Shan-Kui Yuan

Persea americana (avocado) is a fruit rich in nutrients; however, its industry is facing major threats from pathogen infection. Here, we clearly identified Colletotrichum fructicola as the pathogen causing avocado diseases in Pu’er City, Yunnan Province. However, the biological characteristics, genetic transformation system, and early cell cycle regulation of this pathogen remained unclear. In this study, C. fructicola exhibited a maximum growth rate on complete medium (CM), with the conidial yield reaching 2 × 10⁵ conidia/mL after 24 h in liquid CM. Conidia of C. fructicola had nearly fully germinated at 4 h post-inoculation (hpi), with the appressorium formation rate exceeding 95% at 12 hpi. We also established a PEG-CaCl₂-mediated genetic transformation system. The GFP-tagged transformants showed no significant differences in core biological function from the wild type. Using eGFP labeling, we visually elucidated the early cell cycle regulation of C. fructicola. Furthermore, cell cycle inhibitor assays demonstrated that C. fructicola conidial germination is independent of nuclear division and relies on cytoskeletal modulation, whereas appressorium formation and mycelial expansion require functional cell cycle regulation. This is probably the first study to systematically elucidate the cell cycle regulatory characteristics of C. fructicola isolated from avocado, and to successfully develop its genetic transformation system. These results provide important theoretical and technical support for the formulation of integrated control strategies against C. fructicola, as well as facilitating the sustainable development of the avocado industry.

Sustainable chemical control for rice bacterial leaf blight caused by Xanthomonas oryzae pv. oryzae need to be developed due to limited bactericides with high efficiency, low cost, and low toxicity in China. This present study verified a broad-spectrum fungicide named Xinjunan possessing a specific high toxicity to Xanthomonas pathogens, which were further confirmed by affecting the cellular iron metabolism of Xoo as a novel mode of action.

Sensitivity to azoxystrobin and kresoxim‐methyl of 80 single‐spore isolates of Magnaporthe oryzae was determined. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting mycelial growth of the 80 M. oryzae isolates were 0.006–0.056 and 0.024–0.287 µg mL⁻¹, respectively. The EC₅₀ values for azoxystrobin and kresoxim‐methyl in inhibiting conidial germination of the M. oryzae populations were 0.004–0.051 and 0.012–0.105 µg mL⁻¹, respectively. There was significant difference in sensitivity to azoxystrobin or kresoxim‐methyl between the tested isolates representing differential sensitivity to carbendazim (MBC) and kitazin P (IBP); however, there was no correlation between this difference in sensitivity to azoxystrobin or kresoxim‐methyl and sensitivity to MBC or IBP, indicating that there was no cross‐resistance between azoxystrobin or kresoxim‐methyl and MBC or IBP. In the protective and curative experiments, kresoxim‐methyl exhibited higher protective and curative activity than azoxystrobin when applied at 150 and 250 µg mL⁻¹ accordingly, while azoxystrobin exhibited stronger inhibitory activity against M. oryzae isolates than that of kresoxim‐methyl in the in vitro test. The results of field experiments also suggested that both azoxystrobin and kresoxim‐methyl at 187.5 g.a.i. ha⁻¹ gave over 73% control efficacy in both sites, exhibiting excellent activity against rice blast. Taken together, azoxystrobin and kresoxim‐methyl could be a good substitute for MBC or IBP for controlling rice blast in China, but should be carefully used as they were both at‐risk.

Bacterial leaf blight of rice (BLB), caused by Xanthomonas oryzae pv oryzae, is one of the most serious bacterial diseases in China. Presently, bismerthiazol has been the major bactericide for the control of BLB, however, bismerthiazol‐resistant strains of X. oryzae pv. oryzae have appeared in the field in China. Zinc thiazole is a novel bactericide with strong antibacterial activity against Xanthomonas spp. In this study, sensitivity of 109 X. oryzae pv. oryzae strains to zinc thiazole was determined. The EC₅₀ values for zinc thiazole in inhibiting bacterial growth of the 109 X. oryzae pv. oryzae strains were 0.53–9.62 µg mL⁻¹ with the average EC₅₀ value of 4.82 ± 1.86 µg/ml. The minimum inhibitory concentration (MIC) values of zinc thiazole against the 109 X. oryzae pv. oryzae strains were assessed and the results showed that the MIC values of zinc thiazole for completely inhibiting the growth of these 109 strains ranged from 5.0 to 40.0 µg mL⁻¹. In the evaluation of protective and curative activity test, zinc thiazole exhibited great activity against BLB and provided over 88% control efficacy (at 300 µg mL⁻¹) 1 and 3 days before or after inoculations, which was also higher that that of bismerthiazol in the corresponding treatments. Our field trials showed that zinc thiazole at 375 g.a.i ha⁻¹ provided over 70% control efficacy in 2012 and over 80% control efficacy in 2013 at both sites. Moreover, in all the four field trials, zinc thiazole at 250 g.a.i ha⁻¹ provided higher control efficacy than that of bismerthiazol at 250 g.a.i ha⁻¹. Taken together, zinc thiazole is therefore an alternative tool for the management of BLB.