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

Abstract：【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.