Studies On Screening And Physiological Characteristics Of Salt-Tolerant Rootstocks From Cucurbita Moschata Duch. Germplasm

Due to the continuous cultivation and unreasonable fertilization in protected cultivation soil,the secondary salinization soil has become a very serious problem, resulting in a serious reduction of yield and quality of vegetable protection production. Cucurbits are one of the main vegetable species in protected cultivation.It is showed that cucurbits grafting cultivation using salt-tolerant rootstock is an effective measure to utilize the secondary salinization soil reasonable.Pumpkin is the main rootstock species of grafted cucurbits production,which have some features such as well developed roots,good compatibility,resistance soil-borne diseases.Cucurbita moschata is a cultivated species of Cucurbita,which have extensive adaptability,strong stress resistance,abundant germplasm resources in China.It is reasonable that screening salt-tolerant cucurbits rootstock from C. moschata,however,special salt-tolerant rootstock were not used in cucurbits production. Less physiological characteristics of salt-tolerant on C.moschata was studied,these are only in salt-toleran physiological of germination period and seedling stage.We use C. moschata hybrids as trial material,and screening salt-tolerant hybrid,and then using C. ficifolia,widely used in grafted cucumber production as a control,comparisons of salt-tolerant physiological were made between salt-tolerant hybrid and C.ficifolia in their adult stages.1.In vitro comparison of the salt tolerance of C.moschata were made at the seedling stage exposed to a series of NaCl concentration.The results showed that hybrids are stronger than their inbred lines in salt tolerance,there is heterosis about salt tolerance of C. moschata.The growth of 3 inbred lines and 6 hybrids seedlings were inhibited seriously under MS medium supplemented with 120 and 160 mmol·L^-1 NaCl respectively.There were significant differences in salt tolerance among 10 tested materials with 6 salinities(0, 40,80,120,160,200 mmol·L^-1).The salt injury index(SII) of seedlings of 69 pumpkin hybrids ranged from 29.94 to 100 and the frequency distribution was normal by normal test. Salt-tolerant hybrids of 6 were obtained,of which '360-3×112-2' showed the strongest salt tolerance.120 mmol·L^-1 NaCl was determined as an effective concentration to select salt-tolerant materials from pumpkin hybrid seedlings.2.In vitro comparison of the salt tolerance of C.ficifolia and C.moschata hybrid of '360-3×112-2' which showed stronger salt tolerance with previously selected experimental result,were made at the seedling stage exposed to a series of NaCl concentration(0,40,80,120,160,200 mmol·L^-1).The results showed that obvious difference in salt tolerance was exited between C.moschata hybrid of '360-3×112-2' and C.ficifolia,and the salt tolerance of the former was significantly higher than the later.It was suggested that 160 mmol·L^-1 and 120 mmol·L^-1 NaCl were the maximum stress value that C.moschata hybrid of '360-3×112-2' and C.ficifolia could tolerate respectively.Those results make hybrid of '360-3×112-2' available in breeding of salt-tolerant rootstock.3.To compare '360-3×112-2'hybrid of salt tolerance with C.ficifolia,both of them were cultured in nutrient solution added with 0 mmol·L^-1 or 80 mmol·L^-1 NaCl in adult plant period.After 10 days,the growth traits and the contents of Na⁺,K⁺,Ca²⁺ and Mg²⁺ in six organs including root,stem,petiole,upper leaf,middle leaf and lower leaf of all plants were determined.Results showed that growth inhibition of two tested plants was obvious under NaCl stress for 10 days,growth of '360-3×112-2' hybrid plants was less inhibited than that of C.ficifolia Bouche.Na⁺ contents in six organs of two tested materials were all increased,Na⁺ contents of '360-3×112-2' hybrid mainly accumulated in roots,while C. ficifolia Bouche.in stem.K⁺,Ca²⁺ and Mg²⁺ contents generally decreased in plant,however, increased in upper leaf of'360-3×112-2' hybrid.Although K⁺/Na⁺ values in all organs were decreased under NaCl stress,'360-3×112-2' hybrid decreased less than C.ficifolia Bouche. Therefore,difference in organs accumulating high Na⁺ contents,and difference in K⁺,Ca²⁺, Mg²⁺ contents and K⁺/Na⁺ decrease range in shoot were the main reasons for the differences of salt tolerance between the two tested materials under NaCl stress after 10 days.4.To evaluate the salt tolerance of '360-3×112-2' hybrid at adult plant stage(with 10 leaves),the roots physiological and biochemical characteristics and plants growth were further studied comparing with C.ficifolia under NaCl stress in condition of solute culture. The results showed:(1) NaCl stress had lower inhibitory effect on the plants growth of hybrid which reflected in the reduction of fresh weight of roots and shoots,length of main stem,number of functional leaves,especially in individual areas of the youngest functional leaves comparing with C.ficifolia based on the investigation data at 9 day after NaCl treatment(DAT).(2) NaCl treatment could promote the roots vigor of '360-3×112-2' hybrid and inhibit that of C.ficifolia significantly.(3) Although the two osmoregulatory substances in roots of two tested materials had peak value in the first day of NaCl stress and appeared similar change tendency which rose first and fell later,the hybrid were always higher than C.ficifolia.The rising range of soluble sugar and proline in earlier phase were more obvious than the descend range in later stress time in hybrid.(4) O₂^-production rate of two test material roots gradually increased,but the rising range of O₂^-production rate of hybrid became lower than that of C.ficifolia with NaCl stress.Content of MDA of hybrid roots was raised firstly then dropped,yet that of C.ficifolia increased gradually.(5) Activity of SOD,POD and CAT of two material roots were increased under NaCl stress,and SOD and CAT raised firstly then dropped,POD increased continuous,the range of increase of 3 antioxidase of '360-3×112-2' hybrid roots at same stress time were higher than that of C.ficifolia roots.Those results indicated that '360-3×112-2' hybrid plants had lower growth inhibition rate,higher roots vigor,better osmotic adjustment ability and regulation balance of active oxygen under NaCl stress at adult plant stage.The comparing research also concluded that '360-3×112-2' hybrid has higher tolerance to NaCl stress than C.ficifolia.5.Plant growth,O₂^-production rate,H₂O₂ content and contents of free polyamines (PAs) includ free putrescine(Put),Spermidine(Spd),Spermine(Spin) in the roots of Cucuibita moschata Duch.hybrid and C.ficifolia which differing in salt sensitivity at adult plant stage(10 leavies) were investigated under 80 mmol·L^-1 NaCl stress in hydroponic for 10 days.The results showed that salt injuries and growth inhibition occurred both in tested plants after 10d stress,and that of C.ficifolia Bouche were much more serious than '360-3×112-2' hybrid.During NaCl stress,O₂^-production rate and H₂O₂ content in '360-3×112-2' hybrid were increased similar to C.ficifolia Bouche.,yet absolute values were lower than that of the latter.Contents of Put,Spd,Spm,PAs and Put/PAs value on two test material roots were always higher than control,rised first and fall later,while (Spd+Spm)/Put value were lower than control,decreased firstly and then increased. Compared with C.ficifolia Bouche.,Put/PAs value and Put content in '360-3×112-2' hybrid roots were always lower,while(Spd+Spm)/Put value and contents of Spd and Spm were always higher.It was concluded that increasing PAs content levels in two pumpkin roots played an active role on decreasing or scavenging ROS under NaCl stress.The conversion of Put to Spd and Spin was advantageous to the increase of plant salt tolerance. The higher salt tolerance of '360-3×112-2' than C.ficifolia Bouche.was closely related to its some physiological characteristics in roots,such as the lower Put/PAs value,the higher (Spd+Spm)/Put value and PAs content,the stronger the capacity to scavenge active oxygen species.6.The compatibility and grafted seedling growth of different C.moschata hybrids ('360-3×112-2','077-2×112-2','360-3×635-1') and C.ficifolia rootstocks on cucumber cultivar of 'Jinchun 2' were studied by approach grafting and sprout insertion grafting using pot cultivation in greenhouse.the results showed that 3 C.moschata hybrids rootstocks were compatible with 'JinChun 2' cucumber cultivar,but with lower survival rates than C. ficifolia rootstocks,differences in hypocotyls diameter and height between C.moschata hybrids and C.ficifolia rootstocks reduced the survival ratio of grafts,while with higher survival ratio of grafts by sprout insertion grafting than approach grafting.'360-3×112-2' and '360-3×635-1' hybrids have the basic conditions of cucumber rootstock for their average leaves number,the largest leaf area,the fresh weight of roots and tops of grafted seedling no less than that of C.ficifolia rootstocks after grafting 20 days.And '360-3×112-2' hybrid is recommended as a cucumber rootstock for it's stronger grafted seedling with higher root-top ratio,but '077-2×112-2' hybrid is not recommended for it's the lower grafting survival rates and poor growth vigor.