Dipartimento di Scienze Agrarie ed Ambientali , Università degli Studi di Perugia , Borgo XX giugno 74, 06100 Perugia , Italy.
AoB Plants. 2010;2010:plq013. doi: 10.1093/aobpla/plq013. Epub 2010 Sep 12.
The primary physiological mechanism influencing tree vigour in size-controlling rootstocks of peach has been related to the hydraulic conductance of the rootstock. Differences in rootstock hydraulic conductance are a function of rootstock xylem vessel characteristics. The present research examined whether the vigour and xylem vessel characteristics of the rootstock influence the xylem characteristics of the scion. We tested whether using a size-controlling rootstock genotype as an inter-stem influences the xylem vessel characteristics of either the rootstock below the inter-stem or the scion above it and vice versa.
Anatomical measurements (diameter and frequency) of xylem vessels were determined above and below the graft unions of the trunks of peach trees with differing scion/rootstock combinations. The three peach rootstocks were 'Nemaguard' (vigorous), 'P30-135' (intermediate vigour) and 'K146-43' (dwarfing). The vigorous scion cultivar was 'O'Henry'. The inter-stem experiment involved trees with 'Nemaguard' (vigorous) as the rootstock, 'K146-43' (dwarfing) as the inter-stem and 'O'Henry' as the scion. Based on anatomical measurements, we calculated the theoretical axial xylem conductance of each stem piece and rootstock genotype with the Hagen-Poiseuille law.
Xylem vessel dimensions of rootstocks varied in conjunction with tree vigour. Scion xylem vessel dimensions of different scion/rootstock combinations were only marginally affected by rootstock genotype. The inter-stem sections from the dwarfing genotype ('K146-43') had narrower vessels and a lower calculated hydraulic conductance than the xylem from either the vigorous rootstock below ('Nemaguard') or the scion above ('O'Henry').
Rootstock genotype only marginally affected scion xylem vessel characteristics. Thus the xylem vessel characteristics of the dwarfing rootstock genotypes appear to influence tree growth directly rather than through an effect on the xylem characteristics of the scion. A dwarfing rootstock genotype used as an inter-stem appeared to work as a physical restriction to water movement, reducing potential xylem flow and conductance of the whole tree.
影响桃调控大小砧木活力的主要生理机制与砧木的水力传导有关。砧木水力传导的差异是砧木木质部导管特征的函数。本研究旨在探讨砧木活力和木质部导管特征是否影响接穗的木质部特征。我们测试了使用调控大小的砧木基因型作为中间砧是否会影响中间砧以下的砧木或中间砧以上的接穗的木质部导管特征，反之亦然。
通过测量不同接穗/砧木组合桃树树干嫁接部位上下的木质部导管的解剖学测量值（直径和频率）来确定。三种桃砧木分别为“Nemaguard”（活力旺盛）、“P30-135”（中等活力）和“K146-43”（矮化）。旺盛的接穗品种为“O'Henry”。中间砧实验涉及的树木以“Nemaguard”（活力旺盛）为砧木、“K146-43”（矮化）为中间砧、“O'Henry”为接穗。基于解剖学测量，我们根据哈根-泊肃叶定律计算了每个茎段和砧木基因型的理论轴向木质部导度。
砧木木质部导管尺寸随树木活力而变化。不同接穗/砧木组合的接穗木质部导管尺寸仅受到砧木基因型的轻微影响。来自矮化基因型（“K146-43”）的中间砧节段的导管比下面活力旺盛的砧木（“Nemaguard”）或上面的接穗（“O'Henry”）的木质部导管更窄，计算得出的水力传导能力也更低。
砧木基因型仅对接穗木质部导管特征产生轻微影响。因此，矮化砧木基因型的木质部导管特征似乎直接影响树木生长，而不是通过对接穗木质部特征的影响。作为中间砧使用的矮化砧木基因型似乎起到了物理限制水分运动的作用，降低了整个树木的潜在木质部流量和导水能力。
