Nguyen Hoang Nghia, Pham Quang Thu, Nguyen Van ChienForest Science Institute of Vietnam Pathogens usually found on eucalypts are mostly fungi such as Cryptosporiopsis eucalypti, Mycosphaerella marksii, Coniella fragariae, Phaeophleospora epicocoides, Phaeophleospora destructans, Cryphonectria cubensis, Coniothyrium zuluence and a bacterium Ralstonia solanacearum. The percentage and level of damage generally ranges from low to average depending on provenances and site conditions. In provinces like Vĩnh Phúc, Phú Thọ, Bắc Giang and Tuyen Quang, the main pathogen which caused damage for eucalypts is Cryptosporiopsis eucalypti, and the Petford provenance of E. camaldulensis was more sensitive to this pathogen than other species and provenances. Therefore for provinces of Northern Vietnam, except clone PN2 damaged seriously by Ralstonia solanacearum bacterium, improvement work for disease resistance of eucalypts should be selection of clones against fungi mainly Cryptosporiopsis eucalypti and Phaeophleospora destructans. The two above-mentioned fungi have a very wide ecological range and cause damage to all eucalypt species in the region. About 10 pathogens causing damage to acacias in provinces of Northern Vietnam have been detected. Damage levels to Acacia mangium, A. auriculiformis and acacia hybrids was still low. In the last few years in Tuyen Quang province, there were hundreds of hectares of acacias damaged by Lasiodiplodia theobromae (dieback). Pathogens causing leaf damage are Colletotrichum gloeosporioides, blue algae Cephaleuros vierescens and Pestalotiopsis neglecta; fungi causing stem and branch damage are Corticium salmonicolor, Ganoderma tropicum, Phellinus pachyphloeus; and fungi causing damage to seedlings in the nursery are Fusarium oxysporium, Oidium spp. and Meliola spp., however damage level is still low. Therefore, improvement work to acacias should be concentrated on selection of clones against fungi Lasiodiplodia theobromae which causes stem canker.
The first clonal trial was established in 1998 with 49 clones of three eucalypt species (E. brassiana, E. camaldulensis and E. tereticornis) with E. brassiana seed as the control. With a suggested final density 1000 stem/ha (initial density was 1650 stem/ha) after 6.2 years the yield of six ranking clones could reach from 139 m3/ha (clone SM36) to 218,5 m3/ha (clone SM16), and the average annual increment for volume ranged from 22,4 m3/ha/yr to 35,2 m3/ha/yr. In 2005, MARD approved two eucalypt clones, SM16 and SM23, as technical achievements for Southeast Vietnam.
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