Review on Effects of Application of Exogenous Growth Regulating Substance on Fruits Weight of Peach

Zhisheng MA Yunyun JIA,Yuehui WANG,Ruixia BAI,Jiangyu CHENG,Zhixin LIU

Shijiazhuang Pomology Institute,Hebei Academy of Agriculture and Forestry Sciences,Shijiazhuang 050061,China

Responsible editor:Na LI Responsible proofreader:Xiaoyan WU

As an important breeding objective[1]and important commercial traits,and also one of the major elements that depends the fruit price,fruit size has always been the major concerns for breeders,producers and consumers.MA et al.[2]reviewed the genetic regularity of peach fruit size,and found that the fruit size of peach was the inheritable character with multigene control,which made it subject greatly to the cultivation techniques,such as blossom and fruit thinning,pruning,fertilization,watering,bagging,reflective film,greenhouse film and exogenous growth regulator.In addition to using the varieties of larger fruits,various measures need to be taken to produce larger fruits on condition of ensuring fruit quality.MA et al.[3-5]analyzed and summarize the research progress on the effects of blossom and fruit thinning,pruning,fertilization,watering,bagging,reflective film and greenhouse film on fruit size.In this paper,we reviewed the research progress on the effects of exogenous growth regulating substance on the fruit size of peach with the aim to provide theoretical basis for the related research and production of larger fruits.

Growth Retartant of Paclobutrazol

Paclobutrazol (PBZ),codenamed PP333,is a plant growth retardant of high efficiency and low toxicity first produced by ICI Company in Brain in 1981.It can inhibit the vegetative growth of young sprouts,which could balance the nutrition production and reproductive growth in plants,making the internode shorten and plump flowers sprout,and it also has a certain effect on fruit size.Paclobutrazol is the most widely used growth regulator in the production of peach trees.

Much increase of single fruit weight

Studies have shown that paclobutrazol could increase single fruit weight greatly,with the increasing range reaching up to 20.0%-50.59%.WU et al.[6]found that the single fruit weight of Yanguang in the soil applied with paclobutrazol of 4.5 g/plant increased by 50.59% than the control.The study of WANG et al.[7]showed that the single fruit weight of Sunago Wase Peach sprayed with 2 000 mg/L of paclobutrazol increased by 43.66%than the control.DU et al.[8]carried out the soil application of paclobutrazol during the full-blossom period of Huyou 007 (3.5 m×5 m),and the results showed that the single fruit weight increased by 38.79% than the control.The other similar results were as shown in Table1.

Little increase in single fruit weight

Some research results showed that although the application of paclobutrazol could increase the single fruit weight,the increase amount was relatively little,which was 4.0%-20%higher than the control.

DU et al.[8]carried out test on the 3-year perennial Huyou 007 nectarine by furrow application of paclobutrazol in the crown periphery,and found that the single fruit weight increased 19.82% by the control.REN et al.[14]found that after spraying paclobutrazol to Shuguang nectarine,the single fruit weight increased by 16.8%.LI et al.[15]sprayed 6 000 mg/L of paclobutrazol to the 5-year perennial Songhua Peach,which increased the single fruit weight by 15.56%.YANG et al.[16]adopted the soil application of 5 g/plant of paclobutrazol to the 4-year perennial Feicheng Peach,and found that the single fruit weight of the treatment group increased by 15.8% than the control.WU[6]applied 4 g/plant of paclobutrazol to the 3-year perennial sweet nectarine Weifang 2,and found the single fruit weight increased by 15.56%.XUE et al.applied paclobutrazol to the 5-year perennial Zaojiubao,LI et al.to the 4-year perennial Qingzhoumitao,and found the increasing amount was relatively low,which was only 4.0%-7.0%[13,17].

No increase or decrease in single fruit weight

There remained some researches believing that the application of paclobutrazol could not increase the single fruit weight,and some believing it would reduce the single fruit weight.The studies of DING et al.[18]on 3-year perennial Yanguang,ZHU[19]on 5-year perennial flat peach,HUANG et al.[20]on 3-year Sunago Wase,SHI[21]on the 3-5 year perennial Yuandongbaitao white peach,JIANG et al.[22]on the 3 year Hanlumitao and Huanglu peach were all applied with paclobutrazol,and all obtained the same conclusion that the application of paclobutrazol had no effect on the fruit size of peach.However,XU et al.[23]believed that spraying and soil application of paclobutrazol could reduce the single fruit weight,but the single plant yield was higher than the control.The test results of YU et al.[24]showed that the application of paclobutrazol reduced the single fruit weight of 3-year perennial Yuhualu and Sahuahong flat peach.WANG et al.[7]found that the application of high concentration of paclobutrazol could inhibit the growth of Sunago Wase peach fruit,with an average decrease of 16.00%.

Relationship between the application amount and the size of the fruit

Research showed that,in a certain range,with the increase of applied concentration,single fruit weight increased.WANG et al.[25]found that the spraying application of 1 600-2 000 mg/L f paclobutrazol would make the single fruit weight increase with the increase of concentration,which increased by 14.0% -18.5% than the control.WANG et al.[26]sprayed 1 000-1 500 PPM of paclobutrazol to the 4-6 year perennial Qingfeng peach,and found the single fruit weight was 10.04%-19.57%higher than the control.There were still some similar research results[11-12,27].However,when the application concentration of paclobutrazol went over a certain degree,the single fruit weight decreased[7,26,28-29].

Other Growth Inhibitors(B9,Aabscisic acid (ABA)and Ethephon)

XU et al.sprayed different concentrations of ABA to the 8-year perennial Meixiang peach and 6-year perennial Xiahui 6 at the second fruit expansion period,and found that the single fruit weight of the treatment group was higher than that of the control,but with no significant difference[30-31].SHEN[32]applied high concentration (10 mg/L)and low concentration (1 mg/L) of S-ABA to Jinhuadabaitao for 3 times,which fell on April 22,May 2 and May 24,respectively,and found that the application showed significant effect on increasing the single fruit weight of the peach(increased by 11.94%).LIU et al.[33]found that the application of B9 or ethephon showed no significant effect on the fruit size of Yuhualu peach.The study results of SHI et al.[34]showed that the application of B9 could reduce the single fruit weight of the 5-year perennial Nunome Wase peach.YU et al.[35]found that the spraying application of B9 could reduce the single fruit weight of Dabaifeng peach,which decreased the vertical and horizontal diameter by 1.3-6 mm,but it could increase the fruit setting rate by 3.5%-10.2%.

Table1 Effect of pactobutrazol on the size of peach fruit from different researchers

Growth Promoter

The main growth promoters included CPPU,cytokinin and gibberellin(GA3).

Cytokinin as well as cytokinins could significantly increase fruit weight to different degrees.RAO et al.[36]conducted the spraying application of CPPU to Xinongzaozi young peach,and found that the horizontal diameter and vertical diameter of the fruit applied with 20 mg/kg of CPPU increased by 16.0% and 22.4% to the control,respectively,and the single fruit weight increased by 33.3%.The research of CHEN et al.[37]showed that the 5 CPPU treatments (10,20,30,40 and 50 mg/L) all showed increase single fruit weight,which increased respectively by 35.7%,61.1%,26.0%,18.6 and 12.9%,of which the treatment at 20 mg/L was 1.6 times higher than that of the control.ZHANG et al.[38]applied the 1 200 times liquid cytokinin to Okayama Wase early mature fruit,and found the single fruit weight increased by 13.4%.WANG et al.[25]found that spraying 20 mg/L of DA-6(new type of tertiary amine tip cytokinin plant growth regulator) could increase the single fruit weight by 17.5%.XU et al.[31]sprayed cytokinin (6-BA) to Xiahui 6 at the second fruit expansion period,and found that the single fruit weight showed some increase,but showed no significant difference with the control,which might be related with the application time.

Spraying GA3 showed no significant influence on the single fruit weight.LI et al.[39]sprayed GA3 for twice at the flowering stage and after the blossom falling stage to the Qingtao,and found that the treatment showed no significant influence on the single fruit weight of Qingtao,but could increase the yield.XU et al.[31]sprayed cytokinin(6-BA)to Xiahui 6 at the second fruit expansion period,and found that the single fruit weight showed some increase,but showed no significant difference with the control.WANG et al.[40]adopted foliar spraying of GA3 on June 6,and investigated the fruits on June 27; DANG et al.[41]sprayed GA3 to the leaves at 30 d after the flowering stage(May 8),and investigated the fruits on June 14.Both studies showed that the application of GA3 could increase the horizontal and vertical diameters of peach fruit,but showing no significant increase.

Others

LI et al.[42]found that the application of chlorflurenol-methy showed no significant effect on the single fruit weight of Shenzhoumitao and Okubo peach.ABT is a new type of plant growth regulator,which can promote cell division.ZHU et al.[43]believed that the spraying application of ABT during the flowering stage could significantly increase the single fruit weight of Kurakato wase peach,but showed no significant difference to the control.LU et al.[44]found that the application of SA(salicylic acid)at the bud and flowering stage of peach could inhibit the growth of Okubo young peach,and the effect increased with the increase of SA concentration in the range of 0.002-0.020 mmol/L.

Discussion

Effect of paclobutrazol on the size of fruit

Theoretically speaking,the application of paclobutrazol could inhibit vegetative growth,shorten internodes,reduce the leggy branches,form more bearing branches (the proportion increased in medium and short branches),improve the quality of flower bud,enhance leaf quality,promote nutrient transport to the fruit,making it favorable to increase the single fruit weight.

Among all the references related with the effects of paclobutrazol on fruit size effec,19 articles showed increase in single fruit weight,while 8 showed no effect or would reduce the single fruit weight.Most of the references used young peach trees as the test materials,which showed strong growth potential,more leggy branches,relatively fewer bearing branches,and after the application of paclobutrazol,all the peach trees showed moderate growth potential,more bearing branches,and the yield was improved,which could increase the single fruit weight to certain degree.Our previous test showed that due to strong growth and fewer amount of bud,young peach trees also had smaller fruits,but with the increase of tree ages,the growth potential weakened,making the photosynthetic product orientation to fruit development,which could also increase the fruit size.The application of paclobutrazol shortened the process.Among the references,most of them showed increase in both yield and single fruit weight,and even the young fruitless trees showed an increase in yield by 1 times and the fruit size also increased 1 times[45],and the yield increased by 5 times to the peach variety with strong polarity and late production period[39].

The reason why some studies showed no increase or decrease in single fruit weight was that with the unsuited application amount of paclobutrazol[7],the yield of most studies was too high,which could reach up to 2 times of the control,but the fruit thinning was not properly adopted,resulting in the decrease in fruit size[21,28-29,45].The study of HUANG[20]showed that fruit size showed significant negative correlation with the load capacity,and it was meaningless to compare the fruit size without considering the load capacity.Therefore,it should give strict control to the load capacity in the study of the effects on fruit size.

Effect of cytokinins on fruit size

CPPU is a kind of plant growth regulator of cytokinins in the plant.Its physiological activity is higher than that of general purine type,and it is simple and easy to be synthesized,which is considered to be a cheap substitute for zeatin.It can promote the increase of the fruit size,first by prolonging the time of cell division,so as to increase the number of cells in the fruit,second by promoting the elongation of the pulp cells,so that the size of the cell increases[39].Most of the tests showed that spraying cytokinines could increase the single fruit weight,which was mainly because it increased the number of cells.Therefore,it should be applied after the flowering stage,and it would show no effects on the single fruit size when it sprayed after the young fruits stopping growth.

Effects of ABA,B9 and GA3 on fruit size

The effects of ABA on single fruit size showed different results.SHEN et al.[32]applied ABA for 3 times in April-May,and it showed increase in single fruit weight.However,XU et al.[30]applied ABA in the second fruit expansion period,and although the single fruit weight showed increase,it did not show any significant difference.B9 and GA3 had no effect on peach fruit size,but it could even reduce the single fruit weight,and they also showed no significant effects on improving peach fruit quality,while some could reduce fruit quality[31,34-35,39-40].Therefore,it is not suggested using B9 and GA3 in the peach trees.

Research Prospect

It is suggested that the further study should focus on the suitable concentration,application times and time of paclobutrazol to the soil with different fertility levels and young peach trees of different growth potentials.And attention should also be paid to the timely thinning to maintain the suitable load capacity.The production practice has proved that the continuous soil application of paclobutrazol for many years could make the xylem of the main peach branches easy to become brown and rotten,and shorten the peach tree life span.Therefore,it is suggested that no matter in study or in production,the spraying application of paclobutrazol should be preferred.And paclobutrazol should only be applied to the high density orchard but not to the peach orchard of bearding stage with conventional density.Research should be carried out on the application of cytokinins in peach trees to find out the suitable application time,concentration and times,as well as the effects of ABA on peach fruit size.

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