Upland tea tree, an underexplored resource in the domestication of Melaleuca alternifolia

This study examined the variation of resistance within tea tree (Melaleuca alternifolia) to myrtle rust (Puccinia psidii). Tea tree is a subtropical native Australian tree that is farmed intensively for essential oil that has unique antimicrobial properties. Tea tree is susceptible to myrtle rust in bioassay screens but since its introduction to Australia in 2010 has yet to cause economic damage in plantations. Nevertheless, the potential for adaptation by the pathogen has prompted screens for resistance sources in tea tree. Progeny from 9 natural sources, 4 Upland and 5 Coastal, were assessed for pest and disease damage in a common environment trial. Overall, 51% suffered mild damage, 43% were resistant and only 5% were severely affected. Pronounced region, provenance and family level effects were evident. Variation among trees was present in plants from both regions but Upland plants tended to be under represented in the severely damaged class and overrepresented in the unaffected class, whereas the reverse occurred in Coastal plants. The odds of a severely damaged relative to undamaged plant were around three times higher in Coastal sources. While Upland provenances tended to have uniformly higher proportions of resistant individuals, provenance level variation in the Coastal region was more complex, with one provenance, DevilRSQUOs Pulpit, exhibiting the highest resistance overall, whereas three other Coastal provenances (Dyasons, Barcoongere and Candole) had the lowest percentage of resistant trees. Variation at the family level was also extensive and ranged from 0 to 85% of resistant trees per family.