Nutritional Elements Related to Leaf Blight of Pearl Plum in Longtan Town

Xiaohui ZHU, Jinsheng HUANG, Yan ZENG, Liuqiang ZHOU, Rulin XIE, Jiayu PENG, Huiping OU, Zhongning LI, Hongmei LU

Abstract [Objectives] This study was conducted to investigate the correlation between leaf blight of pearl plum and nutrient elements from the perspective of plant nutrition.

[Methods]Branch and leaf samples of pearl plum plants infected by or free of leaf blight and the corresponding 0-30 cm cultivated soil were collected， and statistical analysis was conducted according to the changes in nutrient contents and the incidence of leaf blight， so as to look for nutrients in pearl plum plants associated with leaf blight， as well as soil constraint factors.

[Results] Phosphorus， iron and manganese in nutrients may be related to leaf blight， and the factors affecting leaf blight may be the ratios of P/Fe and P/Mn in leaves.

[Conclusions]This study provides a basis for further research on the relationship between phosphorus， iron and manganese on the effect of leaf blight in pearl plum trees.

Key words Longtan pearl plum; Leaf blight; Nutritional elements; Obstacle factor

Received： April 7， 2022  Accepted： June 9， 2022

Supported by Guangxi Key Research and Development Project （GK AB18294010）; Special Project of Basic Scientific Research Business of Guangxi Academy of Agricultural Sciences （GNK 2021YT036）; Key Project of Science and Technology Development Fund of Guangxi Academy of Agricultural Sciences （GNK 2016JZ09）.

Xiaohui ZHU （1979-）， female， P. R. China， assistant research fellow， PhD， devoted to research about plant nutrition and environment.

*Corresponding author. E-mail： 1035575400@qq.com.

Longtan pearl plum is a variety of plum fruit selected from local wild plum cultivars in Tiane County， Hechi City， Guangxi[1]. It has the characteristics of high and stable yield， extra late maturity， disease resistance， self-fruitful property and excellent quality， and has good production value and commercial value. Therefore， local farmers are very active in planting， and pearl plum have become one of the important ways to increase farmers income[2]. As of 2020， the planting area of pearl plum in Longtan， Guangxi is about 10 000 hm2[3]. However， with the rapid development of pearl plums in Tiane， the problems in the production process have become increasingly prominent， including the frequent occurrence of pearl plum diseases. In particular， leaf blight is widespread and is in an outbreak situation， and the planting area has dropped sharply.

Leaf blight mainly damages leaves. It usually forms reddish-brown spots on the top and margin of leaves， which then expand inwards， lead to leaf dieback， and affect photosynthesis， resulting in weakened growth vigor and reduction in pearl plum yield and quality， resulting in serious economic losses[4]. For leaf blight， local technical departments， as well as various scientific research institutes in the region and across China， have carried out various researches on its pathogen， and it has been identified as Colletotrichum gloeosporioides[3]. Based on this， the corresponding preventive drugs have been found. However， the actual situation shows that the currently used agents have not alleviated the incidence of leaf blight in pearl plum plants in Longtan. Leaf blight is still raging in the pearl plum cultivation areas in Longtan， Tiane County， which continues to affect pearl plum yield and quality， and reduces the economic benefits of local growers.

At present， most of the researches on leaf blight in pearl plum plants in Longtan tend to search for pathogens and prescribe drugs for the symptoms （pathogens）， but the effects are not obvious， and the pathogenesis of leaf blight in pearl plum plants has been rarely studied from the aspect of plant nutrition. In this study， from the perspective of plant nutrition， samples of pearl plum plants infected by or free of leaf blight and the corresponding 0-30 cm cultivated soil were collected， and statistical analysis was conducted according to the changes in nutrient contents and the incidence of leaf blight， so as to look for nutrients in pearl plum plants associated with leaf blight， as well as soil constraint factors.

Materials and Methods

We visited and investigated the pearl plum plantations in villages of Tiane Bala Yao Township， Nazhi Township， Pojie Township， and Liupai Township， and collected branch and leaf samples of pearl plum trees showing symptoms of leaf blight and branch and leaf samples of the same parts of other healthy plants from different plantations， as well as the corresponding 0-30 cm plough layer planting soil samples. The samples were brought back to the laboratory for nutrient analysis. The sampling time is June-July 2021， and 2-4 diseased plants were collected from each plantation for mixed sample preparation. The branches and leaves were sampled separately. Two samples were collected from normal plants for mixed sample preparation， and the branches and leaves were also prepared separately. Soil samples were collected from 5-8 points in each plantation for mixed sample preparation.

Plant samples were digested with H2SO4-H2O2， and total nitrogen was determined by a Kjeldahl analyzer; total phosphorus was determined by a discrete analyzer; and total potassium was determined by a flame photometer. The organic matter of soil and filter mud samples was determined by the potassium dichromate volumetric method， and the total nitrogen was determined by the Kjeldahl analyzer; the available phosphorus was determined by 0.5 M NaHCO3 extraction-molybdenum antimony anti-colorimetric method; available potassium was measured by a flame photometer; and pH value was measured by the potentiometry， with a soil/water ratio=1/2.5.

The data analysis was performed by software such as Excel 2007 and DPS 7.05.

Results and Analysis

Soil conditions of pearl plum plantations infected and uninfected with leaf blight

The results showed that there were no significant differences in the contents of macronutrients， medium nutrients and micronutrients in the planting soils infected and uninfected with leaf blight （Table 1）. Although there was no significant difference in the bioavailability of each nutrient in the topsoil of pearl plum plantations infected and uninfected with leaf blight， the contents were still slightly different. The pH values of the topsoil in the uninfected pearl plum plantations were between 4.31 and 6.19， and the pH values of the topsoil in the infected plantations were between 4.73 and 5.57. The variation range of organic matter content in the topsoil of uninfected pearl plum plantations was 21.42-36.90 g/kg， and that of infected plantations was 20.43-46.19 g/kg. The variation range of hydrolyzable nitrogen content in the topsoil of uninfected pearl plum plantations was 66.56-124.08 mg/kg， and that of infected plantations was 69.25-129.45 mg/kg. The variation range of available phosphorus content in the topsoil of uninfected pearl plum plantations was 1.09-26.19 mg/kg， and that of infected plantations was 0.85-12.79 mg/kg. The variation range of available iron content in the topsoil of uninfected pearl plum plantations was 16.67-156.40 mg/kg， and that of infected plantations was 10.42-126.60 mg/kg. The variation range of available Mn content in the topsoil of uninfected pearl plum plantations was 6.22-31.52 mg/kg， and that of infected plantations was 8.04-31.70 mg/kg.

Nutrient element contents of pearl plum plants infected and uninfected with leaf blight

Table 2 shows the nutrient element contents of infected and uninfected pearl plum plants. The levels of nutrient elements in pearl plum plants showed following orders： N>K， Ca>P， Mg>Zn>Mn>Cu>Fe. Nitrogen， phosphorus， potassium， calcium， magnesium， iron， manganese， copper， zinc and other elements were contained in branch and leaf samples， but their contents showed no significant correlation with whether they were infected with leaf blight and the severity of the disease.

Furthermore， we analyzed the relationship between the elements， as shown in Table 3. There were no significant differences in Fe/Mn， K/Mg， Ca/Mg， Cu/Zn， C/N， P/Zn， P/Fe， P/Mn， P/Mg， Fe/Zn and Fe/Cu between infected and uninfected branch samples， but infected and uninfected leaves differed significantly in P/Fe and P/Mn. The P/Fe and P/Mn ratios in the uninfected leaves were 4 195.79 and 761.31， respectively， and those in the infected leaves were 3 332.68 and 460.51， respectively， showing that the P/Fe and P/Mn was significantly higher in uninfected leaves than those in infected leaves.

Conclusions and Discussion

Experiments showed that the leaf blight of pearl plum may be related to phosphorus， iron， copper and other elements in leaves， and the judgment factor affecting leaf blight may be P/Fe and P/Mn ratios. If the ratios of P/Fe and P/Mn are low， the risk of infecting leaf blight of pearl plum trees may increase. However， the contents of phosphorus， iron， and copper in infected and uninfected leaves did not show significant differences. Therefore， it cannot be concluded that P/Fe and P/Mn in leaves are the judging factors of pearl plum leaf blight， and it should be further verified.

The pH value， organic matter and hydrolyzable nitrogen in the topsoil of the pearl plum plantations infected with leaf blight were slightly lower than those of the uninfected plantations， while the hydrolyzable nitrogen was slightly higher than that of the uninfected plantations. Meanwhile， corresponding to the P/Fe and P/Mn ratios of pearl plum leaves infected with leaf blight lower than those of uninfected leaves， the available phosphorus content of the topsoil of the pearl plum plantations infected with leaf blight was lower than that of the uninfected plantations， but the contents of available iron and available manganese in the topsoil of the infected plantations were also slightly lower than those of the uninfected plantations， which was contrary to the results for leaves. Therefore， it is still necessary to further study the relationship of phosphorus with iron and manganese on the effect of leaf blight in pearl plum trees.

References

[1] GUAN EK， WEI HY， FAN MZ， et al. Performance and cultivation techniques of pearl plums in Tiane， Guangxi[J]. South China Fruits， 2008， 37（1）： 73-74. （in Chinese）.

[2] GUAN EK， ZHAO DY， FAN MZ， et al. Occurrence and control technology of fruit flies of pearl plums in Longtan[J]. South China Fruits， 2013， 42（5）： 117-118. （in Chinese）.

[3] WEI RM. Development status and countermeasures of pearl plum industry in Longtan， Tiane County[J]. Xiang Cun Ke ji， 2021， 12（13）： 35-36. （in Chinese）.

[4] JI ZL， DAI HJ， ZHANG TQ， et al. Identification of the pathogen causing plum leaf blight[J]. South China Fruits， 2015， 44（2）： 39-42. （in Chinese）.