Abstract
Sweet cherry is an important non-climacteric fruit with a high commercial interest, but exploitation of sweet cherry trees (Prunus avium L.) in orchards is usually subject to important economic losses due to fruit decay by pathogenic fungi and other microorganisms. Sweet cherries development and ripening are characterized by profound physiological changes in the fruit, among which the phytohormone abscisic acid (ABA) plays a pivotal role. In addition, sweet cherries are usually affected by fruit decay pathogens, and the role of other stress-related hormones such as jasmonic acid (JA) and salicylic acid (SA) may also be of paramount importance, not only from a developmental point of view, but also from a fruit-microbe interaction perspective. Here, a tissue-specific hormone quantification by LC-MS/MS, including the contents of JA, SA, and ABA, in the fruit exocarp and mesocarp of sweet cherries during fruit development from trees growing in a commercial orchard was carried out. Additionally, this study was complemented with the characterization of the culturable epiphytic and endophytic microbial communities of sweet cherries at various stages of fruit development and during cracking lesion formation. Our results revealed a completely differential behavior of phytohormones between both tissues (the exocarp and mesocarp), with a more dynamic exocarp in front of a more stable mesocarp, and with marked variations during fruit development. Microbial epiphytic community was mainly composed by yeasts, although rot-causing fungi like Alternaria spp. were always also present throughout fruit development. Endophytic colonization was poor, but it increased throughout fruit development. Furthermore, when the exocarp was naturally disrupted in sweet cherries suffering from cracking, the colonization by Alternaria spp. markedly increased. Altogether, results suggest that the fruit exocarp and mesocarp are very dynamic tissues in which endogenous phytohormones not only modulate fruit development and ripening but also fruit-microbe interactions.
Highlights
Sweet cherry (Prunus avium L.) is an important stone fruit crop which has recently received increased interest due to both its organoleptic and visual characteristics and high nutritional value (Kelley et al, 2018)
A fruit tissue-specific behavior of two of the major phytohormones related with plant-microbe interactions, jasmonic acid (JA) and salicylic acid (SA), was observed in cherry fruits during fruit development in a commercial tree orchard
We provide here evidence of variations in the endogenous contents of JA, SA, and abscisic acid (ABA) in the exocarp and mesocarp of sweet cherries and examine its possible relationship with the interaction of the exocarp and mesocarp of these fruits with its own microbiome and potential rot-causing pathogens
Summary
Sweet cherry (Prunus avium L.) is an important stone fruit crop which has recently received increased interest due to both its organoleptic and visual characteristics and high nutritional value (Kelley et al, 2018). Plant-microbe interactions and their underlying mechanisms are increasingly receiving attention in the exploitation of commercial orchards of stone fruity trees because of their economic relevance. In this respect, plant pathogens, which are able to colonize the plant inner tissues causing disease to the host (Schlechter et al, 2019), and epiphytic microorganisms, those that live on the plant surfaces, and endophytes, when they colonize inner tissues without affecting the host’s fitness (Takken and Rep, 2010), may play a major role. Physical barriers and immunity are tightly interconnected, so that when physical barriers fail, immune responses such as pathogen associated molecular pattern (PAMP)‐ and effectortriggered immunity (PTI and ETI, respectively) take place to halt the microbial invasion (Bigeard et al, 2015; Cui et al, 2015)
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