Fruit quality characters and causes of watercore apple in high altitude areas of Guizhou

【Objective】To study the quality characteristics of the watercore apples, to clarify the characteristics and mechanisms of the watercore phenomenon of apples in the high altitude region and provide a theoretical basis for watercore apple production.【Method】Qianxuan 3 apple from Guizhou high altitude area was used as experimental material. The fruit quality indexes at four growth periods(early stage of fruit enlargement S1, harvesting mature stage S2, edible mature stage S3 and physiology mature stage S4) were compared, difference in glucose component content, mineral ele-ments, and sorbitol metabolism related enzyme activity between watercore and non-watercore tissues were analyzed and the paraffin sections of pulp tissue were studied.【Result】The results showed that the longitudinal diameter and transverse diameter of the fruit increased significantly from S1 to S3(P<0.05, the same below), and the growth rates of S3 were 22.37% and 22.67% respectively compared to S1. There was no watercore in the S1 period, and more than 56% of the fruits after the S2 period had watercore, there was no significant difference in watercore rate between S3 and S4 periods (P>0.05, the same below), but the difference in watercore index was significant. The watercore fruit rate and watercore fruit index were extremely positively correlated with picking period, single fruit weight, fruit moisture content, soluble solid content(SSC) and peal a* value(P<0.01, the same below), whereas, were extremely negatively correlated with L* value and b* value of peel. During S2-S4, the contents of fructose, glucose and sucrose in watercore tissue were lower than those in non-watercore tissue, while the content of sorbitol in watercore tissue was significantly higher than that in non-watercore tissue, reached 1.10-1.92 times of that in non-watercore tissue. SDH activity in watercore tissue at S2-S4 period had decreasing trend in fluctuation, only S3 period had significant difference between watercore tissue and nonwatercore tissue, and SDH activity in non-watercore tissues was gradually reduced. SOX activity in non-watercore tissue was reduced, difference between watercore tissue and non-watercore tissue at S2 and S4 periods was significant. Ca content in mature fruit in watercore tissue was significantly higher than that of non-watercore tissue, and was 1.80 to 2.79 times of non-watercore tissue. Except S4 period, K content manifested as a watercore tissue content higher than the nonwatercore tissue. Except for S4, Fe and Zn content in watercore tissue was lower than the non-watercore tissue. Except for S2, Mg content in watercore tissue content was higher than the non-watercore tissue. Cu content decreased in watercore tissue and non-watercore tissue, but the watercore tissue Cu content was lower than the watercore tissue. In the physiological maturity stage, the cells were intact and no fragmentation occurred in both of the two tissues. In addition, from the year of 2016 to 2018, the diurnal temperature from September to November were ranged from 18.43 to 23.34℃.【Conclusion】The apparent diurnal temperature at mature stage results in the inhibition of transformation process of sorbitol in time, hence, sorbitol from leaves accumulation in the core of the flesh, which may be responsible for the formation of the watercore in Guizhou high altitude area.