An anatomical study on flower bud differentiation in Prunus salicina×armeniaca

Abstract:【Objective】The study observed the anatomical changes of bud during the progress of flower dif⁃ferentiation in different cultivars of Prunus salicina×armeniaca in order to characterize flower differentia⁃tion periods of Prunus salicina×armeniaca and the difference between cultivars, so as to provide a refer⁃ence for breeding of Prunus salicina×armeniaca and for reasonable implementation of cultivation manage⁃ment in production.【Methods】Three cultivars of Prunus salicina×armeniaca were used as the main testedmaterials and one common cultivar of apricot and one cultivar of Chinese plum as the cross reference. Inthe late June of 2016, trees of the cultivars in good health and growth were tagged and buds were collectedevery 10 d until late October. The collected buds at each time were placed in 5 mL centrifugal tubes andpreserved in FAA fixative solution. Bud sections were obtained using the conventional paraffin sectionmethod, and the bud structure at each period during the morphological differentiation of flower bud in thetested cultivars were observed and photographed under microscope.【Results】The whole process of themorphological differentiation of flower bud in the three cultivars and the references could be divided intothe pre-differentiation stage, the floral primordial differentiation stage, the sepal primordial differentiationstage, the petal primordial differentiation stage, and the stamen and pistil late primordial differentiationstage. The time of stage transitions and the duration of the whole differentiation period were differentamong cultivars, and there were overlaps between stages and staggered phenomena during each stage. Thethree cultivars of Prunus salicina×armeniaca had entered the early stage of floral primordial differentia⁃tion stage by Jun. 25th, when 90% of buds in‘Konglongdan’had started flower differentiation and 15%in‘Weidi’had entered the late stage of floral primordial differentiation stage. The early stage of floral pri⁃mordial differentiation stage in‘Fengweihuanghou’lasted until Aug. 14th, and 20% of buds in this culti⁃var were still in the late stage of floral primordial differentiation on Oct. 20th. The early stage of floral budprimordial differentiation in‘Konglongdan’and‘Weidi’lasted for about 40 d. In‘Meilili’and‘Saimaiti’,flower bud differentiation began on Jun. 25th, when 45% of flower buds in‘Meilili’had entered the latestage of floral bud primordial differentiation, which lasted for about 30 d. The flower bud in‘Konglong⁃dan’had entered the sepal differentiation stage by Aug. 4th and lasted until Sept. 3rd. The sepal differen⁃tiation stage in‘Weidi’began on Aug. 14th and continued for about 20 d.‘Fengweihuanghou’was thelatest to enter the sepal differentiation stage, which lasted for a long time. The sepal of‘Melili’and‘Saimaiti’began to differentiate on Jul. 5th, and the duration of the stage in‘Meilili’was longer thanthat in‘Saimaiti’, which lasted for about 20 d. By Sept. 13th, the flower bud of‘Fengweihuanghou’hadentered the petal primordial differentiation stage, which lasted till Oct. 3rd. There were 10% of flowerbuds in‘Konglongdan’that showed petal differentiation on Aug. 24th and the stage continued until Sept.23rd, while in‘Weidi’80% flower buds had entered the petal differentiation stage by Sept. 3rd and thisstage lasted until Sept. 23rd. The flower buds of‘Meilili’showed petal differentiation on Jul. 25th, andthis stage lasted for a relatively long period of time. However, in‘Saimaiti’, 90% of flower buds had en⁃tered the petal differentiation stage by Jul. 25th, which lasted for only 10 d. 15% of flower buds in‘Feng⁃weihuanghou’had entered the stamen differentiation stage and 10% flower buds entered the pistil differ⁃entiation stage by Sept. 23rd. By Oct. 20th, 65% of flower buds had entered the pistil differentiation stage,but there were still 15% of flower buds still in the stamen differentiation stage. 5% of flower buds in‘Kon⁃glongdan’had entered the stamen differentiation stage by Aug. 24th, and 40% entered the pistil differenti⁃ation stage by Sept. 13th. Till Oct. 13th, all flower buds in‘Konglongdan’had completed pistil differenti⁃ation. 10% of flower buds in‘Weidi’had begun stamen differentiation, and 10% showed pistil differentia⁃tion on Sept. 3rd. The stamen differentiation stage continued till Oct. 3rd, and all the flower buds in‘Weidi’had completed pistil differentiation by Oct. 20th. The flower buds of‘Meilili’had entered the stamen dif⁃ferentiation stage by Aug. 24th, which continued till Oct. 13th. Pistil differentiation began on Sept. 3rdand lasted until Oct. 20th, when 100% flower buds in‘Meilili’had completed pistil differentiation. 60%of the flower buds in‘Saimaiti’had entered the stamen differentiation stage and 35% of them begun pistildifferentiation by Aug. 4th, and by Sept. 13th all the flower buds of‘Saimaiti’had completed pistil differentiation. The peak period of flower bud differentiation in the three cultivars of Prunus salicina×armeniacaoccurred between the early July and the early October, and pistil differentiated in late the October. Thewhole differentiation period lasted for about 110 d.【Conclusion】The period of morphology differentiationof flower bud in the three cultivars of Prunus salicina × armeniaca is relatively concentrated. Flower buddifferentiation occurs stepwise and there are no clear division lines between stages. The evolution of ana⁃tomical structures of flower buds during the progress of morphological differentiation is similar to that in‘Meilili’. Multiple primordia may occur in the same flower bud. The whole process of differentiation issimilar between cultivars but is slower in‘Meilili’and its stage transitions of flower bud differentiationoccur later than in‘Saimaiti’.