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New Phytophthora boodjera responsible for plant deaths in the Western Australian nursery industry and urban tree plantings
In 2011, an outbreak of a damping-off disease had surfaced in a Western Australian nursery which indicated the presence of a new Phytophthora species. Despite subscribing to the NIASA industry hygiene standards, disease outbreaks continued. This was cause for concern as the plants grown at the nursery were intended for environmental plantings. Despite using chlorine (calcium hypochlorite) solution or dry heat to sterilise used containers, the disease continued to kill seedlings. The pathogen was identified as Phytophthora boodjera, a new species of Phytophthora that had previously been isolated and described as P. taxon arenaria-like by Rea et. al. (2011). Although it is closely related to P. arenaria and P. alticola, it is faster growing and has a higher optimal growth temperature than P. arenaria. Infected Eucalyptus seedling roots in used trays were the source of the reoccurring pathogen as P. boodjera survival spores are resistant to dry heats of up to 65oC. The pathogen was removed from used trays with and without debris through the use of steam pasteurization.
Inoculation trials indicated that Eucalyptus species were the main host of P. boodjera and excess water was not required for the infection process of P. boodjera on eucalypt seedlings. Damping-off and mortality of Eucalyptus seedlings in the nursery was observed only in the first two months after sowing. Tracing the known movement beyond the nursery of infected seedlings planted out in previous years was done to test the survival of P. boodjera in field plantings and its potential to spread beyond the nursery. P. boodjera was found to have survived in a few field locations. The pathogen has also been found in association with declining and dying Agonis flexuosa, Banksia media, B. grandis, Corymbia calophylla, Eucalyptus spp,. and Xanthorrhoea preissii in disturbed ecosystems or urban tree plantings. Extensive sampling from natural ecosystems in southwest of Western Australia resulted in only a few recoveries of P. boodjera and it is now thought to be an introduced species.
Image information: Root reduction of Eucalyptus seedlings inoculated with different Phytophthora species and isolates at 88 weeks old. Whole root systems were visually rated for root rot on a scale 1 to 4 (1=no damage, 4=severe root damage). All control plants had a rating of 1.
About the Author: Agnes Simamora
Agnes Simamora has just submitted her PhD thesis and returned home to Timor (Indonesia) where she has a position at the Faculty of Agriculture, University of Nusa Cendana.
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