Epigenetic variation in guava (Psidium guajava) genotypes during the vegetative and reproductive phases of the production cycle
Psidium guajava (guava) is a fruit tree of the Myrtaceae family of nutritional and economic importance and wide edaphoclimatic adaptation. For commercial orchard purposes, guava trees are derived from clonal propagation and the production cycle begins with drastic pruning. During its development the guava tree displays varied characteristics that may involve epigenetic mechanisms, such as DNA methylation, revealed by the formation of 5-methylcytosine (5-mC). In order to understand the variability of this mechanism, the %5-mC was evaluated in 22 guava genotypes from a working collection, in an experimental orchard, over five development stages – post-pruning, flowering, fructification, harvest and post-harvest – and subsequently in different tissues. Wide variation in DNA methylation was detected among the genotypes. Hypermethylation was found in one, whereas methylation and demethylation mechanisms were observed in 10 genotypes. Greater variability in DNA methylation among genotypes was found during the vegetative phase, mainly after pruning. On the other hand, uniformity was observed among the genotypes with regards to global DNA methylation during flowering, indicating that this mechanism is conserved in this specific phase. No differences in global DNA methylation was detected in the different plant tissues. In this study, the global epigenetic mechanisms of P. guajava were detected more frequently in vegetative than in reproductive phases. Important Brazilian cultivars such as Paluma, Pedro Sato, Sassaoka and Cortibel SLG exhibit changes in their methylation profiles during their production cycle. Others show greater stability, for instance Século XXI and six Cortibel cultivars, suggesting the possibility of selection for this characteristic. Furthermore, the methylation and demethylation mechanisms of adult guava plants indicate the relevance of epigenetics for the wide edaphoclimatic adaptation of the species. In addition, the clonal propagation of guava may provide an opportunity for the development of this crop through epibreeding approaches.