Breeding of a New Fruit Radish Variety "Sheng Qing Yi Hao"

Keyou CAO Xingsheng LI Xiaowei YUAN

Abstract In order to explore the effects of combined foliar spray which was prepared from potassium fulvate and Zn on heavy metal accumulations in three kinds of facility fruit vegetables， cucumber， tomato and white melon， the foliar spray was applied from fruit setting to maturation. The results showed that the combined foliar spray significantly promoted the absorption of Zn and Cu in the three fruit vegetables， blocked the absorption of Cr， As and Pb in cucumber， significantly blocked the absorption of Cd in white melon， blocked the absorption of Pb in white melon， and showed a tendency of blocking the absorption of heavy metals Cd and As in tomato.

Key words Foliar spray; Facility fruit vegetables; Accumulation of heavy metals; Impact

The chemical properties and metabolic pathways of heavy metals are similar or related to crop nutrients. The transport systems through which heavy metals and crop nutrients are absorbed or stored by plants are the same， and there is mutual antagonism or promotion between each other， so foliar spraying of nutrients has become one of the effective ways to block the absorption of heavy metals by plants. At present， there are many studies on foliar spraying of nutrient elements to block the absorption of heavy metals by plants[1-8]. Zhang et al.[9] reported that foliar spraying of selenium fertilizer during the fruit setting period of field watermelon increased the selenium content of watermelon， and simultaneously reduced the contents of Cd and Pb. Xu et al.[10] sprayed zinc and iron fertilizers on cabbage and found that Zn had an antagonistic effect on the absorption of Cd. Huang et al.[11] and Weng et al.[12] believed that foliar spraying of fertilizers could regulate the accumulation of heavy metals in crops. Foliar spraying of iron fertilizer can regulate the accumulation of heavy metals in vegetables. On April 10， 2019， heavy metals and blocking were input to the SooPAT patent website， and the eligible query results included a total of 209 items that have been authorized and were undergoing substantive examination. They were mainly about blocking of soil and water heavy metals， and there were 3 items that can be used for vegetable spraying to block absorption， while the composition is diverse.

Potassium fulvate is a kind of pure natural mineral active potassium element fertilizer， which can promote the physiological metabolism of various fruits， vegetables and field crops， thus promoting developed root systems， lush stems and leaves， preventing flower and fruit falling， increasing the sugar content of fruits， and improving fruit quality. Zn is an important part of many metal enzymes and can activate a variety of enzymes， so Zn plays an important role in the normal metabolism of organisms. In this study， three kinds of fruits and vegetables： cucumber， tomato and white melon， were selected to carry out an application effect test of a combined foliar spray prepared from potassium fulvate and Zn nutrient on facility fruit vegetables during normal production process from fruit setting to maturation in May-August 2018， during which the absorption of 7 heavy metals Cd， Cr， Cu， Pb， Zn， As and Hg by the facility fruit vegetables was investigated， hoping to provide reference for the application of heavy metal blocking technology in facility vegetable fields， and the prevention and control of heavy metals and the intervention of emergency pollution processes in vegetable production.

Materials and Methods

Experimental materials

The tested fruit vegetable varieties： Tomato "Dongsheng"; cucumber "Bomei 28"; white melon "Xingtian 24".

The combined foliar spray was prepared with 0.005-0.015 nl of film forming additive and 0.985-0.995 nl of water in a mixed solution， in which 0.5-1.5 ng of potassium fulvate and 0.2-0.4 ng of zinc sulfate were dissolved. Wherein， n is greater than 0， and the dosage of 667 m2 is 50 L （i.e.， the dosage of 667 m2 is calculated according to n=50）.

Experimental methods

When cucumber， tomato and white melon were all in the peak period of fruit expansion， foliar spraying was performed from May 13 once every 7 d until the end of the harvest period. Fruit and soil samples were taken before spraying. Each plot had an area of 6 rows×1 m×15 m=90 m2， with 3 repetitions， and spraying water was set as a control. Due to the influence of the maturation period， cucumber and tomato were sprayed with the combined agent for 3 times and sampled 3 times for fruit， and white melon was sprayed for 4 times and sampled 4 times for fruit. Soil samples were collected in accordance with the "one-to-one" principle when taking fruit samples for the first and fourth times， and three samples of normal mature fruit mixture and 3 samples of corresponding soil mixture were collected according to the five-point sampling method for each repetition. A total of 192 samples were collected.

Item determination

The soil samples were air-dried， ground， and sieved with a 100-mesh nylon sieve for laboratory analysis. The vegetable samples were rinsed with tap water and distilled water 3 times， deactivated at 105 ℃ for 20 min， dried at 70 ℃， and crushed for testing. The determination of Cd in vegetable samples referred to GBT5009.11-2003 and GBT5009.17-2003 in Methods for Food Hygiene Inspection. For the determination of Cd in soil samples， sample pretreatment was performed with reference to DD2005-01， and 7700XICPMS was used for determination with reference to HJ803-2016. Standard substances were used as internal standards to control the quality of analysis， and the addition of standard samples for soil and plant inspection referred to GBW07427 （GSS-13） and GBW10011 （GSB-2）， respectively. In order to prevent sample contamination， the use of metal products was avoided during sampling， sample storage and treatment.

Melons and fruits are low-absorption crops with low heavy metal content. Referring to the heavy metal limit standards for vegetables in Maximum Levels of Contaminants in Foods （GB 2762-2017）， the heavy metal contents all did not exceed the standards. In order to show the differences， the test results of this study were calculated using the content of 100 kg of fresh fruits and vegetables， that is， Cd content of 100 kg fresh weight （mg/kg）=Heavy metal content detected after drying×（1-Moisture content）×100 kg. The moisture contents are shown in Table 1.

The bioconcentration coefficient （BCF） of fruit vegetables for heavy metals was used to measure the ability of vegetables to absorb and enrich heavy metals from the soil. The calculation formula is： BCF=C vegetable/C soil， where C vegetable represents the content of a certain heavy metal in a certain vegetable （mg/kg）， and C soil represents the content of the certain heavy metal element in the corresponding soil （mg/kg）. The test results were calculated using the content of 100 kg of fresh fruits and vegetables， that is， 100 times of the bioconcentration coefficients of fruit vegetables were compared.

Data analysis

The test data was sorted and analyzed using Excel and SPSS software.

Results and Analysis

Soil heavy metal content analysis

It can be seen from Fig. 1 and Fig. 2 that the average contents of Cr， Cu， Pb and Zn in the soils of cucumber， tomato and white melon all increased after the experimental treatment. Specifically， the average contents of the 4 heavy metals in the soils of the three fruit vegetables increased by 14.35%， 20.08%， 77.32% and 17.88%， respectively. The average soil contents of As， Cd， and Hg decreased. The As contents in the cucumber， tomato， and white melon soils decreased by 60.68%， 54.71% and 41.42%， respectively， with an average decrease in the three kinds of fruit vegetables by 52.27%. The soil Cd contents decreased by 30.11%， 25.76% and 33.42%， respectively， with an average decrease of 29.76%. The Hg contents decreased by 82.25%， 76.34% and 91.64%， respectively， with an average decrease of 83.41%.

Analysis of fruit heavy metal contents

It can be seen from Fig. 3 that the Cu and Zn contents of white melon were the highest among the three fruit vegetables， and those of cucumber were the lowest. The average contents of the two heavy metals in the three kinds of fruit vegetables were both higher than those of the control. The content of Cu increased by 7.02%， 11.01% and 14.37% in cucumber， tomato and white melon， respectively. The content of Zn in cucumber， tomato and white melon increased by 29.31%， 55.10% and 75.78%， respectively. For the samples picked during the second sampling， that is， 7 d after spraying the blocking agent， the absorption of different heavy metals changed significantly， but the trends were different. The Cu and Zn contents significantly increased in the cucumber and white melon samples picked at the second time， and then decreased， and the absorption trends were basically the same. The results of LSD multiple comparison showed that the Cu content of cucumber in the second treatment exhibited the P values of 0.007， 0.030 and 0.011， respectively， when compared with the control， the first and the third sampling， and the Cu content of white melon in the second treatment exhibited P values of 0， 0.002， and 0.004， respectively， when compared with the control， the first and third sampling. The Zn content of cucumber showed very significant differences between various treatments; and for white melon， the second treatment exhibited extremely significant differences， and other treatments had significant differences. The contents of Cu and Zn in tomatoes had been continuously increasing. The results of LSD multiple comparison showed that the Cu content of the third treatment was significantly different from that of the control， and the P value was 0.006; and the Zn content was extremely different， and the P value was 0.000. The continuous increase of Zn content was related to the Zn contained in the sprayed blocking agent. The foliar spray promoted the absorption of Zn by cucumbers in an extremely significant mode， significantly promoted the absorption of Zn by melons during the day and significantly promoted the absorption of Cu and Zn by tomato fruit.

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It can be seen from Fig. 4 that the detection result of Hg content tended to 0 mg/kg， and the change was not obvious， so no further analysis was conducted. The three kinds of fruit vegetables had the highest Cr， As and Pb contents and the lowest Cd content in white melon. The Cd content of tomato was always higher than those of cucumber and white melon.

The detection value of Cr content increased in both the cucumber and white melon samples picked during the second sampling， and then showed a downward trend. The differences were basically not significant， but the third treatment of cucumber was significantly different from the control with the P value of 0.053. The Cr content of tomato first decreased and then increased， without significant differences. Compared with the control， the average Cr contents of white melon and tomato increased by 9.44% and 14.29%， respectively， and the value of cucumber was lower than the control by 15.52%.

The variation trends of As content in the three fruit vegetables were different. The contents of cucumber and white melon increased in the second and third times. The As content of white melon was significantly different between the third time and the control with the P value of 0.000， and then decreased; and compared with the control， the average As content of the cucumber treatments decreased by 23.29%， and that of white melon increased by 16.42%. The As and Cd contents of tomato continued to decrease with the increase of foliar spraying times. The foliar spray showed a relatively stable blocking effect on tomato absorption of As and Cd， which increased by 6.59% and 14.01% respectively compared with the control， and the differences were not significant. The average Cd contents in cucumber and white melon showed a trend of decreasing after the increase in the second time; the value of white melon increased again in the fourth time， and each treatment were significantly different from the control; and compared with the control， the average Cd content of cucumber increased by 33.06%， and that of white melon decreased by 6.09%. The Pb content of cucumber decreased in the third treatment， and the white melon showed a wave change. The Pb content changed in the same trend with Cd content. The Pb contents of cucumber and white melon were lower than the control by 20.28% and 36.24%， respectively， and the content of tomato first decreased and then increased， with an average value higher than the control by 27.70%.

It can be seen from Table 2 that compared with the control， the average contents of Cr， As， and Pb in cucumber sprayed with the combined agent decreased by 15.52%， 23.29% and 20.28%， respectively， the contents of heavy metals in tomato increased， and the average contents of Cd and Pb in white melon decreased by 60.91% and 36.24%， respectively， showing remarkable effects. Compared with the control， the contents of Cu， Zn and Cr among the 6 heavy metals increased in the three fruit vegetables， while the contents of As， Cd and Pb all decreased.

Comparison of concentration coefficients of 7 heavy metals in the three kinds of fruits and vegetables before and after the test

It can be seen from Table 3 that the Cr and Cu concentration coefficients in the three kinds of fruit vegetables all decreased after the foliar spray was applied. There were no effects on the Pb concentration coefficients of cucumber and white melon; the Pb concentration coefficients of Zn all decreased; and those of Cd all increased. The Zn and Hg concentration coefficients of tomato increased， and the others all decreased. The concentration coefficients of the three kinds of fruit vegetables for Cd ranked as tomato>white melon>cucumber. The combined foliar spray affected the absorption characteristics of heavy metals in fruit vegetables， and could inhibit or antagonize the absorption and accumulation of heavy metals such as Cd and As by crops[12].

Discussion and Conclusions

Compared with the control， the contents of Cu， Zn and Cr in the fruit vegetables all increased， and those of As， Cd and Pb all decreased; the average contents of Cu， Zn， Cr and Pb in the soil all increased， and the average contents of As， Cd and Hg in the soil decreased; and the contents of Cu， Zn and Cr all increased in the fruits and soils， while the contents of As and Cd decreased. Therefore， Cu， Zn and Cr have mutual promotion of absorption， and have absorption antagonism with As and Cd. When Cd and Zn coexist， there are complex interactions between them. The interaction of Cd and Zn in plants has long been concerned by people， but no unanimous conclusions have been drawn[13]. However， some scholars consider there is an antagonistic effect between Cd and Zn under certain conditions[14-18]， which is consistent with the results of this study.

The combined foliar spray can be applied to the prevention and control of As and Cd-polluted fruits and vegetables. The heavy metal Cd content of the tomato sprayed with the blocking agent showed a downward trend， but the effect of the blocking agent was not significant; and the average heavy metal Cd content of white melon decreased， and the effect was significant.

The blocking spraying had no effect on the appearance， growth， and harvest of melons and fruits， and abnormal fruit or growth retardation was not observed. Since there are many factors affecting normal production in the field， although horizontal control and the vertical test were done for comparison， the test effect needs to be further studied.

The results of this study showed that the combined foliar spray significantly promoted the absorption of Zn and Cu by the three fruit vegetables， blocked the absorption of Cr， As， and Pb by cucumbers， significantly blocked the absorption of heavy metal Cd by white melon， and blocked the absorption of Pb in white melon， and there was a tendency to block the absorption of heavy metals Cd and As in tomato， although the effect was not significant.

References

[1] ZHANG MK， NI ZY， SHEN Q. Research progress on physiological control of heavy metal pollution in crops[J]. Environmental Pollution & Control， 2017， 39（1）： 96-101. （in Chinese）

[2] WU Z， REN H， MCGRATH SP. Investigating the contribution of the phosphate transport pathway to arsenic accumulation in rice[J]. Plant Physiology， 2011， 157（1）： 498-508.

[3] HE QS， SINGH BR. Crop uptake of cadium from phosphorus fertilizers： I. yield and cadium content[J]. Water， Air and Soil Pollution， 1994， 74（3）： 251-265.

[4] CHEN GQ， ZHANG XJ， XU WH， et al. Effect of different zinc levels on accumulation and chemical forms of cadmium， and physiological characterization in Capsicum annuum L.[J]. Environmental Science， 2010， 31（7）： 1657-1662. （in Chinese）

[5] GAO C， WANG Y， MA L， et al. Effect of Fe nutrition status on Cd2+ influx on root surface of Malus xiaojinensis[J]. Journal of China Agricultural University， 2011， 16（6）： 83-87. （in Chinese）

[6] CUI XF， DING XD， LI SY， et al. Effects of the foliar application of silicon and cerium sol on relieving toxicity of Pb，Cd in the lettuce[J]. Journal of Safety and Environment， 2012， 12（5）： 7-12. （in Chinese）

[7] ZHANG XZ， ZHANG FS， LI YX， et al. The effects of manure composting on distribution of Cu and Zn speciations in soils[J]. Journal of Agro-Environment Science， 2009， 28（9）： 1975-1979. （in Chinese）

[8] LI Y， WANG HX， WU YS. The effects of Cd and Fe on Cd and Fe contents and physiological indicators in leaves of tobacco Nicotiana tabacum[J]. Acta Scientiae Circumstantiae， 1990， 10（4）： 494-500. （in Chinese）

[9] ZHANG CC， CHANG JT， ZHAO P. Effects of foliar application of Se on Cd and Pb accumulation in the leaves and fruits of watermelon[J]. Acta Agriculturae Boreali-Sinica， 2013， 28（3）： 159-163. （in Chinese）

[10] XU C， OUYANG DS， ZHU YS， et al. Influence of foliar application of iron fertilizer on heavy metal accumulation in Brassica parachinensis[J]. Environmental Science & Technology， 2014， 37（11）： 20-25. （in Chinese）

[11] HUANG AH， HUANG KJ， PENG K， et al. Effect of foliar spraying of selenium fertilizer on selenium-enriched content， heavy metal content and yield of sweet corn grain[J]. Journal of Southern Agriculture， 2019， 50（1）： 40-44. （in Chinese）

[12] WENG BQ， LIU PH， ZHANG WL， et al. Ideas and countermeasures research on heavy metal pollution prevention and control for farmland[J]. Ecology and Environment， 2015， 24（7）： 1253-1258. （in Chinese）

[13] LYU XZ， GONG XL， TANG Y. Antagonistic effect of foliar application of Se or Zn on absorption of Cd in lettuce [J]. Acta Pedologica Sinica， 2006， 43（5）： 868-870. （in Chinese）

[14] LI HC， WANG QQ， JIA RY， et al. Antagonistic effects of exogenous zinc on uptake and accumulation of cadmium in various rice organs[J]. Acta Scientiae Circumstantiae， 2018， 38（12）： 4854-4863. （in Chinese）

[15] THOMET U， VOGEL E， KRAHENBUHL U. The uptake of cadmiumand zinc by mycelia and their accumulation in mycelia and fruiting bodies of edible mushrooms[J]. Eur Food Res Technol， 1999（209）： 317-324.

[16] HERRREN T， FELLER U. Transport of cadmium via xylem and phloem in maturing wheat shoots： Comparison with the translocation of zinc， strontium and rubidium[J]. Annals of Botany， 1997（80）： 623-628.

[17] LI XJ， ZHENG XQ， ZHENG SA. Accumulation and sensitivity distribution of cadmium in leafy vegetables[J]. Research of Environmental Sciences， 2017， 30（5）： 720-727. （in Chinese）

[18] LYU GH， XU C， WANG H， et al. Effect of foliar spraying zinc on the accumulation of zinc and cadmium in rice[J]. Journal of Agro-Environment Science， 2018， 7（7）： 1521-1528. （in Chinese）