Delaying Non-Infectious Bud Failure Through Basal Epicormic Propagation
Non-infectious Bud Failure (NBF) is a disorder that affects susceptible almond cultivars, creating a zig-zag branch pattern as apical and nearby buds fail to emerge in spring. The reduction in crop productivity results not just in a potential income loss for that year, but eventual costs in switching out the orchard to new trees as NBF comes to affect the orchard to the point that the crop loss can no longer be borne.
The option to switch to less susceptible cultivars is constrained by high consumer demand for ’Nonpareil’ almond traits despite ‘Nonpareil’ and its progeny’s high susceptibility.
NBF expression in a nine-year-old tree where NBF was first observed in year 5, resulting in abnormal tree growth and loss of commercial productivity.
Decades of research eventually established a correlation between not just the age of the specimen tree and onset of NBF, but how far from the seedling parent tree the specimen is in the line of clonal propagation. Tracking the provenance of the almond propagation material became an important tool in delaying the onset of NBF and nurseries moved to adopt this approach
Photo: Megan Lynch
The results were even more dramatic in ‘Nonpareil’. After 18 years, only 5% of one REO tree type showed signs of NBF. The axillary sources of ‘Nonpareil’ were all showing symptoms by year 9. Even among the ‘Carmel’ and ‘Nonpareil’ commercial sources, those that were younger in clonal age took longer to show symptoms of NBF than commercial sources that were older in clonal age. However, it is clear that propagating from basal epicormic buds of low clonal age gave the best results, staving off emergence of NBF by years, giving the orchards more productive time.
In 2019, the results were published of a study testing whether ‘Nonpareil’ and ‘Carmel’ almond trees propagated from epicormic buds would result in a delay of NBF onset. Epicormic sources of differing clonal age - that is, distance from the seedling parent tree - were used.
Cooperating nurseries contributed their best sources, which per usual were propagated by axillary bud. The scientific team found sources of the lowest clonal age they could and then used basal epicormic buds from these sources to propagate with.
The results were stark. All of the ‘Carmel’ axillary sources had symptoms of NBF by the 3rd year and that cultivar’s testing ended by 10 years because all of the axillary sources had over 50% of the orchard affected by NBF. Three out of four clone types had 100% of the orchard affected.
Low non-infectious bud-failure (NBF) foundation stock is developed from epicormic buds (b,d) pushed from relic trees (planted near the time of cultivar origin) (a). Resulting foundation stock (c) is maintained by aggressive annual pruning to promote both axillary and epicormic shoot growth from older basal wood. (Circled top branch in (a) shows classic NBF symptoms of terminal shoot suppression and resulting erratic branching patterns).
By contrast, the relic-tree basal epicormic origin (REO) trees didn’t show any sign of NBF until the 7th year, when only one of the types showed symptoms. By the 8th year all were showing symptoms, but by the time the ‘Carmel’ part of the study was ended in Year 10, the % of trees affected in most cases was significantly lower than the % of nursery clones affected.
The results were even more dramatic in ‘Nonpareil’. After 18 years, only 5% of one REO tree type showed signs of NBF. The axillary sources of ‘Nonpareil’ were all showing symptoms by year 9. Even among the ‘Carmel’ and ‘Nonpareil’ commercial sources, those that were younger in clonal age took longer to show symptoms of NBF than commercial sources that were older in clonal age. However, it is clear that propagating from basal epicormic buds of low clonal age gave the best results, staving off emergence of NBF by years, giving the orchards more productive time.
NBF is not reversible, but the different properties of epicormic buds can be levied to delay the onset of NBF and obtain more years of productive harvests. The study likewise reinforced what was already generally known - this age-related disorder isn’t just related to the age of the specimen itself, but to the specimen’s clonal age - its distance in generations from the cultivar’s parent seedling tree.
Gradziel; Lampinen; Preece. Propagation from Basal Epicormic Meristems Remediates an Aging-Related Disorder in Almond Clones. Horticulturae 2019, 5 (2), 28. https://doi.org/10.3390/horticulturae5020028.
All photos & illustrations by above unless stated otherwise.
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