| Peach is one of the important fruit trees in China. In recent years, the replacement ofvarieties is increasingly accelerated; a new variety which can strongly acclimatize tovarious environmental factors represents a great significance for the promotion ofrenovation of variety. Hardiness is an agronomically important trait of peach varieties. Theverification of hardiness needs to take a longer time in production, and the large economiclosses might occur. Therefore, the establishment of a brief protocol for hardinessidentification of peach has important practical significance, which can shorten the breedingperiod and achieve suitable cultivation.In the present study, ten peach varities, respectively, showing stronger, moderate andweaker cold resistance, were measured by electrolyte leakage method, as well as usingelectrical impedance spectroscopy based on four parameters (extracellular resistance re,intracellular resistance ri, relaxation time τ, the relaxation time distribution coefficient ψ) infrost hardness and cold hardening with frost-exposed and non-frost-exposed. Throughanalyzing the relationship between four parameters and the hardiness, this study wouldfind an easy way to evaluate peach hardiness, and also provide a theoretical basis for theearly identification and field cultivation of new varieties. Moreover, the relationshipbetween cold resistance and physiological indicators of water content, soluble sugars,starch and free proline was investigated. The main results are as follows:1. We studied the relationship between electrical impedance spectroscopy and coldresistance (LT50was measured by the electrolyte leakage) of non-frost-exposed shoots atdifferent times. The results showed that, a single arc was always observed in thenon-frost-exposed peach shoots, along with the degree of cold hardening the hardiness ofshoots gradually increased, and the arc gradually increased. The maximum of arc appearedin the late cold hardening, and high-frequency arc was more evident. A minimum of arcappeared in the late dehardening, along with that the hardiness of shoots graduallyweakened and the arc span became smaller. Thus, electrical impedance spectroscopy (EIS)could reflect the seasonal variations of shoots’ hardiness. Moreover, the study alsoindicated that the EIS arc of stronger hardiness varieties was greater than the EIS arc ofweaker hardiness varieties; with the increase of hardiness, reactance value decreased at thesame frequency, and the resistance value increased. The size of EIS arc span in10varieties was consistent with the production performanc of cold resistance strength.2. The relationship between electrical impedance spectroscopy (EIS) parameters andcold resistance (LT50was measured by the electrolyte leakage) of the non-frost-exposedpeach shoots in different periods was analyzed. The results showed that, during coldhardening, the extra cellular resistance (re) in10varieties had an significantly negativecorrelation with its frost hardiness (R2=0.521~0.991, r=-0.722~-0.995**), intracellularresistance (ri) had an observably negative correlation with its frost hardiness(R2=0.501~0.995, r=-0.708~-0.998**), relaxation time (τ) had an observably positivecorrelation with its frost hardiness (R2=0.571~0.989, r=0.756~0.995**). Duringdehardening, the extra cellular resistance (re) in10peach varieties had also an observablynegative correlation with its frost hardiness (R2=0.406~0.961, r=-0.637~-0.981**),intracellular resistance (ri) had an observably negative correlation with its frost hardiness(R2=0.484~0.963, r=-0.696~-0.981**), relaxation time (τ) had an observably positivecorrelation with its frost hardiness (R2=0.348~0.978，r=0.590~0.989**). These resultsindicated that relaxation time (τ), extra cellular resistance (re), intracellular resistance (ri)were available as predictors of peach hardiness parameters.The path analysis of hardiness measured by EL method and EIS parameters innon-frost-exposed peach shoots showed that, non-frost-exposed peach shoots’ extracellular resistance (re), Intracellular resistance (ri), relaxation time (τ) had a higher responseon peach hardiness.3. We studied the relationship between the frost-exposed electrical impedanceparameters and electrolyte penetration in different periods. The results showed that, afterfrost-exposed extracellular resistance re(cold hardening r=0.824*~0.998**, dehardeningr=0.848*~0.994**), Intracellular resistance (ri)(cold hardening r=0.821*~0.991**,dehardening r=0.855*~0.989**), relaxation time τ (cold hardening r=0.782~0.986**，dehardening r=0.886*~0.997**), relaxation time distribution coefficient (coldhardening r=0.639~0.996**, dehardening r=0.773~0.997**) showed the higher correlationwith the electrolyte penetration method for measuring hardiness. Therefore, all of the fourparameters of electrical impedance could be used as the parameters to estimate hardinessof peach’s shoots. By the path analysis of electrical impedance parameters and electrolytepenetration, the relationship between EL method and extracellular resistance re,intracellular resistance ri, relaxation time τ, relaxation time distribution coefficient hada higher consistency. However, the EL method and extracellular resistance reshowed thehighest relevance and consistency. Therefore, EIS (re), EIS (ri), EIS (τ), EIS（）areimportant parameters for measuring the hardiness of frost-exposed peach’s shoots, EIS (re)is the best parameter for measuring the hardiness of frost-exposed peach’s shoots.4. By comparing the EL method and the four parameters of EIS, the results showedthat, during the late cold hardening or the early dehardening when shoots had stronger hardiness, the hardiness identified by EIS and EL methods was consistent with theproduction performance of cold resistance in10varieties.5. The contents of soluble sugarand proline contents of the shoots in all varietiescontinued to rise along with the cold hardening, while moisture continued to fall. In thelate cold hardening when the outside temperature reached to the lowest, the solublecontents of sugar and proline reached to the highest; moisture contents reached to thelowest. With dehardening, the soluble sugar contents in the shoots of all varieties continuedto fall, the proline contents showed a rising trend at first, and then fell; moisture continuedto rise. In the late dehardening, the soluble sugar contents and proline contents in theshoots of all varieties reached to the lowest; moisture reached to the highest. Under thecondition of low temperature stress, the soluble sugar contents in the shoots of the strongercold resistant varieties were higher than that of the shoots from weaker cold resistantvarieties. Apparently, soluble sugar content and hardiness existed a positive correlation.The proline contents in the shoots of stronger cold resistant varieties had larger variationduring cold hardening; the proline contents of the shoots from weaker cold resistantvarieties increased slightly during cold hardening, the proline contents in the shoots ofweaker cold resistant varieties were lower than that of stronger cold resistant varieties.Under the condition of low temperature stress, moisture contents of all varieties were quitedifferent, while on a relatively high temperature environment the moisture content ofshoots were little different, which were consistent with the cold resistance changes of allvarieties.The starch content in the shoots of stronger cold resistant varieties were higherthan that from weaker cold resistant varieties. |
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