PCR–RFLP and Sequence Data Delineate Three Diaporthe Species Associated with Stone and Pome Fruit Trees in South Africa

Diaporthe species include canker pathogens on a wide variety of hosts. In South Africa, Diaporthe canker of apple, pear and plum rootstocks has been attributed to Diaporthe ambigua. Recently, we recognized that isolates of D. ambigua exhibited different morphological features and thus questioned the identity of these isolates. A small set of isolates was thus chosen for comparison using DNA-based methods. Polymerase chain reaction amplification of ribosomal DNA, Restriction Fragment Length Polymorphisms and DNA sequencing revealed that isolates which had been regarded as D. ambigua in the past were three distinct species. These are D. ambigua, D. perjuncta and an unknown Phomopsis sp. This discovery has special relevance to research done on a dsRNA virus previously thought to occur in D. ambigua and now shown to infect D. perjuncta.     

Microsatellite and mating type markers reveal unexpected patterns of genetic diversity in the pine root‐infecting fungus Grosmannia alacris

Grosmannia alacris is a fungus commonly associated with root‐infesting bark beetles occurring on Pinus spp. The fungus has been recorded in South Africa, the USA, France, Portugal and Spain and importantly, has been associated with pine root diseases in South Africa and the USA. Nothing is known regarding the population genetics or origin of G. alacris, although its association with root‐infesting beetles native to Europe suggests that it is an invasive alien in South Africa. In this study, microsatellite markers together with newly developed mating type markers were used to characterize a total of 170 isolates of G. alacris from South Africa and the USA. The results showed that the genotypic diversity of the South African population of G. alacris was very high when compared to the USA populations. Two mating types were also present in South African isolates and the MAT1‐1/MAT1‐2 ratio did not differ from 1:1 (χ² = 1·39, P = 0·24). This suggests that sexual reproduction most probably occurs in the fungus in South Africa, although a sexual state has never been seen in nature. In contrast, the large collection of USA isolates harboured only a single mating type. The results suggest that multiple introductions, followed by random mating, have influenced the population structure in South Africa. In contrast, limited introductions of probably a single mating type (MAT1‐2) may best explain the clonality of USA populations.     

Risk assessment for Puccinia psidii becoming established in South Africa

Puccinia psidii, the causal agent of myrtle rust, was first recorded from Latin America more than 100 years ago. It occurs on many native species of Myrtaceae in Latin America and also infects non‐native plantation‐grown Eucalyptus species in the region. The pathogen has gradually spread to new areas including Australia and most recently South Africa. The aim of this study was to consider the susceptibility of selected Eucalyptus genotypes, particularly those of interest to South African forestry, to infection by P. psidii. In addition, risk maps were compiled based on suitable climatic conditions and the occurrence of potential susceptible tree species. This made it possible to identify the season when P. psidii would be most likely to infect and to define the geographic areas where the rust disease would be most likely to establish in South Africa. As expected, variation in susceptibility was observed between eucalypt genotypes tested. Importantly, species commonly planted in South Africa show good potential for yielding disease‐tolerant material for future planting. Myrtle rust is predicted to be more common in spring and summer. Coastal areas, as well as areas in South Africa with subtropical climates, are more conducive to outbreaks of the pathogen.     

Population variation in traits of Deladenus siricidicola that could influence the biocontrol of Sirex noctilio in South Africa

Deladenus siricidicola is the primary biocontrol agent of the invasive woodwasp, Sirex noctilio. The nematode is mass-reared in culture on the S. noctilio symbiotic fungus, A. areolatum, but can also be induced to convert into its infective form in culture. The aim of this study was to explore the level of variation among a collection of D. siricidicola strains to convert into the infective form in culture. In addition, we measured variation in growth of the nematode on a strain of A. areolatum that is commonly used for laboratory rearing. Both traits could influence laboratory rearing and efficiency in the field. The 22 strains from three countries showed significant variation in the frequency of conversion into the infective form in culture. Even genetically uniform strains from South Africa displayed a range of variation in this trait. There was also significant variation in the growth of D. siricidicola on A. areolatum. These results emphasise the importance of considering variation in traits in D. siricidicola that could influence a biological control program. They also provide tools that could be used to screen larger collections of D. siricidicola for variation in traits linked to virulence and reproduction.     

A new genus of Cryphonectriaceae isolated from Lagerstroemia speciosa in southern China

Numerous species in the Cryphonectriaceae have been recorded on the Myrtales and many of these are economically important pathogens of Eucalyptus. Some species have also recently been shown to be endophytes of native Myrtaceae and to have undergone host jumps to infect Eucalyptus species established as exotics in plantations. Recent surveys in the GuangDong and HaiNan Provinces of South China reveal the presence of a species of Cryphonectriaceae associated with cankers on trees of Lagerstroemia speciosa (Lythraceae, Myrtales). Fungal structures were observed on the surface of dead bark covering cankers and on branch stubs. Multigene phylogenetic analyses were conducted based on DNA sequence comparisons of the partial LSU gene, ITS region of the nuclear ribosomal RNA gene and two regions of the β‐tubulin (BT) gene. The results revealed the presence of a previously undescribed genus and species in the Cryphonectriaceae. The fungus is described here as Chrysomorbus lagerstroemiae gen. et sp. nov. Inoculation tests showed that it is an aggressive pathogen on L. speciosa and that it can also infect Eucalyptus.     

Genetic uniformity characterizes the invasive spread of Neofusicoccum parvum and Diplodia sapinea in the Western Balkans

In the past decade, trees and shrubs in the Western Balkans region have been damaged by canker and die‐back disease caused by Botryosphaeriaceae species. These pathogens include Neofusicoccum parvum and Diplodia sapinea. In this study, we determine genetic diversity and structure between populations of N. parvum and D. sapinea from Serbia and Montenegro (Western Balkans) using DNA sequence data of the internal transcribed spacer rDNA, translation elongation factor 1‐alpha, β‐tubulin‐2 and microsatellite markers. The relationship of both pathogens was compared for populations from the Continental (CR) and Mediterranean (MR) regions and for isolates of D. sapinea from Cedrus spp. and Pinus spp. Neofusicoccum parvum and D. sapinea were shown to have a low gene and genotypic diversity across the regions and hosts. All genotypes of D.  sapinea found on Pinus spp. were also present on Cedrus spp. The CR and MR populations of both species were found to be only slightly separated from one another by a geographical barrier. Low genetic diversity and dominance of N. parvum and D. sapinea on non‐native trees suggests that these species have most likely been introduced into Western Balkans, possibly through the movement of infected plants.     

Effects of the aqueous extracts of Zygophyllum fabago on the growth of Fusarium oxyosporum f. sp. melonis and Pythium aphanidermatum

In this study, the effects of aqueous extracts from Zygophyllum fabago L. on two plant phytopathogenic fungal species (namely, Fusarium oxyosporum f. sp. melonis and Pythium aphanidermatum) were studied under laboratory conditions. The plant extracts (10% w/v) were prepared by using deionized water and fresh tissues. Dilutions (2, 4, 6, and 8% w/v) were obtained to test their effect on the mycelial growth of the phytopathogenic species. Additionally, the recovery of the fungi after their exposure to the Z. fabago extract was analyzed. The plant extracts inhibited the growth of F. oxyosporum and P. aphanidermatum (the maximum mean inhibition that was recorded with the 10% w/v extracts was 42.9% and 85.3%, respectively). A second series of experiments demonstrated the existence of residual effects in both species. The amount of residual inhibition by the 10% w/v extracts was 28.6% in F. oxyosporum and 53.8% in P. aphanidermatum. A dose–response was clearly observed in P. aphanidermatum, while an increase in extract concentration was not associated with a significantly greater reduction in the growth of F. oxyosporum. These findings give insights into the potential of Z. fabago as a growth inhibitor of F. oxyosporum and P. aphanidermatum, thus suggesting an interesting potential role for this common weed as a source of natural fungicides.     

Biology of Litosermyle ocanae in Colombian Pinus patula plantations

Plantations of Pinus spp. in Colombia are severely damaged by various phasmid (Phasmatodea: Diapheromeridae) insects. Of these, Litosermyle ocanae is one of the most serious defoliators. Since 1988, several outbreaks have been recorded in Pinus patula plantations, resulting in substantial economic losses. The aim of this study was to determine the life cycle of Litosermyle ocanae in P. patula plantations in Colombia. In addition, we assessed the population levels of L. ocanae and the presence of natural enemies of L. ocanae in these plantations. The development of L. ocanae was monitored under controlled conditions, and population fluctuations and the presence of natural enemies was assessed from field-collected eggs and field observations. The results showed a total life cycle of 225 d and 235 d for males and females, respectively, and a complete fourth instar nymph cycle of 121 d and 116 d for males and females, respectively. The sex ratio was 1:1.7 female to male. Females laid an average of 112 eggs. The number of eggs peaked in November and the most dominant natural enemy observed was a parasitoid wasp Adelphe sp. (Hymenoptera: Chrysididae). The results provide important information for the management of L. ocanae in P. patula plantations.