As is the case with the development of larger lesions stated above, the absence of further development of the chlorosis into spots with strain 13.2B could have been a result of tolerance to our field strain of the maize varieties used during this work, or suboptimal environmental conditions during the pathogenicity tests specific to this strain. maydis (CBS 588.69) was able to produce lesions at lower inoculum levels (at 10 4 conidia/mL levels) than used for strain 13.2B. In addition, during parallel inoculations with strains obtained from WFBI (data not shown), D. Thus, this should have been sufficient for the strain to induce symptoms. The spore density used with strain 13.2B (at 10 6 conidia/mL levels) was higher than for pathogenicity tests with D.
These results were supported by morphological analysis, which showed that conidia of strain 13.2B were particularly large, resembling in size and shape the measurements to the maize pathogen D. Noninoculated control plants remained asymptomatic.Īlthough chlorosis on leaves was only observed after inoculation with strain 13.2B, our phylogenetic analysis grouped this strain into the same clade with the leaf pathogen D. maydis (CBS 588.69) were recovered from lesions in the infected tissue, resembling the initially inoculated conidia, hence fulfilling Koch’s postulates and being considered pathogenic. Although these lesions were similar to those obtained with our pathogenic strains from the field, they exhibited a larger chlorotic area. Among the strains obtained from the Westerndijk Fungal Biodiversity Institute (WFBI), only D. Furthermore, strains 12.18 and 12.20 induced premature death of the leaves. Lesions were surrounded by a yellow halo expanding along the leaf veins, resembling the initial symptoms in the field ( Figure 5). Thereafter, the chlorosis developed into round to oval lesions with an orange centre that turned necrotic. For five strains (12.18, 12.20, 13.2P, 13.2C and 12.23.1), chlorotic lesions (1 to 2 mm) were observed on both maize varieties 2 to 3 days after inoculations. Pathogenicity of the different Phoma-like strains was assessed on leaves of two maize varieties (Ricardinio and Barros) with conidial suspensions. To our knowledge, this is the first study dissecting the Phoma species complex on maize leaves in Central Europe.
The pathogenic group of strains from our collection (after completion of Koch’s postulates) did not cluster with any of these species, indicating a different and novel Phoma-like species infecting maize leaves. Strains were compared with six reference Phoma-like species strains from the Westerndijk Fungal Biodiversity Institute collection reported to colonise maize. The strains were grouped into four clades, and morphological studies supported this classification for most of them.
A total of 16 representative Phoma-like strains were characterised for their pathogenicity on maize leaves, for their morphological characteristics and with a phylogenetic analysis based on multilocus sequence analysis using part of the actin (ACT), calmodulin (CAL), β-tubulin (TUB), internal transcribed spacer (ITS) region of ribosomal DNA and large subunit ribosomal RNA (LSU) genes. In addition to the major leaf pathogens, isolates of Phoma-like species were obtained from oval to elliptical spots on leaves or found in lesions produced by other leaf pathogens. During 20, an inventory of maize leaf spot diseases was carried out in various regions in Central Europe. This has led to more intense maize cultivation, with narrowed crop rotations resulting in the increase in maize leaf diseases. In the last decade, the cultivated area of maize has increased in Central Europe due to its high yield potential and diverse uses for feed and bio-energy.
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