Physiological aspects underlying the improved outplanting performance of Pinus pinaster Ait. seedlings associated with ectomycorrhizal inoculation.

Mycorrhizal inoculation of conifer roots is a key strategy to optimize establishment and performance of forest tree species under both natural and cultivated conditions and also to mitigate transplantation shock. However, despite being a common practice, inoculation in outdoor nursery conditions has been poorly studied. Here, we have evaluated effectiveness of four fungal species (Lactarius deliciosus, Lactarius quieticolor, Pisolithus arhizus, and Suillus luteus) in the production of mycorrhizal Pinus pinaster seedlings in an outdoor commercial nursery and their ability to improve seedling physiology and field performance. All inoculated seedlings showed a significant increase in growth at the end of the nursery stage and these differences remained after 3 years of growth in the field. Differences observed in the content of malondialdehyde, total chlorophyll, carotenoids, anthocyanins, and phenolic compounds from needles of mycorrhizal and control seedlings may reflect a different sensitivity to photo-oxidative damage. We conclude that ectomycorrhizal inoculation improves adaptability to changeable growing conditions of an outdoor nursery and produces a higher quality nursery stock, thereby enhancing seedling performance after planting.

Spatial and temporal dynamics of the colonization of Pinus radiata by Fusarium circinatum, of conidiophora development in the pith and of traumatic resin duct formation.

· Fusarium circinatum causes pitch canker disease in a wide range of pine trees, including Pinus radiata, with devastating economic consequences. · To assess the spatial and temporal dynamics of growth of this pathogen in radiata pine, we examined the process of infection using both real-time PCR to quantify fungal biomass inside the plant host, and confocal microscopy using a green fluorescent protein (GFP)-tagged strain of F. circinatum. · Pathogen growth exhibited three distinct phases: an initial exponential increase in fungal biomass, concomitant with pathogen colonization of the cortex and phloem; a slowdown in fungal growth coincident with sporulating hyphae deep within the host; and stabilization of the fungal biomass when the first wilting symptoms appeared. The number of resin ducts in the xylem was found to increase in response to infection and the fungus grew inside both constitutive and traumatic resin ducts. · These results indicate that conidiation may contribute to the spatial or temporal dissemination of the pathogen. Moreover, the present findings raise the intriguing possibility that the generation of traumatic resin ducts may be of more benefit to the fungus than to the plant.

fost12, the Fusarium oxysporum homolog of the transcription factor Ste12, is upregulated during plant infection and required for virulence.

We have identified a Fusarium oxysporum homolog of the Ste12 transcription factor that regulates mating and filamentation in Saccharomyces cerevisiae. The corresponding gene, fost12, from a highly virulent strain of F. oxysporum f. sp. phaseoli, was confirmed to share a high level of similarity and possessed the STE and C2H2 domains characteristic of the fungal Ste12 transcription factor family of proteins. Disruption of fost12 resulted in no visible alterations of colony morphology or in vitro growth characteristics. However, the disruption mutants showed a substantial reduction in virulence when inoculated in common bean seedlings. In planta transcription of fost12 is drastically increased between 12 and 24h after inoculation, as detected by real-time RT-PCR. The results of the transcriptional analyses carried out in several F. oxysporum strains during axenic growth suggest that the fost12 gene product is a virulence factor required to deal with the nutritional stress confronted by the pathogen during host plant colonization.

The gene coding for a new transcription factor (ftf1) of Fusarium oxysporum is only expressed during infection of common bean.

We report the isolation and analysis of the gene encoding ftf1 (Fusarium transcription factor 1), a previously undescribed putative transcription factor from highly virulent strains of Fusarium oxysporum f.sp. phaseoli that is transcribed specifically during early stages of infection of its host common bean (Phaseolus vulgaris L.). The predicted 1080 amino acid ftf1 protein contains a Zn(II)2-Cys6 binuclear cluster DNA-binding motif. ftf1 expression during axenic growth in culture was not detected by either Northern or RT-PCR. On the contrary, in planta transcription of ftf1 is increased about 24h after plant inoculation, as detected by real-time RT-PCR. This result suggests that ftf1 has a role in the establishment of the fungus within the plant and/or the progress of the disease. Multiple copies of ftf1 are present in highly virulent strains of F. oxysporum f.sp. phaseoli.