Cytologicalstudies On Texture Differences In Fruit Development Of 'Ruiyang', 'Ruixue' And Their Parents

‘Ruiyang' and ‘Ruixue' are new late-ripening apple cultivars selected by the Northwest A&F University,which stands out for its excellent texture characteristics.In order to explore the mechanism of quality formation and the difference with its parent cultivars.The materials selected in this study were ‘Ruiyang',‘Ruixue' and its parent cultivars ‘Fuji',‘Qinguan' and ‘Pink Lady'.The important texture characters were analyzed and compared in the key developmental stage.Moreover,the difference of flesh cell structure were analyzed by electron microscope technologies and the cell wall compounds and its content were analyzedin varied cultivars.We anticipate to providetheoretical basis for the identification of fruit quality and quality breeding.The main results were as follows1.The dynamic developmental process was observed and the change in firmness was also identified in further depth in ‘Ruiyang',‘Ruixue' and its parent cultivars.The results showed that: The fruit firmness showed a declined pattern in developmental process with fast rate in expansion stage and low rate in ripening period.The significance was observed in different apple cultivars and obvious in ripe fruits.According to the results obtained by sensory texture analysis in ripening fruit,the flesh is crisp in ‘Ruiyang' which was better than its parent ‘Qinguan' and similar to its parent ‘Fuji'.The flesh were crisp and hard in ‘Ruixue' and its firmness between its parents.2.The flesh cell and intercellular space expanded continuously in fruit development process and were biggest at ripening,corresponding to the decline in fruit hardness.The cell broken pattern was difference in developmental process.The flesh cells broken at equator in fruitlet and expanding fruit cells.Although the equator was main broken position,it began to separate between cells in ripening.The structure of cell wall changed in ripening fruit flesh and the broken surface showed a significance in different cultivars.3.The flesh cell shape in ‘Ruiyang' were similar to its parents which werelong rounded shapein ripening.In the aspect of the cell size,arrangement and fracture surface,‘Ruiyang' and its parent ‘Fuji' were large,loose in arrangement,smooth and tidy at the broken edges.By contrast,the flesh cells in the other parent ‘Qinguan' fruit were small,tight in alignment and zigzag cracks.4.The flesh cells character of ‘Ruixue'was similar to that in its parent cultivar ‘Fuji'.The flesh cells were special in shape with long fusiform polygon in its parent ‘Pink Lady'.The flesh cell size of ‘Ruixue' between its parents,but it were tighter in alignment than that in its parent ‘Fuji'.Meanwhile,the broken edges of flesh cells in ‘Ruixue' were smoother than that in its parent ‘Pink Lady'.5.The biochemical factors caused the firmness decrease in apple development were as follows: the content increase of WSP,while the content decrease of CWM,ISP,CSP,hemicellulose and cellulose.The difference in initial value and change extent in every physiological indexes between apple cultivars contributed to different texture in ripening,especially CSP and cellulose which were closely related to the texture development in fruit.