Cytological Studies Of Fragaria Plants

Four diploid strawberry species including Fragaria gracilis A.Los, F. nilgerrensis Schidl, F. pentaphylla A.Los. and F. vesca L., a pentaploid strawberry Heilongjiang No. 5 strawberry , two octoploid strawberry F. virginiana Duch. and F. X ananassa Duch. were used to analyze the chromosome karyotype and observe the cytological behavior of 2n gamete formation. The karyotype formula of each strawberry studied were listed as followed: Fragaria gracilis A.Los was 2n=2x= 14= lOm+2sm+2m*, which belong to type 1B; F. nilgerrensis Schidl was 2n=2x= 14= 14m, which belong to type 1A: F. pentaphylla A.Loz. was 2n=2x=14= 12m+2sm, which belong to type 1A; F. vesca L. Was 2n=2x= 14= 14m, which belong to type IA: Heilongjiang No. 5 strawberry was 2n=5x=35=30m+Ssm*, which belong to type 2A; F. virginiana Duch. was 2n=8x=56=48m+8m*, which belong to type 1B; F. X ananassa Duch. was 2n=8x=56= 481n+2m*+6sm*, which belong to type 2B. According to the karyotype analysis of different species, the degree of asymmetry of the samples tested was in the order of F. gracilis A.Los. ) F. pentaphylla A.Loz. ) F. vesca L. ) F. nilgerrensis Schidl, which showed that Fragaria nilgerrensis Schidl was the most primary species. As to the genus of strawberry, F. X ananassa Duch. was the most evolved. A diploid strawberry (F. (vesca) cv.) which can naturally produce unreduced gametes (2n pollen) and doublenreduced gametes (4n pollen) was used to study the cytological mechanism of 2n and 4n gamete formation. The result showed that the formation of 2n gamete was mainly due to the abnormal orientation of spindles at metaphase II. The normal orientation of two spindles at metaphase II is perpendicular to each other, which leads to tetrad formation at the end of meiosis; Two kinds of abnormal orientation of metaphase II spindles, i.e. parallel spindles and triangle spindles, were observed. Of the parallel spindles, the 4 group chromosomes were distributed to 2 poles and formed a dyad which formed two 2n pollen grains later on. Of 39 the triangle spindles, the 4 group chromosomes were distributed to 3 poles and formed a triad which formed one 2n pollen grain and two n pollen grains. Meanwhile, we also observed a few very big pollen grains (4n pollen) which probably due to the fusion of the tetrad. Whatever kinds of pollen (normal pollen, 2n pollen and 4n pollen) were in high activity. There were from 16 to 28 dilents and some multivalent in the diakinasis of about 50 strawberry cultivars. Through the scanning electron microscope, the different types of strawberry pollens were observed. All of the pollens were tricolporate, and ridge and colpus formed its exinous ornamentation. By analyzing the depth of the colpus, the size of the pollen and the value of P/E, the evolutionary relations of the tested strawberries were in the order of: Fragaria nilgerrensis Schidl, F. vesca L., F. pentaphylla A.Loz. and F. gracilis A.Los., which were consistent to that of karyotype analysis.