Temperature and inoculation method influence disease phenotypes and mortality of Eucalyptus marginata clonal lines inoculated with Phytophthora cinnamomi

Survival of 1-year-old plants of three clonal lines of Eucalyptus marginata (jarrah), two ranked as resistant (RR1 and RR2) and one as susceptible (SS1) to Phytophthora cinnamomi, was assessed after pathogen inoculation with either mycelial mats underbark or zoospores on the stem. Plants were grown at 15, 20, 25 and 30°C. Method of inoculation did not produce comparable mortalities of the clonal lines, particularly at 25 and 30°C. At these temperatures, all three clonal lines had 100% mortality when inoculated underbark, but when inoculated with zoospores, RR1 had 60% survival and lines SS1 and RR2 had 100% mortality. Generally, the level of resistance of all clonal lines declined with increasing temperature. RR2 had consistently higher mortality than SS1, and is therefore not considered resistant. Lesion development was also measured in detached stems of RR1 and a susceptible clonal line (SS2) each inoculated underbark with four different P. cinnamomi isolates. Stems were assessed for lesion development at 20, 25 and 30°C for 4 days. For all four isolates, detached stems of RR1 generally had smaller lesions than those of SS2, particularly at 30°C. The increase in lesion length with increasing temperature was greatest for SS2. Detached stems may have potential in screening for jarrah resistant toP. cinnamomi and allow identification of susceptible clonal lines at 30°C

The impact and control of Phytophthora cinnamomi in native and rehabilitated forest ecosystems in Western Australia

Botanists have likened the impact of Phytophthora cinnamomi in Australian plant communities to that of the last ice age, which affected a large number of plant families, genera and species within these families. Phytophthora cinnamomi affects the floristics and structure of many unique plant communities. We discuss the impact of this pathogen and our current knowledge of its biology, genetics and pathology in Western Australian plant communities and the current management strategies used to limit its spread and impact. We hope that the knowledge obtained from some of our experiences in managing this pathogen in Western Australian natural ecosystems will be of some benefit to researchers studying Phytophthora diseases in Quercus, Alnus and Castanea in Europe and America

Stomatal responses of Eucalyptus species to elevated CO2 concentration and drought stress

Five species of Eucalyptus (E. grandis, E. urophylla, E. camaldulensis, E. torelliana, and E. phaeotrica), among the ten species most commonly used in large scale plantations, were selected for studies on the effects of elevated CO2 concentration [CO2] and drought stress on stomatal responses of 2.5-month old seedlings. The first three species belong to the subgenus Smphyomyrtus, whereas the fourth species belongs to the subgenus Corymbia and E. phaeotrica is from the subgenus Monocalyptus. Seedlings were grown in four pairs of open-top chambers, arranged to have 2 plants of each species in each chamber, with four replications in each of two CO2 concentrations: 350 ± 30 mumol mol-1 and 700 ± 30 mumol mol-1. After 100 days in the chambers, a series of gas exchange measurements were made. Half the plants in each chamber, one plant per species per chamber, were drought-stressed by withholding irrigation, while the remaining plants continued to be watered daily. Drought stress decreased stomatal conductance, photosynthesis and transpiration rates in all the species. The effect of drought stress on stomatal closure was similar in both [CO2]. The positive effects of elevated [CO2] on photosynthesis and water use efficiency were maintained longer during the stress period than under well-watered conditions. The photosynthetic rate of E. phaeotrica was higher even in the fourth day of the drought stress. Drought stress increased photoinhibition of photosynthesis, as measured by chlorophyll fluorescence, which varied among the species, as well as in relation to [CO2]. The results are in agreement with observed differences in stomatal responses between some eucalyptus species of the subgenera Symphyomyrtus and Monocalyptus

The potential of copper sulphate to control Phytophthora cinnamomi in bauxite mining operations

Phytophthora cinnamomi Rands is present in many areas prior to mining by Alcoa of Australia, Ltd. To reduce the risk of spreading this pathogen to non-infected areas the company employs a range of control measures at all stages of mining. There is a need to develop a treatment to eradicate P. cinnamomi from relatively small volumes <60m3) of soil. This study examined the efficacy ofCuS04 as a fungicide for rapid death <2h) of P. cinnamomi in topsoil and gravel soil taken from a mining area

Phosphite concentration: its effect on phytotoxicity symptoms and colonisation by Phytophthora cinnamomi in three understorey species of Eucalyptus marginata forest

Pre-treatment of plants with foliar sprays of 0.2, 0.5 and 2% phosphite restricted colonisation by Phytophthora cinnamomi in inoculated stems of Adenanthos barbiger and Daviesia decurrens, and led to a reduction in the isolation of P. cinnamomi from these stems in comparison with unsprayed plants. In plants treated with 2% phosphite,P. cinnamomi was not isolated from D. decurrens but was isolated from 22% of the stems of A. barbiger. InXanthorrhoea preissii, colonisation by, and isolation of,P. cinnamomi from inoculated roots was not significantly affected by pre-treatment of the foliage with 0.2, 0.5 and 2% phosphite. Very low concentrations of phosphite were detected in the roots of X. preissii (maximum mean of 2.2 g/g dry weight), in comparison with the phosphite concentrations measured in the foliage of A. barbiger and D. decurrens plants treated with phosphite (maximum means of 80 and 871 g/g dry weight, respectively). Treatment with 0.2% phosphite resulted in minimal phytotoxicity in each of the three species, whereas treatment with 2% phosphite led to the development of severe phytotoxicity symptoms. This study indicates that phosphite has potential for the management of P. cinnamomi in native plant communities

Selecting plants resistant to Phytophthora cinnamomi

Phytophthora cinnamomi is the most devastating forest disease world wide. It is mostly an introduced pathogen as in southern Australia where it devastates native forests, woodlands and heaths, directly and indirectly affecting vegetation types from a wide range of families. P. cinnamomi has also been introduced into European and North American hardwood and softwood forests. The pathogen is now cosmopolitan in the horticultural industry and it is a particular problem in nurseries. The significance of this is that P. cinnamomi has the opportunity to interact with and the potential to evolve in association with a wide range of new hosts and in a wide range of ecosystems. Distribution of the pathogen at the local, national and international level is of concern to the management of forest, native vegetation and horticulture industries

Evaluation of resistance to Phytophthora cinnamomi in seed-grown trees and clonal lines of Eucalyptus marginata inoculated in lateral branches and roots

Seed-grown trees and six clonal lines of 3-5-4-5-year-old Eucalyptus marginata (jarrah) growing in a rehabilitated bauxite mine site in the jarrah forest were underbark-inoculated on lateral branches (1995) or simultaneously on lateral branches and lateral roots (1996) with isolates of Phytophthora cinnamomi in late autumn. Individual seedlings from which the clonal lines were derived had previously been assessed as either resistant (RR) or susceptible (SS) to P. cinnamomi. At harvest, the acropetal lesion and colonization lengths were measured. Overall, the length of colonization in roots and branches was more consistent as a measure of resistance than lesion length, because colonization length recorded the recovery of P. cinnamomi from macroscopically symptomless tissue ahead of the lesion which, on some occasions, was up to 6 cm. In both trials, one RR clonal line was able to contain the P. cinnamomi isolates consistently, as determined by small lesion and colonization lengths in branches and roots. In contrast, the remaining two RR clonal lines used in both trials were no different from the SS line in their ability to contain lesions or colonization. These latter two RR lines may therefore not be suitable for use in rehabilitation of P. cinnamomi-infested areas. Differences in lesion and colonization lengths among P. cinnamomi isolates occurred only in the 1995 trial. Colonization and lesion lengths in branches were up to eight times greater in 1996 than in 1995, but the relative rankings of clonal lines were consistent between trials. Although colonization was always greater in branches than roots, the relative rankings of the lines were similar between branch and root inoculations. Branch inoculations are a valid option for testing the resistance and susceptibility of young jarrah trees to P. cinnamomi

Temperature changes resistance of Eucalyptus marginata to Phytophthora cinnamomi

Eucalyptus marginata (Jarrah) varies in its resistance to infection by the introduced pathogen, Phytophthora cinnamomi. This trait has been exploited to yield jarrah clones ranging in resistance to P. cinnamomi. However, isolates of P. cinnamomi vary in their capacity to induce disease in resistant jarrah clones. We have shown that isolates differ in their growth rates in jarrah and marri (E. calophylla) tissue and in agar media. Disease outbreaks in jarrah, other native vegetation and horticultural crops due to P. cinnamomi are more likely to occur in warm moist conditions. These factors raise questions about the interactions between the pathogen, hosts and temperature, and the consequent disease development

Phosphite: its phytotoxicity and effectiveness in the protection of Eucalyptus marginata forest from Phytophthora cinnamomi

Recent trials conducted by the Western Australian Department of Conservation and Land Management have shown that phosphite protects trees in E. marginata forest from P. cinnamomi. However, phytotoxicity has been observed in some plant species, and phytotoxic concentrations of phosphite have increased the susceptibility of Banksia coccinea to P. cinnamomi. The aim of this project was to examine the effect of phosphite concentration on phytotoxicity and on colonisation by P. cinnamomi in three understorey species of the E. marginata forest