I. W. Smith

Mycosphaerella diseases of juvenile foliage in a eucalypt species and provenance trial in Victoria, Australia

Summary The incidence of mycosphaerella leaf diseases and the severity of seven species of Mycosphaerella were assessed on the juvenile foliage of 13 eucalypt species and 35 provenances in a 2–3 year old trial in south-eastern Australia. Significant variation was observed between the 13 host species, with E. cypellocarpa and E. nitens recording the highest disease incidence and E. elata and E. oreades having no assessable disease. While wide variation was observed between provenances within species, variation was significant only between provenances of E. nitens. Seven species of Mycosphaerella were recorded on diseased leaves collected from the trial. M. cryptica and M. nubilosa were the most damaging, with M. cryptica being the most common and having the widest host range.

Combinations of potassium phosphonate and Bion (acibenzolar-S-methyl) reduce root infection and dieback of Pinus radiata, Banksia integrifolia and Isopogon cuneatus caused by Phytophthora cinnamomi

Phytophthora cinnamomi infects the roots of and causes dieback of Pinus radiata, Banksia integrifolia and Isopogon cuneatus. Foliar sprays of potassium phosphonate (0.1 g a.i./L or 1.0 g a.i./L) and Bion 500 WG (500 g/kg acibenzolar-S-methyl; 1.0 μ a.i./L or 2.5 μ a.i./L), separately and in combinations, were applied to these plants immediately after transplanting into potting mix infested with P? cinnamomi. After 14 weeks the incidence of root infection by P cinnamomi was assessed and plant growth measured. The incidence of root infection was reduced by sprays of potassium phosphonate or Bion. Combinations of phosphonate and Bion additively reduced the incidence of root infection, but no treatment eradicated the pathogen from roots or soil. Phytotoxicity was not observed in any treatment, demonstrating that effective control of Phytophthora root rot can be achieved on phosphorus-sensitive plants using low rates of phosphonate in combination with Bion. Additional keywords: Activon, benzo[l,2,3]thiadiazole-7-carbothioica cid-S-methyl ester, BTH, phosphite

Photosynthetic responses of field-grown Pinus radiata trees to artificial and aphid-induced defoliation

The phloem-feeding aphid Essigella californica represents a potential threat to the productivity of Pinus radiata plantations in south-eastern Australia. Five- and nine-year-old field trials were used to characterize the effects of artificial and natural aphid-induced (E. californica) defoliation, respectively, on shoot photosynthesis and growth. Photosynthetic capacity (A(max)) was significantly greater following a 25% (D25) (13.8 µmol m(-2) s(-1)) and a 50% (D50) (15.9 µmol m(-2) s(-1)) single-event upper-crown artificial defoliation, 3 weeks after defoliation than in undefoliated control trees (12.9 µmol m(-2) s(-1)). This response was consistently observed for up to 11 weeks after the defoliation event; by Week 16, there was no difference in A(max) between control and defoliated trees. In the D50 treatment, this increased A(max) was not sufficient to fully compensate for the foliage loss as evidenced by the reduced diameter increment (by 15%) in defoliated trees 36 weeks after defoliation. In contrast, diameter increment of trees in the D25 treatment was unaffected by defoliation. The A(max) of trees experiencing upper-crown defoliation by natural and repeated E. californica infestations varied, depending on host genotype. Despite clear differences in defoliation levels between resistant and susceptible genotypes (17 vs. 35% of tree crown defoliated, respectively), growth of susceptible genotypes was not significantly different from that of resistant genotypes. The observed increases in A(max) in the lower crown of the canopy following attack suggested that susceptible genotypes were able to partly compensate for the loss of foliage by compensatory photosynthesis. The capacity of P. radiata to regulate photosynthesis in response to natural aphid-induced defoliation provides evidence that the impact of E. californica attack on stem growth will be less than expected, at least for up to 35% defoliation.

Phytophthora niederhauserii sp. nov., a polyphagous species associated with ornamentals, fruit trees and native plants in 13 countries

A non-papillate, heterothallic Phytophthora species first isolated in 2001 and subsequently from symptomatic roots, crowns and stems of 33 plant species in 25 unrelated botanical families from 13 countries is formally described here as a new species. Symptoms on various hosts included crown and stem rot, chlorosis, wilting, leaf blight, cankers and gumming. This species was isolated from Australia, Hungary, Israel, Italy, Japan, the Netherlands, Norway, South Africa, Spain, Taiwan, Turkey, the United Kingdom and United States in association with shrubs and herbaceous ornamentals grown mainly in greenhouses. The most prevalent hosts are English ivy (Hedera helix) and Cistus (Cistus salvifolius). The association of the species with acorn banksia (Banksia prionotes) plants in natural ecosystems in Australia, in affected vineyards (Vitis vinifera) in South Africa and almond (Prunus dulcis) trees in Spain and Turkey in addition to infection of shrubs and herbaceous ornamentals in a broad range of unrelated families are a sign of a wide ecological adaptation of the species and its potential threat to agricultural and natural ecosystems. The morphology of the persistent non-papillate ellipsoid sporangia, unique toruloid lobate hyphal swellings and amphigynous antheridia does not match any of the described species. Phylogenetic analysis based on sequences of the ITS rDNA, EF-1α, and β-tub supported that this organism is a hitherto unknown species. It is closely related to species in ITS clade 7b with the most closely related species being P. sojae. The name Phytophthora niederhauserii has been used in previous studies without the formal description of the holotype. This name is validated in this manuscript with the formal description of Phytophthora niederhauserii Z.G. Abad et J.A. Abad, sp. nov. The name is coined to honor Dr John S. Niederhauser, a notable plant pathologist and the 1990 World Food Prize laureate.

Effect of potassium phosphonate on root rot of Pinus radiata caused by Phytophthora cinnamomi

Seedlings of Pinus radiata transplanted into washed river sand or sand/peat potting mix pre-inoculated with Phytophthora cinnamomi developed severe wilt and root rot symptoms within 7 weeks, and died within 12 weeks. By contrast, direct inoculation of pathogen mycelium into stem wounds produced only restricted lesions. Soil incorporation of inoculum was subsequently used to assess the ability of potassium phosphonate to protect pine seedlings against wilt and root rot caused by P cinnamomi. Three concentrations of potassium phosphonate (0.1, 1.0 and 5.0 g/L), applied as either a single foliar spray or as a single root drench at transplanting into pots containing pathogen-infested sand or sand/peat, significantly reduced the incidence of root rot symptoms. At each concentration, soil drenches were more effective than foliar sprays in delaying and suppressing dieback symptoms in container-grown plants. Phosphonate applications were more effective in sand/peat potting mix than in washed river sand. Recovery of the pathogen from diseased plant roots and potting mix was lower in pots drenched with phosphonate than from pots treated by foliar sprays. Potassium phosphonate foliar sprays at a rate of 5.0 g/L were phytotoxic, causing burning of needles and temporary branch dieback.

Forest health surveillance in Victoria

Summary Forest health surveillance (FHS) has been undertaken in Victorian native forests and plantations on an ad hoc basis since the early 1960s in response to incursions and outbreaks of native and introduced insect pests and plant pathogens, such as sirex wood wasp, Monterey pine aphid, Phytophthora dieback, phasmatids and other defoliators. The purpose of surveillance is to provide a broad overview of forest health and data for land managers to allow them to take appropriate strategic decisions and manage risks to their estate. Early targeted FHS in Victoria consisted mainly of drive-through surveys with aerial surveillance where required to determine the extent of a particular damaging agent. In 1991, a plot-based surveillance system targeting high-risk sites was developed to monitor levels of Dothistroma disease. These plots were used to trigger more intensive surveillance (e.g. aerial) to enable early management intervention once the levels reached predetermined thresholds. In 2001, a broader plot-based monitoring system was implemented for HVP Plantations as part of its risk management program to determine the status, changes and trends in tree health on an annual basis, and provide data for management decisions to control outbreaks threatening the health of plantations. This paper describes the establishment of a plot-based monitoring system, combined with supplementary surveys to provide information on the extent and damage potential of pest agents in the HVP Plantations estate, and its possible application in native forests.

Holocryphia eucalypti on Tibouchina urvilleana in Australia.

Tibouchina spp. (Melastomataceae) are native to South America, but have been planted as ornamentals in many southern hemisphere countries. The Melastomataceae are members of the Myrtales and are close relatives of the Myrtaceae, to which the genus Eucalyptus belongs. The recent discovery of several Chrysoporthe spp. on Tibouchina spp. has prompted a more detailed survey for other Eucalyptus pathogens that might occur on this tree. In this study, the discovery in Australia of Holocryphia eucalypti, a Eucalyptus pathogen, on diseased stems of Tibouchina urvilleana is reported. Characterisation of this fungus was based on morphology and comparisons of β-tubulin gene sequences. Greenhouse pathogenicity tests, including isolates of H. eucalypti from Eucalyptus spp. in Australia and South Africa, showed that the isolates of H. eucalypti from T. urvilleana were significantly more pathogenic on T. urvilleana than isolates from Eucalyptus.

Foliar diseases of Eucalyptus spp. grown for ornamental cut foliage

Eight Eucalyptus species grown for ornamental foliage have been seriously affected by leaf blight and leaf spot caused by Mycosphaerella cryptica, Dichomera versiformis and Phaeophleospora eucalypti. Other fungi such as Readeriella mirabilis, Sarcostroma brevilatum, Thyrinula eucalypti, Vermisporium aff. falcatum and Harkrtessia victoriae were found associated with smaller spots. Most of these are new host records.

The Sirex wasp and its biological control in plantations of radiata pine variably defoliated by Dothistroma septospora in north-eastern Victoria.

Summary The distribution and severity of pine needle blight disease (PNB), caused in spring 1989 by an outbreak of the needle cast pathogen Dothistroma septospora, was assessed within a 10 km radius of two study sites near Myrtleford in the Wangaratta Pinus radiata plantation complex of north-eastern Victoria. Areas of severe needle cast were located on colour aerial photographs in spring 1989, then checked by ground survey for the percentage of visible crowns infected. Population levels of the Sirex wasp (Sirex noctilio), rated in terms of the cumulative percentage tree mortality induced by the wasp since 1989, were estimated in autumn/winter 1991. Twenty-one unthinned plots, each of 400 trees aged 14–15 years, were examined for S. noctilio and associated symptoms of D. septospora. The effectiveness of parasitoids was evaluated in the laboratory by monitoring total insect emergents from 222 billets (0.8 m long), cut in winter 1991 from 100 herbicide-injected ‘Sirex’ trap trees. All emergents of S. noctil...

Investigating the Presence of Biotic Agents Associated with Mundulla Yellows

The role of biotic agents in the dieback syndrome Mundulla Yellows (MY) was investigated by analysis of 40 Eucalyptus camaldulensis, E. leucoxylon, or E. cladocalyx trees and soil samples from South Australia and Victoria, Australia. No pathogenic fungi, bacteria, phytoplasmas, or insect pests or vectors were found to be associated with MY. However, nematode analysis identified Merlinius spp. to be associated with soil, but not roots, from symptomatic trees. Interveinal chlorosis symptoms were not transmissible by seed, mechanical inoculation, or grafting using plant material derived from symptomatic trees. Virus-like particles were detected at a single symptomatic study site using transmission electron microscopy. MY symptoms were induced in E. camaldulensis seedlings by sowing seed from asymptomatic trees into sterilized and unsterilized soil collected from underneath symptomatic trees. Significantly, sterilized soil induced more severe symptoms in seedlings than unsterilized soil. Soil collected from under asymptomatic trees did not induce MY symptoms. This preliminary investigation indicates that, with the exception of Merlinius spp., pathogenic organisms and pests were not consistently associated with MY symptoms.