Detection and Characterization of QoI-Resistant Phytophthora capsici Causing Pepper Phytophthora Blight in China

Abstract

Phytophthora capsici is a highly destructive plant pathogen that has spread worldwide. To date, the quinone outside inhibitor (QoI) azoxystrobin has been the choice of farmers for managing this oomycete. In this study, the sensitivity of 90 P. capsici isolates collected from Yunnan, Fujian, Jiangxi, Zhejiang, and Guangdong in southern China to azoxystrobin was assessed based on mycelial growth, sporangia formation, and zoospore discharge. Furthermore, the mitochondrial cytochrome b (cytb) gene from azoxystrobin-sensitive and -resistant P. capsici isolates was compared to investigate the mechanism of QoI resistance. The high values for effective concentration to inhibit 50% of mycelial growth and large variation factor obtained provide strong support for the existence of azoxystrobin-resistant subpopulations in wild populations. The resistance frequency of P. capsici to azoxystrobin was greater than 40%. Sensitive P. capsici isolates were strongly suppressed on V8 medium plates containing azoxystrobin supplemented with salicylhydroxamic acid at 50 µg ml, whereas resistant isolates grew well under these conditions. Multiple alignment analysis revealed a missense mutation in the cytb gene that alters codon 137 (GGA to AGA), causing an amino acid substitution of glycine to arginine (G137R). The fitness of the azoxystrobin-sensitive isolate is similar to that of the G137R mutant. Additionally, the P. capsici isolates used in this study exhibited decreased sensitivity to two other QoI fungicides (pyraclostrobin and famoxadone). Necessary measures should be taken to control this trend of resistance to QoI that has developed in P. capsici in southern China.

Activity and Resistance-Related Point Mutations in Target Protein PcORP1 of Fluoxapiprolin in Phytophthora capsici

“…are the most commonly used fungicides (). However, many fungicides against oomycetes have generated serious resistance problems because of unreasonable and frequent applications in fields. − Therefore, it is urgently required to develop new environmentally friendly oomycete inhibitors with high activity.…”

Comparative Performance of Fungicides, Biofungicides, Host-plant Defense Inducers, and Fertilizer in Management of Phytophthora Root Rot on Boxwood

“…Another experiment on managing P. sojae on soybean using pyraclostrobin as seed treatment showed efficacy for increased chlorophyll level, shoot and root length, root activity, and continuous positive effect on enhancing the plant defense (Li et al, 2020). In contrast, some studies showed decreased sensitivity of P. capsici causing Phytophthora blight in pepper against quinone-outside inhibitor (QoI) fungicides including pyraclostrobin (Ma et al, 2018), suggesting the necessity of using fungicides in rotation to save crops from increased resistance. gens (La Spada et al, 2020), but in our study the combined application of water-soluble nitrogen, soluble potash, and T. harzianum Rifai strain T-22 1 T. virens strain G-41 was effective, which might be due to the synergistic effect of both fertilizer and biofungicide.…”

High-Throughput Customization of Plant Microbiomes for Sustainable Agriculture

“…Both harmful and beneficial bacteria and fungi need to be considered, especially with regard to how they communicate with plant hosts, such as providing biological nutrient sources or suppressing the host’s immune response ( Zhu et al., 2018 ). Endophytes are similar to pathogens, having the ability to enter the host tissue and stay there without causing harm to the host and even being beneficial ( Ma et al., 2018a ). Both partner plants and microorganisms, such as fungi, benefit from the relationship: mycorrhizal fungi improve the nutrient status of their host plants, influencing mineral nutrition, water absorption, growth and disease resistance, whereas in exchange, the host plant is necessary for fungal growth and reproduction ( Bonfante and Genre, 2010 ).…”