Research on yellowing causes and correction efficacy in a new red-peeled pear variety Hongsumi

Abstract:【Objective】Differences in mineral element contents in soil and leaves between the yellowing and healthy trees were compared to figure out the reason for yellowing symptoms of Hongsumi. In addition, the effects of three fertilizer treatments were screened by analyzing the changes in leaf color, fruit quality and soil mineral element contents to unravel the best management practice for reducing yellowing symptoms on Hongsumi.【Methods】Three treatments were set up on Hongsumi trees with yellowing symptoms: Treatment 1 (20 g Biyi iron + 20 g microcrystalline C+ 20 kg water), Treatment 2 (20 g freeilene + 20 g algin+ 20 kg water), and Treatment 3 (200 ml soil conditioner+ 20 kg water). This experiment also set two controls: yellowing trees control (yellowing CK with irrigating water) and normal trees control (green CK with irrigating water). Five replicates per treatment were conducted in a single plant block design. A 30 cm deep hole was dug at 1/2 of the canopy and covered with soil after irrigating for three treatments. Soil samples (1 kg, 20 to 40 cm deep) were collected around the trees before the treatments. One month after the application, photos were taken for each tree and soil samples were collected around each treatment and control tree. Meanwhile, 1 kg soil sample, 20 fruit samples and 30 leaf samples were randomly collected. PH value, the contents of organic matter, nitrogen, total Mn-salt, available phosphorus, available potassium, total iron, available iron, available zinc, available copper and available manganese in each soil sample were determined. The contents of nitrogen, phosphorus, potassium, total iron, manganese, zinc, copper and active iron in leaves were measured. The contents of single fruit weight, Vc, soluble solids, total acid and soluble sugar in fruits were evaluated. By analyzing the differences in pH value and mineral element contents in soil between normal and yellowing trees, the cause of Hongsumi yellowing symptoms was discovered. The best treatment was selected not only by observing and analyzing the changes of yellowing leaf color, but also by evaluating fruit quality and the changes of mineral element contents in soil and leaves before and after processing. The determination of Vc, total acid and soluble sugar contents in fruits was carried out with reference to the national food safety standard GB 5009.86—2016, GB 12456—2021 and the colorimetric method of 3, 5-dinitrosalicylic acid in NY/T 2742—2015, respectively. The determinations of soil pH value and organic matter were based on the agricultural industry standard NY/T 1121.2—2006. Kjelsberg method was used to determine soil nitrogen content. The determinations of available phosphorus and available potassium were based on the agricultural industry standard NY/T 1121.7-2014 and NY/T 889-2004. The determinations of soil available iron, available zinc, available copper and available manganese were conducted with the diethyl triamine pentaacetic acid (DTPA) extraction method based on the agricultural industry standard NY/T 890—2004. The determinations of nitrogen and phosphorus in leaves referred to the agricultural industry standard NY/T 2017—2011. The determinations of potassium, iron, manganese, zinc and copper in leaves referred to the national standard GB 5009.91—2017, the national standard GB 5009.90—2016, the national standard GB5009.242—2017, the national standard GB 5009.14—2017, and the national standard GB 5009.13—2017, respectively.【Results】Alkaline soil led to the deficiency of available iron, phosphorus, potassium and manganese in soil. The content of available iron in soil was significantly and positively correlated with the content of manganese, nitrogen, available phosphorus and zinc in the soil. The contents of organic matter, available iron, available phosphorus, available zinc and available copper in the soil around Hongsumi trees with yellowing symptoms were significantly lower than those in soil around healthy trees. There was no difference in the contents of nitrogen, total iron, active iron, manganese and zinc in leaves between yellowing and healthy trees, while the contents of phosphorus, potassium and copper in leaves of trees with yellowing symptoms were significantly higher than those with normal trees. The lack of available iron in soil was the direct cause of the yellowing symptoms in 'Hongsumi'. The treatments of Biyi iron + microcrystalline C and freeilene + algin can significantly increase the contents of available iron in soil, which had a significant effect on alleviating yellowing symptoms. Soil conditioner had no effect on controlling the chlorosis, and the yellowing symptoms were remaining. The contents of available phosphorus, zinc, iron, manganese and copper in soil treated with Biyi iron + microcrystalline C were significantly higher than those with the control. The contents of available iron and copper in soil that was treated with freeilene + algin were significantly higher than those in the control, also with the best fruit quality from the corresponding treated trees. 【Conclusion】The results revealed the yellowing symptoms in Hongsumi were caused by physiological iron deficiency. The treatments with Biyi iron + microcrystalline C and freeilene + algin had the best effects on alleviating yellowing. The contents of soil available iron, phosphorus, zinc and copper in trees with yellowing symptoms were significantly lower than those with normal trees. Our study highlighted that the available iron contents were positively correlated with the contents of available manganese, nitrogen, phosphorus and zinc in soil.