The rice disease bakanae, caused by Fusarium fujikuroi Nirenberg, has been present in Taiwan for over a century. To better understand the genetic diversity and structure of F. fujikuroi, a set of 16 polymorphic simple sequence repeat (SSR) markers were newly developed and used to analyze 637 F. fujikuroi isolates collected in 14 cities or counties around Taiwan from 1996 to 2013. On the basis of Bayesian clustering, the isolates were classified into four highly differentiated clusters: cluster B likely derived from the more widespread and genetically diversified clusters A or C, and cluster D was restricted to four cities or counties and may have been introduced from unknown sources genetically distinct from clusters A, B, and C. The coexistence of both mating types (MAT1-1:MAT1-2 = 1:1.88) and the highly diversified vegetative compatibility groups (VCG) (16 VCG among the 21 assessed isolates) suggest the likelihood of sexual reproduction in the field. However, the biased mating type ratios and linkage disequilibrium in the population suggest nonrandom mating between individuals. A significant pattern of isolation by distance was also detected, which implies a geographical restricted gene flow and low dissemination ability of F. fujikuroi. Evaluation of 24 representative isolates on eight rice varieties revealed differential levels of virulence, however no clear pattern of specific variety x isolate interaction was observed. Investigations of the differences in virulence and fungicide sensitivity between 8 early isolates (1998 and 2002) and 52 recent isolates (2012) indicate the evolution of increased resistance to the fungicide prochloraz in F. fujikuroi in Taiwan.
The entomopathogenic fungus Metarhizium anisopliae MA05-169 is a transformant strain that has been metabolically engineered to express dihydroxynaphthalene-melanin biosynthesis genes. In contrast to the wild type strain, the transformant displays a greater resistance to environmental stress and a higher virulence toward target insect host. However, the underlying mechanisms for these characteristics remain unclear; hence experiments were initiated to explore the possible mechanism(s) through physiological and molecular approaches. Although both transformant and wild type strains could infect and share the same insect host range, the former germinated faster and produced more appressoria than the latter, both in vivo and in vitro. The transformant showed a significantly shorter median lethal time (LT50) when infecting the diamondback moth (Plutella xylostella) and the striped flea beetle (Phyllotreta striolata), than the wild type. Additionally, the transformant was more tolerant to reactive oxygen species (ROS), produced 40-fold more orthosporin and notably overexpressed the transcripts of the pathogenicity-relevant hydrolytic enzymes (chitinase, protease, and phospholipase) genes in vivo. In contrast, appressorium turgor pressure and destruxin A content were slightly decreased compared to the wild type. The transformant's high anti-stress tolerance, its high virulence against five important insect pests (cowpea aphid Aphis craccivora, diamondback moth Pl. xylostella, striped flea beetle Ph. striolata, and silverleaf whitefly Bemisia argentifolii) and its capacity to colonize the root system are key properties for its potential bio-control field application.
From August to November 2020, reduced emergence and damping-off of soybean seedlings were observed in two fields (Benzhou and Wandan) in Taiwan. Disease incidence was approximately 40% in Benzhou by field scouting. The roots of damping-off seedlings were brown. Affected seedlings could be easily pulled out from the soil and the lesions on the roots/stem were generally dry and sunken. These symptoms suggested the possibility of Rhizoctonia infection. Soil surrounding symptomatic seedlings were collected to bait the potential pathogen and symptomatic plants were used for pathogen isolation. The diseased tissues were washed with tap water and surface-disinfected with 1% bleach before placing on the Dexon selection medium at 26°C for 2 days (Ko and Hora 1971). Hyphae were transferred to potato dextrose agar (PDA), and a brown colony with brown and irregular-shaped sclerotia grew from 90 out of 99 isolates. The hyphae exhibited typical characteristics of Rhizoctonia solani, including a constriction and a septum near the end of branching hyphae (Ajayi-Oyetunde and Bradely, 2018). Two isolates from Benzhou and two isolates from Wandan were tested for their pathogenicity, and eight surface-disinfected seeds were distributed evenly on the water agar plates covered by 2-day-old mycelia at 25°C in dark for 7 days. All isolates caused cotyledon rot and reduced germination. To verify their pathogenicity in pots, double-sterilized sorghum seeds were inoculated with two strains and incubated at 25°C for 2 weeks to be used as fungal inoculum (Ajayi-Oyetunde and Bradely, 2017). A layer of 15 ml of fungal inoculum was placed 5 cm beneath the soil surface in pots. Four soybean seeds were planted approximately 3 cm above the inoculum in each pot. After two weeks, reddish lesions on the hypocotyls or taproots of all seedlings in the inoculated pots were observed, while seedlings in the control pots inoculated with sterile sorghum seeds remained healthy. The pathogen was re-isolated from lesions and had identical morphology to the original isolates. To characterize the fungal identity, the internal transcribed spacer (ITS) was sequenced using the primers ITS1/ITS4 (Sharon et al., 2006). Using BLASTN in the NCBI database, the sequence (GenBank no. MW410857 and MW410858) showed 100% (639/639 bp) similarity to KF907734 and 99.83% (635/636 bp) similarity to AF354099, both belong to R. solani anastomosis group 7 (AG-7) (Hua et al. 2014; Gonzalez et al. 2001). Phylogenetic analysis comparing sequences with different AGs (Ajayi-Oyetunde and Bradely, 2017) grouped our isolates within the AG-7 clade with a 100% bootstrap confidence. In the anastomosis test, an incompatible zonation and unequal mycelial growth rates were observed when AG-7 isolates were paired with an AG-1 IA isolate. On the other hand, the compatible tuft reaction was observed when two AG-7 isolates were paired, and the compatible merge reaction was observed in the self-pairing tests (Macnish et al. 1997). Accordingly, the molecular and morphological characterizations confirmed the causal pathogen as R. solani AG-7. R. solani AG-7 was first reported on radishes in Japan (Homma et al., 1983), first found on carnation in Taiwan (Lo et al., 1990), and in field soils of various crops but not soybean (Chuang, 1997). It was suggested that Rhizoctonia diseases of soybean may be present in Taiwan, but molecular confirmation was lacking (Anonymus, 1979). As R. solani AG-7 causes diseases of soybean in the US and Japan (Baird et al., 1996), the importance of AG-7 as an endemic pathogen of soybean in Taiwan should be recognized and its prevalence determined as a first step to managing this disease.
Red crown rot (RCR), caused by the soilborne fungus Calonectria ilicicola, is an emerging soybean disease in Taiwan, and fungicide screening is desired to identify effective management for C. ilicicola. This study screened 11 fungicides, including azoxystrobin, boscalid, cyprodinil, cyprodinil+fludioxonil, difenoconazole, fluopyram, flutolanil, mancozeb, prochloraz, pyraclostrobin, and tebuconazole, for their inhibitory effects on the mycelial growth of 10 C. ilicicola field isolates. Subsequently, a microplate-based high-throughput screening (MHTS) method was established to measure the fungicide sensitivity in a population composed of 80 C. ilicicola isolates to three effective fungicides, cyprodinil+fludioxonil, fluopyram, and tebuconazole. The MHTS was optimized for multiple factors including the optical scanning pattern, absorption wavelength, conidial concentration, and measurement timing based on the quality controls of Z′ factor and the log-phase growth curve. The population mean EC50 estimated by MHTS were 0.14 ppm, 2.34 ppm, and 2.46 ppm to cyprodinil+fludioxonil, fluopyram, and tebuconazole, respectively. In addition to the in vitro assessment, fungicide efficacy was evaluated by coating cyprodinil+fludioxonil, fluopyram, or tebuconazole on soybean seeds in the pot assay. The results showed that cyprodinil+fludioxonil significantly reduced both post-emergence damping-off and disease severity, while fluopyram and tebuconazole reduced only the post-emergence damping-off but not disease severity. Based on the MHTS and the pot assay results, this study demonstrated cyprodinil+fludioxonil to be the potential fungicide to manage soybean RCR.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.