Host-specificity of Uromyces heliotropii, a fungal agent for the biological control of common heliotrope (Heliotropium europaeum) in Australia

Common heliotrope, Heliotropium europaeum (Boraginaceae), a summer annual, is a serious weed of pastures in Australia causing poisoning in sheep and other grazing animals. The weed is native to Mediterranean and Middle Eastern regions of Eurasia where it is attacked by several arthropods and pathogens including the rust fungus Uromyces heliotropii. The host-specificity of a virulent and effective strain of the rust from Turkey has been tested by inoculating 96 plants of importance to the Australasian region using both microscopic and macroscopic observations of the reaction of host and non-host plants. The test plants included several members of the Boraginaceae and related families as well as species of Heliotropium native to Australia. The infection was mostly limited to European species of Heliotropium. U. heliotropii was thus found to represent a safe introduction and has recently been introduced to Australia for the biological control of common heliotrope.     

Development of cercospora blight epidemics and effect on the summer annual Heliotropium europaeum in the field

Heliotropium europaeum, common heliotrope, is a serious economic weed in southern Australia. Cercospora blight occurs on H. europaeum in both its native (Mediterranean) and non-native (Australian) range. The causal agents are genetically different forms of an asexual pathogen in the form-genus Cercospora in each region. Natural epidemics of cercospora blight killed weed infestations in both Australia and France. The epidemiology of the disease did not differ between the two regions once differences in rainfall had been considered. Rainfall was important for disease spread. In France, field inoculation experiments were conducted using different concentrations of conidia prepared from a monospore isolate. Cercospora blight reduced seed production 89%, but did not reduce viability. Increased inoculum concentration and inoculation of younger plants encouraged an early epidemic, but did not affect the rate of disease development once the epidemic took hold. In order to be effective at controlling this weed in Australia, these pathogens need to attack young hosts and have regular rain-splash to facilitate spread to new growth.     

Variation in pathogenicity of isolates of Cercospora spp. attacking Heliotropium spp.

The pathogenicity of a set of 13 Cercospora samples collected in France, Turkey and Australia from four Heliotropium species has been evaluated with a detached leaf technique. All of five Euro-Asian Heliotropium species tested were susceptible to all Cercospora species isolates. However, variation in the degree of partial resistance to different isolates was observed and showed some similarity for isolates from the same region of origin. Further studies are required to clarify the taxonomy of Cercospora blight strains, but the consequences of the noted differences in pathogenicity are discussed in relation to the biological control ofH. europaeum L. in Australia.     

Total antioxidant potential of resinous exudates from Heliotropium species,and a comparison of the ABTS and DPPH methods

Total reactive antioxidant potential (TRAP) of resinous exudates from Heliotropium species was evaluated by measuring the bleaching of stable free radicals. The antioxidant capacity of the resinous exudates in Trolox equivalents, evaluated from the bleaching of ABTS derived radical cations, ranged from 2.0M (H. huascoense) to 5.2 M (H. stenophyllum), indicating a very high concentration of phenolic compounds. Considerably smaller values were obtained by measuring the bleaching of DPPH radicals. The ratio between the values obtained employing ABTS derived radicals and DPPH, ranged from 37 (H. megalanthum) to 4.5 (H. chenopodiaceum variety typica). The magnitude of the difference can be considered as an indication of the relative reactivity of the antioxidants present in the exudates. Similar ratios were observed when stoichiometric coefficients were evaluated for representative purified flavonoids obtained from the resinous exudates.     

Morphology of Heliotropium (Boraginaceae) Dispersal Units1

In flowers of Heliotropium s.l. the primary carpel tips are overtopped by commissural outgrowths. Therefore the stylar cleft mimics a lateral orientation of the carpels. In species in which the fruit splits into four diaspores the separation tissues run through both the median and the transverse fruit planes. In species where only two two-seeded nutlets are developed the fruit splits within the false septa and each half is composed of parts of both carpels (“syn-mericarpids”).     

Studies on the rust,Maravalia cryptostegiae,a potential biological control agent of rubber-vine weed,Cryptostegia grandiflora (Asclepiadaceae: Periplocoideae), in Australia,III: Host range

Seventy-one plant species, which were selected using a centrifugal phylogenetic method, were screened againstMaravalia cryptostegiae, an endemic rust of rubber-vine (Cryptostegia grandiflora) in Madagascar. All species and variants of the genusCryptostegia proved to be highly susceptible to the rust under optimum greenhouse conditions. Two other species belonging to the same subfamily Periplocoideae,Gonocrypta grevei from Madagascar andCryptolepis grayi from Australia, developed fertile sori but could still be classified as partially resistant, based on the results of a leaf clearing and staining technique. Fifteen assessment categories and 10 susceptibility ratings were designated by analysing both macro- and microsymptoms. Five resistance mechanisms were identified in the non-hosts and these are described and illustrated. Resistance reactions ranged from complete suppression of spore germination on the plant cuticle to restriction of sorus development due to the collapse of rust haustoria. The significance of host range studies are discussed in relation to the use of rust fungi as classical biological control agents of weeds, and specifically the release ofM. cryptostegiae in Australia.     

Seasonal dynamics in the pyrrolizidine alkaloids of Heliotropium europaeum

An analysis of the pyrrolizidine alkaloids (PA) of the introduced annual weed, Heliotropium europaeum (Boraginaceae), at two sites in south-eastern Australia showed that percentage PA in above-ground parts of the weed differed significantly between sites and declined markedly through the season, from initial levels of >2.2% in the seedling stage to <0.5% prior to senescence. N-oxide forms of PA predominated at both sites, averaging >95% of total alkaloid. Major PA constituents — europine, heliotrine, and lasiocarpine — varied significantly between sites and sampling dates but no marked seasonal trend was detected. Lasiocarpine and europine content varied reciprocally in the free base and N-oxide forms, indicating that these compounds may be readily interconvertible. Correlation of rainfall and average number of leaves per plant with lasiocarpine and europine levels suggested that rainfall, either directly by altering the metabolism of existing leaves or indirectly through plant growth, initiated large short-term shifts in PA composition of H. europaeum without corresponding changes in total PA concentration. At both sites, sheep consumed H. europaeum, reducing both plant density and biomass. Biomass differences between exclosure and access plots of H. europaeum were correlated with grazing intensity. Since heliotrine, lasiocarpine and europine differ markedly in their toxic properties, large shifts in their relative concentrations may have important consequences for these and other herbivores. Environmentally induced quality shifts in these secondary compounds may be as important as, or even override, changes in total quantity in causing PA toxicity to grazing animals.     

Specificity and host specialization of Puccinia chondrillina

Various strains of Puccinia chondrillina, the Chondrilla rust, were collected during surveys in the Mediterranean, undertaken to discover biological control agents suitable for use in Australia against skeleton weed, Chondrilla juncea. Only the strain collected at Vieste (S.E. Italy) was highly virulent against the common Australian form of C. juncea. The specificity of this strain of the rust was tested by inoculation of many unrelated cultivated plants, related cultivated plants and closely related wild plants; all were immune to the rust. These tests satisfied the Australian plant quarantine authorities and this strain of the rust has now been introduced into Australia as a biological control agent for C. juncea.     

The biology and host specificity of the onion weed rust, Puccinia barbeyi, a potentially useful agent for biological control in Australia

Onion weed, Asphodelus fistulosus L., (Liliaceae) a weed of Mediterranean and Middle Eastern origin is widespread in southern Australia where it invades pastures making them unsuitable for grazing. A program of research is underway to discover natural enemies of this plant and to study their possible role in the biological control of onion weed. A rust fungus Puccinia barbeyi (Roum.) Magnus has been found to severely attack A. fistulosus . Observations on the biology of the rust confirmed that it is monoecious and microcyclic and multiplied essentially by aecial and telial stages, although occasionally urediniospores also appeared among teliospores. Several members of the Liliaceae exposed to the aeciospores of the rust remained unattacked indicating that it is most probably specific to Asphodelus spp. and thus its potential for the biological control of A. fistulosus in Australia should be studied further.     

Association mapping of resistance to Puccinia hordei in Australian barley breeding germplasm

Key message

“To find stable resistance using association mapping tools, QTL with major and minor effects on leaf rust reactions were identified in barley breeding lines by assessing seedlings and adult plants.”

Abstract

Three hundred and sixty (360) elite barley (Hordeum vulgare L.) breeding lines from the Northern Region Barley Breeding Program in Australia were genotyped with 3,244 polymorphic diversity arrays technology markers and the results used to map quantitative trait loci (QTL) conferring a reaction to leaf rust (Puccinia hordei Otth). The F_3:5 (Stage 2) lines were derived or sourced from different geographic origins or hubs of international barley breeding ventures representing two breeding cycles (2009 and 2011 trials) and were evaluated across eight environments for infection type at both seedling and adult plant stages. Association mapping was performed using mean scores for disease reaction, accounting for family effects using the eigenvalues from a matrix of genotype correlations. In this study, 15 QTL were detected; 5 QTL co-located with catalogued leaf rust resistance genes (Rph1, Rph3/19, Rph8/14/15, Rph20, Rph21), 6 QTL aligned with previously reported genomic regions and 4 QTL (3 on chromosome 1H and 1 on 7H) were novel. The adult plant resistance gene Rph20 was identified across the majority of environments and pathotypes. The QTL detected in this study offer opportunities for breeding for more durable resistance to leaf rust through pyramiding multiple genomic regions via marker-assisted selection.     

Epidemic increase of Endophyllum osteospermi (Uredinales, Pucciniaceae) on Chrysanthemoides monilifera

The epidemiology of the rust fungus Endophyllum osteospermi was investigated. This rust fungus is considered to be a candidate biological control agent for Chrysanthemoides monilifera ssp. monilifera, which is an invasive alien weed of native vegetation in south-eastern Australia. Between 10 and 20 plants of C. monilifera were marked at each of five sites in the Western Cape Province of South Africa, where both organisms are native. The infection levels and number of witches' brooms were determined every 2 months over a 2-year period. Additionally, at three of these sites, the infection levels and number of witches' brooms of all bushes in the host population was determined annually over 4 years. The increase in number of witches' brooms per bush ranged between 0 and 282 within 1 year, with an average increase per bush of 28 (SE±4.8) in 1993, and 39 (SE±9.2) in 1994. The average r_s for all bushes during 1993 was 0.015 month^-1 (SE±0.0041, n=72) and 0.0098 month^-1 (SE±0.0073, n=43) during 1994. When host bushes that either died back or died during the course of each year were excluded, then the average r_s during 1993 was 0.023 month^-1 (SE±0.0048, n=45) and 0.0348 month^-1 (SE±0.0106, n=20) during 1994. Under suitable conditions in South Africa, E. osteospermi undergoes epidemic increase within its host plant's populations. This rust fungus should therefore be considered as a suitable candidate biological control agent for use in Australia against C. monilifera ssp. monilifera.     

Influences of the biophysical environment on blister rust and mountain pine beetle,and their interactions,in whitebark pine forests

Aim To understand how the biophysical environment influences patterns of infection by non‐native blister rust (caused by Cronartium ribicola) and mortality caused by native mountain pine beetles (Dendroctonus ponderosae) in whitebark pine (Pinus albicaulis) communities, to determine how these disturbances interact, and to gain insight into how climate change may influence these patterns in the future. Location High‐elevation forests in south‐west Montana, central Idaho, eastern and western Oregon, USA. Methods Stand inventory and dendroecological methods were used to assess stand structure and composition and to reconstruct forest history at sixty 0.1‐ha plots. Patterns of blister rust infection and mountain pine beetle‐caused mortality in whitebark pine trees were examined using nonparametric Kruskal–Wallis ANOVA, Mann–Whitney U‐tests, and Kolmogorov–Smirnov two‐sample tests. Stepwise regression was used to build models of blister rust infection and mountain pine beetle‐related mortality rates based on a suite of biophysical site variables. Results Occurrence of blister rust infections was significantly different among the mountain ranges, with a general gradient of decreasing blister rust occurrence from east to west. Evidence of mountain pine beetle‐caused mortality was identified on 83% of all dead whitebark pine trees and was relatively homogenous across the study area. Blister rust infected trees of all ages and sizes uniformly, while mountain pine beetles infested older, larger trees at all sites. Stepwise regressions explained 64% and 58% of the variance in blister rust infection and beetle‐caused mortality, respectively, indicating that these processes are strongly influenced by the biophysical environment. More open stand structures produced by beetle outbreaks may increase the exposure of surviving whitebark pine trees to blister rust infection. Main conclusions Variability in the patterns of blister rust infection and mountain pine beetle‐caused mortality elucidated the fundamental dynamics of these disturbance agents and suggests that the effects of climate change will be complex in whitebark pine communities and vary across the species’ range. Interactions between blister rust and beetle outbreaks may accelerate declines or facilitate the rise of rust resistance in whitebark pine depending on forest conditions at the time of the outbreak.     

Preliminary host specificity testing of Endophyllum osteospermi (Uredinales, Pucciniaceae), a biological control agent against Chrysanthemoides monilifera ssp. monilifera

Chrysanthemoides monilifera ssp. monilifera, indigenous to the Western Cape Province of South Africa, is a serious invader of native vegetation in south-eastern Australia. The rust fungus Endophyllum osteospermi causes witches' brooms on C. monilifera ssp. monilifera in South Africa, and is associated with a reduction in growth and seed production of its host under natural conditions, as well as mortality of severely infected bushes. This rust fungus is considered to be a potential biological control agent for use against C. monilifera ssp. monilifera in Australia. Endophyllum osteospermi has a long latent period, typically between 6 and 24 months between infection and the initiation of witches' brooms. This long latent period makes the logistics of doing traditional host specificity testing, in which all test plant species are inoculated and observed for symptom development, unfeasible for this rust fungus. Germination of aecidioid teliospores and penetration by basidiospores were observed on the surface of excised leaves of 32 test plant species at 4 days after inoculation, and compared to that on C. monilifera ssp. monilifera. Germinating aecidioid teliospores aborted on 14 test plant species, whilst no penetration was attempted on a further 12 test plant species. Penetration only occurred on nine of the 32 test plant species, in addition to C. monilifera ssp. monilifera. Inoculating whole plants of nine selected test plant species confirmed the above results. Therefore, only the test plant species in which penetration occurred, or at least was attempted, need to undergo comprehensive host specificity testing. Pending these results, E. osteospermi may be suitable for release in Australia for the biological control of C. monilifera ssp. monilifera.     

A new shell disease in the mud crab Scylla serrata from Port Curtis, Queensland (Australia)

In 1994 a previously unreported rust spot shell disease was seen in mud crabs Scylla serrata - Forskal from Port Curtis, central Queensland, Australia. Of 673 crabs surveyed, 21.7% had shell lesions. Of these, 82.9% had rust spot lesions on the carapace. The majority of rust spot-affected crabs (78.8%) were female. Rust spot lesions were predominantly non-perforated (89.4%) and 54.8% were bilaterally symmetrical. There was also a gender difference in the areas of the carapace most commonly affected. The main histological features of the rust spot lesion included: a cavity in the upper endocuticle; indentation of the endocuticle below the cavity; remains of muscle attachment adhesive epithelium within the cavity; fibrous connective tissue between the damaged carapace and the attached muscle; and islands of endocuticle in this fibrous connective tissue. Histopathology of the internal organs failed to find evidence of an infectious or parasitic cause of the rust spot lesions. The cause(s) of the syndrome appear(s) to be non-infectious.     

Morphological and molecular characterisation of Puccinia lagenophorae, now present in central North America

In June 2004, a rust fungus not previously reported for Oklahoma was found occurring naturally on the weed, common groundsel, Senecio vulgaris, in pots in a commercial container nursery in northeastern Oklahoma. Host symptoms and morphology of teliospores and aeciospores of the fungus were consistent with those of Puccinia lagenophorae, a recent introduction into North America that has, as yet, been reported only on the East and West Coasts of the USA. This is the first report of the rust in central regions of North America. The rust is believed to be native to Australia and New Zealand and subsequently reported in most continents on numerous species and genera of the Asteraceae. Some authors in Europe consider the rust on Bellis as different from the one on Senecio, naming it Puccinia distincta. Our ITS1‐5.8S‐ITS2 ribosomal DNA sequence data, however, show homology with P. distincta sequences from Europe, indicating there is only one morphologically‐variable polyphagous species. Presumably, the rust was introduced into Oklahoma on infected plants from the West Coast of the USA, the source of most plant material in the commercial nursery where it was found. The rust is potentially important on several ornamental Asteraceae in North America as it has become in Europe, where it spreads rapidly throughout that continent following its introduction there in the early 1960s.     

A new strain of the rust fungus Puccinia chondrillina for biological control of skeleton weed in Australia

A strain of the rust fungus Puccinia chondrillina introduced into Australia in 1971 for the biological control of skeleton weed, Chondrilla juncea, attacked only the narrow-leaf form of this weed. Studies were, therefore, undertaken in the Mediterranean region to discover strains of the rust which will attack the other two Australian forms of skeleton weed, intermediate- and broad-leaf. Several strains of the rust were found to be highly virulent against the intermediate form. One of these strains from Manisa, western Turkey, was both highly specific to its host and safe for use as a biological control agent. This strain has recently been introduced into Australia for the control of the intermediate form of Chondrilla.