The 2011 ASHS Annual Conference

Evaluating rootstock potential for better anchorage, bacterial canker resistance, and tolerance to shallow soils and high rainfall environments is useful in adapting orchards to the diverse environments where California almonds [Prunus dulcis (Mill.) D.A. Webb] are grown.  Regional rootstock field trials were planted in Colusa and Kern counties in 1997 and in Butte and San Joaquin counties in 1998 using randomized complete block designs.  Although not all rootstocks are in all trials, the peach rootstocks; ‘Nemaguard’, ‘Lovell’, and ‘Guardian’, the peach x almond hybrids; ‘Bright’s’, ‘Hansen 536’, and ‘Nickels’ (UC 1-82), and the interspecific (peach x almond x plum x apricot) hybrids; ‘Viking’ and ‘Atlas’ are included in this summary. The almond cultivar used as a scion in the Kern trial is 'Butte' while scions in the other three trials are the 'Nonpareil' cultivar. All orchards are managed using typical commercial irrigation, fertilization, pruning, disease and pest control practices.  This summary focuses on the rootstocks influence on the mineral nutrient content of almond leaves.  Leaf samples were collected in 2004 and 2005 after trees were mature and had reached their full bearing potential.  Samples were analyzed for mineral nutrient content at the University of California Agriculture and Natural Resources Analytical Laboratory at UC Davis. Analyses of variance and mean separation was done by using either Duncan’s multiple range test, the least significant difference test, or Fishers protected LSD.  Rootstocks of similar parentage tend to have similar leaf nutrient levels.  Trees on peach rootstocks (‘Nemaguard’, ‘Lovell’, and ‘Guardian’) tend to have the highest leaf nitrogen, sodium and chloride levels and lowest leaf levels of calcium and manganese.  Peach x almond hybrid rootstocks (‘Hansen’, ‘Nickels’, and ‘Bright’s’) tend to be highest in calcium and lowest in leaf nitrogen, potassium, boron, sodium and chloride levels with the exception of ‘Bright’s’ which had the highest level of sodium.  The leaf nutrient levels of almond on interspecific hybrids (‘Atlas’ and ‘Viking’) are generally high in nitrogen and potassium but intermediate for most other nutrients.  ‘Atlas’ consistently has the highest boron leaf levels while ‘Viking’ stands out as significantly lower in magnesium leaf levels.