ABSTRACT
Bipolaris maydis is the pathogenic microorganism of southern corn leaf blight, a persistent biotic constraint responsible for substantial yield losses of corn worldwide. In the present study, 96 isolates from six representative fields growing single and multiple sweet corn cultivars in Pingnan, Fuqing, and Jian'ou in Fujian Province, which are characterized by different geographical characteristics and cropping patterns, were genetically analyzed using inter-simple sequence repeat (ISSR) markers to assess the impact of geographical origins and corn cultivars on B. maydis population differentiation. B. maydis isolates originated from diverse regions possessed higher genetic variety than those from single and multiple sweet corn cultivars. Phylogenetic analysis showed that the isolates from single and multiple sweet corn cultivars were randomly grouped into different clusters, with those from the same location tending to form clusters. A greater genetic differentiation among different geographical populations than between those from single and multiple sweet corn cultivars was observed by pairwise comparison. Hierarchical analysis indicated that among-population variation was higher when comparatively analyzed B. maydis populations from different locations than in those from single and multiple sweet corn cultivars. In conclusion, these results suggest that geographical origin acts a more considerable role in genetic differentiation of B. maydis than corn cultivar. Two divided genetic clusters were detected in the B. maydis populations from single and multiple sweet corn cultivars at the three locations in Fujian Province, with major genetic variation being derived within populations. The high haplotypic diversity and expected mating type ratio of 1:1 in combination with significant linkage disequilibrium suggested that a mixed reproductive strategy occurs in the B. maydis population in Fujian Province. This study will enrich the information on the role that geographical origins and corn cultivars play in the population structure of the pathogen as well as the reproductive strategies in B. maydis population in Fujian Province.
ABSTRACT
Sanqi (Panax notoginseng (Burk.) F. H. Chen) is a precious traditional Chinese herbal medicine. During April of 2021, a root rot disease with approximate 15% incidence was observed on 2-year-old Sanqi plants in a field of Zhouning (27º12' N, 119°33' E), Fujian Province of China. The disease symptoms included severe stunting, leaf chlorosis, root rotting and necrosis, as the disease progressed, the whole plant gradually wilted and died. To recover the causal agent, symptomatic roots were excised, surface sterilized in 75% alcohol for 1.5 min, rinsed in sterilized water three times, dried, and placed on PARP selective medium (Jeffers and Martin 1986), and incubated at 20°C in dark. After 5 days, total of 26 Pythium-like isolates were obtained, and one representative isolate Py21-6 (available from the Institute of Plant Protection, Fujian Academy of Agricultural Sciences) was selected for further identification. Colonies of Py21-6 on PARP plate were white with dense, cottony, aerial, and transparent mycelia. Sporangia were terminal or intercalary, non-papillate, spherical, pyriform or ovoid, measuring 21.7 ± 2.8 × 19.3 ± 2.3 µm (n = 30). Zoospores were saucer-like, released out of sporangium after maturation, and dispersed quickly by swimming. Oogonia were spherical, terminal or occasionally intercalary. Oospores were globose, smooth and aplerotic. The dimensions of zoospores, oogonia, and oospores were 6.8 ± 0.7 µm, 21.6 ± 2.2 µm and 18.2 ± 2.7 µm (n = 30), respectively. Antheridia were bell-shaped or irregular, terminal, monoclinous, and usually one per oogonium. According to the morphological characteristics the isolate was initially identified as Pythium spp. (Van der Plaats-Niterink 1981, Yong et al. 2016). For further identification, DNA extracted from Py21-6, the cytochrome c oxidase subunit I (COI) gene and internal transcribed spacer (ITS) region were amplified and sequenced with primers FM55/FM52R (Long et al. 2012) and ITS1 /ITS4 (White et al. 1990), respectively. BLAST analysis of 680-bp COI (OM688194) and 728-bp ITS (OM663703) sequences revealed 99.86% and 99.99% similarity to Pythium vexans in GenBank (HQ708995 [COI], GU133572 [ITS]). Therefore, the pathogen was identified as P. vexans. In order to fulfill Koch's postulates, isolate Py21-6 was grown on Martin's liquid medium (Martin 1992) for 72 h to produce a spore suspensions of 106 oospores/ml, and the pathogenicity test was conducted by root-dip method. Three groups of 2-year-old Sanqi (15 plants per group) with root soaked for 20 min in oospore suspension were used for pathogenicity, and the other three groups (15 plants per group) with root dipped in sterilized water as control. All treated plants were replanted in (15-cm-diameter) pots (2 plants/pot) filled with mixture of sterilized soil: vermiculite: pearlite (2:1:1, v/v), maintained in greenhouse under 60% black shade cloth at 20 to 26°C with 80% relative humidity, and watered once every three days. After 21days, all inoculated plants showed the same symptoms observed on the original diseased plants in the field, whereas, the control plants remained symptomless. The same pathogen was successfully re-isolated from the inoculated plants, and identical to those of the originals based on morphological and sequence data. To our knowledge, this is the first report of P. vexans causing root rot on Sanqi in China (Farr and Rossman 2022). Root rot is one of the destructive diseases in Sanqi production, identification of the pathogen will be useful to develop effective field management strategies to control this disease.
ABSTRACT
The northern corn leaf blight (NCLB) pathogen Setosphaeria turcica (Luttrell) Leonard and Suggs is one of the main biotic constraints on sweet corn (Zea mays L.) yield and quality in Fujian Province, China. Currently, however, there is comparatively little information available regarding the distribution of mating types, population genetics, and reproductive strategies of this pathogen in Fujian. In this study, we investigated the distribution of mating types and population genetics of 117 isolates of S. turcica collected from seven of the main sweet corn-growing regions in Fujian Province, based on multiple polymerase chain reaction analyses using two mating type-specific primer pairs and 11 inter-simple sequence repeat markers. Furthermore, we examined the mode of reproduction of Fujian S. turcica populations. Both MAT1-1 and MAT1-2 mating types were detected throughout all seven sampling locations. The majority of MAT1-2 isolates were detected from Dongyou, Jian'ou, Pingnan, Songxi, and Longyan, whereas a large proportion of the detected MAT1-1 isolates were among those collected from Dongfeng and Nanjing. Furthermore, we detected five shared multi-locus haplotypes among S. turcica isolates from Dongyou, Jian'ou, Pingnan, Nanjing, and Songxi, whereas no shared haplotypes were observed between the Dongfeng (or Longyan) population and these five populations. Pairwise comparisons of the indices ΦPT and Nm, and population structure and principal coordinate analyses indicated genetic differentiation between both the regional and the mating type populations of S. turcica in Fujian. The skewed mating type ratio associated with low a haplotypic diversity and evident linkage disequilibrium reveals a mixed reproductive strategy for S. turcica populations in Fujian Province. The findings of this study advance our current understanding of the genetic diversity, population structure, and reproductive strategies of S. turcica populations infecting sweet corn in Fujian Province, and will potentially contribute to further resistance breeding efforts.
ABSTRACT
Root exudates of banana resistant variety ('Nantianhuang') and susceptible variety ('Guijiao No. 6') to Fusarium wilt were collected in vitro by bathing root system to examine the biological effects of root exudates from banana varieties on Fusaiurm oxysporum f. sp. cubense and Bacillus subtilis. We explored the effects of root exudates of different banana varieties on the abundance of soil microorganisms and the growth of F. oxysporum f. sp. cubense and B. subtilis. The results showed that root exudates from resistant variety could significantly reduce the abundance of soil fungi and inhibit the spore germination of F. oxysporum f. sp. cubense. Root exudates from susceptible variety could significantly stimulate mycelia growth and spores germination, whereas root exudates from the tested banana varieties could significantly increase the growth and biofilm formation of B. subtilis. By dealing with the root exudates of resistant and susceptible varieties, the growth rate of mycelia were 11.28 and 12.28 mm·d-1, and the germination rate of spores were 34.6% and 79.5%, respectively. After culturing for 12 h, the growth rates of B. subtilis (OD600) were 1.27 and 1.14, and the biofilm formation (OD570) were 1.11 and 1.30 after static culturing 72 h, respectively. There were significant differences between the values of resistant and susceptible varieties. The colonization amount of B. subtilis in the rhizosphere of susceptible variety was significantly higher than that of resistant variety. The contents of free amino acids and organic acid in root exudates of the resistant variety were higher than that of susceptible variety. The content ratio of acetic acid and proline in the root exudates of resistant variety were 3.7 times and 2.4 times of that of susceptible variety. In conclusion, root exudates of banana resistant variety could inhibit the growth of F. oxysporum f. sp. cubense. Root exudates from susceptible variety could promote the growth of F. oxysporum f. sp. cubense,while that from the tested banana varieties could all significantly enhance growth, biofilm formation and colonization ability of B. subtilis.
Subject(s)
Fusarium , Musa , Bacillus subtilis , Plant Diseases , Rhizosphere , SoilABSTRACT
Asparagus stem blight caused by Phomopsis asparagi is a major hindrance to asparagus production worldwide. Currently, fungicides are used to manage the disease in commercial production, but resistance to common fungicides has emerged in the wild population. In the present study, 132 isolates of P. asparagi collected from different provinces in China were tested for sensitivities to pyraclostrobin, tebuconazole, and fluazinam. We also determined the efficacies of six fungicides against P. asparagi. The frequency distributions of EC50 values of the isolates tested were unimodal, but the curves for pyraclostrobin and tebuconazole had long right-hand tails. The mean EC50 values for pyraclostrobin, tebuconazole, and fluazinam were 0.0426 ± 0.0029, 0.6041 ± 0.0416, and 0.0314 ± 0.0013 µg/ml, respectively. In addition, the EC50 values for pyraclostrobin were very similar with or without salicylhydroxamic acid (SHAM), 20 µg/ml, indicating that SHAM is not needed to determine the sensitivity of P. asparagi to pyraclostrobin when using the mycelial growth inhibition assay. In greenhouse assays, Merivon (42.4% fluxapyroxad plus pyraclostrobin SC), Frown-cide (500 g/liter fluazinam SC), Cabrio (250 g/liter pyraclostrobin EC), and Nativo (75% trifloxystrobin plus tebuconazole WG) showed excellent preventive efficacy against P. asparagi. And these fungicides were more effective before inoculation than when they were applied after inoculation (P < 0.05). Therefore, these fungicides should be applied prior to infection to control stem blight. In field trials, Frown-cide, Merivon, Nativo, and Cabrio also performed good control effects, ranging from 75.2 to 86.0% in 2017 and 75.4 to 87.1% in 2018. We demonstrated that Frown-cide, Merivon, Nativo, and Cabrio had considerable potential to manage asparagus stem blight. In addition, rotations of these fungicides are essential for precluding or delaying the development of resistance and for controlling the disease.
Subject(s)
Ascomycota , Asparagus Plant , Fungicides, Industrial , Mitosporic Fungi , ChinaABSTRACT
Due to the natural destructiveness and persistence of the southern corn leaf blight (SCLB) fungus Bipolaris maydis (Nisikado et Miyake) Shoem, the characterization of B. maydis field isolates is essential to guide the rational distribution of resistant materials in corn-growing regions. In the present study, 102 field isolates collected from seven locations covering the entire region of Fujian Province, China, were assessed for mating type distribution, genetic diversity, and pathogenicity toward local sweet corn cultivars. Mating type detection via polymerase chain reaction indicated that 36.3 and 63.7% of isolates were MAT1-1 and MAT1-2, respectively; more than 80% of these isolates were confirmed using cross assays with known mating type isolates. Thirteen intersimple sequence repeat (ISSR) markers within and among two mating type populations revealed a high level of DNA polymorphism for all combined isolates and between MAT1-1 and MAT1-2 populations. The MAT1-2 population was more diverse based on DNA polymorphism than the MAT1-1 population. The value of GST was 0.0070, ranging from 0.0399 to 0.3044 based on analysis of combined isolates and individual regional populations, respectively, suggesting the presence of genetic differentiation in the two mating type populations from different locations. Pathogenicity assays revealed that both MAT1-1 and MAT1-2 populations were pathogenic to all 11 local sweet corn cultivars tested in this study. The potential of sexual reproduction, existence of genetic diversity in the two mating type populations, and pathogenicity suggest that B. maydis populations have independently clonally adapted under natural field conditions during corn cultivation.