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- Author or Editor: Dale E. Kester x
Plants of non-bud-failure (susceptible but without symptoms) ‘Nonpareil’ almond [Prunus amygdalus Batsch] produced severe bud failure (BF) symptoms internally in the growing point after 5 and 10 weeks exposure to high temperature (43°C ± 2) in a growth chamber, but not in comparable plants grown in a greenhouse at a normal temperature (about 27°C). High levels of abscisic acid (ABA) were detected in normal plants exposed to the high temperature. Buds on non-BF plants showed much lower ABA under the same conditions although there was more prior to the beginning of high temperature exposure. Little significant effects on gibberellic acid (GA)-like levels were detected.
A method for growing almond (Prunus amygdalus Batsch) and almond-peach hybrid shoots in vitro is described using dormant shoot buds collected from December to February and stored at 3°C. Shoot tips can be in cultured in 0.7 to 0.8% agar, modified Knop’s macroelement mineral solution, 2% sucrose, FeEDTA, microelements and organic supplements of Murashige and Skoog medium, 6-benzyladenine (BA), and light. At 0.1 mg/liter, BA produced shoot elongation; at 1 mg/liter, lateral shoot proliferation. Limited rooting has been obtained.
The incidence of noninfectious bud-failure (BF) in ‘Nonpareil’ almond (Prunus amygdalus Batsch) trees propagated from a single source tree increased continuously with time at different rates in different orchards. Development was fastest and symptom expression was most severe in areas with the highest summer temperatures. BF-potential (susceptibility) could be modified by nursery conditions, although only to a minor degree compared with the effect of orchard location. Symptomless can be converted to BF by shifting from a low to a high-temperature regime. A reverse shift gave no reversion in BF-potential, but symptoms may not be expressed at a low-temperature location.
The mean inbreeding and coancestry coefficients were calculated for almond, Prunus dulcis (Miller) D.A. Webb, cultivars from the United States, France, Spain, Israel, and Russia. To improve cultivars to meet market demand, the recurrent use of four selections as parents in U.S. breeding programs has resulted in a mean inbreeding coefficient (F) of 0.022 in this collection. In France, a single cultivar, Ferralise, has an inbreeding value of F = 0.250, while cultivars of other almond-producing countries are noninbred (F = 0). Due to the use of common parents, U.S., Russian, and Israeli cultivars share coancestry, while coancestries also exist between French and Spanish almond germplasm. Cultivars of known parentage in the United States, Russia, Israel, France, and Spain trace back, respectively, to nine, eight, three, four, and three founding clones. Future almond-breeding programs may narrow the genetic base and thereby limit genetic gain.
`Jeffries', a mutant of `Nonpareil' almond [Prunus dulcis (Mill.) D.A. Webb], showed “unilateral incompatibility” in that its pollen failed to fertilize cultivars in the `Carmel' (CIG-V), `Monterey' (CIG-VI), and `Sonora' (CIG-VII) pollen cross-incompatibility groups (CIGs), as well as specific cultivars (`Butte', `Grace', and `Valenta') whose CIG group is unknown. `Jeffries' is not self-compatible, but produced good set when pollinated by 12 almond cultivars representing the entire range of CIGs involving `Nonpareil' parentage, as well as the parent `Nonpareil'. It was concluded that the `Jeffries' mutant—both gametophyte and sporophyte—expressed a loss of a single S allele of the `Nonpareil' genotype.
The relationship between hardiness of flower buds and blossoms, and time of leafing was studied in 25 almond cultivars, species and interspecific hybrids. In artificial freezing tests, genotypes of almond (Prunus amygdalus Batsch) and related species and interspecific hybrids exhibited a wide range of hardiness. A relationship was observed between blossom hardiness and time from leafing to bloom with some exceptions. Results show that genetic sources for blossom hardiness, not necessarily related to time of bloom, exist in these species.
Potentiality exists for noninfectious bud-failure (BF) to develop in stocks from almond breeding programs. The manifestation of BF among varieties introduced in California since 1920 is similar to the pattern of development of BF among offspring of controlled crosses. Nonpareil, the leading almond variety, has been a parent of most newer varieties, and is predominantly featured in breeding programs. Nonpareil has BF-potential and can transmit it to offspring.
Different propagation sources within ‘Nonpareil’ almond (Prunus amygdalus Batsch) showed wide differences in susceptibility to noninfectious bud-failure (BF). Seven years observations in a high temperature test location showed a range in BF-susceptibility from 0 to 100% depending on the source tree used for budwood. Selection of individual symptomless source trees resulted in separate clones that produced either no BF or high uniform percentages of BF-trees. Such single tree selection is a basis for selecting BF-resistance within cultivars. The nursery sources studied showed percentages from 0 to 62% suggesting that mixtures of normal and BF susceptible plants existed within the propagation sources. Propagation material randomly sampled from 10-year-old symptomless orchard trees from a hot summer location produced significantly higher percentages of BF trees in 6 years (2.3%) than propagation material from a cooler location (1.2%).
The potential for noninfectious bud-failure in propagation source material for `Carmel' almond in California has been determined in progeny tests from commercial nursery sources. Percentage BF increased with time (temporal), but decreased in severity (spatial). Analysis of variability in nursery sources showed that the key to successful selection for low BF potential is the individual tree, although variability exists among nurseries, budsticks (within trees), and individual buds (within budsticks). One-half of the individual trees of the nursery population tested have produced BF progeny so far within the test period. Future BF from the remainder was project by a BF model to be beyond the critical economic threshold. Two low BF-potential single tree sources were identified for commercial usage and progeny tests have started on an additional 19.