Abstract:

Resistance of Eucalyptus spp. against bacterial wilt, caused by Ralstonia solanacearum, was determined by dipping inoculation of shoot cuttings and shoot tip inoculation using potted seedlings and tissue culture plantlets, as well as field disease survey in a eucalypt plantation. The inhibition effects of root exudate and supernatant of tissue triturate collected from different resistant clones of Eucalyptus against R. solanacearum were performed using liquid culture to explore the relationship between exudate, tissue triturate and the levels of disease resistance. The results showed that the clones, bd1, bd2, E. camaldulensis and E. grandis×E. urophylla from Nanning were highly resistant to bacterial wilt; U6, E. urophylla from Nanning,Lei9 and Qin32-29 were the mid wilt-resistant clones; and DH32-27, Qin 9, Nanningguang 9, Qin8, E. dunnii, Qin32-22, Lei2, E. grandis, E. urophylla and Qinguang 9 were susceptible clones. The results also indicated that root exudates and the supernatant of triturated tissue had no direct inhibition to the growth of R. solanacearum. However, the proliferation number of R. solanacearum in root exudate and tissue triturate from wilt-susceptible clones was markedly higher than the ones from highly wilt-resistant clones, which was in accordance with the determination results of disease resistance using dipping inoculation and tip inoculation of shoot cuttings, indicating that the resistance ability of different clones could be manifested by the growth of R. solanacearum in root exudate and supernatant of triturated tissue.

Key words: clones of Eucalyptus, bacterial wilt, disease resistance, root exudate, tissue triturate