Hybrid vigor in Eucalyptus increases resistance against Phytophthora root rot

Abstract

Eucalyptus nitens is a cold-tolerant eucalypt that is native to Eastern Australia. Pure E. nitens as well as its hybrids, such as Eucalyptus grandis × Eucalyptus nitens, is propagated commercially in various regions of the southern hemisphere, including South Africa. In a plantation environment, E. nitens is susceptible to a variety of native and invasive pathogens, including Phytophthora alticola and P. cinnamomi. Recently, there have been increasing reports of root and collar rot in E. nitens in South Africa. The severity of this disease was substantially lower among interspecific hybrids of E. grandis × E. nitens compared to purebred E. nitens. In South Africa, the susceptibility of commercially propagated provenances of pure E. nitens and varieties of hybrid E. grandis × E. nitens to Phytophthora species is unknown. Therefore, we conducted greenhouse trials to evaluate the pathogenicity of P. alticola and P. cinnamomi to two families of pure E. nitens, one self-fertilized and the other outcrossed, as well as a single clonal variety of the most widely planted interspecific hybrid, E. grandis × E. nitens. The outcomes from these trials revealed that both self-fertilized and outcrossed families of E. nitens were highly susceptible to the tested Phytophthora species. The severity of root rot was greatest among plants inoculated with P. cinnamomi. The tested interspecific hybrid was tolerant to both Phytophthora species and developed new lateral and fine roots to offset the effects of root rot.

Recruitment failure of keystone trees in Phytophthora infested forest

“…Additionally, fertilizer tablets can greatly assist tuart seedling growth (Ruthrof et al., 2016) and may also assist survival and growth of jarrah and marri seedlings within P. cinnamomi infestations (Stoneman et al., 1995). We also highlight the importance of finding and planting genetically resistant trees in P. cinnamomi infestations (Bose et al., 2023; Shearer, 2014; Stukely & Crane, 1994) so that future generations of trees can potentially grow with resistance as a trait (e.g., Stukely & Crane, 1994; Vivas et al., 2021). Broadcasting of seeds may be a successful restoration strategy within infestations as observed on restored mine sites (Colquhoun & Hardy, 2000; Koch & Samsa, 2007); however, annual phosphite applications for the initial 2–3 years of growth may be required to ensure seedling establishment.…”

“…It is also possible that trees within P. cinnamomi infestations produce more P. cinnamomi ‐resistant seedlings, as seen in Quercus ilex L. (holm oak) forests (Vivas et al., 2021). There is some evidence of this for jarrah (Bose et al., 2023; Stukely & Crane, 1994) but none for marri. This study was a snapshot in time and may not be representative of historic conditions that may have prevented recruitment.…”

“…(oak) across the Mediterranean basin (Brasier & Scott, 1994; Camilo‐Alves et al., 2013), multiple forest tree species in North America (Sena et al., 2018), and Eucalyptus spp. across Australia (Bose et al., 2023; Davison, 2018; Peters & Weste, 1997; Tippett et al., 1985; Weste et al., 1973). Phytophthora ramorum is responsible for sudden oak death across North America (Grünwald et al., 2012; Rizzo et al., 2002; Rizzo & Garbelotto, 2003).…”

Global change solutions must embrace biodiverse multifunctional planted forests

“…The concept of a biologically diverse, multifunctional planted forest ecosystem is framed by three key elements, i.e., Science, Policy, and Practice. commercial tree species, such as species from the genera Pinus, Eucalyptus, Acacia, Populus, and Elaeis (oil palm), can greatly limit the regeneration potential of natural forests (Brancalion and Holl, 2020;Mcewan et al, 2020;Bose et al, 2023). Consequently, less diversified multifunctional planted forests, such as monocultures, are often recognized to be less resilient to natural disturbances such as pest and pathogen attacks that may be further intensified by human disturbances and climate change including droughts and extreme temperatures (Paquette and Messier, 2010;Mcewan et al, 2020;Gómez-González et al, 2022).…”

“…In the future, there will likely be a higher demand for quickgrowing forest-based products, but decisions on where to establish commercial short-rotation plantation systems should prioritize the ecological impacts on the land to be used (Brancalion and Holl, 2020;Mcewan et al, 2020;Bose et al, 2023). These plantations (Ferrier, 2020;Silveira et al, 2022).…”