In the cut flower market, traditional breeding is still the best way to achieve new rose cultivars. The geographical delocalization of cultivar constitution (generally made in Europe and North America) and plant cultivation (large areas in Africa and South America) represents a limit point for crossing and selection. Rose breeders often need to overcome geographical distances, resulting in asynchrony in flowering among crossing parents, by storing and sending pollen. Hence, a key aspect in breeding programs is linked to pollen availability and conservation, jointly with the identification of parameters related to pollen fertility. In this study we present the results of three different trials. In the first, pollen diameter and pollen viability were chosen as fertility predictors of 10 Rosa hybrida commercial cultivars. In the second trial, aliquots of dried pollen grains of six R. hybrida cultivar were stored under two different temperatures (freezer at T = −20 °C and deep freezer at T = −80 °C) and after a wide range of conservation period, their viability was measured. In the third trial, the effective fertilization capacity of frozen pollen of 19 pollen donor cultivars was evaluated during 2015 crossing breeding plan, performing 44 hybridizations and correlating the number of seeds and the ratio seeds/crossing, obtained by each cultivar, with in vitro pollen germination ability.

Modern rose cultivars require hand pollination for rose hip production and collection of seeds. Breeding programs are often focused on the quality of rose pollen, which is genotype dependent and it is affected by the conditions used for its conservation. In this study in vitro pollen germination and shelf life of six commercial rose cultivars were evaluated under different storage conditions in order to establish preservation procedures. Flowers of Rosa 'Alba', 'Anastasia', 'Encanto', 'Marvelle', 'Swan' and 'Touch of Class' were collected from plants cultivated in the NIRP International greenhouses. Anthers were removed from flowers and dried on Petri dishes for 24 hours (T= 24°C). Then, they were placed into polyethylene tubes in the freezer (T= -20°C) and in the deep freezer (T= -80°C). Pollen germination was measured soon after 24 hours from flower collection and after 44, 134, and 190 days of storage, respectively. The pollen grains were spread on a culture medium containing agar (0.7%), sucrose (15%), calcium chloride (152 mg L -1 ) and boric acid (40 mg L -1 ). Our results confirmed that the viable level in fresh pollen varied among cultivars and also that pollen preservation at low temperatures is cultivar dependent.

Concentrations of endogenous abscisic acid (ABA) and indole-3-acetic acid (IAA) in Rosa hybrida seed coat and embryos were determined at 28, 35, 42, and 49 days after pollination (DAP), a period encompassing the early-middle stages of seed development. No studies on rose have ever documented simultaneous change in ABA and IAA during these developmental phases in both seed coat and embryo. Plant growth regulators were extracted and then quantified by using high performance liquid chromatography based on solid phase extraction purification. In both the seed coat and embryo, ABA content decreased from 28 DAP (4.39 and 1.36 pmol mg -1 , respectively) and onward. Endogenous IAA in seed coat followed the same trend. In contrast, IAA in embryo began to increase at 28 DAP (2.06 pmol mg -1 ), peaked at 42 DAP (5.06 pmol mg -1 ), and then declined dramatically at 49 DAP (1.17 pmol mg -1 ). In embryo, the IAA/ABA ratio was always [1.0 and showed a tendency to increase from 28 DAP to the maximum significant rate at 42 DAP (9.20).The ABA decrease associated with increased IAA levels in embryo could be a result of crosstalk between these two phytohormones. Such a change in the IAA/ABA ratio may signal the end of endodormancy caused by ABA at the precotyledonary stage and the start of increased embryo cell division during the cotyledonary stage, which also results in increased hip weight.

Breeders are always looking for new and novel varieties to be competitive in the flower market. Low seed germination rate is still a major problem encountered in traditional rose breeding programs. Mutagenic agents, such as ionizing radiation, may be used to enhance seed vigor and increase the productivity, improving sprouting and emergence of buds that are carried out through seed coating. The effects of ionizing radiation on seed vigor are in most cases genotype-dependent, thus irradiation treatments need to be optimised for each different cultivar. In the present study, gamma-rays (0, 50, 100 and 200 Gy) were applied on hybrid tea rose seeds in order to set up a radiation protocol for increasing seed germination. Seeds coming from six different crossings of Rosa hybrida commercial cultivars were used in order to gain information on radiotolerance and germination ability.

In vitro culture to improve breeding activities in Rosa hybrida / Caser, M.; Ballardini, M.; Cassetti, A.; Ghione, G.G.; Mansuino, A.; Giovannini, A.; Scariot, V.. -In: ACTA HORTICULTURAE. -ISSN 0567-7572. -1155-ISSN 0567-7572. - (2017, pp. 141-148. Original Citation:In vitro culture to improve breeding activities in Rosa hybrida