Colchicine, 8–hydroxyquinoline, ice-water mixture, and a mixture of cold water and colchicine (0.1%) were used as pretreatment reagents for Corymbia citriodora root tips for varying durations. The root tips were obtained from new seed germinants. Metaphase chromosomes numbers obtained were highest and chromosome separation was best with the pretreatment of 0.1% colchicine for 1.5 h. Relatively few metaphase chromosomes were obtained these showed poor separation for root tips pretreated with 2 mmol·L-1 8-hydroxyquinoline. The pretreatment involving ice-water mixture for 12 h resulted in higher numbers of metaphase chromosomes and better spread of these than the latter treatment, along with moderate chromosome condensation. The numbers of metaphase chromosomes appeared higher and good chromosome separation was also obtained when the root tips were treated with proportion of ice water and 0.1%colchicine mixed at a ratio of 2:3, and chromosome length was moderate. Based on a comprehensive comparison, the root tip pretreatment methods in order of decreasing effectiveness were: 0.1% colchicine > 2:3 mixture >ice-water > 2 mmol·L-1 8-hydroxyquinoline. It was also found that the optimal sampling time for taking root-tips was about 11:30 am–12:30 pm when using the best pretreatment method (i.e. 0.1%colchicine for 1.5 h).%以柠檬桉种子的根尖为研究材料,通过比较了3种浓度的秋水仙素、2 mmol·L-1的8-羟基喹啉、冰水混合物及以不同比例冰水混合物和0.1%的秋水仙素的混合液等预处理，在多个时间梯度对柠檬桉根尖染色体制片的影响进行了研究，结果发现：3种浓度秋水仙素预处理中，0.1%秋水仙素预处理1.5 h的染色体浓缩适中，分散性好，有较多的分裂相；2 mmol·L-1的8-羟基喹啉预处理的染色体均分散性较差，且分裂相较少；冰水混合物预处理12 h 的染色体浓缩适中且分裂相较多，分散程度较好。其余处理时间的染色体浓缩程度不理想，不易进行染色体分析；混合液中2：3比例下的染色体分散性较好，且浓缩程度适中，有较多的分裂相，综合比较结果由优到劣的处理方法为：0.1%秋水仙素预处理1.5 h＞2：3混合液＞冰水混合物处理12 h＞2 mmol·L-1的8-羟基喹啉，其中在上午11：30—12：30取材，0.1%的秋水仙素处理根尖1.5 h，效果最佳。
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