Genetic variation for resistance to Mycosphaerella leaf disease and Eucalyptus rust on Eucalyptus globulus in Uruguay

Over the last 5 years foliar diseases had caused devastating damages in young plantations of Eucalyptus globulus in Uruguay. The sustainability of this species, the most important in the country with more than 270,000 ha of commercial plantations, depends on the rapid development of resistant genetic stock. The genetic variation in resistance of juvenile foliage to diseases and in the onset to adult foliage were examined in a field trial of E. globulus naturally infected by Mycosphaerella leaf disease (Mycosphaerella spp. and Teratosphaeria spp.) and Eucalyptus rust (Puccinia psidii). The genetic material included 226 open pollinated seed lots from 16 provenances of Australia, Chile and Uruguay. Disease severity (% of leaf spots and % defoliation) was assessed 8 months after planting and precocity of phase change (% of adult foliage) at 20 months. Tree growth and survival were evaluated every 2 years up to the ninth year. Differences in disease severity and in precocity of phase change were significant among countries of origin and provenances. Within provenances, the narrow-sense individual tree heritabilities for leaf spot severity (0.37), defoliation (0.41) and proportion of adult foliage (0.40) were higher than those obtained for tree growth (0.19 to 0.33) and similar to those obtained for survival (0.33 to 0.45). Genetic correlations between disease severity and growth traits were negative (-0.20 to -0.44) and were also negative between disease severity and survival (-0.28 to -0.51). There were positive genetic correlations between precocity of phase change and growth traits (0.34 to 0.41) and between precocity of phase change and survival (0.29 to 0.37). Our results demonstrate that selection for low disease severity in the first year and for high proportion of adult foliage in the second year are feasible in order to obtain genetic material for sites at risk of infection of both Mycosphaerella leaf disease and Eucalyptus rust.