The UC Davis Walnut Breeding Program has recently released a new walnut variety, ‘Durham’. Researchers say the trees produce good quality kernels with some degree of resistant to a common walnut issue.
By Chuck Leslie, UC Davis Walnut Improvement Program, Dept. of Plant Sciences
‘Durham’ harvests mid-season, earlier than ‘Chandler’, with excellent kernel color, well-filled nuts, large plump kernels that are easily extracted in halves, and relatively late leafing and bloom dates. The large oval nuts are uniform in size with good strength, solid seals, and an attractive shell appearance suitable for alternate use in-shell. The expected low blight and kernel quality should be of particular interest to growers in the Sacramento Valley.
‘Durham’ kernels have large size and excellent color, averaging 95% light and extra light with a high proportion of extra light and averaging 55.4 RLI in trials. The uniform, oval-shaped nuts average 15.1 grams in weight and contain large 8.3 g kernels with excellent appearance. ‘Durham’ nuts average 55% kernel yield and are expected to produce a good proportion of kernel halves. The shells have a particularly attractive appearance which, in combination with the seal and shell strength and a harvest date earlier than Hartley, suggests dual use as an in-shell nut if desired.
‘Durham’ leafing, flowering, and harvest dates are similar to ‘Tulare’ but this variety has larger nuts, better fill and superior kernel color. ‘Durham’ is 100% laterally fruitful and leafs out a few days before ‘Chandler’ with a protandrous bloom habit (the catkins shed before the female bloom). Leafing and bloom are later than ‘Solano’ or ‘Ivanhoe’ and therefore provide better blight avoidance. Harvest timing is about ten days before ‘Chandler’. Canopy structure in grower trials has been upright and without evidence of limb breakage to date. The ‘Durham’ tree appears to have average vigor and size at maturity, similar to ‘Chandler’. Comparable orchard spacing would be suitable for ‘Durham’ and ‘Chandler’ can also serve as a pollenizer for this variety.
‘Durham’, known as selection UC93-028-20 prior to its release, results from a 1993 cross using PI159568, a USDA introduction from Afghanistan, for its nut size, fill, plump kernel shape, and reduced blight susceptibility and ‘Chandler’ as a parent for kernel color and yield. ‘Durham’ has performed well in regional selection test blocks in Butte, Yolo and Fresno counties and in grower trials in Butte, Sutter, Yolo, Stanislaus, and Merced counties. Grower feedback from trials has been very positive.
‘Durham’ is now commercially available and can be ordered from any licensed nursery.