Screening Of Zinc Deficiency Tolerance And Response To Zinc Deficiency Stress In Apple Rootstocks (Malus.)

Zinc is an essential micronutrient as the composition or activation of enzyme, it plays animportant role in photosynthesis and carbohydrate metabolism. Zinc deficiency can disrupt Znhomeostasis and carbohydrate metabolism and block plant growth. The apple tree is sensitive to Zndeficiency, which can lead to little-leaf disease. The little-leaf disease of apple tree havespread in the apple orchards in Shandong province, and it has become one of the mostimportant limiting factors on production and the quality of apple. The rootstock mainly affectthe vegetative growth of the scion by affecting the roots absorb water, mineral nutrition andhormones. To compare the tolerance of different rootstocks to zinc deficiency stress, whichhas important significance in screening apple rootstocks well adapted to zinc stress andreducing the occurrence of little-leaf disease.The experiment was carried out under zinc deficiency filed with the nine applerootstocks which are common used in production, such as M.Hupehensis Rehd., and westudied the different responses to zinc deficiency among rootstocks. Finally, we use themethod of principal component analysis to evaluating the sensitivity to zinc deficiency amongrootstocks. According to the sensitivity these rootstocks were divided into three parts.Subsequently we selected the M. xiaojinensis Cheng et Jiang., M. Hupehensis Rehd., M.robusta Rehd. and M. baccata to validate the field results under hydroponic. What’s more, tocompare the tolerance of different znic deficiency tolerant apple rootstocks under zinc stress.The main results are as follows:(1) Results showed that many obvious zinc deficiency symptoms were observed in theapple rootstock seedlings under zinc deficiency soil, such as, the plant height decreased, thenew smaller leaves and rosette. The zinc-deficiency symptoms of M. xiaojinensis Cheng etJiang., M. Hupehensis Rehd. and M. flame were not obvious. The root length, root surfacearea, root volume and root tip number were significantly decreased under zinc deficiency.(2) Zinc deficiency significantly reduced the net photosynthetic rate and intercellularCO2concentration of apple rootstocks leaves, increased the stomata conductance andtranspiration rate. Zinc deficiency also reduced the chlorophyll, carotenoid content and leafarea of apple rootstocks and this might be the reasons that the Pn decreased caused by zincdeficiency. (3) The Zn concentration and content of apple rootstocks seedlings significantly decreased, butthe scale of the reduction of M. xiaojinensis Cheng et Jiang. was very small comparing with control.Iron uptake of root is promoted by zinc deficiency.(4) The characters such as, root dry matter, Pn, root length, root surface area, root averagediameter, root volume, root tips, leaf Zn concentration and Zn content per plant were themainly index to measure the ability of apple rootstocks to tolerate Zn-deficiency. Accordingto the Zn-deficiency tolerance value, the nine apple rootstocks were classified: the ability oftolerance to deficient zinc of M. xiaojinensis Cheng et Jiang. and M. flame are higher than thatof others; M. sikkimensis koehne, M. rockii Rehder, M. rockii Schneid and M. sikkimensiswere sensitive to Zn-deficiency; The ability of tolerance to Zn-deficiency in M. baccataBorkh, M. hupehensis Rehd. and M. robusta Rehd. were middle.(5) Zinc deficiency reduced SOD activity in the roots and leaves of apple rootstockseedlings, and the APX activity was increased to scavenge the reactive oxygen species toalleviate the damage caused by the zinc deficiency.(6) The ion maximum absorption rate of M. xiaojinensis Cheng et Jiang. wassignificantly higher than that of other three species under zinc deficiency. The Km was lessthan other varieties of apple rootstocks and the ion affinity was high. The maximumabsorption rate of M. xiaojinensis Cheng et Jiang was also significantly higher than the otherthree species under control treatment. The absorption, utilization efficiency and ion absorptionof M. xiaojinensis Cheng et Jiang. were higher than other rootstocks under zinc deficiency,and it indicated that it may be a rootstock which tolerate to deficient zinc.