Observation on pollen grains of Feicheng peaches

Abstract:【Objective】Feicheng peach is one of the four famous peaches in our country, and it has a histo-ry of more than 1 000 years.After years of artificial selection and breeding, Feicheng peach has formedmany strains, such as 'Haili Feitao''Baili Feitao''Liuye Feitao', etc..Studies of Feicheng peach main-ly focus on its cultivation and physiology, including the characteristics of photosynthesis, shaping andpruning, water use, effects of growth retardants, composition of aroma components, harvest timing andquality improvement.In recent years, the quality of Feicheng peach has decreased and the fruit set be-come weaker.There has been no study about pollen and stigma morphology.In this paper, the morphologyof pollen grains was characterized in Feicheng peach varieties and their genetic relationships clarified.【Methods】The pollen grains of 9 varieties of Feicheng peach preserved in peach germplasm resources ofShandong Institute of Pomology were used as the materials.The pollen grains were fixed according to thefresh sample method, which was helpful to maintain the morphological characteristics of pollen grains.The pollen samples were rinsed for 3 times using 0.1 mol·L^-1 phosphate buffer and dehydrated successive-ly with 30%, 50%, 70%, 80%, 90% and 100% ethanol solutions, and then replaced twice with isoamyl ac-etate and dehydrated using an HCP22 type critical point drying apparatus with liquefied CO2.After dry-ing, the pollen sample was glued onto the sample stand with conductive adhesive tape, and then a HIT-ACHIE-1010 type ion sputtering apparatus was used to conduct vacuum spray coating of the samples, which were observed, photographed and recorded under a JSM-6610 LV scanning electron microscope ofJEOL Company.Morphological characteristics of pollen grains including pollen polar axis length, equatori-al axis length, germination ditch groove width, ridge width, ridge spacing, ridge density, and germinationaperture density, were measured and observed at magnifications of 250, 2 000 or 4 000.The pollen polarand equatorial plane, pollen germination ditch and ridge as well as the exine ornamentation were de-scribed.The data were first statistically analyzed with Excel and standardized with DPS software, and thencluster analysis of the data was carried out using Euclidean distance and average linkage method.【Results】The pollen grains of Feicheng peach strains were nearly flat globose, isopolar, tadially symmetrical, blunttriangular in polar views, and elliptical in equatorial views with an arc in three sides.The averagepolar axis length of pollen grains was 32.94 μm, and the average equatorial axis length was 40.71 μm.The'Baili Feitao'peach pollen grain was the smallest with an average length of the polar axis of 31.22μm and the average length of the equatorial axis about 39.73 μm;'Liutai Feitao No.1'pollen was thelargest one with an average length of the polar axis of 34.87 μm and an average length of the equatorial ax-is about 41.95 μm.The differences in pollen grain size were statistically significant.The Feicheng peachpollen grains belong to the N3 P4 C5 type whose exine surface had a striate pattern with some small pores, and the striate pattern was compound-striation.While the exine ornamentations of'Baili Feitao'peachwere relatively simple, the ridge distance was bigger and the perforation density was small.'Feitao No.2''Feitao No.3''Zaoshu Feitao''Liuye Feitao''Liutai Feitao No.1'and'Zhonghua Shoutao'had fine or-namentations and the ridge distance was narrow and the perforation density was high.【Conclusion】Withthe evolution of plant, pollen grains also evolved and the exine ornamentation evolved from regular to irreg-ular pattern and from simple to complex.'Baili Feitao'and'Hongli Feitao'Feicheng peaches are themost primitive peaches.'Baili Feitao'is the most primitive, followed by'Hongli Feitao', and the othervarieties are evolutionary varieties.According to the clustering of quantitative traits in 10 pollen analyses, Feicheng peach could be divided into 2 categories with the level of 7 in the Euclidean distance.The firsttype had larger pollen size with unique exine ornamentation and high perforation density;the second typehad smaller pollen grains with a wider ridge but low perforation density.This study, from the perspectiveof palynology, provides references for the evolution degree and the genetic relationships among Feichengpeach varieties.In order to make the results more accurate, the data of fruit morphology, molecular biolo-gy and other aspects should also be combined to conduct a comprehensive analysis.