Causes and correction efficacy of leaf chlorosis of Shine Muscat grapevine

Abstract: 【Objective】The experiment was undertaken to explore the reasons for the widespread chlorosis of Shine Muscat grape leaves and the effective correction scheme, so as to provide a reference basis for solving the problem of grape leaf chlorosis.【Methods】Shine Muscat grapevines with chlorotic symptoms were chosen as the materials, 24 chlorotic vineyards in Zhengzhou were investigated, and their soil pH value, EC value, soil organic matter, soil iron and available iron contents were determined. Aiming at the same vineyard, the differences in soil and leaf element contents, FCR enzyme activity and root iron contents between chlorosis and normal grapevines were analyzed to explore the causes ofleaf chlorosis. Pot experiment was used to treat potted seedlings with NaHCO3 solution and NaOH solution, respectively. The chlorosis was observed, and the leaf iron content, FCR enzyme activity and root iron content of chlorotic plants were determined. The differences in above indexes between chlorotic and normal grapevines were analyzed and compared with the conclusions in field experiments. According to the conclusions of field and potted experiments, three correction schemes were designed to deal with etiolated plants. The causes of leaf chlorosis were verified and a feasible correction scheme was suggested by observing the situation of green restoration and the changes of nutrient elements in leaves. 【Results】The results of chlorosis investigation of Shine Muscat showed that the content of available iron in most of the chlorosis vineyards was not low, and the degree of chlorosis was not significantly correlated with soil pH value, EC value, organic matter content, and total iron and available iron contents. In the field, the soils of chlorotic and normal grapevines were alkaline, and the nitrogen elements in the soil were mainly nitrate nitrogen. The contents of available nitrogen, phosphorus, iron, copper and zinc in soil of chlorosis grapevines were significantly lower than those of normal grapevines, while available potassium was significantly higher than that of normal grapevines, but there was no significant difference in soil total iron content between them. The contents of nitrogen, phosphorus, potassium, available iron, copper and zinc in chlorotic leaves were significantly lower than those in normal grapevines. The content of total iron in the roots of chlorotic grapevines was significantly higher than that of normal grapevines. The total iron content in normal leaves was significantly higher than that in chlorotic leaves, and the total iron content in chlorotic leaves increased with the increase of chlorosis, indicating that there was no iron deficiency in chlorotic grapevines. The upward transport of iron from the root and from the apoplast to the mesophyll cell was blocked, and iron accumulated in the apoplast of the root and leaf. There was no significant difference in root activity between chlorotic and normal grapevines, but the activity of FCR enzyme in chlorotic leaves was inhibited compared with normal leaves. In the pot experiment, chlorosis occurred in the grapevines treated with 90 mmol· L^{- 1} NaHCO3 solution, but not in the grapevines treated with NaOH solution with pH 9, indicating that the high pH value of soil is not the direct cause of chlorosis. The root iron content, leaf iron and FCR enzyme activity of chlorotic grapevines induced by NaHCO3 were similar to those in field experiments. Iron accumulation in chlorotic grapevine roots was significantly higher than that of normal grapevines, and the FCR enzyme activity of leaves was inhibited, and the total iron content in chlorotic leaves was significantly higher than that in normal leaves. There were different degrees of green recovery after the treatments including three schemes in the correction experiment, which further verified that leaf chlorosis was related to HCO3 - and NO3 - . In the scheme, ammonium fertilizer combined with citric acid was the best, foliar spraying with iron fertilizer plus citric acid was second, and foliar spraying with citric acid was the worst. The contents of nitrogen, phosphorus, potassium, zinc and copper in the green leaves of each treatment were lower than those of the chlorosis control, but the total iron content in leaves sprayed with citric acid was still higher than that of ammonium fertilizer combined with citric acid.【Conclusion】Due to the induction of high pH value in soil, a large amount of HCO3 - and NO3 - accumulated in the soil, which decreased the activity of iron reductase in roots and leaves and inhibited the absorption and transport of iron in grapevines, and the iron accumulated in the apoplast of roots and leaves could not be successfully reduced and transported to root cells and mesophyll cells, resulting in iron deficiency chlorosis in the leaves of Shine Muscat. The scheme of chlorosis correction by applying ammonium fertilizer and acid to relieve the inhibition of iron reductase in roots has the best efficacy