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Derection of the Resistance in Sclerotinia Sclerotiorum and Controlling

Author: MaHuiXia
Tutor: ZhouMingGuo
School: Nanjing Agricultural College
Course: Pesticides
Keywords: Sclerotinia stem rot carbendazim dimethachlon boscalid
CLC: S435.654
Type: Master's thesis
Year: 2009
Downloads: 29
Quote: 1
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Abstract


Sclerotinia sclerotiorum (Lib.) de Bary is a cosmopolitan fungal pathogen which attacks more than 400 species of higher plants, Sclerotinia stem rot continues to impose serious limitations on oilseed rape production all over the world, application of fungicides is the principal tool in most oilseed rape crops for managing Sclerotinia stem rot. A benzimidazole fungicide, carbendazim (MBC), was widely used to control this disease routinely during the 1980s in China, but wide spread control failures attributed to development of MBC resistance in S. sclerotiorum were reported in 2001 and 2002.The dicarboximide fungicides (e.g., iprodione, procymidone, vinclozolin, dimethachlon) have also been used for control of plant diseases incited by S. sclerotiorum, S. homoeocarpa and S. minor for 5 to 6 years. We detected the resistance of Sclerotinia sclerotiorum to carbendazim and dimethachlon, compared the mycelial growth, sclerotial production and pathogenicity, and determinded the cross-resistance patterns. The results indicated the wide spread of MBC resistance and occurrence of dimethachlon insensitivity in S. sclerotiorum in the oilseed rape crops of Jiangsu Province. The baseline sensitivity to boscalid was established, and the results showed that boscalid exhibited excellent activity against S. sclerotiorum and might became a new fungicide for the control of Sclerotinia stem rot.The MBC resistance in S. sclerotiorum populations was widely spread throughout Jiangsu Province with the resistance frequency 29.5% among the 1786 collected isolates during the growing seasons of oilseed rapes between 2006 and 2008. The resistance frequencies were different among sampled cities, ranging from 3.1%-54.9%. The field MBC-resistant isolates showed comparable mycelial growth, sclerotial production and pathogenicity to the wild-type sensitive isolates, which suggested that the field MBC-resistant isolates might have sufficient parasitic fitness to compete with the field sensitive isolates in the field. Fungal populations were collected throughout Jiangsu Province between 2006 and 2008 in order to determine their sensitivity to dimethachlon. A total of 1786 single-sclerotium isolates of S. sclerotiorum were collected and most of the isolates were considered sensitive to dimethachlon. Five isolates collected in Yancheng and Changzhou showed normal growth at 5μg/ml dimethachlon with the resistance factor≈10 compared to the sensitive isolates. Through in vitro selection for resistance to the fungicide,25 dimethachlon-resistant mutants were derived from 10 wild-type isolates of S. sclerotiorum. The resistance factors for the isolates ranged from 198 to 484, and the isolates were considered highly resistant to dimethachlon. Therefore, at least two different mechanisms of resistance seem to be involved:one that may provide a moderate resistance (insensitivity) and a second that may give a high resistance level under laboratory conditions. There was positive cross-resistance between dimethachlon and other dicarboximide fungicides, such as iprodione and procymidone in these S. sclerotiorum isolates. The field dimethachlon-insensitive and the laboratory-induced dimethachlon-resistant isolates appeared to have mycelial growth, sclerotial production and pathogenicity to comparable their wild-type parental isolates. Also, results of osmotic tests showed that there were no significant difference in mycelial radial growth between the field dimethachlon-sensitive and field dimethachlon-insensitive isolates on potato dextrose agar (PDA) plates amended with 2,4,6, or 8%(w/v) NaCl, but the laboratory-induced dimethachlon-resistant isolates grew significantly slower than their wild-type sensitive parents under all concentrations of NaCl.120 isolates of Sclerotinia sclerotiorum were isolated from oilseed samples from Nantong, Yancheng, Taizhou, Yangzhou, Suqian, Zhenjiang and Suzhou of Jiangsu Province, where boscalid had never been used before. The sensitivities to boscalid were determined by the method of mycelial growth test on PDA medium. The results that the sensitivity of wild-type population in the nature against boscalid exhibit a certain extend diversity and the EC50 values of the compound inhibiting growth of S. sclerotiorum was ranged from 0.028～0.408μg/mL and with the mean value of 0.170±0.085μg/mL. The MIC were and 0.712±0.255μg/mL, respectively. It showed that boscalid inhibited strongly mycelial growth of S. sclerotiorum. Though the sensitivity of carbendazim, dimethachlon and boscalid, it showed that there was no cross resistance between these fungicides.

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CLC: > Agricultural Sciences > Plant Protection > Pest and Disease Control > Crop pests and diseases and their prevention > Economic crop pests and diseases > Oil Crop pests and diseases > Rapeseed ( Brassica ) pests and diseases
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