Inoculation methods for selecting Populis tremuloides resistant to hypoxylon canker

Canker expansion and the amount of callus tissue formed were measured monthly on 60 ramets from each of five trembling aspen (Populus tremuloides Michx.) clones that had been inoculated in wounds with Entoleuca mammata (= Hypoxylon mammatum (Wahl.) Mill.) over a 12-month period. At the clone level, the prevalence of nonlethal cankers within clones prior to the study had no correlation with canker expansion with three of the five clones. Greenhouse inoculation of ramets derived from the same five clones resulted in the same resistance rankings as main-stem inoculations in the field. One isolate, Hm-27, produced longer cankers, and less callus developed on all clones compared with trees inoculated with the less aggressive strain, Hm-24. Cankers developed only on clones that were inoculated during the months of April through July with April inoculations resulting in the largest cankers. These results indicate that there is a limited time frame when wounds on aspen are susceptible to infection by artificial inoculation with the pathogen as many wound inoculations neither produced cankers nor wound callus. Comparing inoculation methods, either main-stem inoculations in the field or greenhouse inoculations coupled with the natural canker prevalence could be used to include or exclude clones for use in an aspen breeding program

Virulence of Leptographium serpenson longleaf pine seedlings under varying soil moisture regimes

Recently, Leptographium serpens has been recovered from the roots of declining and dead longleaf pine (Pinus palustris) in stands associated with various abiotic stresses. Although most data suggest that L. serpens is pathogenic to various Pinus spp., there is little known of its virulence on longleaf pine or its relationship with abiotic stress in causing disease. These trials examined the effects of L. serpens infection coupled with drought stress. Trials began with wound inoculations of bareroot longleaf pine seedlings in spring 2006 and 2007 at the seedling stress facility at Auburn University. Soon after inoculation, seedlings were also subjected to adequate moisture, moderate drought, or severe drought. Sixteen weeks after inoculation, longleaf pine survival, L. serpens virulence, and seedling growth characteristics were measured. Longleaf pine seedlings inoculated with L. serpens had 33% mortality (138/420) which was significantly greater than nonwounded control seedlings (22%, 47/211). Survival and lesion size on longleaf pine suggests that L. serpens is moderately pathogenic to longleaf pine seedlings. Separately, moisture stress associated with low soil moisture also contributed to seedling mortality. Results suggest that L. serpens infection and moisture stress commonly experienced by southern pines act independently to stress longleaf pine

Indução de resistência a doenças foliares em tomateiro por indutores biótico (Bacillus subtilis) e abiótico (Acibenzolar-S-Metil) Induction of resistance in tomato by biotic (Bacillus subtilis) and abiotic (Acibenzolar-S-Metil) inducers

O objetivo deste trabalho foi investigar se doenças foliares do tomateiro (Lycopersicon esculentum) podem ser afetadas pela indução de resistência proporcionada pela aplicação de Bacillus subtilis, no solo e nas folhas e aplicação via foliar de acibenzolar-S-metil. A fim de investigar o modo de ação envolvido no controle foi avaliada a atividade de peroxidases nas folhas do tomateiro tratado com os indutores biótico e abiótico. Para se avaliar a severidade das doenças foliares foi avaliado o número de folhas de tomate com algum sintoma de doença e determinado o percentual de folhas doentes em relação ao total de folhas por planta. O aumento significativo da concentração de peroxidases nas plantas tratadas com os indutores, assim como a ausência de controle das doenças no tratamento com pulverização direta de B. subtilis nas folhas, são evidências que sugerem que o mecanismo de controle das doenças em questão está relacionado à resistência induzida.<br>This study was conduced to investigate whether the tomato (Lycopersicon esculentum) leaf diseases may be affected by the induction of resistance provided by the application of Bacillus subtilis, soil and leaf and foliar application of Acibenzolar-S-Methyl. In order to investigate the mode of action involved in the control was measured the peroxidases activity in the leaf of tomato treated with inducers biotic and abiotic. To evaluate the severity of foliar diseases has been estimated the number of leaf of tomatoes with symptoms of disease and determinate the percent of disease leaf in the total of leaf per plant. The significant increase in levels of peroxidase activity in plants exposed to treatment with inducers and lack of control of leaf diseases, in direct spray of B. subtilis in the leaves, are evidence that suggest that the mechanism of control diseases in question is related to induction resistance