Effects of different stocks on the accumulation of cadmium and fruit quality in watermelon

WANG Zhiwei; LI Han; SUN Bo; SUN Xiaowu; LIANG Zhihuai; XIE Hanzhong

doi:10.13925/j.cnki.gsxb.20160420

Abstract：[Objective]Watermelon (Citrullus lanatus) is loved by people because of its juicy and sweet interior flesh,especially in summer.Watermelon has long been and widely cultivated in Hunan,with about 140 000 hm2 planting area per year,ranking the 4th in China.Because of the considerable economic benefits,watermelon is becoming an important horticultural crop in the province.Along with the adjustment of crop structure in heavy metal contaminated areas in Hunan province,trials of watermelon planting in these areas are underway.For sustainable development of local industry,it is important to use proper rootstocks.Studies of the characters of cadmium (Cd) accumulation in grafted watermelon are necessary for sustainable development of watermelon industry in heavy metal polluted areas.[Methods] We used top plug for grafting,‘8424’ as the scion,and eight rootstocks including 3 ‘Yelang’ lines (T1-T3),‘Qiangzhen 1’ (T4),‘Xijiaqingsheng’ (T5),‘Jingxinzhenwang’ (T6),‘Qingpingtiemujia’ (T7)and ‘Huangjindadang’ (T8).The grafted plants were trained into a 2-truss trellis system with each truss bearing one fruit.When fruit ripened,cadmium contents in root,stems at different positions,leaves and fruit were measured,and data of single fruit weight,fruit shape index,and quality traits were collected.[Results]The results showed that root Cd content in different rootstocks had significant difference.T5 and T8 roots had a cadmium content 32.6％ and 36.9％ lower than the non-grafted plants,respectively.Cd content in T4 root was 0.109 mg·kg-1,77.7％ higher than the seedling roots.The basal stem in grafted watermelon plants had a Cd content in the range of 0.028 6-0.086 6 mg· kg-1,i.e.27.9％-84.4％ of that of the seedlings (0.102 6 rmg· kg-1),and Cd content in T2,T3 and T5 was the lowest,being 0.043,0.038 6 and 0.028 6 mg· kg-1,respectively.However,the Cd content in the central stem of T4 rooted plants increased significantly compared to the self-rooted seedlings,while that in those on other stocks was lower than in the seedlings at varying degrees.The Cd content in the central leaves in T1,T2 and T5 rooted plants was 54％,55.7 and 54％ lower than in the seedlings,respectively.The Cd content in the upper stems was different among rootstocks.In T4,it was 0.047 mg · kg-1.Other rootstocks reduced the Cd content in the upper stems at various degrees,and reduction in T5 was the largest,followed by those in T1 and T8.There were significant differences between the self-rooted seedlings and plants on different rootstocks in leaf Cd content.In T4,the basal leaf Cd content reached up to 0.3 mg· kg-1 and was significantly higher than in the self-rooted seedlings.In T1,T2 and T5,the basal leaf Cd content was 0.06,0.068,and 0.057 mg· kg-1 lower compared to that in the seedlings,respectively.In T4,the Cd content in the central leaves was 0.233 mg· kg 1,and significantly higher than that in the seedlings,while in plants on other rootstocks,Cd content in the central leaves was reduced at different degrees compared with that in the self-rooted seedlings.T1,T2 and T3 were 70％,70％ and 68％ lower,respectively.The effects on Cd content in the upper leaves differed according to rootstocks.For example,T3 and T4 significantly increased but others reduced it.Among them,the decrease in T5 was the greatest.Different grafting combinations displayed influence on Cd content in the fruit.T1,T2 and T5 reduced it by 60.5％,61.3％ and 60.5％ respectively,while T4 increased it by 41.6％ compared with the self-rooted control.Among different treatments,the highest Cd content in fruit was 0.006 4 mg· kg-1,lower than the limitation of 0.05 mg· kg-1 defined by GB 2762-2012.Rootstocks also showed influence on fruit weight.T2 and T6 had a lower fruit weight than the control,but the difference was not significant.Fruit weight in T5 increased significantly and reached 5.79 kg.T2 and T3 greatly influenced fruit shape index,but others showed no influence.Rootstocks affected skin thickness,and the effect was significant in T1 and T4.T5 had the highest sugar content (10.53％) in central fruit tissue.T4 had the highest sugar content (8.03％) in side fruit tissues,and T2 had the lowest value of 6.07％.[Conclusion] Under Cd stress,grafted watermelon on different rootstocks had different Cd absorption capacity and Ca distribution among organs.The Cd content in different plant positions followed a descending order of base＞middle＞ upper part.In root,Cd content is influenced by rootstock genotypes.Our results showed that T1,T2 and T5 had the lowest fruit Cd content and T1 and T5 significantly reduced the Cd content in all plant parts and improved fruit weight with no significant effect on fruit quality.These rootstocks could be suitable for grafted watermelon planted in heavy metal polluted areas.