1998 Nickels Field Trials Of Self-compatible Almonds
Tom Gradziel, Dale Kester
Department of Pomology
University of California, Davis, CA
Continued profitability of Sacramento Valley almond production relies
upon dependable and quality production with reduced inputs. The breeding of improved,
self-fruitful, and disease and pest resistant varieties, adapted to local conditions,
offers opportunities to meet these demands while remaining both ecologically and
economically feasible. Breeding success depends upon locating sources of needed germplasm,
the efficient indexing, testing and transfer of selected genes through controlled crosses,
the generation of large numbers of progeny from controlled crosses to ensure recovery of
the rare, horticulturally superior individuals, and the thorough testing of promising
selections in the range of soil and weather types typical of California almond production.
A key objective of the UCD almond breeding program is a series of almond varieties having
kernel and tree qualities comparable to ‘Nonpareil’ but with self-compatibility
to allow single-variety blocks, thus reducing orchard management needs and improving
insect pollination efficiency.
Four advanced UCD almond selections which had previously shown evidence
of self-compatibility of pollen on their own stigma/pistil were planted in solid 4-tree x
4-row blocks and also in a separate interplanted block at Nickels in order to evaluate
their capacity for self-fertilization in the presence of adequate honey-bees as
pollinators. [Individual tree crop set of interior and so primarily selfed trees is
compared with crop set on peripheral and interplanted trees which are pollinated by both
self and nearby outcrossed pollen. Similar sets on both the interior and peripheral trees
would indicate opportunities for single cultivar plantings, while dramatic differences
would indicate poor selfing (pollen transfer from the anther to nearby sigma on these
self-compatible trees)].
Crop set differences between interior and peripheral trees were again
observed in 1998, though the magnitude of the difference was less than observed in 1997.
This smaller difference is attributed more to generally low overall sets in this block for
1998 and probably does not indicate any improvements with tree age for self-pollinating
ability.
Selection UCD25-75 again demonstrated both the best sets as well as the
most uniform crop set among interior and peripheral trees. Considerable within-tree
variability was observed for this selection, with most nuts setting on interior wood which
is hard to knock due to the peach-like growth habit of this item. Nuts were small and
often shriveled in 1998.
Selection UCD34-26 showed moderate to poor crop set primarily on
terminals though also on short webbii-type thorny spurs. Trees are also medium in height
with a bushy habit further reducing crop potential. Nuts have a thin, similar shaped barky
shell with often shriveled nuts.
Selection UCD45-8 had the lowest crop overall mostly on young interior
shoots. Extensive vegetative growth was observed primarily at the tops of the upright
trees. Fruit showed fleshy, reddish hulls with open shells with small Mission type
nuts. Extensive blanks were observed.
Selection UCD36-52 produced a moderate to good crop primarily on
interior spurs and webbii-like radial branches giving the tree an upright growth habit
with a more open interior. Greater interior/peripheral crop set differences were observed
for this item relative to the others, due probably to the generally higher sets.
Evaluations at this block will be continued for two additional years to
allow observation of mature tree performance. In addition, controlled crosses have been
made between UCD selection showing high self-compatibility with breeding lines possessing
superior tree and nut quality. Progeny from these crosses will be read for regional
testing beginning next year.
