Effective Management of Citrus Melanose Based on Combination of Ecofriendly Chemicals

Citrus melanose, caused by the ascomycete fungus Diaporthe citri, is one of the most important diseases in China that affects not only the production but also the quality of citrus. In China, mancozeb is recommended to control melanose disease at the dose of 1.34 g/liter. However, it is widely applied in practice at the dose of 2.66 g/liter or even 4 g/liter, because reduced efficacy of the recommended dose was observed in regions severely damaged by melanose. In this study, some ecofriendly chemicals for melanose management were evaluated. First, the sensitivity to fungicides was screened in the laboratory based on the inhibition of mycelial growth and conidial germination of D. citri. Results showed that both quinone outside inhibitor (QoI) fungicides kresoxim-methyl and trifloxystrobin inhibited conidial germination of D. citri up to 100% at 0.1 μg/ml. The in vivo control efficacy on detached fruit indicated that treatments with elastic nanocopolymer film at 2 g/liter, mancozeb at 1 g/liter, and kresoxim-methyl at 0.1 g/liter significantly inhibited the infection process compared with the control treatment of mineral oil alone. In field trials, the efficacy of kresoxim-methyl at 0.1 g/liter and elastic nanocopolymer film at 2 g/liter mixed with mancozeb at 1 g/liter was equal to that of mancozeb at 2.66 g/liter. The use of mancozeb could be reduced greatly, and the newly developed fungicide combinations are more environmentally friendly due to the low toxicity of both QoI fungicides and elastic nanocopolymer film. The newly developed method with ecofriendly chemicals should play an important role in the management of citrus melanose in the future.

Phylogenetic Analysis and Fungicide Baseline Sensitivities of Monilia mumecola in China

Monilia mumecola is one of the causal agents of peach brown rot in China. In this study, M. mumecola isolates from different locations and hosts were used to analyze the genetic diversity and to assay the sensitivity to four generally used fungicides: carbendazim, tebuconazole, azoxystrobin, and boscalid. Results showed that isolates from different locations tended to be separated. Interestingly, isolates from different hosts (e.g., peach and apricot) at the same locations generally clustered together, indicating that the M. mumecola isolates may infect different hosts in the same areas. The fungicide sensitivity assay of 93 M. mumecola isolates showed that the average effective concentration for 50% mycelial growth inhibition values for carbendazim, tebuconazole, azoxystrobin, and boscalid were 0.103, 0.034, 0.325, and 0.419 µg/ml, respectively. The sensitivity distributions of the tested isolates to the four fungicides showed continuous unimodal curves, indicating no qualitative shift of resistance. No significant difference of sensitivity to tested fungicides was observed among isolates from either different locations or different hosts.