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Correlations were made between the responses of seeds, physiologically dwarfed seedlings and dormant cuttings to similar chilling treatments. Seed germination correlated highly with growth of physiologically dwarfed seedlings and shoot growth of dormant cuttings. Emergence and seedling growth correlated poorly with germination, growth of physiologically dwarfed seedlings and shoot growth of dormant cuttings. Thus, germination was a better seed predictor of the mature peach chilling response than emergence or seedling growth. Growth of dwarfed seedlings correlated highly with shoot growth of dormant cuttings. The anomalous leaf condition of peach seedlings may have confounded seedling growth after seed chilling, but was not a problem when the chilling treatment was provided to physiologically dwarfed seedlings. The dormancy release mechanisms that promoted seed germination, growth of physiologically dwarfed seedlings and growth of dormant cuttings were similar.
We compared peach [Prunus persica (L.) Batsch cv. Johnson Elberta] seed germination (G) and seedling emergence (E) after various stratification (St) treatments. Treatments were arranged in factorial combinations of five St durations (20 to 60 days) at eight constant temperatures (0 to 18C) in a completely randomized design followed by repeated measures during forcing time. G and E were recorded every 5 days during forcing. Seed St at 0 to 10C and 0 to 14C promoted G and E, respectively. G and E increased with longer St treatments at promoting temperatures. There was a weak correlation between G and E averaged over the forcing measurements (r 2 = 0.54). The best correlation was between E after 15 days and G after 10 days (r 2 = 0.83). The results indicate that G and E in peach are not identical indicators of endodormancy (ED) release and should not be used interchangeably. Forcing times must be considered when making comparisons between G and E.
We observed initial peach [Prunus persica (L.) Batsch] seedling growth after endodormant (ED) seeds (`Johnson Elberta') had been stratified for five durations (20 to 60 days) at eight constant temperatures (0 to 18C). Seedling growth increased and became more normal when seeds were stratified for longer durations at chilling temperatures. Stratification (St) at 0 to 6C (especially 2C) produced seedlings with more abnormal growth than St at higher temperatures (8 to 10C) at intermediate St durations (30 to 50 days). Growth of the primary stem increased with additional St (0 to 14C). Abnormal (epinastic) leaf development decreased following longer St treatments at 4 to 14C. Lateral shoot growth increased initially, then decreased after longer treatments at low temperatures (0, 4, and 6C) and decreased after St at higher temperatures (8 to 10C).
We studied the response of physiologically dwarfed (PD) to near normal peach [Prunus persica (L.) Batsch] seedlings (`Johnson Elberta' seeds) to various chilling treatments. Peach seedlings were obtained by forcing seeds that had been subjected to a brief stratification treatment. Seedlings were divided into four types (groups) according to the length of the primary stem and the presence and size of lateral branches. The seedlings were used in a chilling study with treatments of five durations (20 to 60 days) at four temperatures (2 to 14C). Terminal shoot growth and lateral budbreak were recorded 17 days after forcing. Shoot and leaf dry weight were obtained after seedlings had grown for 64 days. Budbreak and growth improved with the duration of the chilling treatment. Generally, 7C was the best chilling temperature, with 2 or 10C only slightly less effective. Treatment at 14C did not promote budbreak or growth. Budbreak and growth had significant interactions between treatment duration and temperature. The seedling type and treatment duration interaction was significant for terminal shoot length, lateral budbreak, and leaf dry weight, but were probably the result of differences between the seedling types before treatment and not true interactions with the length of the treatment. There was a significant interaction between the seedling type and treatment temperature on terminal shoot growth. Subsequent shoot growth did not differ significantly between the seedling types after similar chilling treatments. Thus, shoot growth was the best indicator of the chilling process of `Johnson Elberta' peach seedlings. Indicators of dormancy removal such as lateral budbreak or terminal shoot growth after 17 days forcing were not good predictors of subsequent seedling growth.
Cuttings from peach (Prunus persica (L.) Batch cv. Johnson Elberta) trees were subjected to five chilling durations (20 to 76 days) at seven temperatures (0 to 14C) and five concentrations of gibberellic acid [GA, (0.0 to 1 mm)]. There was a significant increase in terminal shoot length with longer chilling treatments. Cuttings treated at 2 to SC had the longest shoots, and shoot length decreased, in order, following treatment at 10, 0, and 14C. Treatment with the highest concentration of GA, resulted in the longest terminal shoots. Interactions between GA and chilling durations indicated that either higher concentrations of GA, or longer chilling treatments increased terminal shoot growth. Thus, endogenous promoters, like GA, are evidently produced or released during chilling. Sensitivity to GA, was also important. Chemical name used: Gibberellic acid (GA3).
We determined whether the chilling process (endodormancy release) was similar in peach [Prunus persica (L.) Batch cv. Johnson Elberta] seeds, seedlings (near normal to physiologically dwarfed), and mature plants (cuttings) by comparing correlation coefficients of various growth measurements following similar chilling treatments. Seed germination (10 days after forcing at 20C) and seedling emergence (15 days after forcing in the greenhouse) correlated highly with leaf and shoot growth (56 days of growth) of seedlings and terminal shoot growth of cuttings (13 days after forcing). The correlations were higher for germination than for emergence. Initial (first season) seedling growth correlated poorly with germination, emergence, budbreak, and growth of seedlings (second season) and shoot growth of cuttings. Budbreak and growth of seedlings correlated highly with shoot growth of cuttings. The abnormal leaf problem, which can cause apex abortion (common with initial seedling growth), confounded correlations with initial seedling growth. Yet, the abnormal leaf problem did not hinder correlations with the second seasons growth. Good relationships between the chilling mechanisms that promoted germination, emergence, budbreak, and growth of seedlings and shoot growth of cuttings existed, but were dependent on what was measured and when the measurement was taken. Germination (forced at 20C) was the most accurate indicator of the seed chilling status for comparisons with the responses of the other propagules.
A Latin Square design was used to determine effects of undertree irrigation on orchard temperatures during freezes. Plots (40 × 40 m) in a tart cherry orchard included 72 trees. Water was applied at 0, 125, 250 and 380 (± 5%) liters/min. Four meter towers held shielded thermocouples at 1, 2, 2.5, 3 and 4 meters. Thermocouples were monitored at 10-second increments using a Campbell Scintific CR10 micrologger. AM32 multiplexers switched between the 96 thermocouples involved. An IBM AT compatible computer retrieved and stored data from the micrologger at 10-minute intervals. The data acquisition system was activated shortly after midnight and operated continuously until after sunrise on three near-freeze nights. No significant heating effect was present at any water level. On one of the nights, a refrigeration effect was documented.
‘Navaho’ and ‘Apache’ blackberry plants were maintained at 10, 15, 20, 25, 30, or 35 °C in growth chambers to determine optimum temperature for budbreak and flowering (fewest days to flowering). In a separate experiment, bloom dates were observed for a collection of 117 Rubus genotypes over four seasons. Using these phenological data, predictive linear and curvilinear models were tested using a range of cardinal temperatures. The growth chamber experiment indicated optimum temperatures for bloom were 25.6 °C for ‘Apache’ and 29.2 °C for ‘Navaho’. For the field observations, time to bloom was best defined by a linear model with base and optimum temperatures of 6 and 25 °C and a curvilinear model defined by base and optimum temperatures of 4 and 27 °C, respectively. Based on the linear growing degree hour (GDH) model, heat units to bloom varied among cultivars in the collection from 9,200 GDH for ‘Chickasaw’ to 18,900 GDH for ‘Merton Thornless’.
Dormant seeds of `Johnson Elberta' peach [Prunus persica (L.) Batsch] were stratified at constant 2, 6, or 14 °C or cycled between 2 and 14 °C in 12/12, 14/10, 16/8, 20/4, 22/2, or 23/1 h cycles. Emergence (measured every 3 d after planting) and normal seedling growth (measured after 49 d) increased with longer stratifiction durations. Seeds stratified at 2 °C had the most rapid emergence (only 28 d of stratification was required) but seedling growth was abnormal until 70 d of stratification. Isothermal stratification at 6 °C resulted in normal seedlings after 56 d of stratification but quality and quantity of growth improved with stratification up to 70 d. Seeds stratified at 14 °C showed limited improvement in seedling emergence with time; seedling growth was poor and cotyledonary reserves were not used. Seedling growth after cycled stratification treatments gained normalcy faster than in the constant 2 °C treatment. The 22/2 and 20/4 (2/14 °C) cycles produced normal growth after 56 d of stratification that was comparable to the growth produced by the constant 6 °C treatment. Other cycles required 70 d or more for equivalent seedling growth. Improved seedling growth under cycled treatments could be due to developmental or growth promoting temperature effects of 14 °C during stratification or a combined effect of thermal accumulation and chilling occurring together after a minimal chilling requirement has been completed.