Biology And Ecology Of Furia Gastropachae A Fungal Pathogen Of The Forest Tent Caterpillar Malacosoma Disstria

Fusarium head blight (FHB) on small-grain cereals is one of the most devastating diseases. Several species can cause head blight, though Fusarium graminearum is the predominant pathogen in most regions. F. graminearum is one of the most intensively studied fungal plant pathogens. This book presents the current state of knowledge regarding mycological aspects that make wheat-Fusarium interaction, such as hyphal growth, morphogenesis in germinating spores, visualization of enzymatic hydrolysis, production of mycotoxins, inhibition of the hyphal growth by antagonist microorganisms, use of natural substances or by modification of the host resistance, as well as genetic analysis and expression of genes that regulate the infection. Fungal ecology and epidemiology will also be discussed. Just as the analysis of environmental requirements for the establishment of the disease, the use of forecasts of disease risk with meteorological base and integrated management and control. This book includes the study of disease in Latin America, therefore will be of interest to researchers who are working on the issue, as for those who are interested in knowing about the disease.

Chondrostereum purpureum is a common stem-invading fungus of trees and shrubs. The fungus has attracted interest as a bioherbicide, but a better understanding of its biology is required. This study was undertaken to determine the range of virulence of isolates of C. purpureum from a given region on major hardwood species in British Columbia. The investigators inoculated wounds of stems of standing red alder (Alnus rubra) and bigleaf maple (Acer macrophyllum) saplings with 11 isolates of the fungus and measured the resulting stem cankers as an index of virulence. They also inoculated eight hardwood and shrub species with two isolates to demonstrate the range of susceptibility of species to the fungus, as well as the intraspecific variation.

Insect outbreaks in forest ecosystems are an important natural disturbance, and the source of much timber loss. The forest tent caterpillar (Malacosoma disstria Hubner) is a major defoliator throughout the distribution of trembling aspen (Populus tremuloides Michx.), its preferred host. Forest tent caterpillar outbreaks have been shown to cause reduced growth and even mortality in the past, and recently, the presence of 'white' rings in trembling aspen have been linked to severe early season defoliation. While a good correspondence between the formation of white rings and severe defoliation has been found, white rings are, as yet, not described anatomically. In addition, white rings are presumed to be useful in the reconstruction of past forest tent caterpillar outbreaks. A study was undertaken to determine the difference between white rings and 'normal' rings in trembling aspen. White rings were also used in the spatiotemporal reconstruction of forest tent caterpillar outbreaks in the Duck Mountain Provincial Forest. To assess the difference in white ring formation and other forest tent caterpillar characteristics among vegetation and age classes, sites were sampled within four vegetation types and two age classes. White ring development in the tree stem was found to occur uniformly around the stem from the base, up to approximately 70% of the stem height at the time of white ring formation. White rings were also found to be narrower and less dense than normal rings and to have thinner fiber cell walls, smaller fiber diameter and a higher proportion of fiber lumen than normal rings. It is speculated that the growth hormones within the stem, and the re-allocation of reserves for re-foliation are affected by severe defoliation, causing a structural sacrifice. White rings were associated with all major forest tent caterpillar outbreaks in the Duck Mountain Provincial Forest, as well as many of the smaller, suspended outbreaks. Major outbreaks in the Duck Mountain Provincial Forest occurred between 1939 and 1948, 1961 and 1965 and 1982 and 1985, with another suspected major outbreak occurring during the 1870s. Smaller possible outbreaks were also observed in the 1950s 1970s and the 1990s. These outbreaks were also recorded in the balsam poplar (Populus balsamifera L.) and paper birch (Betula papyrifera Marsh.) chronologies, and white rings observed in these two species also corresponded with these periods of forest tent caterpillar outbreaks. The 1960s outbreak was different than all other outbreaks, occurring directly after a year of extreme drought, and spreading to the entire Duck Mountain Provincial Forest within a single year. The other major outbreaks were not associated with extreme drought events, and did not cause growth suppression in trembling aspen as severe as that produced during the 1960s outbreaks. In addition, during the 1960s outbreak, sites which were composed of trembling aspen and jack pine (Pinus banksiana Lamb.) recorded more severe growth suppression and white ring formation than any other stand type. The increased severity of forest tent caterpillar outbreaks in dry sites may become more important in a warmer climate, as has already been predicted. White rings, while being useful in the reconstruction of forest tent catepillar outbreaks, must be used cautiously and in addition to other markers like growth suppression, as they were not always present in trees from the same sites, nor did they occur in all sites in the Duck Mountain Provincal Forest.

For the biological control of the cassava green mite (Mononychellus tanajoa, Bondar), Brazilian strains of the entomopathogen Neozygites tanajoae were recently introduced into Africa to improve the control achieved by predatory mites. In order to monitor the establishment of the Brazilian strains two PCR primer pairs, NEOSSU_F / NEOSSU_R and 8DDC_F / 8DDC_R were tested on N. tanajoae strains collected from several locations in Brazil and from three countries in Africa, Benin, Ghana and Tanzania. The first primer pair enabled the species-specific detection of N. tanajoae, while the second differentiated the Brazilian isolates from those of other geographical origin. The results confirmed that the two primer pairs tested are suitable for the detection of N. tanajoae and the differential identification of Brazilian and African strains. PCR can therefore be used to monitor the establishment and spread of the Brazilian strains in Benin and in other African countries where they have been introduced recently in order to improve cassava green mite (CGM) control. In this work the establishment and spread of Brazilian strains of N. tanajoae were followed in a countrywide survey in Benin in which a total of 141 cassava fields were inspected. Samples of M. tanajoa suspected of being infected by N. tanajoae were found in 60 fields distributed between the coastal Southern Forest Mosaic (SFM) and the Northern Guinea Savannah (NGS) zones. PCR analysis of DNA samples extracted from samples from these fields revealed that N. tanajoae is well distributed in Benin and that Brazilian strains were effectively established and have spread throughout the country. However, the highest rates of infection due to Brazilian strains were observed in the sub-humid and humid savannah zones of the country. Identification of N. tanajoae strains using molecular tools, however, is very costly. Hence, development of alternative techniques is desirable. Therefore, the difference in biocontrol performance and in host ranges was compared to discriminate between African and Brazilian strains of N. tanajoae. The results suggest that the biocontrol potential and the host ranges bioassays are suitable for evaluating the infectiveness of N. tanajoae on cassava green mite. However, those methods were not suitable for differentiating among different origins of strains of the entomopathogenic fungus. The establishment of N. tanajoae in Benin after its introduction for the control of cassava green mite resulted in co-occurrence with the predatory mite Typhlodromalus aripo in cassava fields. However, little is known on the interaction of the two antagonists and on the biological control potential of M. tanajoa. In a series of greenhouse experiments, effects of single and combined releases of N. tanajoae and T. aripo on their respective population dynamics and on the suppression of M. tanajoa populations were evaluated. In order to complement the greenhouse experiments, laboratory experiments were conducted to evaluate the feeding, oviposition and longevity of T. aripo fed with healthy or N. tanajoae-infected M. tanajoa. The results showed that simultaneous release of T. aripo and N. tanajoae in the same cassava field may be detrimental to the biological control of the cassava green mite. It is therefore preferable to release in each area only the antagonist species known to be well adapted to the prevailing environmental conditions. In conclusion, this thesis shows that molecular techniques are the most suitable methods to detect infection of CGM by N. tanajoae and to differentiate among strains. Molecular techniques are also useful for monitoring the establishment and dispersal of introduced N. tanajoae species in the field. Furthermore, this study increased our knowledge on the performance and host ranges of the African and Brazilian strains of N. tanajoae. It also improves our understanding of the interaction between N. tanajoae and the most effective predatory mite T. aripo as both biocontrol agents are sharing the same habitats. Future research should focus on in vitro production and cryopreservation of African strains of N. tanajoae in order to develop specific primers for detecting African isolates. Furthermore, studies of the genetic diversity of N. tanajoae populations in the cassava fields using molecular techniques could strongly improve our understanding of the interaction between exotic and native fungi in the cassava ecosystem. Further investigations are required on the interaction between the predatory mite T.aripo and the pathogen N. tanajoae at a larger spatial scale and under natural conditions, and on factors affecting the loss in biocontrol potential of exotic species of N. tanajoae when introduced in their new environment.