Isolation and characterization of tow species of fungus causing diseases on eucalypt seedlings and their susceptibility to pesticides

摘要

When eucalypt seedlings were under cultivation, fungi cause diseases unexpectedly and cause them to spread rapidly. The diseases made seedlings wilt, lodge and finally rot in about 15 days. The fungi were identified as two species of Fusarium based on the procedure of isolation, purification, morphologic and molecular characterization. These two species possess a close genetic relationship with genus Fusarium and, therefore, are named as GXN-E-1 and GXN-E-2. Back inoculation of GXN-E-1 and GXN-E-2 on eucalypt seedlings showed that both could quickly induce pothogenesy[3 days after inoculation, recorded when Disease Grade (DR) II appeared] under Condition 1 [temperature:25–30 °C; humidity: 70–90%; light application time(natural light): ≈11h] pathogenetic rate 3.4% by GXN-E-1 and 1.6% by GXN-E-2 and the lower DR of all seedlings would increase to DR V 15 days after inoculation of GXN-E-1, 19 days of GXN-E-2. However, the initial pathogenetic time was 4 days after inoculation of both GXN-E-1 and GXN-E-2 under Condition 2 [temperature:20–25 °C; humidity: 50–70%; light application time (natural light): ≈ 11h] (recorded when DR II appeared) with a pathogenetic rate of 2.7% caused by the former and 1.3% by the later and these would respectively be 61.2% and 49% 16 days after initial record. The result of tests of the susceptibility of GXN-E-1, GXN-E-2 against 4 kinds of pesticide (Huishengsan, Daconi, Difenoconazol and Thiophanate methy l) is that only Huishengsan efficiently inhibited the growth of both pathogens. Meanwhile, experiments were also conducted on the effect of pesticide - Huishengsan- against both pathogenium GXN-E-1 and GXN-E-2.