously published data. However, some mutations in the CYP51, which are known to be an adaptation response to DMIs have been found in a part of the population (e.g. mutations A379G, I381V), but there is still a portion with wild type isolates, which has already disappeared in Northern Europe. The current data indicate a favourable situation for QoI and DMI sensitivity, but it should be considered in any disease management strategy to include different modes of action to avoid QoI resistance and further adaptation to DMIs.
► All Isolates were sensitive to pyraclostrobin. ► Isolates showed different sensitivity to epoxiconazole. ► Different CYP51 haplotypes were detected.
Strobilurin fungicides can be used to manage blackleg (Leptosphaeria maculans) of canola (Brassica napus); however, they have a high risk of selecting for resistance in fungal populations. In 2011, ...single-spore isolates of L. maculans were obtained from infected canola stubble representing six fields in Alberta, Canada. The isolates were grown on fungicide-amended agar plates and percent growth inhibition was calculated based on colony diameter relative to non-amended controls. Using probit regression analysis, the effective concentration of pyraclostrobin needed to inhibit mycelial growth by 50% (EC50) was determined to be 0.09 mg L-1 based on 13 isolates. To identify highly insensitive isolates, 117 isolates were grown on agar plates amended with a discriminatory dose of 6.25 mg L-1. Isolates in which growth was inhibited <50% were considered insensitive. Growth inhibition values ranged from 66.6% to 100.0% with a mean of 84.3%, indicating that all of the isolates were sensitive to pyraclostrobin. Forty-one of the 117 isolates were also tested via a microtiter plate assay. Based on conidial germination and subsequent growth, the EC50 values obtained for each isolate ranged from 1.0 × 10-4 to 7.4 × 10-3 mg L-1, which were not significantly different from those of the sensitive controls (4.1 × 10-3 and 5.7 × 10-3 mg L-1). While pyraclostrobin insensitivity was not detected in L. maculans populations from Alberta, continued monitoring will be necessary to track future changes.
Since the invasion of Phakopsora pachyrhizi (Syd. & P. Syd.) in Brazil, there have been detrimental yield losses of soybeans Glycine max (L.) Merr.. Disease management is mainly based on fungicide ...treatment. The sensitivity of single P. pachyhrizi isolates towards different demethylation-inhibitors (DMIs) and quinone-outside-inhibitors (QoI) was surveyed and the corresponding resistance mechanisms were analysed. The QoI-response remained stable, while a loss of sensitivity towards DMIs occurred. Molecular analyses of cytochrome b showed an intron after codon 143 which is reported to prevent the development of a G143A mutation. Analysis of cyp51 revealed that point mutations and overexpression are involved in the sensitivity reduction towards DMIs. Of the detected mutations, Y131F and Y131H, respectively, and K142R are likely homologous to mutations found in other pathogens. As suggested by modelling studies, these three mutations as well as additional mutations F120L, I145F and I475T correlate to increased effective doses of 50%, ED50-values, towards all tested DMIs. Furthermore, a constitutive up-regulation of the cyp51-gene up to ten-fold was noticed in some of the DMI-adapted isolates, while all sensitive isolates responded as the wild type. The G143A mutation is thought to result in significant as well as stable resistance factors towards QoIs, while other mutations play only a minor role. Since G143A development is prevented in Phakopsora pachyhrizi, a stable control of soybean rust with QoIs in future is rather likely. In contrast, a shifting in sensitivity towards DMIs has been observed, which is due to multiple independent mechanisms. PUBLICATION ABSTRACT
Sequence analysis of the cytochrome b gene of Guignardia bidwellii showed that the occurrence of the most important resistance mechanism for QoI fungicides, the G143A mutation, is relatively ...unlikely. This is due to the presence of an intron directly after codon 143. A mutation in this codon (from glycine to e.g. alanine) would presumably lead to incorrect mRNA maturation and a non-functional, lethal protein. Intron sequences have not been detected in immediate vicinity to the codons 129 and 137; therefore, the occurrence of those two mutations cannot be excluded. Since the effects of these mutations on field performance on QoI fungicides are rather low, the overall resistance risk of G. bidwellii to this fungicide class is estimated to be low.
A monitoring study on the current sensitivity situation of wheat powdery mildew (
Blumeria graminis
f.sp.
tritici
) towards metrafenone was performed in 2009 with 2509 isolates. Airborne isolates ...were randomly collected in different regions of the most important European cereal growing regions. The sensitivities of the majority of isolates were comparable to the baseline sensitivity, which was determined in 2000 before market launch of the compound. Ninety-two isolates showed sensitivities outside the baseline. Eighty-four of them were classified as moderately adapted and could still be inhibited with registered rates of metrafenone in glasshouse tests under various preventive or curative conditions. Eight isolates were identified to be resistant, which were not fully inhibited at registered rates. Resistance management strategies and further extensive monitoring studies are indicated for a sustainable use of metrafenone against wheat powdery mildew.
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