title: Relationships between xylem vessel characteristics, calculated axial hydraulic conductance and size-controlling capacity of peach rootstocks.
abstract: OBJECTIVE
  Previous studies indicate that the size-controlling capacity of peach rootstocks is associated with reductions of scion water potential during mid-day that are caused by the reduced hydraulic conductance of the rootstock. Thus, shoot growth appears to be reduced by decreases in stem water potential. The aim of this study was to investigate the mechanism of reduced hydraulic conductance in size-controlling peach rootstocks.
  
  
  METHODS
  Anatomical measurements (diameter and frequency) of xylem vessels were determined in shoots, trunks and roots of three contrasting peach rootstocks grown as trees, each with different size-controlling characteristics: 'Nemaguard' (vigorous), 'P30-135' (intermediate vigour) and 'K146-43' (substantially dwarfing). Based on anatomical measurements, the theoretical axial xylem conductance of each tissue type and rootstock genotype was calculated via the Poiseuille-Hagen law.
  
  
  RESULTS
  Larger vessel dimensions were found in the vigorous rootstock ('Nemaguard') than in the most dwarfing one ('K146-43') whereas vessels of 'P30-135' had intermediate dimensions. The density of vessels per xylem area in 'Nemaguard' was also less than in 'P30-135'and 'K146-43'. These characteristics resulted in different estimated hydraulic conductance among rootstocks: 'Nemaguard' had higher theoretical values followed by 'P30-135' and 'K146-43'.
  
  
  CONCLUSIONS
  These data indicate that phenotypic differences in xylem anatomical characteristics of rootstock genotypes appear to influence hydraulic conductance capacity directly, and therefore may be the main determinant of dwarfing in these peach rootstocks.
authors: Dipartimento di scienze agrarie ed ambientali, Università degli Studi di Perugia, Perugia, Italy.
authors: Sergio
authors: S
authors: Tombesi
authors: R Scott
authors: RS
authors: Johnson
authors: Kevin R
authors: KR
authors: Day
authors: Theodore M
authors: TM
authors: DeJong
mesh_terms: D018517:Plant Roots / Q000033:anatomy & histology / Q000502:physiology; D018520:Plant Shoots / Q000033:anatomy & histology / Q000502:physiology; D018547:Plant Stems / Q000033:anatomy & histology / Q000502:physiology; D027861:Prunus / Q000033:anatomy & histology* / Q000502:physiology*; D052584:Xylem / Q000033:anatomy & histology* / Q000502:physiology*