Studies On The Biological Characters Of Aschersonia Spp. From The Citrus Orchard And Their Pathogenicity To The Diaelorude Citrus

Aschersonia is an important entomopathogenic fungi which infects whitefly and scale insects. It widely distributed in Latin America, South Asia and Southeast Asia and it was also found in citrus producing areas such as Taiwan, Sichuan, Guangxi, Fujian, Zhejiang and Jiangxi provinces in China. Aschersonia is a model organism for biodiversity research and phylogenetic analysis for its ecological adaptability and wide distribution. Recent researches have shown that this fungi has high infection rate in whitefly and scale insects. Moreover, it is safe with high adaptabililty. Therefore, Aschersonia is a significant fungi resource for biological control.The bionomics of 80 Aschersonia spp. strains collected from orange orchards were studied and strains with high infection ability were selected by bioassays. The purpose of the study is to select dominant strains with high spores'germination ability causing high infection rate for further study in this field.Main results are as follows:According to the results of the study, the strains with maximum sporulation quantity is SBC001 with 27.93×104/mm2; KH006 ranks the second with 22.09×104/mm2. However, some strains such as YZ, DHX001, HK015, HYQ003, WDC005, ZG001, MJO, QZ002, BS006, HK002, RL006, JS012, JX002, CY, QZ003, TZ001, YW001, GX006, HK006 and BS007 have sporulation quantity lower than 1.0×104/mm2. There is a significant difference among strains.Dry mycelial weight of 80 Aschersonia spp. were investigated. The average dry mycelial weight of 24 strains, YD001, DHX002, JX002, GX006, TZ003, JX004, CD011, LD004, NF002, JS012, ZJ006, FZ002, ZJ005, BS005, TZ001, BS007, GX002, HYQ001, LN, GLC003, KH001, HYQ002, KH003 and NF003 are above 1.00g, and are significantly higher than others. While SBC005, WD003, CQ005, QZ004, SBC003, YZ004, TLH003, SBC001, YZ, WD007, RL006, MJO and YZ005 are below 0.5g.We also studied initial time of producing spores of the 80 strains. The earliest 13 strains are JS006, JS012, NF001, NF002, NF004, CY, JX002, DHX002, ZG001, TZ003, YZ, CQ005 and BS006 starting from the 8th day; SBC001, SBC003, SBC005, HK011, TX001, TX003, TX005, TX006, CD011, CQ003, BS005, YZ001, YZ005, JX006, DY, AY002, BS007, GX002, GX006, HK012 and HK015 altogether 21 strains start to produce spores on the 9th day; 17 strains start to produce spores on the 10th day, TLH003, JS008, YD005, KH003, QZ006, NF003, NF005, HK006, YW001, YW003, MJO, RL006, TZ001, YD001, YD003, YZ004 and ZG002.7 strains, QZ002, KH002, HK002, HYQ003, GLC002, HYQ001 and HYQ002 start to produce spores after 12 days.The results of colony growth rate indicate that the NF002 grows the fastest on average day growth rate after 15d on PDA medium with 1.21±0.75mm every day and the diameter of the colony reaches 18.2mm in the end. The strain with lowest average day growth is YW001, about 0.26±0.15mm and the diameter of the colony is 3.5mm in the end.The pathogenetic capacity of the 72 fungi strains to white fly nymphae was measured in the spray bioassays. WD003, YDOOland YW003 have the maximum infection rate to white fly and the rates are YD001,72.84% and 68.16% respectively. SBC003 and WDC005 have the lowest infection rate for several reasons, such as the virus in the plant. So further study is necessary for these two strains.