Analysis of resistance risk and resistance‐related point mutations in Cyt b of QioI fungicide ametoctradin in Phytophthora litchii

Abstract

BACKGROUND: Litchi downy blight, caused by Phytophthora litchii, is one of the most important diseases of litchi. Ametoctradin, as the only QioI (quinone inside and outside inhibitor) fungicide, has been registered in China in 2019. However, the ametoctradin-resistance risk and molecular basis in Phytophthora litchii have not been reported. RESULTS: In this study, the sensitivity profile of 144 Phytophthora litchii strains to ametoctradin was determined, with a mean median effective concentration (EC 50 ) value of 0.1706 ± 0.091 ∼g mL −1 . Nine stable resistant Phytophthora litchii mutants [resistance factor (RF) > 400] were derived from sensitive isolates using fungicide adaption. The compound fitness index of three resistant-mutants (HN10-1-1, HN10-1-2 and HN10-2-1) was similar or higher than that of their parental isolates in vitro. All these ametoctradin-resistant mutants were sensitive to metalaxyl, dimethomorph, oxathiapiprolin and cyazofamid. Two point mutations, leading to the S33L and D228N changes in PlCyt b (cytochrome b) were found in ametoctradin-resistant mutants. Eight ametoctradin-resistant mutants containing S33L showed increased sensitivity to azoxystrobin and amisulbrom, and one mutant containing D228N exhibited increased sensitivity to cyazofamid. In vitro enzyme activity test showed that ametoctradin could not inhibit the activity of cytochrome bc1 complex with S33L and D228N point mutation. AS-PCR primers were designed based on the S33L change to detect the ametoctradin-resistant strains in the future.CONCLUSION: These results suggest that Phytophthora litchii has a medium to high resistance risk to ametoctradin in the laboratory. Two changes, S33L and D228N, in PlCyt b are likely to be associated with the observed ametoctradin resistance.

Attributes of Cyazofamid-Resistant Phytophthora litchii Mutants and Its Impact on Quality of Litchi Fruits

“…The comprehensive PlCyt b gene sequence was amplified using the primer pairs: F: 5′-TGATTACGGTTTTGAAGGACATCCTTTACGTAAAGAT-3′ and R: 5′-TTATTAATATTATAACGTACTAAAAAGCTTCAAATTTACCTAAAAATG-3′ . PCR amplifications utilized 50 μL samples preparations.…”

“…The comprehensive PlCyt b gene sequence was amplified using the primer pairs: F: 5′-TGATTACGGTTTTGAAGGACATCCTTTACGTAAAGAT-3′ and R: 5′-TTATTAATATTATAACGTACTAAAAAGCTT-CAAATTTACCTAAAAATG-3′. 15 PCR amplifications utilized 50 μL samples preparations. The reaction mixture comprised 100 ng of genomic DNA, 25 μL of 2× M5Taq HiFi PCR mix from Mei5 Biotechnology Co., Ltd. (Beijing, China), and 2 μL of individual primers at 10 μM.…”

“…14 The application of synthetic fungicides during the flowering and fruiting stages has proven effective in reducing the incidence of LDB. 8,12,15 In China, 31 registered fungicide products are available for the management of LDB (http://www. chinapesticide.org.cn/).…”

“…The application of synthetic fungicides during the flowering and fruiting stages has proven effective in reducing the incidence of LDB. ,, In China, 31 registered fungicide products are available for the management of LDB (). It is worth noting that a majority of the registered fungicides are single-target fungicides, resulting in the inevitable development of fungicide resistance over time. − This situation emphasizes the importance of assessing the resistance risk associated with the judicious use of fungicides, delaying resistance onset and implementing suitable strategies for integrated disease management.…”

First report of quinone outside inhibitor stigmatellin binding type (QoSI) resistance in Plasmopara viticola in India

“…To our knowledge this is the first occurrence of QoSI (ametoctradin) resistance in P. viticola in India. It is interesting to note that the related oomycete, Phytophthora litchii , has also developed resistance to ametoctradin which has been attributed to changes in PlCyt b (S33L and D228N) (Gao et al., 2022); S33L in P. litchi is orthologous to S34L in Plasmopara (Oliver et al., 2023). Further work is required to monitor resistance to QoSI fungicides in the P. viticola population and to alert the grower community to use alternative fungicides to effectively manage the disease.…”