Rosa Romana apple: A heritage of the apple germoplasm of the Tuscan-Emilian Apennines to be recovered and promoted

Highlights

• Pomological and molecular characterization of 47 accessions of ‘Rosa Romana’ cultivars were investigated.

• Significant differences were observed between the mountain and plain cultivars for the measured characters.

• The clustering dendrogram (UPGMA) based on the obtained data showed two main clusters for the ‘Rosa Romana’ samples.

Abstract

A molecular characterization on the ancient variety ‘Rosa Romana’ was carried out to improve biodiversity knowledge and preserve these trees from extinction risks.

In this work, 47 accessions were collected throughout an investigation in the Emilia-Romagna region (Italy) and particularly in the mountain area of the Bologna province (19 collection sites). The analysis at molecular level by using 15 SSR (microsatellites) identified two main genotype groups and ascertained their relationship with several phenotypic traits. This two clusters contained most of the collected accessions, while remaining genotypes differ clearly, according with the phenotypic diversity on the behavior of the trees or fruits.

This study also revealed the highest quality traits of ‘Rosa Romana’ apple grown in the Apennines mountain around Bologna (in a range between 400 and 1000 m.a.s.l.) if compared to each main clone produced at the lowland corresponding to the Bologna University Agricultural Experimental Station (30 m.a.s.l). Therefore, the apple quality as color, appearance, taste (flesh firmness and texture, sweetness, acidity, aroma, polyphenol soreness), were improved in the higher altitudes. In conclusion, the results of this environmental and genetic investigation on the residual cultivation of ‘Rosa Romana’ apple provided a genomic validation of its best identified clones (correspondent to the main two clusters), which now can be recovered and promoted as new planting, with a own brand ‘Rosa Romana’ produced in the Apennines mountain of north Italy.

Introduction

Apple (Malus x domestica Borkh.) is the main fruit crop of temperate regions of the world such as Europe, the west area of Turkestan and the south-east and Centre of Asia (Velasco et al., 2010), in terms of production levels. It occupies a central position as nutritional value and also in culture, art and folklore (Janick, 2005; Cornille et al., 2014). Much of the genetic diversity of the old cultivated apples is currently maintained in germoplasm repositories and amateur collections (Alessandri et al., 2016).

The ‘modern’ apple was domesticated in Central Asia from Malus sieversii (Velasco et al., 2010; Cornille et al., 2012; Volk et al., 2005, 2013) and was brought to Europe through human migrations between 6000 and 3000 years ago (Janick, 2005; Ross-Ibarra et al., 2007; Cornille et al., 2012). Humans have been exploiting, selecting, and transporting apples for centuries, and several thousand apple cultivars have been historically documented (Ross-Ibarra et al., 2007; Cornille et al., 2014). Over time, many of the ‘old’ varieties of Italian apple trees however have been marginalized and now are present only in small local area. In some cases, only single specimens of trees have survived, a memory of a glorious past, while unfortunately some genotypes have been forever lost.

The first historical quotation of a ‘Rosa’ apple in Emilia-Romagna region dates back to the 16th century, by the famous naturalist Aldrovandi and a first pictorial representation was released at the end of the 17th century by Bartolomeo Bimbi, a famous painter of the Medici’s court, who painted more than one hundred apple varieties and reported their correct names (Fideghelli, 2017).

‘Rosa Romana’ was grown in the Reno Valley for its high fruit quality (flavor, taste, texture), high storability, easy harvesting, short juvenile phases, synchronicity in blooming and fruit ripening (Gregori et al., 2013). The Reno Valley represents the propagation point of the ‘Rosa Romana’ variety. Probably because this valley was a passage area during the Roman age since it allowed the connection between the regions of Emilia-Romagna and Tuscany.

In 1929, this variety represented the 25 % of the apple production in the Bologna area. However, this apple has almost disappeared in the time frame of thirty years (Sansavini et al., 2018).

The ‘Rosa Romana’ fruit descriptor evidences a flattened shape, a short peduncle, a yellow ground color with bright red on 20–30 % of the skin (only in the mountain areas). The fruit has a thick and slightly waxy skin when the apple is ripe. Normally the peduncle cavity is covered by russeting (Fig. 1). Flesh is firm, juicy, fine, non-crispy and non-astringent. The taste highlights a well-balanced equilibrium of sweetness and acidity with a slightly bitter aftertaste. Storability without refrigeration is excellent (even till 4 months), but a controlled atmosphere it can be suggested for much longer storage. Fruits are susceptible to physiological disorders such as bitter pit, especially in young, too vigorous, over-nourished trees. The picking time is late autumn as well as the ripening time (Fideghelli, 2017; Sansavini et al., 2018).

The international literature on commercial, nutritional and genetic information relating to the ‘Rosa Romana’ variety is scanty despite its cultivation and use in the Reno Valley dates back to ancient times (at least since the Roman age).

Sansavini et al. (2018), showed like this variety currently consumed and promoted in the market by local farmers pointing out its health and gustatory qualities together with its strong link with the Reno Valley territory and history – heritage which deserves proper protection and interest.

Farneti et al. (2015) evidenced that ancient apple varieties as ‘Rosa Romana’ have a higher level of phenols compared to commercial apple cultivars. In particular, the organic acids and the phenolics compounds were significantly influenced and dependent by human selection. Bignami et al. (2001) carried out the only reported work on the variability of qualitative traits of the ‘Rosa Romana’ genotype. The analysis of nutrients and polyphenols showed the high quality of this apple.

The local germplasm of apple varieties represents a good source for breeding programs so as to guarantee the availability of a wide genetic variability (Bignami et al., 2001). To preserve this genotype, in particular, it is necessary to identify and classify the possible variables that can be differentiated over the long cultivation time.

Other two accessions grown in this area are: ‘Rosa Romana Gentile’ and ‘Rosa Nostrana’. ‘Rosa Romana Gentile’ differs from ‘Rosa Romana’ for its low russeting, the smaller extension of the red fruit skin overcolor (Fig. 1c), the greater greasiness and for its earlier ripening while ‘Rosa Nostrana’ differs from the other apple Roses for its conical fruit shape (Fig. 1b), its high greasiness after storage and for the not excellent sensorial traits, susceptible to scald.

It is important to be not confuse this apple genotypes with the other Rose apple varieties which present distinctive characteristics such as different fruits and lenticelllar shape and coloration.

As showed by Fig. 1, ‘Rosa d'Osta’ and ‘Rosa Mantovana’ differ mainly in the rounder shape compared to the flat shape of ‘Rosa Romana’ (Fig. 1d, e). In addition, ‘Rosa d’Osta’ is characterized by a scarce over-color and absence of rust. ‘Rosa d’Oliveto’ has a longer stalk and a more uniform red color diffused at lenticellar level compared to 'Rosa Romana' (Fig. 1f). Lastly, ‘Rosa Marchigiana’ presents a shorter stalk and more evident lenticels on the skin compared with ‘Rosa Romana’ fruit (Fig. 1g).

Molecular markers [Simple Sequence Repeat (SSR)] are fundamental for verifying the correct propagation in the nurseries, the true-to-type correspondence and for reducing redundancies in collections. In particular, microsatellites are considered the most suitable and useful markers for exploring the genetic diversity because they are i) abundant and well distributed in the genome; ii) codominant and multi-allelic; and iii) analyzed by multiplexed PCR (Polymerase Chain Reaction) assays (Baric et al., 2020; Testolin et al., 2019; Larsen et al., 2017; Urrestarazu et al., 2016; Patocchi et al., 2009; Hayden et al., 2008).

The aims of this work are: i) the phenotyping of the selected clones for the fruit quality traits and the relative comparison with fruits from the lowland; ii) the identification of the genetic variability present among the ‘Rosa Romana’, ‘Rosa Romana Gentile’ and ‘Rosa Nostrana’ accessions sampled in Reno Valley (hill around 400−600 m.a.s.l. and mountain area around 600–1000 m.a.s.l.).

The identification of historical trees and best reference plants for propagation are fundamental steps for the development of nursery activities. This will also promote and support the exploitation and protection of such ancient Italian apple cultivars. An increased interest in local products and ancient flavors is expected to follow.