Rodrigo Ahumada

Retracing the routes of introduction of invasive species: the case of the Sirex noctilio woodwasp

Understanding the evolutionary histories of invasive species is critical to adopt appropriate management strategies, but this process can be exceedingly complex to unravel. As illustrated in this study of the worldwide invasion of the woodwasp Sirex noctilio, population genetic analyses using coalescent‐based scenario testing together with Bayesian clustering and historical records provide opportunities to address this problem. The pest spread from its native Eurasian range to the Southern Hemisphere in the 1900s and recently to Northern America, where it poses economic and potentially ecological threats to planted and native Pinus spp. To investigate the origins and pathways of invasion, samples from five continents were analysed using microsatellite and sequence data. The results of clustering analysis and scenario testing suggest that the invasion history is much more complex than previously believed, with most of the populations being admixtures resulting from independent introductions from Europe and subsequent spread among the invaded areas. Clustering analyses revealed two major source gene pools, one of which the scenario testing suggests is an as yet unsampled source. Results also shed light on the microevolutionary processes occurring during introductions, and showed that only few specimens gave rise to some of the populations. Analyses of microsatellites using clustering and scenario testing considered against historical data drastically altered our understanding of the invasion history of S. noctilio and will have important implications for the strategies employed to fight its spread. This study illustrates the value of combining clustering and ABC methods in a comprehensive framework to dissect the complex patterns of spread of global invaders.

A diverse assemblage of Botryosphaeriaceae infect Eucalyptus in native and non-native environments

The Botryosphaeriaceae cause endophytic infections of leaves and bark of various trees, including Eucalyptus, and they apparently persist in this state for extended periods of time. Under conditions of stress, these fungi cause many different disease symptoms on Eucalyptus, of which stem and branch cankers and die-back are the most prominent. Given their cryptic, endophytic nature, the Botryosphaeriaceae are easily overlooked when moving seeds and plants around the world. It is, therefore, not surprising to see a growing number of examples of introductions of Botryosphaeriaceae into new environments. In the past, three species were commonly reported from Eucalyptus, namely Botryosphaeria dothidea, Neofusicoccum ribis (reported as B. ribis) and Lasiodiplodia theobromae. It is now known that B. dothidea and N. ribis are generally rare on Eucalyptus, and that Aplosporella yalgorensis, B. mamane, N. parvum, N. eucalyptorum, N. eucalypticola, N. australe, N. macroclavatum, N. andinum, N. mangiferum, Dichomera eucalypti, Dichomera versiformis, Fusicoccum ramosum, Pseudofusicoccum stromaticum, P. adansoniae, P. ardesiarum, P. kimberleyense, Lasiodiplodia crassispora, L. gonubiensis, L. pseudotheobromae and L. rubropurpurea also infect this host. Interestingly, different species dominate on Eucalyptus in different regions of the world, irrespective of whether other species occur in that environment or not. As examples, in parts of eastern Australia, N. eucalyptorum and N. eucalypticola dominate, although N. australe is common on Acacia spp. in this area, while in Western Australia N. australe dominates. In South Africa and Chile N. parvum, N. eucalyptorum and N. eucalypticola are common, despite the presence of N. ribis and N. australe on related hosts such as Syzygium. In Venezuela, there are five other species not common on Eucalyptus elsewhere, but L. theobromae dominates. In Colombia, B. dothidea and N. ribis, and in Uganda and Ethiopia, L. theobromae and N. parvum, are most common. These fascinating patterns of distribution are explored, while their pathogenicity and potential influence on Eucalyptus plantations and surrounding native plant communities are considered.

Pathogenicity and sporulation of Phytophthora pinifolia on Pinus radiata in Chile

Phytophthora pinifolia causes the needle and shoot disease of Pinus radiata known as Daño Foliar del Pino (DFP) in Chile. The first pathogenicity trials with this organism utilized mycelial plugs placed on stem wounds. These resulted in lesions in the tissue, but did not reproduce the resinous bands on the needles, which are the most characteristics symptoms of the disease under natural conditions. In this study, stem inoculations were repeated, but to complete Koch’s postulates fully, and to confirm that P. pinifolia causes the symptoms observed on naturally infected trees, zoospore/sporangial suspensions were used to inoculate pine foliage. This method produced the same symptoms observed on needles infected naturally. These results confirm that P. pinifolia is the causal agent of the Daño Foliar del Pino on P. radiata in Chile and successfully completed Koch’s postulates for the first time. Pathogenicity tests on different Pinus spp. and hybrids showed a wide range of responses to inoculation with P. pinifolia mycelial plugs, from highly susceptible to resistant. Monitoring of sporulation revealed that the sporangia commonly remain on the needles for extended periods of time and their frequency of occurrence and dispersal appear to increase during the rainy season.

Southern Hemisphere Exotic Pine Plantations Threatened by Insect Pests and their Associated Fungal Pathogens

Plantation forestry based on non-native tree species in the southern hemisphere expanded rapidly during the latter part of the 20 th Century. These plantations now cover many millions of hectares, mainly of Pinus and Eucalyptus and to a lesser extent Acacia species in countries of South America, Africa and Australasia. They represent a major industrial resource, in many cases contributing substantially to local economies through trade in solid timber and pulp products. In addition, nonnative plantation forestry has provided local sources of timber products, in some cases alleviating the need to utilize native forest resources. The success of plantation forestry based on non-native trees in the southern hemisphere has clearly been associated with remarkably rapid growth of trees, often exceeding that associated with the same trees in their native environment. Recent technological advances making it possible to propagate plantation trees vegetatively have also contributed to the success of plantation forestry in the southern hemisphere. This capacity has for example made it possible to capitalize on hybridization between species with highly desirable characteristics and thus to develop specialized products and niche markets. It is widely believed that the exceptional growth and productivity of plantations in the southern hemisphere is closely linked to the separation of the propagated trees from their natural enemies. The so-called enemy escape hypothesis, although open to debate has relatively wide support (Jeffries & Lawton, 1984; Keane & Crawley, 2002) and we believe that it represents a major factor associated with the success of plantation forestry in the Southern Hemisphere. Thus trees have been able to grow in the absence of damage caused by insect pests and diseases that can severely impede their potential productivity.

Parallel host range expansion in two unrelated cossid moths infesting Eucalyptus nitens on two continents

1. Two cossid moths, Coryphodema tristis Drury and Chilecomadia valdiviana Philippi, have recently become pests on Eucalyptus nitens H. Deane & Maiden in South Africa and Chile, respectively. Both C. tristis and C. valdiviana have large host ranges and high levels of similarity in their host distributions. Their infestations of E. nitens are the first records of these moths on Myrtaceae.

Potential of Phytophthora pinifolia to spread via sawn green lumber: a preliminary investigation

Phytophthora pinifolia causes the needle and shoot disease of Pinus radiata in Chile known as Daño Foliar del Pino. Although P. pinifolia is primarily a needle pathogen, there are concerns that it might be spread to new environments via the export of contaminated timber. In order to determine whether P. pinifolia can enter or persist in green sawn lumber, its presence in lumber produced from trees exposed to the pathogen for at least four years was examined. Green lumber produced from the infected trees, and green wood samples artificially exposed to P. pinifolia inoculum, were analysed by making extensive isolations on Phytophthora selective media. In addition, PCR was conducted using species-specific primers developed for P. pinifolia. Results of the study showed that the green sawn lumber taken from trees infected by P. pinifolia, or green lumber exposed in infected pine plantations, displayed no evidence of the pathogen surviving in this material.

Mega-trap-plots: a novel method of Sirex woodwasp management on Pinus radiata plantations in Chile

Sirex noctilio is one of the most important invasive pests that affect Pinus radiata plantations in Chile. Its management is based on a biological control complex, the most important component of which is the nematode, Deladenus siricidicola. However, in some areas, S. noctilio populations attain epidemic levels and no effective control methods exist to reduce large populations in a short period. In this study, we evaluated a novel method called mega-trap-plots (MTPs), which consist of an area of 1 ha with trap trees, which were debilitated in four different months (from November to February) with the purpose of reducing the Sirex wasp population through harvesting of trees attacked. The main objective was to reduce the potential population of S. noctilio, by evaluating four periods or months of MTP installation to maximise the colonisation of trap trees by wood wasps. The results showed that the MTPs that were installed from November to January had the highest wood wasp infestation, which was coincident with the flight period of the insect. The trap trees were clearly attractive to S. noctilio females up to 90 d following their establishment. The MTPs that were established in November concentrated a potential population of 57 901 females of S. noctilio, which represents a population 5.4 times greater than that in the control, with 10 701 females. The population of S. noctilio attracted between November and January shows that the use of MTPs is an effective system for the management of wood wasps on plantations with a high level of infestation and thereby can reduce their spread and the attack of new trees within the same forest compartments.