## 1 Introduction  
Gene expression analysis is crucial in dissecting the regulation network of physiological and metabolic processes in plants [1, 2, 3]. At present, transcriptome sequencing is the most widespread method to explore transcriptional changes during diverse biological processes in various species [4, 5, 6]. However, transcriptome data are not always reliable, and qRT-PCR analysis is the most used approach to validate transcriptome data [7, 8, 6]. It is highly sensitive, specific, accurate, and reproducible [9, 10, 11]. Nevertheless, its accuracy is influenced by diverse factors, including the quality of RNA, initial sample capacity, primer specificity, reverse transcription efficiency, and amplification efficiency [11, 12]. It is necessary to utilize one or more stable reference genes as the calibration standard to normalize the relative expression levels of target genes [2, 13]. In plant science, reliable reference genes are commonly chosen from the stably expressed housekeeping genes, including polyubiquitin (_UBQ_), actin (_ACT_), glyceraldehyde 3-phosphate dehydrogenase (_GAPDH_), 18S ribosomal RNA (_18S_), elongation factor (_EF_), Tubulin (_TUB_), and so on [2, 3, 10, 14, 15]. These genes are associated with fundamental cellular functions and processes, maintenance of cell structure and properties, and primary metabolism [12]. A reliable reference gene should exhibit stable expression in all plant organs at different physiological and developmental stages and under various experimental conditions [10, 16]. However, some studies have shown that reference genes' expression levels are not always stable under changing growth conditions in many species [15; 17; 18; 19; 20]. Thus, an improper selection of reference genes may lead to erroneous results and conclusions by qRT-PCR analysis [21; 22; 23]. Accordingly, it is essential to identify suitable and stable reference genes for specific experimental conditions and in each species [10]. Lily (_Lilium_ spp.) is an important ornamental plant that contributes considerably to the global cut flower market economy. Yunnan, China, is one of the main producers of lily cut flowers in the world. With the expansion of lily planting areas, lily diseases have become more serious in recent years. _Fusarium_ will disease (also labeled as basal rot, stem rot, or root rot) is one of the most limiting threats to bulbs and flower production in liliies, specifically under special growing conditions in greenhouses [24; 25; 26]. The soilborne fungus _Fusarium oxysporum_ f. sp. _Liliu_ is the main pathogen that causes lily _Fusarium_ wilt. It can survive for a long time as mycelium, chlamdospore, or sclerotium with diseased residue in the soil or as mycelium in the lily bulbs [27]. _F. oxysporum_ is difficult to control effectively. Therefore, the most effective and safe approach for controlling this disease is to understand resistance-related molecular mechanisms and identify and exploit key genome resources in breeding novel _F. oxysporum_-resistant lily varieties. A few lily breed cultivars (Asiatic hybrids, LA hybrids) and some wild species (_L. sargentiae_ [PERSON], _L. regale_ [PERSON], and _L. pumilum_ [PERSON]) have shown resistance to _F. oxysporum_[24; 27; 28; 29; 30]. _L. sargentiae_ is endemic to China and is naturally distributed in the southwest regions [31]. Due to its resistance to _F. oxysporum_ and ornamental characters, it represents one of the important parents used in lily cross-breeding [32; 33]. However, the regulation of the resistance to _F. oxysporum_ in _L. sargentiae_ is largely unknown. In a recent study (unpublished data), we applied high-throughput transcriptome sequencing technology and identified potential candidate genes for _F. oxysporum_ resistance in _L. sargentiae_. To enable in-depth studies of these genes, reliable reference genes for qRT-PCR normalization are required. Herein, we selected nine candidate reference genes based on the RNA-seq data and evaluated their expression stability at different time points following _F.