Molecular Microbiology Research 2024, Vol.14, No.6, 259-270 http://microbescipublisher.com/index.php/mmr 264 better efficacy than treatment after A. alternata inoculation. Similar to DMSO inhibiting the mycelial growth of ES4-2, DMSO also affected the infection of A. alternata in G. jasminoides leaves, but the inhibitory effect was significantly lower than that of the high-concentration melatonin treatment. The concentration of 1 mM melatonin after inoculation with A. alternata 12 h was the most effective in reducing the infection of ES4-2 (Figure 6a). However, treatment with 5 μM, 10 μM, and 100 μM melatonin did not result in significant differences in the lesion area (Figure 6b). For the melatonin treatment before inoculation, 1 mM of melatonin significantly enhanced the resistance to A. alternata infection (Figure 6a). The lesion area of leaves treated with 1 mM melatonin was 4.1% of those treated with H2O and 14.7% with DMSO (Figure 6b). Taken together, these results suggest melatonin can control the infection of A. alternataon G. jasminoides leaves. Figure 6 Effects of melatonin treatments on the resistance of G. jasminoides leaves against A. alternata Image caption: (a) Leaf lesions 14 d after melatonin treatment before and after inoculation. (b) Lesion area 14 d after melatonin treatment before and after inoculation. Bars, 1 cm. Significance was determined according to Duncan’s multiple range test at P < 0.01. The data (mean ± SD) were calculated using three replicates 3 Discussion Leaf spot disease has already plagued the G. jasminoides industry with a high incidence rate in Hubei Province, China. In this study, six isolates of Alternaria spp., identified as causal agents of Gardenia jasminoides Ellis leaf spot, were determined to belong to A. alternata based on the phylogenetic analysis and morphological characteristics. The pathogenicity test showed that all these isolates can cause leaf spots on Gardenia jasminoides Ellis, indicating that these isolates were pathogenic to gardenia leaves. Furthermore, we studied the effect of melatonin on the prevention and treatment of A. alternata. Alternaria fungi have always been identified with a combination of morphological and molecular methods. We also used these two approaches to characterize Alternaria isolates collected from symptomatic leaves. The Alternaria spp. isolated in this study can be categorized into two groups. There was no significant difference in their pathogenicity, spore size, and colony growth rate. All six isolates on PDA resulted in typical A. alternata morphological features reported previously (Xu et al., 2022). Subsequent molecular analysis also identified them as A. alternata.
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