نوع مقاله : مقاله پژوهشی
نویسندگان
گروه علوم باغبانی، دانشکده کشاورزی، دانشگاه تربیت مدرس، تهران، ایران
چکیده
کلیدواژهها
موضوعات
عنوان مقاله [English]
نویسندگان [English]
In order to enhance the rate of successful fruit set in controlled and out-of-season hybridizing programs or to improve crop production at a given time, it is important to have viable pollens during stigma acceptance. This study aimed to investigate the effect of duration (3, 6, 9, and 12 months) and temperature of storage (laboratory ambient temp, 4, -20, and -80 °C) on pollen germination of 'Sebri' cultivar and promising A95 genotype of European pear on medium containing %15 sucrose, 20 ppm boric acid, 1.219 mM calcium nitrate, and %0.8 agar. The experiment was performed as a factorial in a randomized complete design (RCD). Morphological characteristics of pollen grains were also explored using a scanning electron microscope (SEM). Results showed that the highest viability of pollen grains was observed in A95 promising genotype, stored for three months at -20°C. Furthermore, the percentage of pollen germination significantly increased as temperature and duration of storage were reduced. In addition, our findings showed that the studied pollen grains were monads, spheroidal in shape, radially symmetrical, and had three longitudinal furrows on their surface. Moreover, the shape of the pollen grains was prolate, and their sizes varied from 35.31 to 39.51 μm.
کلیدواژهها [English]
Extended Abstract
Introduction
Pollen grains, as units of sexual reproduction and carriers of genetic material, play a crucial role in breeding programs and the successful fruit formation. Studying the characteristics of pollen grains, such as germination percentage and pollen tube growth, is essential for evaluating their viability and longevity in horticultural research. Furthermore, the specific traits of pollen grains contribute to identifying the type of a given parent and its position in plant taxonomy. In general, determining the characteristics of pollen grains for a genotype is decisive in plant breeding programs.
Selection of superior chance seedling genotypes has always been of particular importance in pear breeding. The promising genotype A95 (a chance-selected seedling from the Asian pear collection orchard with the 'Dargazi' European pear seedling rootstock in the Department of Horticultural Science at Tarbiat Modares University) has attracted attention due to its desirable aroma, flavor, and good fruit appearance. In this context, this study aimed to examine pollen grain germination in response to different storage temperatures (laboratory room temperature, -4, -20, and -80 degrees Celsius) for long-term storage in two European pears, including 'Sebri' and the A95 promising genotype. Moreover, the micromorphology of pollen grains was studied.
Materials and Methods
This research was conducted in the pear research orchard in the Department of Horticultural Science at Tarbiat Modares University (TMU) in Tehran, Iran, during the 2021 growing season. At the beginning of the blooming of the `Sebri’ cultivar and the A95 promising genotype, several branches with sufficient and suitable flower buds were selected and labeled for flower and pollen sampling. To prevent unwanted pollen contamination, the selected branches were covered with cotton bags before anthesis. Following anthesis, flower samples were collected from the tagged shoots and transferred to the Pomology Lab, Department of Horticultural Science at TMU. The anthers were allowed to dry for 24 hours on filter paper inside petri dishes under the ambient environment. Pollen grains were collected in small glass vials and sealed with parafilm to prevent moisture and any contamination, and stored under four different temperatures (laboratory environment, 4°C, -20°C, and -80°C) at four time periods (3, 6, 9, and 12 months). Pollens were then examined for viability and germination tests. At the specified time intervals, the pollen grains were scattered on petri dishes containing sucrose (15%), boric acid (20 ppm), calcium nitrate (1.219 mM), and agar (0.8%). The germination percentage of the pollen grains was examined under a research microscope and calculated based on the number of germinated pollen in five separate selected areas of each petri dish. A pollen grain was considered germinated when its tube was at least as long as or longer than the diameter of the pollen. For the descriptive examination of pollen grains, the scanning electron microscope (SEM, Philips XL30) was used. Pollen grains were collected as above and transferred onto a stub with pre-glued double-sided special tape, and afterward coated with gold before viewing.
The samples were examined at magnifications of 500 to 20,000 times. The polar axis (P), equatorial axis (E), ratio of polar to equatorial axis (P/E), distance between two grooves, and width of projections on the pollen grains were measured using the Microstructure Measurement software.
Results and Discussion
The germination response of the `Sebri’ cultivar and the A95 promising genotype of European pear to different temperatures and storage periods was different. Results indicated the highest pollen germination percentage in the A95 promising genotype at -20°C after 3 months of storage (21.2%). Besides, the germination test results showed that both the `Sebri’ cultivar and the A95 promising genotype had low viability under different temperature treatments, and their viability decreased significantly over the storage period. The results from the morphological examination of the pollen grains of the `Sebri’ cultivar and the A95 promising genotype of European pear using Scanning Electron Microscopy (SEM) showed that the highest polar axis (P), equatorial width (E) (1.11 ± 39.51 and 0.65 ± 23.12 micrometers, respectively), the highest P/E ratio (1.72 micrometers), the longest furrow and the widest projection (1.10 ± 33.51 and 1.13 ± 15.47 micrometers, respectively) were attributed to the pollen grains of the A95 promising genotype. This study revealed that the examined pollen grains had three longitudinal grooves on their surface, which extended to the polar axis. Moreover, the pollen grains also varied from 35.31 to 39.51 μm, and the largest size (39.51 ± 1.11 μm) was observed in the A95 promising genotype.
Conclusion
The results of the present study showed that while -20°C was the optimum temperature for pollen storage of the A95 promising genotype, ambient temperature dramatically reduced pollen viability over the storage period. In terms of the descriptive pollen analysis using SEM, the studied pollen grains were all single, polar type, and had radial symmetry; they also had three longitudinal grooves on their surface, representing tricolporate pollen type.
Author Contributions
Atefeh Kahnouji: Made a major contribution to the proposal and the experimental work, Investigation and data collection, validation, formal analysis, and writing – original draft and further revisions. Kazem Arzani: Writing – review & editing the research proposal and manuscript for this publication, supervision, validation, and project administration, also provided facilities and access to the Pomology Lab at TMU for the first author.
Data Availability Statement
The authors declare that all the data supporting the findings of this research are available within the article.
Acknowledgment
We would like to thank Tarbiat Modares University (TMU) for providing facilities and financial support for this research. In addition, the orchard and laboratory facilities provided by Pomology Lab, Department of Horticultural Science at TMU are acknowledged.
Ethical considerations
This article does not contain any studies involving human and animal subjects.
Conflict of interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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