‘lucía myrtea’ and ‘victoria myrtea’: Two New Japanese Plum Cultivars with Low Chilling Requirements, Early Ripening, and High-quality Fruit for the Fresh Market

HORTSCIENCE 56(11):1453–1455. 2021. https://doi.org/10.21273/HORTSCI16017-21 ‘luc ıamyrtea’and ‘victoria myrtea’: Two New Japanese Plum Cultivars with Low Chilling Requirements, Early Ripening, and High-quality Fruit for the Fresh Market Alfonso Guevara Department of Biotechnology, Genomics and Plant Breeding, Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA), C/Mayor, s/n. 30150 La Alberca (Murcia), Spain Mar ıa Nicol as-Almansa Department of Plant Breeding, Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBASCSIC), P.O. Box 164, E-30100, Espinardo, Murcia, Spain Jos e Enrique Cos Department of Biotechnology, Genomics and Plant Breeding, Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA), C/Mayor, s/n. 30150 La Alberca (Murcia), Spain Juan Alfonso Salazar Department of Plant Breeding, Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBASCSIC), P.O. Box 164, E-30100, Espinardo, Murcia, Spain Domingo L opez Department of Biotechnology, Genomics and Plant Breeding, Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA), C/Mayor, s/n. 30150 La Alberca (Murcia), Spain Jos e Egea Department of Plant Breeding, Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBASCSIC), P.O. Box 164, E-30100, Espinardo, Murcia, Spain Antonio Carrillo Department of Biotechnology, Genomics and Plant Breeding, Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA), C/Mayor, s/n. 30150 La Alberca (Murcia), Spain Manuel Rubio Department of Plant Breeding, Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBASCSIC), P.O. Box 164, E-30100, Espinardo, Murcia, Spain Federico Garc ıa Department of Biotechnology, Genomics and Plant Breeding, Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA), C/Mayor, s/n. 30150 La Alberca (Murcia), Spain David Ruiz Department of Plant Breeding, Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBAS-CSIC), P.O. Box 164, E-30100, Espinardo, Murcia, Spain Additional index words. adaptation, fruit quality, Japanese plum breeding, Prunus salicina, ripening time, self-compatibility ‘luc ıamyrtea’and ‘victoria myrtea’are early-season cultivars of Japanese plum (Prunus salicina Lindl.) typology, both characterized by their low chilling requirements, so their adaptation is ideal for warm growing areas in the current context of climate change. High productivity, high-quality fruit and attractiveness are three characteristics common to both new cultivars. ‘luc ıamyrtea’and ‘victoria myrtea’stand out for their attractive dark purplish skin; their striking and intense red flesh; and their excellent taste qualities, with firm, juicy and aromatic fruit. Another remarkable characteristic is the floral self-compatibility in the case of ‘victoria myrtea’, uncommon in Japanese plum cultivars and especially interesting for farmers. These new cultivars will contribute to improve the availability of early, redflesh plums for the fresh market. Origin ‘luc ıamyrtea’and ‘victoria myrtea’resulted from the Japanese plum breeding program developed jointly by Centro de Edafolog ıa y Biolog ıa Aplicada del Segura-Consejo Superior de Investigaciones Cient ıficas (CEBASCSIC) and Instituto Murciano de Investigaci on y Desarrollo Agrario y Alimentario (IMIDA) of Murcia, with which the ‘myrtea plums’ series is initiated. The objectives of this breeding program are to obtain early-ripening cultivars, floral self-compatibility, high productivity, excellent taste, and resistance to sharka disease (Plum pox virus)asmuchas possible (Ruiz et al., 2016). Both cultivars resulted from open pollination of ‘Black Splendor’. Seeds obtained were germinated through in vitro embryo rescue according to the protocol described by Perez-Jimenez et al. (2021). This technique has allowed us to increase the percentage of viability of germination of seedlings. Seedlings were acclimatized in a greenhouse until they were planted in a high-density system in the experimental orchard located in Calasparra (Murcia, southeastern Spain; lat. 3816'N, long. 135'W; elevation, 282 m). ‘luc ıamyrtea’and ‘victoria myrtea’were selected on their own roots and were then grafted onto ‘Mariana 2624’(P. cerasifera munsoniana) rootstock (three replicates each) in the same experimental orchard, in a plantation framework of 5 3m,foragronomic evaluation. Description Tree characteristics Tree description. Trees are vigorous with medium-upright habit for ‘luc ıamyrtea’and moderately spreading habit for ‘victoria myrtea’. The leaves in both cultivars have a medium length and width of the blade, with an elliptical shape, and the upper surface is medium green. ‘luc ıamyrtea’has a long petiole, whereas ‘victoria myrtea’has a medium length. They both have nectaries positioned at the base of the blade and on the petiole, and the incisions on the edge of the leaf are bicrenate. Both cultivars are characterized by HORTSCIENCE VOL. 56(11) NOVEMBER 2021 1453 their high flower density. Their fruiting occurs on both spurs and long shoots. ‘luc ıa myrtea’trees have a moderate need for thinning whereas ‘victoria myrtea’needs intense thinning to obtain good fruit size (Table 1). Chilling requirements and blooming time. Chilling requirements have been assessed according to the methodology described by Ruiz et al. (2018). ‘luc ıa myrtea’and ‘victoria myrtea’need 30 and 25 chill portions respectively according to the Dynamic Model (Fishman et al., 1987a, 1987b) to break dormancy under our conditions in Murcia (southeastern Spain). Therefore, these new cultivars show very low chilling requirements—significantly less than any of the Japanese plum cultivars currently grown in Spain (Ruiz et al., 2018)—so its adaptation is ideal for warm growing areas, which is a key aspect in the current and future context of climate change. Full bloom for ‘luc ıamyrtea’ and ‘victoria myrtea’occur in the second week of February, on average on 12 Feb. and 10 Feb., respectively—very early flowering dates. The blooming of the new cultivars is significantly earlier than traditionally cultivated varieties such as ‘Red Beaut’and ‘Santa Rosa’(Table 1). In addition, the intensity of flowering is very high in both ‘luc ıa myrtea’and ‘victoria myrtea’. Floral compatibility. ‘victoria myrtea’is self-compatible, as demonstrated in the field (by bagging branches) and in the laboratory (by observing pollen tube growth in 20–25 pistils), according to the methodology described by Guerra et al. (2009). ‘luc ıamyrtea’is selfincompatible, with ‘victoria myrtea’being the most suitable pollinator, given the coincidence in flowering dates. In addition, the identification of their Sgenotypes by polymerase chain reaction using the consensus primers PaConsIF-PaConsIR2 (Guerra et al., 2020) revealed for ‘luc ıamyrtea’the band corresponding to the Se RNase allele and a band of 237 bp, whereas ‘victoria myrtea’showed the Sc RNase allele and the same band of 237 bp. The noncoincidence of incompatible RNase alleles confirms the intercompatibility between both cultivars, which enables the pollination of ‘luc ıamyrtea’with the pollen of ‘victoria myrtea’. Their intercompatibility was also verified in the field through controlled pollination between both cultivars. Fruit characteristics Ripening time. The ripening date for ‘luc ıa myrtea’in the experimental conditions of Murcia is between 1 June and 10 June, only a few days later than the early-ripening reference cultivar Red Beaut, and 20 d earlier than ‘Santa Rosa’(Table 1), which makes it one of the first red-flesh plums of the season. The ripening date for ‘victoria myrtea’is between 10 June and 20 June, coinciding with the end of harvesting of ‘luc ıamyrtea’, which is 10 d earlier than the traditional cultivar Santa Rosa (Table 1). Fruit of both cultivars ripen uniformly. In addition, fruit of both cultivars have shown optimal behavior at physiological maturity, with the fruit holding very well on the tree, which allows an extension of the harvesting period, as well as an optimal postharvest behavior. Fruit description. ‘luc ıa myrtea’and ‘victoria myrtea’trees and reference cultivar trees (‘Red Beaut’,‘Santa Rosa’)weregrown in the same orchard according to standard plum orchard management. Fruit characterization was made in 3 consecutive years at commercial ripeness based on their visual ground color (degreening stage and fully colored) and optimal firmness. Three replicates of 25 fruit were selected by cultivar and year. ‘luc ıa myrtea’bears globose fruit with an average weight of 74.5 g and a 51.2-mm equatorial section, which means larger fruit than the early-ripening reference cultivar Red Beaut and a little greater than the reference cultivar Santa Rosa (Table 1, Fig. 1). ‘victoria myrtea’bears large and slightly flattened fruit with an average weight of 87.6 g and an equatorial section of 55.9 mm, which is larger than the reference cultivars Red Beaut and Santa Rosa (Table 1, Fig. 1). ‘luc ıamyrtea’ and ‘victoria myrtea’are characterized by high fruit firmness at commercial ripeness when they are harvested—an improvement in firmness over the traditional cultivars Red Beaut and Santa Rosa. Both new releases resist skin cracking. Fruit of ‘victoria myrtea’ is freestone whereas ‘lucia myrtea’is semiadherent. ‘luc ıamyrtea’and ‘victoria myrtea’ are characterized by their highly attractive fruit. Both new cultivars have dark purplish skin with lenticels and dark-red flesh (Fig. 1), which makes them very attractive to consumers. Organoleptic characteristics. At the commercial-maturity stage, the two new cultivars stand out for their excellent quality. Fruit of ‘luc ıamyrtea’and ‘victoria myrtea’are very Table 1. Description of tree and fruit traits of ‘luc ıa myrtea’and ‘victoria myrtea’and the traditional cultivars Red Beaut and Santa Rosa under experimental conditions in Calasparra (Murcia, southeastern Spain). Characteristics luc ıa myrtea victoria myrtea Red Beaut Santa Rosa Tree Vigor Vigorous Vigorous Vigorous Vigorous Habit Medium-upright Moderately spreading Moderately spreading Medium-upright Flower density High High Medium–high Medium–high Flowering date Second wk in February Second wk in February Fourth wk in February First wk in March Self-compatibility Self-incompatible Self-compatible Self-incompatible Self-compatible Pollinator victoria myrtea —Mayeros, Ambra — Level of thinning Moderate High Moderate Moderate Fruit Ripening date 1–10 June 10–20 June 25 May–2 June 25 June–3 July Fruit weight (g) 74.5 87.6 57.7 72.1 Size (mm) z 51.2 55.9 46.6 51.0 Firmness High Very high Medium Medium–high Skin color Dark purple Dark purple Dark red Reddish purple Flesh color Red Red Yellow Amber-tinged red Sugar content (Brix) 15.5 16.5 13.4 14.2 Acidity (g/100 mL) y 22.8 16.8 16.1 22.2 z Size expressed as diameter of equatorial section in millimeters. y Titratable acidity expressed as grams of malic acid/1000 mL juice. The data and dates shown in the table are average values of 3 years of evaluation at the experimental orchard located in Calasparra, Murcia, Spain (lat. 3816'N, long. 135'W; elevation, 282 m). Fig. 1. (Left)‘luc ıa myrtea’and (right)‘victoria myrtea’fruit in the tree and after harvesting. Received for publication 26 May 2021. Accepted for publication 27 July 2021. Published online 6 October 2021. D.R. is the corresponding author. E-mail: [email protected]. This is an open access article distributed under the CC BY-NC-ND license (https://creativecommons. org/licenses/by-nc-nd/4.0/). 1454 HORTSCIENCE VOL. 56(11) NOVEMBER 2021 sweet—16 Brix on average, which is greater than the reference cultivars (Table 1). ‘luc ıa myrtea’has a medium level of acidity (22.8 g malic acid/1000 mL juice), similar to ‘Santa Rosa’, and a little greater than ‘victoria myrtea’ (16.8 g malic acid/1000 mL juice), which is similar to ‘Red Beaut’(Table 1). These characteristics, together with a high content of aromatic compounds, supply the fruit of both cultivars an excellent flavor and eating quality. In addition, the texture of the fruit of the two new cultivars is crunchy and juicy, both of which are features valued highly by consumers. Availability ‘luc ıamyrtea’and ‘victoria myrtea’are registered in the European Union Community Plant Variety Office with the registration nos. 2020/2972 and 2020/2973, respectively. Virus-free budwood of both new cultivars are available from CEBAS-CSIC and IMIDA (Spain), tested as free of Prunus necrotic ringspot virus,Applemosaicvirus,Apple chlorotic leaf spot virus,Prune dwarf virus, and Plum pox virus. Literature Cited Fishman, S., A. Erez, and G.A. Couvillon. 1987a. The temperature dependence of dormancy breaking in plants: Computer simulation of processes studied under controlled temperatures. J. Theor. Biol. 126:309–321, doi: 10.1016/S00225193(87)80237-0. Fishman, S., A. Erez, and G.A. 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