VX211, a vigorous new walnut hybrid clone with nematode tolerance and a useful resistance mechanism.

VX211 is a highly vigorous Paradox hybrid clone that outgrew other walnut seedlings in the presence of nematodes. A four-year macroplot trial involving Paradox VX211 and a standard Paradox selection, AX1, demonstrated that the damage threshold level of Pratylenchus vulnus on commercially available walnut rootstocks is < 1 nematode/250 cm³ of soil. Using 1 as the initial population level (Pi) within an inoculation zone of 80 L of soil, the P. vulnus population level increased 2,500-fold in the first year of growth. Three years after inoculation soil population levels of P. vulnus on VX211 were significantly reduced compared to that of the moderately vigorous AX1. Growth of VX211 was 35% greater than that of AX1 regardless of the Pi. Examination of stained roots revealed that feeding and reproduction by P. vulnus on VX211 was primarily ectoparasitic. This is the first report on a new walnut rootstock that can be readily cloned, has high vigor, exhibits tolerance to low population levels of P. vulnus, reduces nematode feeding and reproduction within the root terminus, and is currently available to California growers.