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<jats:title>Abstract</jats:title><jats:sec> <jats:title>Main conclusion</jats:title> <jats:p>Susceptibility to neck shrivel in European plum is due to cuticular microcracking resulting from high surface area growth rates in the neck region, late in development.</jats:p> </jats:sec><jats:sec> <jats:title>Abstract</jats:title> <jats:p>Susceptibility to the commercially important fruit disorder ‘neck shrivel’ differs among European plum cultivars. Radial cuticular microcracking occurs in the neck regions of susceptible cultivars, but not in non-susceptible ones, so would seem to be causal. However, the reason for the microcracking is unknown. The objective was to identify potential relationships between fruit growth pattern and microcracking incidence in the neck (proximal) and stylar (distal) ends of selected shrivel-susceptible and non-susceptible cultivars. Growth analysis revealed two allometric categories: The first category, the ‘narrow-neck’ cultivars, showed hypoallometric growth in the neck region (i.e., slower growth than in the region of maximum diameter) during early development (stages I + II). Later (during stage III) the neck region was ‘filled out’ by hyperallometric growth (i.e., faster than in the region of maximum diameter). The second category, the ‘broad-neck’ cultivars, had more symmetrical, allometric growth (all regions grew equally fast) throughout development. The narrow-neck cultivars exhibited extensive radial cuticular microcracking in the neck region, but little microcracking in the stylar region. In contrast, the broad-neck cultivars exhibited little microcracking overall, with no difference between the neck and stylar regions. Across all cultivars, a positive relationship was obtained for the level of microcracking in the neck region and the difference in allometric growth ratios between stage III and stages I + II. There were no similar relationships for the stylar region. The results demonstrate that accelerated stage III neck growth in the narrow-neck plum cultivars is associated with more microcracking and thus with more shrivel.</jats:p> </jats:sec>

<jats:title>Abstract</jats:title><jats:sec> <jats:title>Main conclusion</jats:title> <jats:p><jats:italic>Nicotiana attenuata’s</jats:italic> capacity to interact with arbuscular mycorrhizal fungi influences its intraspecific competitive ability under field and glasshouse conditions, but not its overall community productivity.</jats:p> </jats:sec><jats:sec> <jats:title>Abstract</jats:title> <jats:p>Arbuscular mycorrhizal (AM) fungi can alter the nutrient status and growth of plants, and they can also affect plant–plant, plant–herbivore, and plant–pathogen interactions. These AM effects are rarely studied in populations under natural conditions due to the limitation of non-mycorrhizal controls. Here we used a genetic approach, establishing field and glasshouse communities of AM-harboring <jats:italic>Nicotiana attenuata</jats:italic> empty vector (EV) plants and isogenic plants silenced in calcium- and calmodulin-dependent protein kinase expression (ir<jats:italic>CCaMK</jats:italic>), and unable to establish AM symbioses. Performance and growth were quantified in communities of the same (monocultures) or different genotypes (mixed cultures) and both field and glasshouse experiments returned similar responses. In mixed cultures, AM-harboring EV plants attained greater stalk lengths, shoot and root biomasses, clearly out-competing the AM fungal-deficient ir<jats:italic>CCaMK</jats:italic> plants, while in monocultures, both genotypes grew similarly. Competitive ability was also reflected in reproductive traits: EV plants in mixed cultures outperformed ir<jats:italic>CCaMK</jats:italic> plants. When grown in monocultures, the two genotypes did not differ in reproductive performance, though total leaf N and P contents were significantly lower independent of the community type. Plant productivity in terms of growth and seed production at the community level did not differ, while leaf nutrient content of phosphorus and nitrogen depended on the community type. We infer that AM symbioses drastically increase <jats:italic>N. attenuata</jats:italic>’s competitive ability in mixed communities resulting in increased fitness for the individuals harboring AM without a net gain for the community.</jats:p> </jats:sec>