Atkinson C J, Else M A, Taylor L, Dover C J
Crop Science Department, Horticulture Research International, East Malling, West Malling, Kent ME19 6BJ, UK.
J Exp Bot. 2003 Apr;54(385):1221-9. doi: 10.1093/jxb/erg132.
The anatomy of the graft tissue between a rootstock and its shoot (scion) can provide a mechanistic explanation of the way dwarfing Malus rootstocks reduce shoot growth. Considerable xylem tissue disorganization may result in graft tissue having a low hydraulic conductivity (k(h)), relative to the scion stem. The graft may influence the movement of substances in the xylem such as ions, water and plant-growth-regulating hormones. Measurements were made on 3-year-old apple trees with a low-pressure flow system to determine k(h) of root and scion stem sections incorporating the graft tissue. A range of rootstocks was examined, with different abilities of dwarfing; both ungrafted and grafted with the same scion shoot cultivar. The results showed that the hydraulic conductivity (k(hroot)) of roots from dwarfing rootstocks was lower compared with semi-vigorous rootstocks, at least for the size class of root measured (1.5 mm diameter). Scion hydraulic conductivity (k(hs)) was linked to leaf area and also to the rootstock on to which it was grafted, i.e. hydraulic conductivity was greater for the scion stem on the semi-vigorous rootstock. Expressing conductivities relative to xylem cross-sectional areas (k(s)) did not remove these differences suggesting that there were anatomical changes induced by the rootstock. The calculated hydraulic conductivity of the graft tissue was found to be lower for grafted trees on dwarfing rootstocks compared to invigorating rootstocks. These observations are discussed in relation to the mechanism(s) by which rootstock influences shoot growth in grafted trees.
砧木与其接穗之间嫁接组织的解剖结构可以为矮化苹果砧木减少接穗生长的方式提供一个机理解释。相对于接穗茎而言，大量木质部组织紊乱可能导致嫁接组织具有较低的水力传导率（k(h)）。嫁接可能会影响木质部中离子、水和植物生长调节激素等物质的运输。使用低压流动系统对3年生苹果树进行测量，以确定包含嫁接组织的根和接穗茎段的k(h)。研究了一系列具有不同矮化能力的砧木；既有未嫁接的，也有嫁接了相同接穗品种的。结果表明，至少对于所测量的根的尺寸类别（直径1.5毫米），矮化砧木的根的水力传导率（k(hroot)）低于半矮化砧木。接穗的水力传导率（k(hs)）与叶面积有关，也与它所嫁接的砧木有关，即半矮化砧木上的接穗茎的水力传导率更高。将传导率相对于木质部横截面积（k(s)）表示并不能消除这些差异，这表明砧木会引起解剖结构的变化。与增强活力的砧木相比，发现矮化砧木上嫁接树的嫁接组织的计算水力传导率更低。结合砧木影响嫁接树接穗生长的机制对这些观察结果进行了讨论。
