Cyto-Embryological Analysis of Wild Kentucky Bluegrass Germplasm in Gansu Province, China

Abstract

Reproduction studies, particularly embryology, represent basic information of any plant. However, the current embryological information is fragmentary for Kentucky bluegrass (Poa pratensis L.). Here, paraffin sections were used to examine the cyto-embryological characteristics, including microsporogenesis, microgametogenesis, megasporogenesis, megagametogenesis, and apomixis, of wild Kentucky bluegrass germplasm from Gannan (GN) and Longnan (LN) in Gansu Province. The study found no significant differences in pollen diameter, characteristics, viability, and stigma receptivity between the two germplasm materials. The Kentucky bluegrass consisted of three anthers, and each contained four pollen sacs that were divided into left and right halves. After meiosis, the microspore mother cells formed dyads and tetrads, which were primarily symmetrical and underwent mitosis to form three-celled pollen. Kentucky bluegrass has a one-locular ovary, two-feathery stigmas, thick nucleolar and anatropous ovules, and a typical polygonum embryo sac as its reproductive organs. The main type of apomixis observed was apospory, resulting in the coexistence of multiple embryo sacs. Polyembryonic seeds were frequently observed in Kentucky bluegrass due to apospory. Most importantly, our research found that apospory caused early embryogenesis during fertilization, which is a vital embryological feature for identifying sexual reproduction and apomixis in Kentucky bluegrass. Sexual reproduction followed strict double fertilization, while in apomixis a complete seed was only formed through pseudogamy. These embryological characteristics are documented here, and their study can aid in understanding the evolution of Kentucky bluegrass.