Sensitivity of Rhizopus oryzae to six fungicides and the screening of its preservation conditions

The sensitivity of Rhizopus oryzae to six fungicides (mancozeb, carbendazim, pyrimethanil, azoxystrobin, boscalid, fluazinam) and the preservation conditions of this pathogen were determined using the conidia germination method. Efficacy of these fungicides against tobacco pole rot disease was also evaluated on the detached leaves. Results showed that all the six fungicides presented different inhibitory activities against both conidia germination and pole rot. For the conidia germination, the highest inhibitions were found in the cases with fluazinam and boscalid, with EC₉₀ values of 0.67 mg/L and 1.53 mg/L, respectively. Lower inhibition rates were detected in the cases with mancozeb and azoxystrobin (15.16 and 17.66 mg/L). And the lowest inhibition rates were observed in the cases with pyrimethanil and carbendazim (71.87 and 81.96 mg/L). For the disease control efficacy, the highest inhibition rate was observed in the group treated by azoxystrobin at 50 mg/L with the efficacy of 85%. Lower inhibition rate was detected after the boscalid treatment, which showed 83% efficacy at 200 mg/L, while a poor inhibition rate (48%) was observed by fluazinam treatment at the concentration of 1 000 mg/L. And mancozeb, carbendazim, pyrimethanil all exhibited efficacy of < 20% at their respectively highest dosages of 4 000, 800 and 800 mg/L. The screening results of six different pathogen preservation conditions showed that conidia germination ratio of R. oryzae decreased variously by using different methods. The conidia germination ratio of the conidial suspension in 20% glycerol was 60% at 4 ℃, and, for dry conidia samples, that was 36% at 4 ℃. In terms of the conidial suspension stored at 4 ℃ and the conidial suspension stored at –20 ℃, the germination ratios in 20% glycerol were both < 20%. With regard to the dry conidia samples stored at –20 ℃, the conidia germination ratio was 11%, and, for the conidial suspension stored at –20 ℃, that was 6%. Results of this study have provided reference and basis for both the chemical control of tobacco pole rot and the storage of R. oryzae.