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

False-negative isolations or absence of lesions may cause mis-diagnosis of diseased plants infected with Phytophthora cinnamomi

In a series of growth cabinet, glasshouse and field experiments, tissue samples from living clonal Eucalyptus marginata (jarrah) were incubated immediately after sampling on agar (NARPH) selective for Phytophthora. Phytophthora cinnamomi was recovered 3-6 months after inoculation from 50% of samples with lesions and 30% of symptomless samples. However, up to 11% of samples with and without lesions and from which P. cinnamomi was not initially isolated contained viable pathogen. This was shown by removing tissue which had not produced any growth of P. cinnamomi on NARPH plates, cutting it into smaller sections, washing in sterile deionised water repeatedly for 9 days, and replating. Plating stem or bark tissue directly onto NARPH produced false-negative results for nine P. cinnamomi isolates and six jarrah clones. The behaviour of the pathogen indicates that it could be present as dormant structures, such as chlamydospores, that need to be induced to germinate. Alternatively, fungistatic compounds in the tissue needed to be removed to allow the pathogen to grow. These results have important implications for disease diagnosis and management, disease-free certification and quarantine clearance

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

Pseudohomothallism in Armillaria luteobubalina isolates from south-western Australia

The majority of Armillaria species have a bifactorial heterothallic mating system. Some primary homothallic and secondary homothallic behaviour has been observed in a small number of different A. mellea and A. heimii strains from Africa and Asia. In a typical bifactorial heterothallic Armillaria species four haploid nuclei are produced in the basidia during meiosis and the subsequent migration of each nucleus produces haploid basidiospores. Although it is known that A. luteobubalina is a bifactorial heterothallic species the nuclear life cycle is not thoroughly described. This present study aimed to investigate the cytology and nuclear arrangement within the different basidiome tissues and basidiospores in A. luteobubalina

Temperature changes resistance of clonal Eucalyptus marginata to Phytophthora cinnamomi

Eucalyptus marginata (jarrah) varies in its resistance to colonization 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, with no association between pathogenicity levels and either A1 and A2 mating types or isozymes types. We have shown that isolates differ in their capacity to colonize jarrah and marri (E. calophylla) tissue. 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 consequent disease development