苹果新品种‘瑞阳’及其亲本果实组织结构的比较分析

Comparative the anatomy of the fruit between a new apple cultivar ‘Ruiyang' and its parents

【目的】苹果新品种‘瑞阳’由‘秦冠’和‘富士’杂交选育而成。感官评价‘瑞阳’肉质明显比‘秦冠’细脆,略差于‘富士’,本研究从组织结构方面分析‘瑞阳’与亲本果实质地差异的原因。【方法】本实验以‘瑞阳’及其亲本果实为研究对象,在成熟期测定果实的基本质地指标(硬度、脆度等),并采用半薄切片和扫描电镜技术对3个品种果实的组织结构进行比较,分析3个品种之间的微观差异。【结果】通过半薄切片观察,‘瑞阳’和‘富士’与‘秦冠’相比,果肉细胞平均面积大,细胞间隙小,细胞间排列紧密,圆度小,细胞纵横比大。‘瑞阳’与‘富士’相比,果肉细胞平均面积、周长、圆度等指标相近,而细胞间隙略大。通过扫描电镜观察果肉的纵切面,可知‘瑞阳’和‘富士’细胞排列整齐、紧密,而‘秦冠’细胞排列混乱,成簇分散排列,细胞间隙大;观察果肉的断裂面可得,‘瑞阳’和‘富士’均以细胞内断裂为主,且断口光滑、平齐,而‘秦冠’以细胞间和细胞内断裂为主,断口粗糙,具有毛状细丝。【结论】通过对3个苹果品种微观形态的比较分析,表明苹果的组织结构特征与质地有一定关系,从果实组织结构方面为苹果新品种选育提供理论依据。

【Objective】The new apple cultivar‘Ruiyang＇was bred by Northwest A F University from the hybrid of‘Qinguan＇and‘Fuji＇. It has a crispy and juicy texture, which is obviously tender and crispier than that of‘Qinguan＇by sensory evaluation but not so good as that of ＇Fuji＇. In order to understand the reason of fruit texture difference between‘Ruiyang＇and its parents, tissue structure of the three varieties were studied in this experiment.【Methods】Fruit texture indexes were measured at full maturity with a TMS-pilot from Food Technology Corporation. According to the previous evaluation criteria, sensory evaluation of the fruit of the three varieties was carried out at the mature stage. The microstructure of the flesh was observed using semi-thin slice technique. The flesh was cut into 5 mm ×2 mm × 2 mm squares and fixed with 4% glutaraldehyde at 4 ℃ for 12 h. After washing with phosphoric acid buffer solution for 4 times, 0.5 mL 1% osmium acid was used to immobilize the sample for 1.5-2.5 h at 4 ℃. Sample dehydration with five concentration gradients of ethanol for 10 min at each concentration was conducted followed by dehydration with 100% ethanol for 3 times each for 20 min. Finally, a semi-thin slicer（Laika Company） was used to shape the blocks and cut sections with thickness of 2μm. An Olympus automatic microscope device was used to observe the structure. The ultrastructure of the flesh tissue was observed and compared by scanning electron microscope（SEM）. The flesh was cutinto strips, which were broken into halves by hand for fracture observation with SEM. All the samples for SEM observation were fixed with 4% glutaraldehyde for 10 h, washed with 0.1 mol· L-1 phosphoric acid buffer solution for 4 times, 10 minutes each time, and dehydrated with alcohol as above mentioned.The samples were replaced with isoamyl acetate solution for 15 minutes and then dried in an EMITECH K-850 carbon dioxide critical point drying apparatus. The samples were coated with a JFC-1600 ion sputtering apparatus and observed under a JSM-6360 scanning electron microscope.【Results】The results of semi-thin sections showed that the average areas of the flesh cells of‘Ruiyang＇and‘Fuji＇were large and that the cell shape was flat with small gaps between cells and thus a tight arrangement of the cells, while the average area of the flesh cells of‘Qinguan＇was smaller and rounder. Its cells were shorter in round shape and had larger intercellular space with a loose arrangement. Observing the longitudinal section of the flesh at 50 times magnification showed that the flesh cells of‘Ruiyang＇and‘Fuji＇were obviously larger than those of‘Qinguan＇. The cell arrangement of‘Ruiyang＇and‘Fuji＇was regular and tidy, while the cell arrangement of‘Qinguan＇was irregular with large gaps between cells distributed in piles. Observing the fracture surface of the flesh of the three cultivars at 50 times magnification revealed that the tissue fracture surface of‘Fuji＇and‘Ruiyang＇was relatively neat, and many broken cells were distributed on the surface; but the fracture surface of the flesh of‘Qinguan＇was extremely uneven, with a few intact cells, indicating that the cells were not tightly bound and prone to breaking. At 500 times magnification, it was found that the cell surface of‘Fuji＇and‘Ruiyang＇was smooth and clean, while the cell surface of‘Qinguan＇was very rough and had many filaments observable under scanning electron microscope.【Conclusion】Through the anatomical analysis of the fruits of‘Ruiyang＇and its parents, it was shown that the flesh texture of apple is related to tissue structure. The new apple cultivar‘Ruiyang＇inherits the crisp texture from‘Fuji＇, and its texture is obviously superior to that of‘Qinguan＇.‘Ruiyang＇and‘Fuji＇are very similar in the tissue structure in the flesh, but quite different from that of‘Qinguan＇. The results show that the apple cultivars with crisp texture had larger flesh cells, tight arrangement of cells, regular and flat cells, small intercellular space, and neat and smooth fracture surface.