Screening disease resistance of Acacia auriculiformis clones against Ceratocystis manginecans by artificial and natural inoculation methods

Tropical species of Acacia are grown in plantations for pulpwood in many countries of South-east Asia. A vascular wilt disease caused by Ceratocystis manginecans is compromising their productivity and continued use as a commercial species and has become an issue in Vietnam. In this study, we evaluated the potential resistance of 45 three-year-old Acacia auriculiformis clones to C. manginecans using different pathogenicity tests: natural infection in the field, natural infection in the field promoted by artificial wounding, and the inoculation of excised branch segments in a controlled environment. Ten of the 45 clones expressed disease symptoms in the field under natural infection conditions; mean percentage of infection varied from 3.5 to 21.7%. Although the screening protocols of artificial wounding in the field to promote natural infection and excised branch segment inoculations led to a greater number of clones being infected, respectively 22 and 38, there were significant correlations between the percentage of infected trees, disease index and lesion length (L) following natural infection and each of these protocols. There were no significant differences in L between the top 15 most tolerant clones following excised branch segment inoculations. Seven clones (AA78, AA83, AA89, AA92, AA93, AA95 and AA103) were resistant (L = 0.0) with MAIs of >20 m(3)/ha/y. This finding suggests that there may be opportunities to employ resistant clones in breeding programs and to increase disease tolerance to C. manginecans in A. auriculiformis and Acacia hybrid (A. mangium x A. auriculiformis) through genetic gain