摘要
为明确‘东试早柚’果实无核成因,以‘东试早柚’及其杂交群体为试材,利用醋酸洋红和苯胺蓝染色法、杂交授粉及分子标记等手段探究‘东试早柚’无核原因。结果显示:‘东试早柚’的花结构完整,花粉活力及萌发率分别为94.80%和86.20%;‘东试早柚’自交表现为不亲和,而与‘沙田柚’杂交亲和;利用S5、S6基因型分子标记从‘沙田柚’ב东试早柚’的175株杂交子代中共鉴定出F1代杂种164株,排除了‘东试早柚’雄性不育的可能;连续2 a田间试验观察显示,‘东试早柚’刺激性单性结实和天然单性结实的平均座果率分别为13.04%和25.56%。结果表明,‘东试早柚’自交不亲和并具有一定的单性结实能力是导致其无核的主要成因。
柑橘在我国鲜果市场中占据十分重要的地位,2022年全国柑橘总产量 6 000余万t,占全球柑橘产量的近40%(FAOSTAT数据库)。我国柑橘品种培育以易剥皮、有香气、风味足及无核等为主要目
柑橘无核成因主要包括雄性不育、胚囊败育、胚乳败育、自交不亲和及环境因素等。雄性不育在柑橘中是非常普遍的现象,也是导致柑橘无核的主要原因,表现为花粉败
在柑橘中,自交不亲和及单性结实也是导致其果实无核的重要原因。自交不亲和性(self-incompatibility, SI)是指植物拒绝或抑制自身的花粉进入花柱而防止自交,促使异交的现象,是植物调节自身来适应环境变化的一种进化策
‘东试早柚’是云南西双版纳东风农场试验站实生选育的特早熟无核优良品种,故称为‘东试早柚’,是云南热带亚热带地区主要的柚栽培品种之一,在全省种植面积达0.8万h
供试柑橘材料包括:西双版纳州景洪市热带作物科学研究所柚试验基地的以‘酸柚’为砧木的23年生‘东试早柚’(Citrus grandis [L.] Osbeck cv. ‘Dongshi Zaoyou’)和湖北武汉市洪山区华中农业大学国家柑橘种质资源圃的以‘酸柚’为砧木的8年生‘沙田柚’(Citrus grandis [L.] Osbeck cv. ‘Shatianyou’)及‘沙田柚’ב东试早柚’的F1代杂交群体。
醋酸洋红染色液的配置参照文献[
花粉活力测定:载玻片涂上醋酸洋红染色液,用镊子取出花药,捣碎释放花粉粒,染色5 min,使用光学显微镜观察花粉活力。用于检测花粉活力的花粉2 264粒。
花粉培养基的制备参照谭美
自交授粉亲和性鉴定试验于2022年2月11―12日在西双版纳进行,花粉的采集、保存及授粉参照朱晨
去雄套袋处理为刺激性单性结实,选择‘东试早柚’即将开放的顶端花蕾,去除已开放花朵、小花蕾及畸形花,用镊子小心剥开花瓣,去除花药,保留花丝,尽量不损伤雌蕊,立即套袋,用回旋针固定,作好标记。非去雄套袋处理则为天然单性结实,选择‘东试早柚’即将开放的顶端花蕾,直接套袋。套袋85 d后统计其座果数。
‘东试早柚’及杂交子代叶片DNA提取参照程运
引物名称 Primer name | 引物序列(5′―3′) Sequence | 退火温度/℃ Annealing temperature |
---|---|---|
S5 | F:ATGAAGGTGGCATCCATCAAC; R:CTACCACCGTGGTGGGAAAATAATATCC | 56 |
S6 | F:ATGGGGACTAATTTCCTCATTATC; R:CTATATTTTAACGTATCGCGGC | 55 |
‘东试早柚’树形一般为自然开心形,树势强、花量大、花器官较大,花期以2月上旬至3月上旬为主,在热带地区具有周年开花的特性。座果一般以当年12月及翌年2月开花为主,果实特早熟,可于7月下旬至8月上旬上市。果型呈倒卵形,果皮和果肉浅黄色,果皮易剥,果肉多汁且化渣性好,有香

图1 ‘东试早柚’花结构
Fig. 1 Flower structure of ‘Dongshi Zaoyou’ pummelo
‘东试早柚’花粉染色活力结果如

图2 ‘东试早柚’花粉染色活力(A)及花粉萌发(B)观察
Fig. 2 Pollen staining activity (A) and pollen germination (B) of ‘Dongshi Zaoyou’ pummelo
项目 Items | 视野1 Sight 1 | 视野2 Sight 2 | 视野3 Sight 3 | 视野4 Sight 4 | 视野5 Sight 5 | 平均值±标准差 Mean±SD |
---|---|---|---|---|---|---|
花粉活力比率 Pollen vitality | 94.19 | 94.80 | 93.99 | 95.45 | 95.58 | 94.8±0.72 |
花粉萌发率 Germination rate | 89.31 | 90.21 | 89.22 | 80.65 | 81.63 | 86.2±4.65 |
观察‘东试早柚’自交授粉后花粉管的生长萌发状态,发现大量的花粉粒在花柱顶端萌发,但花粉管向子房伸长却受到抑制而停止生长(

图3 ‘东试早柚’自交和杂交授粉后花柱的荧光成像
Fig. 3 Fluorescence images of pollen tubes in pistils after self and cross-pollination of ‘Dongshi Zaoyou’ pummelo
待果实成熟后采摘‘沙田柚’ב东试早柚’杂交果实,取其种子进行催芽播种,共获得F1代杂交群体175株。通过S基因型鉴定发现,‘东试早柚’的S基因型为S5、S6(

图4 ‘东试早柚’的S基因型鉴定
Fig. 4 S-genotypes of ‘Dongshi Zaoyou’ pummelo identified

图5 ‘沙田柚’ב东试早柚’杂交F1代S基因型遗传鉴定
Fig. 5 Genetic identification S-genotypes in F1 hybrid population of ‘Shatianyou’ pummelo × ‘Dongshi Zaoyou’ pummelo
单性结实一般是指在子房未经授粉或授粉但未受精而产生无核果实的性状。2021―2022年对‘东试早柚’进行去雄套袋和非去雄套袋的田间重复性试验,第1年去雄套袋30朵,挂果数为1,座果率为3.33%,非去雄套袋70朵,座果数为9,座果率为12.86%;第2年去雄套袋200朵,挂果数为29,座果率为14.50%,非去雄套袋200朵,挂果数为60,座果率为30.00%(
年份 Year | 处理 Experimental treatments | 花朵数 Flowers No. | 座果数 Fruits No. | 座果率/% Rate of fruit set |
---|---|---|---|---|
2021 |
去雄套袋 Emasculation-bagging | 30 | 1 | 3.33 |
非去雄套袋 Non-emasculation-bagging | 70 | 9 | 12.86 | |
2022 |
去雄套袋 Emasculation-bagging | 200 | 29 | 14.50 |
非去雄套袋 Non-emasculation-bagging | 200 | 60 | 30.00 |
植物界显花植物的花一般由花托、花萼、花瓣、雄蕊和雌蕊构成,而雄蕊由花丝和花药构成,花丝主要负责花药所需各种营养物质的运输,花药则是产生花粉粒的器官,因此花药能否正常发育很大程度上决定了植物的育
柑橘自交不亲和是指花结构完整且生殖系统均能正常发育,如‘琯溪蜜柚’‘缅甸柚’
单性结实是许多作物产生无核果实的重要原因。目前柑橘品种温州蜜柑、‘黔阳无核’椪柑、克里曼丁橘和大多数脐橙等均具有一定的单性结实能力和座果
在柑橘无核机制研究中,雄性不育、自交不亲和等因素是导致果实无核的重要原因。本研究利用形态学、分子标记等方法虽初步厘清了自交不亲和性和单性结实是‘东试早柚’无核的重要成因,但未解析其相关的基因调控网络。未来可进一步利用基因组、转录组、代谢组等多组学手段,探究‘东试早柚’自交不亲和、单性结实及自交不亲和与单性结实之间的相互作用来解析其无核成因的分子机制。
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