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Susceptible Trees (susceptible + tree)
Selected AbstractsOccurrence of the wattle wilt pathogen, Ceratocystis albifundus on native South African treesFOREST PATHOLOGY, Issue 5 2007J. Roux Summary Ceratocystis albifundus causes the disease known as wattle wilt of non-native Acacia mearnsii trees in South Africa, Uganda and Kenya. Infection results in rapid wilt and death of susceptible trees and stem cankers on more tolerant trees. It has been suggested that C. albifundus is indigenous to southern Africa, possibly having spread from native Protea spp. to non-native A. mearnsii and A. decurrens trees. Although C. albifundus has been collected from Protea spp., these reports are based on limited records for which only aged herbarium specimens exist. During surveys of wound-infecting fungi on native tree species in South Africa, a fungus resembling C. albifundus was collected from Protea gaguedi, Acacia caffra, Burkea africana, Combretum molle, C. zeyheri, Faurea saligna, Ochna pulchra, Ozoroa paniculosa and Terminalia sericea. The identity of the fungus was confirmed as C. albifundus, using comparisons of DNA sequence data for the ITS and 5.8S gene of the rRNA operon. In pathogenicity trials, lesions were produced on C. molle and A. caffra, with some trees beginning to die at the termination of the experiment. This study represents the first report of C. albifundus from native tree species in South Africa and provides unequivocal evidence that the fungus occurs naturally on native Protea spp. The wide host range of C. albifundus, as well as its abundance on these indigenous hosts lends further support to the view that it is a native African pathogen. [source] Bark beetle-mediated fungal infections of susceptible trees induce resistance to subsequent infections in a dose dependent mannerAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2009Nadir Erbilgin Abstract 1,Experiments were conducted to determine whether propagule loads on the twig beetles Pityophthorus setosus and Pityophthorus carmeli (Coleoptera: Scolytidae) influence the pathogen infection of the host tree in the Monterey pine- Fusarium circinatum system. 2,On an average, F. circinatum was isolated from 2.6% and 3.3% of trapped P. setosus and P. carmeli, respectively, although the isolation percentages varied over the season, being highest in the spring and lowest in late summer and fall for both species. Mean pathogen load was 13.4 and 22.6 propagules per beetle, on P. setosus and P. carmeli, respectively, and decreased from May to November for both species. The pathogen was also isolated from approximately 55% of both beetle species that emerged from infected branches. Mean propagule load on emerged P. setosus and P. carmeli was 39 and 66.5, respectively. 3,On the basis of these data, beetle species were treated with one of three propagule loads (low, medium, high) and caged onto live branches to determine whether they could transmit the pathogen. At all propagule loads, both species transmitted the pathogen, and transmission percentage and lesion length, a measure of tree susceptibility, were positively correlated with propagule load. 4,To investigate further whether the previous transmission by beetles could affect response of the same trees to subsequent infection with F. circinatum, different branches were inoculated on the same trees used in the transmission study, and lesion lengths were measured. Lesion lengths were lower on trees that had been previously exposed to beetles treated with high or medium propagule loads than on trees that had previously been exposed to beetles treated with low propagule loads. This suggests that the initial infection by beetles carrying high or medium propagule loads induced resistance to subsequent infections of the host, whereas infections caused by beetles with low propagule loads did not. [source] The control of sirex wood wasp using biological control agents in Victoria, AustraliaAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 3 2009N. G. Collett Abstract 1,The sirex woodwasp, Sirex noctilio has been a significant pest of radiata pine plantations in Victoria since 1961. Outbreaks are usually associated with susceptible trees being under some form of stress including the effects of drought and overcrowding. 2,This paper reviews the spread of sirex and the history and efficacy of biological control programmes implemented against sirex in Victoria from 1970 to 2006. 3,Of the numerous biological control agents released, the most effective in managing sirex have been the nematode Beddingia siricidicola and the parasitic wasp Ibalia leucospoides. Several other parasitic wasps such as Schlettererius cinctipes and Megarhyssa nortoni nortoni have also established but provide only minimal control. 4,While rates of I. leucospoides parasitism have improved over time, it is unlikely that this improvement will continue substantially past current levels. 5,In recent years, issues have arisen regarding a decline in the infectivity of B. siricidicola necessitating a re-evaluation of strategies and development of techniques to overcome this problem. 6,Ongoing research using Random Amplification of Polymorphic DNA (RAPD) testing is underway to accurately determine nematode strains and associated infectivity present in plantations in the field in order to develop management strategies to re-introduce more effective strains. [source] Differential defoliation of Eucalyptus grandis arises from indiscriminant oviposition and differential larval survivalAGRICULTURAL AND FOREST ENTOMOLOGY, Issue 1 2009M. L. Henery Abstract 1,The influence of six open-pollinated families (OPFs) of Eucalyptus grandis on both the growth and development of larvae and the oviposition preference of a paropsine chrysomelid (Paropsis atomaria) was investigated. The OPFs had previously been identified as differing in their susceptibility to defoliation by P. atomaria in forestry progeny trials. 2,Oviposition preference for resistant and susceptible foliage was tested using binary choice tests. These tests did not demonstrate any significant preference for either resistant or susceptible open-pollinated material indicating that adult host preference for susceptible trees was not a likely cause of differential defoliation. 3,Quantification and analysis of growth and development parameters for all larval stages of P. atomaria showed that feeding on genetic material identified as resistant resulted in a significant reduction of relative growth rate of first instar larvae and an alteration to normal feeding behaviour. There was also a trend towards increased larval mortality on resistant E. grandis. 4,We argue that although the magnitude of these effects was minor, interactions with additional biotic and abiotic sources of mortality in the field have the potential, when magnified over successive generations, to result in significant variation in defoliation of host genotypes in the field. [source] Variations in bark-stripping by red deer Cervus elaphus across EuropeMAMMAL REVIEW, Issue 3 2006HÉLÈNE VERHEYDEN ABSTRACT 1The literature on bark-stripping by red deer Cervus elaphus in Europe is reviewed to reveal quantitative variation in this behaviour and relate it to deer density and local characteristics such as dominant tree species, occurrence of artificial feeding, altitude, region and size of the study site. We also review the importance of bark in red deer diets over the seasons and discuss the causes of bark-stripping, focusing on the significance of bark as food. 2Over the 36 sites examined, the rate of bark-stripping was highly variable (from 0 to 84% of susceptible trees debarked), with less damage in Scotland than in other European sites for which bark-stripping rates were higher at high red deer density. Altitude, the size of the study site, the number of dominant tree species and the occurrence of artificial feeding do not significantly relate to the rate of bark-stripping. 3Bark sometimes made up a large proportion of red deer diet (> 10%), especially in areas with severe winters (high levels of snow), whereas in study sites with mild winters, bark was practically not eaten at all. 4These results suggest that severe bark-stripping could be related to a reduction in food resource availability. This food availability hypothesis needs to be better documented, dealing particularly with the possible interaction between food availability and red deer density. [source] | ||||||||||