BROWN ROT DISEASE DEVELOPMENT IN PEACH(P. PERSICA L. BATSCH): FROM FUNGAL BIOLOGY TO HIGH-THROUGHPUT ON-FIELDPHENOTYPING

Brown rot (BR) disease, caused by Monilinia spp., causes significant pre-and post-harvest losses in stone fruit production, especially in humid and warm temperatures. In this thesis, we tried to tackle the subject with three complementary approaches. First, the recent progress in BR resistance in peach fruit was reviewed. Then we highlighted best practices in phenotyping BR susceptibility/resistance procedures in field and in vitro. We concluded that the main factors contributing to disease development are Monilinia inocula availability, environmental conditions, cultivars, fruit stage and management practices. Secondly, we investigated the anti-fungal effect of some phenolics such as chlorogenic and ferulic acids and triterpenoids such as oleanolic, betulinic, and ursolic acids. Furthermore, fruit surface compound (FSC) extracts of peach fruit at two developmental stages on Monilinia fructicola and M. laxa characteristics during in vitro growth were studied. A new procedure for assaying anti-fungal activity of triterpenoids, which are notoriously difficult to assess in vitro because of their hydrophobicity, has been developed. Also, a follow-up of this study revealed that certain phenolics and triterpenoids showed modest anti-fungal activity while dramatically modulating M. fructicola gene expression. MfRGAE1 gene was overexpressed by chlorogenic and ferulic acids and MfCUT1 by betulinic acid at 4- and 7-days post-inoculation. The third objective was to investigate the genetic background responsible for disease resistance in peach by detecting Quantitative Trait Loci (QTL) and attempts to identify molecular markers for assisted selection (MAS) in peach. For this, three F2 progenies, derived from three selfied F1 selections obtained from "Contender" (C, resistant) × "Elegant Lady" (El, susceptible), were investigated for two seasons (2019 and 2021). The whole progeny was genotyped by Single-Primer Enriched Technology (SPET) and a recently developed 18K SNP array. The genome-wide QTL analysis showed intriguing areas relevant to disease resistance, mainly the QTLs on chromosomes 2 and 4, which may be candidates for future MAS applications. Several new QTLs were detected for other fruit quality traits, including maturity date, soluble solid content and fruit weight.