The flowering biological characteristics of Chimonobambusa rigidula Introduced to Hangzhou City

This study aims to investigate the flowering biological characteristics and pollen viability of Ch. rigidula Introduced to Hangzhou, with the goal of reveal the flowering traits of bamboo species under artificial cultivation and providing technical guidance for effective hybridization breeding. Field observations were conducted to document the flowering phenology and pollination vectors of Ch. rigidula. The floral organ structure was analyzed by dissecting its spikelet. Pollen viability was assessed using the iodine-potassium iodide (I₂-KI) staining method and an in vitro germination assay. Stigma receptivity was evaluated via the benzidine-hydrogen peroxide method. Additionally, the pollen-ovule ratio (P/O) and outcrossing index (OCI) were calculated to analyze the type of breeding system. Results indicated　that the flowering period of Ch. rigidula spans from early November to mid-late February of the following year, with the peak flowering stage occurring from mid-January to early February. Pollen viability and germination rates were highest when the anthers were fully exposed, with proportions of vigorous pollen and total germination rates reaching 59.22% and 19.58%, respectively. Pollen germination rates declined rapidly over time, but low-temperature storage effectively prolonged pollen longevity. Stigma receptivity peaked during anther release pollen and was completely lost by the second day after pollen release. The outcrossing index (OCI) of Ch. rigidula was calculated as 4, and the pollen-ovule ratio (P/O) ranged approximately from 16,200 to 36,500. Primary floral visitors included flies, ants, and spiders. Under artificial cultivation in Hangzhou, Ch. rigidula exhibits well-developed pollen and stigma fertility. The stigma and anthers display optimal fertility when the anthers are fully exposed, with short-term pollen storage feasibility. Its breeding system is predominantly outcrossing, characterized by open anemophily (wind pollination), while also retaining partial entomophilous features. Considering its superior shoot-producing traits, Ch. rigidula is suitable as parental material for hybridization breeding aimed at developing new shoot-producing bamboo varieties.