Noninfectious Bud Failure in `Carmel' Almond: I. Pattern of Development in Vegetative Progeny Trees

Abstract

<jats:p>The spatial and temporal pattern of noninfectious bud failure (BF) expression (BF<jats:sub>exp</jats:sub>) was studied during seven growing seasons in a population of `Carmel' almond trees originating from twelve commercial propagation sources. All progeny trees were grown in a single experimental site with high prevailing summer temperatures. BF<jats:sub>exp</jats:sub> increased continuously but irregularly in each nursery population as measured as the proportion of trees showing BF and as an average BF<jats:sub>exp</jats:sub> rating. Populations from the 12 nurseries represented increasing clonal generations from the original seedling tree and showed increasing levels of BF, as well as a decreasing shape value and increasing scale value derived by a failure statistics model. Models for development, distribution and hazard functions were defined for each of the 12 sources studied. Only sources from the original tree and source A demonstrated potential for commercial use. A significant correlation was found between average yearly increase in BF<jats:sub>exp</jats:sub> and the average daytime temperature for the previous June. The June period coincides with a specific stage in the seasonal growth cycle when vegetative buds mature.</jats:p>

Propagation from Basal Epicormic Meristems Remediates an Aging-Related Disorder in Almond Clones

“…For Nonpareil, 60 trees of each source-clone were tested. Planting took place in 1990 near Wasco, California in the southern San Joaquin Valley where high summer temperatures have been shown to be conducive to early NBF development [18]. Planting was carried out in randomized groups of 10 trees each, in north-south rows with a 7.3 × 6.4 m spacing on a Wasco-Sandy-loam soil.…”

“…One tree (subsequently designated as the Delta mother tree) was propagated from basal buds of the original Carmel seedling tree with 3 trees subsequently propagated from this Delta mother tree (Foundation Plant Services (FPS) sources 3-56-1-90, 3-56-8-92 and 3-56-2-90) ( Table 2). Four standard commercial propagation sources (C1-C4) of Carmel were provided by cooperating nurseries as part of a larger evaluation of NBF risk in commercially available California propagation stocks [18]. Four REO source-clones for Nonpareil were derived from 100+ year old trees from orchards in the cooler northern Sacramento Valley (Table 1).…”

“…An additional REO source designated (E3) was developed by a cooperating commercial nursery. Four standard commercial propagation sources (C1-C4) of Nonpareil were provided by cooperating nurseries as part of a larger evaluation of NBF risk in commercially available California propagation stock [18].…”

“…Trees were evaluated using established ratings for NBF expression [18] over the next 18 years or until plot removal due to excessive tree decline and loss of commercial productivity. Trees were evaluated in March following primary shoot development.…”

“…Extensive research has failed to find any association of NBF with known pathogens, including viruses and viroids [13][14][15][16][17]. A comprehensive evaluation of nursery foundation stock for the highly NBF vulnerable cultivar Carmel demonstrated lower incidence in orchards propagated from 'relic-trees' (i.e., trees closely related by their propagation lineage to the original Carmel seedling tree) [18]. Consequently, most current nursery production of both Carmel as well as Nonpareil are based on foundation-stock originating from epicormic shoots developing at the base of 50 to 100 year-old 'relic' trees of Carmel and Nonpareil, respectively.…”