Fungicides and plant resistance inducers - indispensable for controlling cereal pathogens, detrimental to the environment

W chemicznej ochronie zbóż stosowane są g łównie fungicydy azolowe, morfolinowe, strobilurynowe, benzimidazolowe oraz inhibitory dehydrogenazy kwasy bursztynowego. Fungicydy azolowe i morfolinowe są inhibitorami biosyntezy steroli (SBI). Fungicydy strobilurynowe (QoI) i inhibitory dehydrogenazy kwasu bursztynowego (SDHI) zaburzają proces oddychania grzybów, a benzimidazolowe (MBC) tworzenie ß-tubuliny podczas mitozy. W populacjach wielu patogenów zbóż wykryto formy odporne na wszystkie grupy fungicydów, jednak niebezpieczeństwo powstawania tych form dla fungicydów strobilurynowych i benzimidazolowych jest szczególnie duże. Większość fungicydów strobilurynowych wyróżnia się mniejszą trwałością w glebie i większą podatnością na wymywanie. Toksyczność fungicydów wobec Daphnia magna określona wskaźnikiem ED50 waha się w poszczególnych klasach fungicydów w następujących zakresach: 1,3–51 (azole), 1,3–25 (morfoliny), 0,011–1,3 (strobiluryny), 0,044–100 (SDHI), 0,15–5,4 ml·l⁻¹ (bezimidazole). Sporadycznie literatura opisuje również przypadki endokrynnego działania azoli lub rakotwórczego wpływu benzimidazoli na zwierzęta. Alternatywą dla fungicydów mogą być przyjazne środowisku preparaty indukujące odporność systemiczną roślin (SAR), rzadko stosowane w ochronie zbóż przed patogenami.Major fungicides groups used in chemical plant protection are: azoles, morpholines, strobilurins (QoI), benzimidazoles and thiophanates (MBC) and succinate dehydrogenase inhibitors (SDHI). In recent years, SDHI popularity continues in grow because of its efficiency. Among active SDHI chemicals there are long-known substances, e.g. carboxin, fenfuram and new synthesized compounds. Modes of action of each fungicide groups are different and their classification is based on specific active compounds mechanism of action. Azole and morpholine fungicides are inhibitors of sterol synthesis. One of the main sterols in fungal cells is ergosterol which is an important building compound in cell wall. Ergosterol is necessary to maintain cell membrans proper functions. Strobilurins and succinate dehydrogenase inhibitors interrupt respiratory chain in fungal cells by blocking electrons transfer. Strobilurins connect with ubichinon coenzyme in cytochrome b and c1 whereas SDHI connect with succinate dehydrogenase complex. Benzimidazoles and thiophanates inhibit synthesis of β-tubulin during mitosis. Crop pathogens resistance to all these active compounds has been discovered so far. The most serious hazard of pathogen resistance acquisition is a characteristic of benzimidazole and strobilurin fungicides. There is high probability of forming resistant pathogens due to new fungicides production. There are four major resistance mechanisms in fungi: (1) change in target site (mutations), (2) metabolic detoxification of active substance, (3) production of the additional enzyme target site, (4) removal of the target site. Durability in soil is determined by half-life time (DT₅₀) of active compounds: azoles 1.6–120, morpholines 21–49,5, strobilurins 7–180.5, SDHI 3.5–118.8, benzimidazoles and thiophanates 5–724 days. Short period of half-life time of selected strobilurins is linked with susceptibility to eluviation. Fungicides toxicity to Daphnia magna is defined as EC₅₀ index which varies between each group of fungicides, e.g.: azoles 1.3–51, morpholines 1.3–25, strobilurins 0.011–1.3, SDHI 0.044–100, benzimidazoles 0.15–5.4 ml L⁻¹. However, several case reports of azoles endocrine and benzimidazoles carcinogenic effects on animals have been reported. Environmentally friendly alternative for chemical plant protection are preparations inducing systemic acquired resistance (SAR). Salicylic acid (SA), 2,6-dichloroisonicotinic acid and gamma-aminobutyric acid (GABA) and chitosan are inducers (called elicitors) of SAR in plants. The main advantage of preparations containing elicitors is no risk of pathogen resistant forms spread. So far, such preparations are not often used in crops protection

The effectiveness of Aureobasidium pullulans, Debaryomyces hansenii and Rhodotorula glutinis yeasts in inhibiting the development of Septoria leaf blotch (Zymoseptoria tritici) in wheat

Grzyb Zymoseptoria tritici, sprawca septoriozy paskowanej liści, jest jednym z najgroźniejszych patogenów pszenicy między innymi z powodu bardzo długiego okresu inkubacji w tkankach roślin (faza bezobjawowa trwa nawet 10 dni) oraz bardzo szybkiego tempa rozprzestrzeniania się na plantacji, a także trudności w jego zwalczaniu metodami chemicznymi. Jedną z naturalnych metod ograniczenia rozwoju tego patogenu jest uprawa odmian o mniejszej podatności na infekcję. Alternatywą jest także poszukiwanie skutecznych biologicznych metod ochrony. Doświadczenia polowe prowadzono w dwóch lokalizacjach w północno-wschodniej Polsce na dwóch odmianach Triticum aestivum (‘Tonacja’ i ‘Skagen’) i jednej T. durum (‘Komnata’). Celem badań była ocena skuteczności zabiegów biologicznych polegających na opryskiwaniu roślin zawiesiną drożdży Aureobasidium pullulans, Debaryomyces hansenii i Rhodotorula glutinis w ograniczeniu objawów septoriozy paskowanej liści pszenicy. Odmiana Komnata charakteryzowała się mniejszą podatnością na infekcje liści Z. tritici niż odmiany Skagen i Tonacja. Skuteczność zabiegów biologicznych w ograniczeniu objawów septoriozy paskowanej liści odmiany Tonacja oszacowano na poziomie 59,3% dla izolatu A. pullulans oraz 56,7% dla D. hansenii. Zabiegi biologiczne nie miały istotnego wpływu na plonowanie pszenicy.The causal agent of Septoria leaf blotch is one of the most dangerous fungal pathogens of wheat. It has a very long incubation period in plant tissues, spreads rapidly in crops and is highly resistant to chemical agents. Biological control methods could be used together with fungicides, but only between ten and twenty biocontrol agents have been approved for use in Europe to date. The aim of this study was to evaluate the effectiveness of foliar-applied cell suspensions of Aureobasidium pullulans, Debaryomyces hansenii and Rhodotorula glutinis yeasts in eliminating the symptoms of Septoria leaf blotch in winter wheat. A field experiment was carried out in two locations in north-eastern Poland on two cultivars of Triticum aestivum (‘Tonacja’ and ‘Skagen’) and one T. durum cultivar (‘Komnata’). The yeast isolates used in the experiment were obtained from the grain of winter wheat cv. Tonacja (A. pullulans, Rh. glutinis) and apples cv. Antonówka (D. hansenii). The ITS1-5,8SrRNA-ITS2 sequences of A. pullulans, D. hansenii and R. glutinis yeasts were deposited in the NCBI database under accession numbers KX444670, KX444669 and KX444653, respectively. Yeast suspensions with density of 0.4–2.5·105 cells per cm3 of sterile water were sprayed onto plants with the use of a backpack sprayer at the first node stage, at the heading stage and at the full flowering stage. The effectiveness of biological treatments in controlling the spread of Septoria leaf depended on the susceptibility of wheat cultivars to infections caused by Zymoseptoria tritici and the yeast strain used as a biocontrol agent. Durum wheat cv. Komnata was less susceptible to leaf infections caused by Z. tritici than common wheat cvs. Skagen and Tonacja. In all analyzed wheat cultivars, the severity of Septoria leaf blotch was considerably lower on flag leaves than on penultimate leaves. The effectiveness of biological treatments in controlling the spread of Septoria leaf blotch in common wheat cv. Tonacja was estimated at 59.3% for the suspension containing the Aureobasidium pullulans isolate and 56.7% for the suspension containing the Debaryomyces hansenii isolate. In the remaining wheat cultivars, the effectiveness of biological treatments did not exceed 54.5%, and it was not statistically significant, mostly due to the low density of the cell suspension of the Rhodotorula glutinis isolate, which was characterized by a low growth rate on agar. Biological treatments had no significant influence on wheat yield. Since yeasts used as biocontrol agents are not highly effective against Z. tritici, they should be combined with chemical methods

Evaluation of the usefulness of yeast and chemical fungicides to reduce development of fungi colonizing Scots pine seedlings

In the nurseries, Scots pine seedlings that show symptoms of the damping−off usually die. Rhizoctonia solani, a rapidly growing fungus, is one of the pathogens that infect the roots of plants. The aims of this study were: (1) to evaluate the susceptibility of R. solani and saprotrophic fungi Mortierella elongata, Trichoderma hamatum and T. rossicum to fungicides, (2) to determine whether yeast isolates can be used as effective inhibitors of the pathogen's growth, and (3) to analyze phylogenetic relationships between filamentous fungi. The Switch 62.5 WG fungicide, containing cyprodinil and fludioxonil, most effectively suppressed the growth of the tested R. solani isolates, but also exerted ecotoxic effects on the analyzed saprotrophs. The R. solani RS 1 isolate did not respond to the presence of azoxystrobin in PDA. Most of the 13 yeast isolates tested in the study inhibited the growth of pathogen colonies, but only one isolate was characterized by inhibitory activity of 59.03% and exerted a strong antagonistic influence on the pathogen. A phylogenetic analysis revealed that the tested isolates represented three clades: 1) T. hamatum, 2) T. rossicum, and 3) R. solani. The phylogenetic tree of M. hamatum and T. rossicum showing their divergence due to mutations did not reflect their speciation