Abstract
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.
Highlights
IntroductionRose breeding companies may overcome geographic distances and differences in flowering time by storing selected pollen until pollination of the flowers used as female parents can be performed
In the cut flower market, many modern rose cultivars are tetraploid (2n = 4x = 28) and they are produced by traditional genetic improvement methods
Pollen germination rate tends to decline over storage, Zlesak et al (2007) found that the pollen tube length of pollen stored for 2 or 52 weeks at −80 ◦ C was comparable to fresh pollen and Plants 2017, 6, 17; doi:10.3390/plants6020017
Summary
Rose breeding companies may overcome geographic distances and differences in flowering time by storing selected pollen until pollination of the flowers used as female parents can be performed. Recent studies on hybrid tea roses shows that the viable level of fresh pollen varies among cultivars and the pollen preservation at −20 ◦ C and −80 ◦ C is cultivar dependent [11]. An efficient protocol for pollen storage under low temperatures was applied to six cultivars in order to establish pollen preservation procedures useful for rose breeding and germplasm resource research. The effective fertilization capacity of the preserved pollen was studied in 2015 breeding plan of the company NIRP International (Italy) and the correlation between pollen viability and fertility was investigated
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