A study of grafting compatibility in Carya

Abstract: 【Objective】The seeds of Carya Nutt.are the economic organs in species of this genus.Grafting is a breakthrough in propagation of the crop, and grafting compatibility is the crucial factor determining grafting success.The study examined the grafting compatibility among species in Carya Nutt.in order to select suitable grafting rootstocks and improve the success of grafting.【Methods】Three different Carya Nutt.species (Carya cathyensis, C.hunanensis Cheng et R.H Chang ex Chang et Lu, and C.illinoensis K.Koch) were used as rootstocks to graft with three different scion species (C.cathyensis Sarg, C.hunanensis Cheng et R.H Chang ex Chang et Lu, and C. illinoensis K. Koch) .The grafting compatibility was judged by survival percentage, and the properties of grafted trees including the light response curve of photosynthesis and chlorophyll fluorescence parameters were analyzed.Grafting was carried out in the mid April, 2014.Budding scion sticks and surviving grafted plants were counted in the mid May, and shoot length and diameter were measured after leaf shed in November.On a sunny day in August, light response of pho- tosynthesis was measured using a LI-6400 portable photosynthesis system with an automatic light curve procedure at 8:30-11:30.Light saturation point (LSP) , maximum net photosynthetic rate (Pmax) , light compensation point (LCP) and dark respiration rate (Rd) were obtained from the regressed light-photosynthetic rate curves.In one morning in September, a portable modulated chlorophyll fluorescence spectrometer (PAM-2500, Walz, Germany) was used to measure the chlorophyll fluorescence parameters of mature leaves, including the fast light response curve and the relative electron transfer rate.The measurements were carried out with 3 to 5 replicates (one leaf each from 3 to 5 plants) .To measure the specific weight of the leaves, 5 leaf discs 0.9 cm in diameter were punched out from both sides of the midrib, killed out at120℃for 30 min, dried at 80℃ for 24 h, and weighed for dry weight with an electronic balance.In the late August, mature leaves at the middle and lower positions of new shoots were collected and 0.5 m2leaf slices were cut from both sides along the central vein with a sharp blade and fixed with FAA.After dehydration with a series of concentrations of alcohol, the leaf slices were dipped in wax for sample embedding.Sections of 10μm were cut with a rotary microtome (BCQ-202) , double stained with Safranine-Fast Green, sealed with neutral gum, and observed under a microscope.Leaf thickness and the thickness of the palisade and the spongy tissues were measured at different locations.【Results】When C.hunanensis and C.illinoensis were used a rootstocks, budding rate of the scion sticks was the highest, being 80.26%and 78.52%, respectively.C.hunanensis as rootstock increased the budding rate of C.cathyensis scion by12%.When scion growth was considered, C.illinoensis should not be grafted onto C.cathyensis and C.hunanensis.C.illinoensis as rootstock promoted the growth of C.cathyensis and C.hunanensis.The Amax in plants grafted on C.illinoensis was significantly higher than in those grafted on C.cathyensis and C.hunanensis.The LSP in C.illinoensis stocked plants were the highest.C.hunanensis grafted on C.cathyensis had a higher LSP.LSP were generally higher in C.cathyensis than in the other scions.The LSP in plants grafted on C.illinoensis rootstock was the highest.C.hunanensis grafted on C.cathyensis increased LSP.Self-rooted C.illinoensis plants had a thick (145.665μm) palisade tissue and thus a high light energy efficiency.C.illinoensis as rootstock also increased the thickness of palisade tissue in C.cathyensis and C.hunanensis scions.【Conclusion】C.cathyensis and C.hunanensis had the best grafting compatibility among the tested rootstock-scion combinations.C.illinoensis as rootstock had also a good grafting compatibility with C.cathyensis and C.hunanensis, while C.cathyensis and C.hunanensis as rootstock had a poor grafting compatibility with C.illinoensis.