Response to Fungicides of Colletotrichum spp. Isolated from Red Peppers in Sunchang, Korea

In August 2020, 377 anthracnose strains were isolated from anthracnose-infected peppers collected from 25 farms in Sunchang-gun, Jeollabuk-do. Inhibition rate of mycelial growth of 11 pepper anthracnose fungicides registered in Korea was investigated for 62 strains selected by region and the degree of susceptibility to each fungicide was investigated. As a result of the fungicide susceptibility test of anthracnose to the fungicide, no resistant strains were observed in fluazinam, prochloraz manganese, and benomyl, but resistant strains appeared in at least three areas for other fungicides, and all strains in all regions were resistant to dithianon. Through this, it was confirmed that the fungicide resistance was expressed in the strain group due to the continuous treatment of the fungicide in some areas. By region, resistant strains to seven pesticides appeared in Sunchang-eup and Paldeok-myeon, and resistant strains to six pesticides appeared in Geumgwa-myeon, Bokheung-myeon, Ssangchi-myeon, Yudeung-myeon, and Pungsan-myeon. There was no significant correlation between fungicide registration time and emergence of resistant strains.

Sensitivity and Resistance Risk Assessment of Puccinia striiformis f. sp. tritici to Triadimefon in China

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a destructive disease of wheat that seriously threatens production safety in wheat-producing areas worldwide. In China, the disease has been largely controlled with fungicide triadimefon. Although high levels of fungicide resistance in other fungal pathogens have been reported, failure to control Pst with any fungicides has seldomly been reported and fungicide sensitivity of Pst has not been evaluated in China. The distribution of triadimefon-resistant Pst isolates was investigated in the present study. The baseline sensitivity of 446 Pst isolates across the country to triadimefon was determined, and the concentration for 50% of maximal effect (EC50) showed a unimodal distribution curve, with a mean value of 0.19 μg mL-1. The results indicated a wide range of sensitivity to triadimefon, with more insensitive isolates collected from Pst winter-increasing areas and northwest over-summering areas, whereas more sensitive isolates were collected from southwest over-summering areas and epidemic areas of Xinjiang and Tibet. The majority of the tested Pst isolates were sensitive to triadimefon; only 6.79% had developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. Positive cross-resistance was observed between triadimefon and tebuconazole or hexaconazole, but not between pyraclostrobin or flubeneteram. The point mutation Y134F in the 14α-demethylase enzyme (CYP51) was detected in triadimefon-resistant isolates. A molecular method (Kompetitive Allele Specific PCR) was established for the rapid detection of Y134F mutants in the Pst population. Two genotypes with one point mutation Y134F conferred resistance to triadimefon in Pst. The risk of resistance to triadimefon in Pst may be low to moderate. This study provided important data for establishment of high throughput molecular detection methods, fungicide resistance risk management, and the development of new target fungicides.

Fungicide Resistance in Alternaria alternata from Blueberry in California and Its Impact on Control of Alternaria Rot

Alternaria rot caused by Alternaria alternata is one of the major postharvest diseases affecting blueberries in California. The sensitivity profiles of A. alternata from blueberry field to quinone outside inhibitors (QoIs), boscalid, fluopyram, fludioxonil, cyprodinil and polyoxin D in California were examined in this study. EC50 values of 51 A. alternata isolates for boscalid varied greatly among the isolates, ranging from 0.265 to >100 µg/ml. EC50 values of 51 A. alternata isolates to fluopyram, fludioxonil, cyprodinil, and polyoxin D were 5.188 ± 7.118 µg/ml, 0.078 ± 0.021 µg/ml, 0.465 ± 0.302 µg/ml, and 6.238 ± 7.352 µg/ml, respectively. In total, 143 isolates were screened for resistance at 5 and 10 µg/ml for fludioxonil, cyprodinil, and fluopyram, 10 µg/ml for polyoxin D, and 10 and 50 µg/ml for boscalid. Based on the published discriminatory concentrations for phenotyping resistance, of the 143 isolates, all were considered resistant to boscalid; 32, 69 and 42 were sensitive, low resistant, and resistant to fluopyram, respectively; and all were sensitive to fludioxonil and cyprodinil. In a PCR-RFLP method for phenotyping, 60 out of the 143 isolates were classified as resistant to QoIs. Control tests on detached blueberry fruit inoculated with different Alternaria isolates showed that fludioxonil and cyprodinil significantly reduced disease incidence and severity; however, pyraclostrobin, boscalid, fluopyram and polyoxin D significantly reduced only disease severity. The obtained results will be helpful in making decisions on fungicide programs to control A. alternata isolates with resistance or reduced sensitivities to multiple fungicides.

Selection and Amplification of Fungicide Resistance in Aspergillus fumigatus in Relation to DMI Fungicide Use in Agronomic Settings: Hotspots versus Coldspots

Aspergillus fumigatus is a ubiquitous saprophytic fungus. Inhalation of A. fumigatus spores can lead to Invasive Aspergillosis (IA) in people with weakened immune systems. The use of triazole antifungals with the demethylation inhibitor (DMI) mode of action to treat IA is being hampered by the spread of DMI-resistant “ARAf” (azole-resistant Aspergillus fumigatus) genotypes. DMIs are also used in the environment, for example, as fungicides to protect yield and quality in agronomic settings, which may lead to exposure of A. fumigatus to DMI residues. An agronomic setting can be a “hotspot” for ARAf if it provides a suitable substrate and favourable conditions for the growth of A. fumigatus in the presence of DMI fungicides at concentrations capable of selecting ARAf genotypes at the expense of the susceptible wild-type, followed by the release of predominantly resistant spores. Agronomic settings that do not provide these conditions are considered “coldspots". Identifying and mitigating hotspots will be key to securing the agronomic use of DMIs without compromising their use in medicine. We provide a review of studies of the prevalence of ARAf in various agronomic settings and discuss the mitigation options for confirmed hotspots, particularly those relating to the management of crop waste.

Epidemiological Studies of Pan-Azole Resistant Aspergillus fumigatus Populations Sampled during Tulip Cultivation Show Clonal Expansion with Acquisition of Multi-Fungicide Resistance as Potential Driver

Pan-azole resistant isolates are found in clinical and environmental Aspergillus fumigatus (Af) populations. Azole resistance can evolve in both settings, with Af directly targeted by antifungals in patients and, in the environment, Af unintendedly exposed to fungicides used for material preservation and plant disease control. Resistance to non-azole fungicides, including methyl benzimidazole carbamates (MBCs), quinone outside inhibitors (QoIs) and succinate dehydrogenase inhibitors (SDHIs), has recently been reported. These fungicide groups are not used in medicine but can play an important role in the further spread of pan-azole resistant genotypes. We investigated the multi-fungicide resistance status and the genetic diversity of Af populations sampled from tulip field soils, tulip peel waste and flower compost heaps using fungicide sensitivity testing and a range of genotyping tools, including STRAf typing and sequencing of fungicide resistant alleles. Two major clones were present in the tulip bulb population. Comparisons with clinical isolates and literature data revealed that several common clonal lineages of TR34/L98H and TR46/Y121F/T289A strains that have expanded successfully in the environment have also acquired resistance to MBC, QoI and/or SDHI fungicides. Strains carrying multiple fungicide resistant alleles have a competitive advantage in environments where residues of multiple fungicides belonging to different modes of action are present.

Ramularia leaf spot in barley

Ramularia leaf spot is an emerging pathogen across barley growing regions of the world. It's rise from minor to major disease has been rapid over the last twenty years. The causal pathogen, Ramularia collo-cygni is poorly understood but it has been shown to have a complex life cycle and the ability to exist on many hosts in an endophytic state. The rate of development of fungicide resistance in the fungus is also extremely fast and many of the major single site fungicides are no longer effective in many countries. With multisite fungicides having their approval or reconsidered and no consistent varietal resistance available, control of the disease is increasing challenging. This chapter reviews the latest research into Ramularia biology and control and highlights the areas where recent advances have been made.

Advances in understanding the epidemiology, molecular biology and control of net blotch and the net blotch barley interaction

Net blotches are the most widely distributed foliar diseases of barley worldwide, causing significant losses in grain yield. They occur as net form net blotch, caused by Pyrenophora teres f. teres and spot form net blotch caused by P. teres f. maculata. Both sexual and asexual reproduction play a role in the P. teres disease cycles leading to changes in genetic variation of populations. Breeding programs have to keep pace with pathogenic changes and ensure different sources of resistance are present in current barley cultivars. Knowledge of the genetic architecture and genes involved in virulence is thus vital to increase the durability of net blotch resistance in barley cultivars. This chapter explores the molecular biology, life-cycle and epidemiology of the net blotch fungi and discusses the key challenges we are facing in managing the net blotches using both fungicide resistance and breeding strategies to achieve durable disease resistance in barley.