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Many ectomycorrhizal fungi (EMF) are generalists, but most plant genera that form ectomycorrhizas have at least some fungal partners that are specific to that host genus. Because shared mycorrhizal fungi mediate plant community interactions, host preference has implications for plant succession and competition. We studied the EMF of oaks (Quercus spp.) and pines (Pinus spp.) in a forest in northern Florida, USA, focusing on symbionts shared with longleaf pine (Pinus palustris Mill.). Longleaf pine is an important species in the southeastern USA, both for timber plantations and for restoring savanna and woodland habitat. However, we found no research on the composition of naturally occurring EMF on longleaf pine roots. A lower proportion of EMF operational taxonomic units (OTUs) were found colonizing both oaks and pines than expected, providing evidence of host preference within the community. Although most EMF were detected only on either oaks or pines, the OTUs found on both tended to be frequently occurring and abundant. Cenococcum OTUs were found to be significantly associated with oaks, an unexpected finding as this genus is widespread, with a broad host range. These results suggest that host preference of EMF may structure EMF communities and therefore influence ecosystem effects of mycorrhizal networks. Key words: host specificity, host preference, ectomycorrhizal fungi, mycorrhizal networks, Pinus palustris. Plusieurs champignons ectomycorhiziens (CEM) sont des generalistes mais la plupart des genres de vegetaux qui forment des ectomycorhizes comptent au moins un certain nombre de partenaires fongiques specifiques a un genre hote donne. Parce que les champignons mycorhiziens partages sont a la base des interactions dans les communautes vegetales, la preference pour un hote a des repercussions sur la competition et la succession chez les plantes. Nous avons etudie les CEM des chenes (Quercus spp.) et des pins (Pinus spp.) dans une foret du nord de la Floride, aux Etats-Unis. Nous avons mis l'accent sur les symbiotes partages avec le pin des marais (Pinus palustris Mill.). Le pin des marais est une espece importante dans le sud-est des Etats-Unis pour la production de bois en plantation et la restauration des savanes et des habitats boises. Cependant, nous n'avons trouve aucune etude portant sur la composition des CEM naturellement presents sur les racines du pin des marais. La proportion d'unites taxonomiques operationnelles (OTU) de CEM qui colonisaient autant les chenes que les pins etait plus faible que ce qui avait ete anticipe, ce qui constitue un indice d'hote preferentiel au sein de la communaute. Bien que la plupart des CEM aient ete detectes exclusivement soit sur les chenes, soit sur les pins, les OTU trouvees sur les deux avaient tendance a etre presentes frequemment et de nombreuses OTU de Cenococcum etaient associees de facon significative aux chenes, un resultat inattendu etant donne que ce genre est largement repandu et possede une vaste gamme d'hotes. Ces resultats indiquent que la preference des CEM pour un hote peut structurer les communautes de CEM et par consequent influencer les effets des reseaux mycorhiziens sur l'ecosysteme. [Traduit par la Redaction] Mots-cles : specificite de l'hote, preference pour un hote, champignons ectomycorhiziens, reseaux mycorhiziens, Pinus palustris., Introduction Specificity in species' interactions is important in understanding community ecology, coevolution, and even predicting extinction risk (Molina et al. 1992; Bruns et al. 2002; Thompson 2009; Devictor et al. [...]

Sprayable formulation of 1-methylcyclopropene (1-MCP) was tested as a preharvest application on European pears to determine the best timing and rate of 1-MCP application for maintaining fruit firmness and quality of trees during harvest and in storage after harvest. Two rates of 1-MCP, 0.06 and 0.13 g.L-1 active ingredient (a.i.) (minimum and maximum rates, respectively), were sprayed 1 week and 2 weeks before commercial harvest on two cultivars, Bosc and Comice, in 2017 and 2018. After 2 months in cold storage (0 ± 1° C), differences in fruit firmness of both cultivars were observed among treatments. For ‘Bosc’, fruit treated with both rates 1 week before harvest were 50% firmer than nontreated control fruit. For ‘Comice’, fruit treated with the maximum rate both 2 weeks and 1 week before commercial harvest were 46% and 31% firmer than nontreated control fruit, respectively. However, after 4 months in storage, no differences in fruit firmness of both ‘Bosc’ and ‘Comice’ were observed among treatments. The sprayable 1-MCP application applied 2 weeks before commercial harvest also affected the fruit firmness on trees. The maximum rate of 1-MCP treatment consistently maintained the fruit firmness by 5.0 N compared with fruit treated with the minimum rate and nontreated controls. This effect was significant until 1 week after commercial harvest for both cultivars and until 2 weeks after commercial harvest for ‘Bosc’. The poststorage fruit firmness and overall eating quality of ‘Bosc’ were unaffected by the maximum rate of 1-MCP application as well as the extended harvest time. However, for ‘Comice’, the overall eating quality was negatively impacted by 1-MCP treatments. This study suggests that the maximum rate (0.13 g.L-1 a.i.) of 1-MCP application 2 weeks before commercial harvest maintains the fruit firmness of ‘Bosc’ for at least 2 weeks more and offers an extended harvest window for better preharvest management. Furthermore, this treatment improves the physiological fruit quality such as senescence scald during the poststorage period without significantly affecting the poststorage ripening of ‘Bosc’ after 4 months of storage. [ABSTRACT FROM AUTHOR]