Pollen morphology of chestnut cultivars in southern China by using scanning electron microscope

The morphological characteristics of pollen grains of 16 cultivars belonging to two species of the genus Castanea (Castanea mollissima and C. henryi) collected from southern China were observed by using scanning electron microscope (SEM). The length of polar axis (PL), the equatorial diameter (ED), the length of colpus (CL) of grain, P/E ratio (polar axis to equatorial diameter), P/C ratio (polar axis to colpus length), and C/E ratio (colpus length to equatorial diameter) were measured and their variations were compared among studied taxa. The result of this study indicated that chestnut pollen grain was a tricolporate in aperture type, and aperprolate type in equatorial view. The morphological characteristics were mainly represented by PL, ED and CL as revealed by principal components analysis, which accounted for 99.56% of the total variations. The cluster analysis by the UPGMA tree divided the taxa into three groups and showed a great morphological affinity among the 16 cultivars. Introduction Chestnut has been placed in the family of Fagaceae which is monoecious, wind-pollinated and self-incompatible (Mckay 1942, Bounous and Marinoni 2005). In China, this species is economically important for timber and nut production. Three species in this genus are native to China, including two main economic species, namely: Castanea mollissima Blume and C. henryi Rehd. & Wils (Huang 1998). C. mollissima is widely distributed in Jilin, Hebei, Shangdong, Sichuan, Hubei, Anhui, Jiangsu, Hainan Island, Taiwan, and Yunnan Provinces (Zou et al. 2014). However, C. henryi is distributed in the southern China, especially in Fujian, Zhejiang and Hunan Provinces (Huang 1998, Fan et al. 2015, Xiong et al. 2018). The pollen grains have a definite shape, size, color and structure for each species, genus and family, and these characteristics are useful for systematic botany (Lee et al. 2008, Mert 2010). In the study of chestnut pollens, Lee and Kim (2004) reported that chestnut (Castanea spp.) pollens were significantly different among interspecies and inter-cultivars in pollen morphology. Mert and Soylu (2006, 2007) described the flower and stamen structures of four male-fertile and two male-sterile chestnut cultivars by scanning electron and light microscopes. Liu et al. (2008) studied the relationship between pollen morphology and nut yield in 20 chestnut cultivars and have found that the exine ornamentations of the chestnut pollens were different. Chen and Shi (2009) also examined the four chestnut cultivars in Yunnan by scanning electron microscope (SEM) and they found that the sizes of pollens were different among the varieties. Although there are some descriptions of pollen morphology in Castanea, studies of this genus are still limited. While China has about 300 chestnut cultivars (Huang 1998), the differences in chestnut pollen morphological characteristics among species and cultivars have not been well investigated. The purpose of this study was to enrich the knowledge of the pollen morphology characteristics of selected chestnut cultivars and to examine the pollen features in order to develop an additional identification tool of plant materials. *Author for correspondence: <zoufeng06@126.com>.