Breeding strategies for identifying superior peach genotypes resistant to brown rot
Introduction
The storage life and commercial shelf life of the peach [Prunus persica (L.) Batsch] are negatively influenced by pre- and post-harvest diseases that are principally associated with brown rot (Sisquella et al., 2014). Brown rot of stone fruits is a disease primarily caused by Monilinia species, such as: M. laxa (Aderh. and Ruhland) Honey; M. fructigena Honey; M. fructicola (G. Winter) Honey and M. polystroma (G. Leeuwen) L.M. Kohn (Jansch et al., 2012). In peach, the pathogen initiates and encourages flower blights, twig and branch death, spurs, and fruit rot in the field (Gell et al., 2007). The activity of the pathogen on peach is therefore highly destructive from the flowering stage, to fruit production, and storage (Thomidis and Exadaktylou, 2010; see Obi et al., 2018b for a review).
In Spain, M. laxa and M. fructicola have been the most recurrent pathogens since the dislodgment of M. fructigena from Spain in 2010 (Villarino et al., 2013). These species cause over 60% fruit loss after harvest (Villarino et al., 2012; Egüen et al., 2015), mostly under favourable environmental conditions for the commencement and growth of diseases in orchards.
Host tolerance to plant pathogens is important for the development of cost effective and environmentally safe strategies for disease management (Gradziel, 1994). Similarly, according to Gell et al. (2007) the use of resistant cultivars in crop improvement is critical for crop protection, since plants and plant products are usually protected from (prophylactic) (Mooney et al., 2012), rather than cured of, diseases (chemotherapeutic) (Obi et al., 2018b). The choice of cultivar significantly influences rot incidence and severity among other potential factors in stone fruits (Tarbath et al., 2014). and, therefore, are effective at disease control (Kreidl et al., 2015). The long-term prophylactic treatment of peach, using M. laxa resistant cultivars, will ensure prevention of pathogenic problems in orchards. Resistant genotypes will allow sustainable control with zero pesticide residues on fruits, improving the safety of harvesting and decreasing disease problems during storage, thereby leading to enhanced economic benefits. The total absence of pesticide residues in prophylactic resistant peach cultivars would be environmentally beneficial (Usall et al., 2016). However, disease resistant cultivars are not readily available for many fruit crops (Spiers et al., 2005), including commercial peach cultivars.
Developing peach cultivars that are resistant to M. laxa pathogen requires, in the first instance, the identification of existing resistant and susceptible genotypes by screening individuals from a germplasm (Rubos et al., 2008). Although most commercial peach cultivars are susceptible to Monilinia spp., a few resistant cultivars have been identified (Gradziel and Wang, 1993; Martínez-García et al., 2013; Oliveira-Lino et al., 2016; Obi et al., 2017). The relative tolerance or susceptibility of fruit to disease has therefore often been used to select disease resistant genotypes for the purpose of breeding peach (Gradziel, 1994). Selection within breeding descendant populations has been carried out for both peach and nectarine (Bassi et al., 1998; Pacheco et al., 2014; see Oliveira-Lino et al., 2016 and Obi et al., 2018b for details), and for other fruit germplasm such as apricot (Walter et al., 2004), plum (Pascal et al., 1994), and apple (Biggs and Miller, 2004). Previous studies have demonstrated that powerful antioxidants such as phenolic acids, flavonoids, and anthocyanins are present in the phytochemical compounds produced by peach cultivars (Giménez, 2013; Ágreda, 2016; Saidani et al., 2017). These bioactive compounds, especially chlorogenic and neochlorogenic acids, may confer important preservative functions during postharvest handling in the peach industry (Villarino et al., 2011; Pacheco et al., 2014; see Oliveira-Lino et al., 2016 and Obi et al., 2018b, in details). In addition, considering the recent drive for alternative technologies that can effectively control postharvest diseases of stone fruits (Mari et al., 2015; Usall et al., 2015, 2016), any evidence regarding compounds inhibitory to brown rot development would influence breeding schemes, and would be useful for the postharvest peach industry.
There is limited information on peach pathogenic tolerance to M. laxa brown rot in their breeding descendants, and their relationships with quality and phytochemical traits in fruits during postharvest handling. This study aimed to identify superior Spanish peach cultivars that exhibit high tolerance to M. laxa brown rot, and possess high levels of antioxidants. The specific objectives of this work, therefore, were to evaluate tolerance to Monilinia laxa brown rot within the breeding descendant population of ‘Babygold 9’ × ‘Crown Princess’, and to examine whether fruit quality and phytochemical composition correlate with pathogen tolerance. Finally, the identification of biochemical compounds associated with brown rot tolerance would impact breeding strategies, beneficial to the postharvest industry, and facilitate environmental sustainability.
Section snippets
Plant material
The plant materials are progenies from a controlled biparental cross of two commercial cultivars, ‘Babygold 9’ × ‘Crown Princess’ (B9 × CP). These genotypes were propagated during 2000 and 2001 in collaboration with Agromillora Catalana S.L. (Barcelona, Spain). Both the progenitors and the entire progeny are yellow fleshed, clingstone peach. The resulting seedlings were budded on GF677 rootstock, and established in 2002 at the Estación Experimental de Aula Dei-CSIC (Zaragoza, Spain). Trees were
Results
We studied a total of 68 descendants from the ‘Babygold 9’ × ‘Crown Princess’ population over a period of 3 years (2013, 2014, and 2015) for tolerance to Monilinia laxa brown rot (Supplementary Table 1). The disease parameters used included: %BRI, LD, LS, %C, CEx, and CS. As previously mentioned, we selected 17 genotypes that exhibited a M. laxa LS of < 40 mm, either in 2013 or 2014, or with the mean value for both years (Supplementary Table 2), to evaluate and validate the M. laxa tolerance of
Discussion
The annual disparity found in the responses of the genotypes to brown rot after inoculation may be due to different levels of cuticular cracking or fractures, as has been reported for stone fruits by other authors (Gradziel et al., 2003; Kappel and Sholberg, 2008). Cuticular cracks are considered to be the preferential portal of entry for fungi pathogens in the Monilinia genus (Gibert et al., 2007), and the incidence of fruit infection increases with increasing fruit cuticular crack surface
Conclusions
The selection of genotypes for peach breeding that are rich in bioactive compounds, and which are possess brown rot tolerance, may avoid negative outcomes in the industry, and provide safe alternative to the use of pesticides. Based on our 3-year screening protocol, we found phenotypic differences in the susceptibility to brown rot caused by Monilinia laxa in the ‘Babygold 9’ × ‘Crown Princess’ population. It was also found that FF decreased due to 5 days of storage and to the activity of M.
Funding
This work was financed by the MINECO and the Government of Aragón with projects AGL2014-52063-R; AGL2017-83358-R and A44; co-financed with FEDER and ESF, respectively.
Acknowledgments
Thanks to L. Ágreda and R. Giménez for technical assistance, Dr. M. A. Moreno (EEAD-CSIC), the Agromillora Group for providing plant material, and the Collection of Postharvest Pathology Group of IRTA (Lleida, Spain) for supply of the initial inoculum. The Research Center and Food Technology of Aragón (CITA) allowed us the use of its plant protection facilities. We thank all of them for their assistance.
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