| Garlic（Allium sativum L.）has important nutritional and medicinal value;bulbs are the main edible organs.Under the effact of the environmental and genetic factors,bulbs’shape and size are different.However,the research involved on the development of garlic needs to be strengthened and little information is available.Therefore,the study of morphological anatomy and molecular level of garlic bulbs will provide valuble guidance for research on garlic yield and quality improvement.In the present study,the agronomic traits,the anatomical structureis of different stages of bulb development were investigated,and the transcriptomes of 8 different development stages of bulbs were analyzed.The main results are summarized as follows:1.Investigation of agronomic traits of bulb development.In this study,the white garlic,‘T261’and‘T36-1’,and the purple garlic,‘Zhongsuan-1’,‘TuoduSuan’and‘T17’,were used in current investigation.The bulb diameter,bulb height and dry weight of underground of all the varieties increased throughout.However,the dry weight of root and aboveground part weight was increased in the earlier stage than in later stage.Variety‘Zhongsuan-1’was superior to other varieties in most phenotypic traits.After 8th May,the dry weight of underground part of‘T261’,‘T17’and‘T36-1’had a little decline,while‘TuoduSuan’and‘Zhongsuan-1’increased,that means the maturity time is different among varieties.Consequently,optimum harvest dates should be set to the different varieties to obtain the highest bulb yield.The obtained result showed that‘Zhongsuan-1’and‘TuoduSuan’belong to the late-maturing garlic,while‘T17’,‘T261’and‘T36-1’belong to the early-maturing garlic.Moreover,the increasing rate of the bulb diameter of‘Zhongsuan-1’,‘TuoduSuan’and‘T17’was higher than the white garlic,‘T261’and’T36-1’.Besides,the bulb dry weight of purple garlic was also significantly higher than that of white garlic close to maturation time,and the value of dry matter utilization was higher.The dry weight of aboveground was positively related to the dry weight of bulb in the earlier stage and decreased later.By the observation of multiple traits of garlic varieties,and according to the change of dry weight and fresh weight of garlic bulb,the key point period of garlic growth was found.The study will benefit the breeding and production of garlic.2.Observation of anatomical structure of bulb development.According to the observation of freehand section and paraffin sections of bulbs at different developmental stages,the growth and development of garlic bulbs could be divided into four stages:the germination period of garlic,the differentiation stage of scalp bud,the stage of scaly bud enlargement and the bulb maturity.Regarding to bulb differentiation characteristics,most of the small bulblets locate around the stems innermost layer1-2 axillary and arranged in two rounds;the formation of small bulblets location is correlated with the position of meristematic cells,and the growth cone appeared original orthopedic structure.The nuclei chromosomal in meristematic cells are active,and the starch granules accumulate in the meristematic cell mass,the formation of vascular tissues also occurs around the cell mass.The xylem has a well-developed vessel;the mature garlic has a higher degree of lignifications.The numerous vascular bundles in bulbs are amphicribral and closed collateral,the vessels are spiral.Above results provide a theoretical basis for explaining the bulb enlargement mechanism at the cellular level.And moreover,it utilizes the further studies on function analysis of the differentially expressed genes in different developmental stages of bulbs.3.Transcriptome analysis of garlic bulbs at different developmental stages.A total of 103.12 Gb clean data and 64,242 unigenes were generated from the transcriptome sequencing of bulbs from eight different development stages and 24,604 unigenes were annotated by blasting to COG,GO,KEGG,Pfam,Swissprot and NR databases.Besides,a total of 5,353 SRR markers were obtained sing MISA software based on unigenes those bases longer more than 1kb.Furthermore,the differential expression genes were analyzed for the adjacent two periods,and the expression of the gene in the development of garlic bulbs was studied.The differentially expressed genes were analyzed by GO enrichment,and a total of 135 GO terms were obtained.Among them,there were 76 involved in biological processes,33involved in cell components,and 26 involved in molecular function.Moreover,the differentially expressed genes analyzed by KEGG enrichment recorded 20 significant enrichment terms.The significantly enriched pathways,such as starch and sucrose metabolism,plant hormone signal transduction,galactose metabolism pentose and glucuronate interconversions,photosynthesis,were elevated as playing crucial roles in bulbs development. |
