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- Author or Editor: Nancy W. Callan x
Exposure of `Meteor' tart cherry (Prunus cerasus L.) flower buds to deacclimating conditions resulted in an increase in the temperature of the low-temperature exotherms (LTEs) produced by the flower primordia during controlled freezing. Primordium supercooling temperature was related to chill unit accumulation, an indicator of depth of flower bud endodormancy. LTEs ceased to be detected after deacclimation earlier in 1986-87, a season of more rapid chill unit accumulation, than in 1987-88. Before deacclimation, the range of primordium LTE temperatures within a flower bud was normally ≤1C, but in deacclimated buds considerable variability in LTE temperatures was observed. However, primordia within a flower bud lost the ability to supercool simultaneously. This change was generally concurrent with the appearance of mature xylem vessel elements (XVE) in the upper bud axis and in the flower primordium but did not entirely depend on vessel element maturation.
Preharvest applications of Ca(OH)2 reduced splitting of ‘Lambert’ sweet cherry (Prunus avium L.) in laboratory trials. Three sequential preharvest sprays of Ca(OH)2 consistently reduced splitting, while single sprays of Ca(OH)2 in combination with NAA, ethephon, or B were moderately effective. Ca(OH)2 was a more effective Ca source than CaCl2 for reduction of splitting. Ca applications did not affect fruit size, but 3 applications of Ca(OH)2 increased fruit soluble solids. Chemical names used: (2-chloroethyl)phosphonic acid (ethephon) and 1-naphthaleneacetic acid (NAA).
Biological seed treatment offers a safe, environmentally responsible option for protection of seeds and seedlings from attack by soilborne pathogens. Most effective biological seed treatments have used either bacterial or fungal agents. The efficacy of a biological seed treatment depends upon the ability of the biocontrol agent to compete and function on the seed and in the rhizosphere under diverse conditions of soil pH, nutrient level, moisture, temperature, and disease pressure. Seed treatment performance may be improved through application and formulation technology. An example of this is the bio-priming seed treatment, a combination of seed priming and inoculation with Pseudomonas aureofaciens AB254, which was originally developed for protection of sh-2 sweet corn from Pythium ultimum seed decay. Bio-priming has been evaluated for protection of seed of sweet corn and other crops under a range of soil environmental conditions.
Cross-pollination increased fruit set, fruit size and seed content of ‘Cornice’ pear (Pyrus communis L.) in 3 large orchards without pollenizers. Supplemental self-pollination was equivalent to open pollination in its effect on fruit set and size. Low female fertility of ‘Comice’ could not be accounted for by early ovule degeneration or frost injury. Pollen transfer by bees was observed to be low in 2 orchards, with 36 and 41% of seedless fruit the result of open pollination. In comparison, only 6% of open-pollinated fruit were seedless in the orchard of greatest bee activity. Seedlessness was due to seed abortion during early fruit development. Classification of aborted seeds as to size at time of abortion revealed that in most fruits a minimal amount of seed growth occurs, although fruit retention does not require the presence of fully developed seeds. Fruit size was positively correlated with seed content, although this relationship was less pronounced in fruits with high seed count. The importance of seed development before abortion and of fully developed seeds in fruit set as well as fruit size is shown.
Shrunken-2 supersweet (sh2) sweet corn is susceptible to preemergence damping-off caused by Pythium ultimum, especially when planted into cold soil. Bio-priming, a seed treatment which combines the establishment of a bioprotectant on the seed with preplant seed hydration, was developed to protect seeds from damping-off.
In a series of field experiments conducted in Montana's Bitterroot and Gallatin Valleys, bio-priming or seed bacterization with Pseudomonas fluorescens AB254 protected sweet corn from P. ultimum damping-off. Bio-priming corn seed with P. fluorescens AB254 was comparable to treatment with the fungicide metalaxyl in increasing seedling emergence. Seedlings from bio-primed seeds emerged from the soil more rapidly than from nontreated seeds and were larger at three weeks postplanting. Seeds of sh 2 and sugary enhancer (se) sweet corn, as well as that of several sh 2 cultivars, were protected from damping-off by bio-priming.
In field experiments, bio-priming and coating with Pseudomonas fluorescens AB254 consistently protected sweet corn (Zea mays L.) seeds from preemergence damping-off caused by Pythium ultimum Trow. The bio-priming seed treatment was evaluated under various disease pressures and with seeds of three sweet corn genotypes: shrunken-2 supersweet (sh-2), sugary enhancer (se), and sugary (su). While no damping-off occurred in the su sweet corn, bio-priming protected sh-2 and se sweet corn seeds at a level equivalent to that obtained by treatment with the fungicide metalaxyl. Biopriming increased seedling height of all three sweet corn genotypes at 4 weeks post-planting. Coating of sweet corn seeds with P. fluorescens AB254 provided an equivalent degree of protection from damping-off under all but the most severe conditions.
Penicillium oxalicum is a seed- and soilborne fungal pathogen that causes preemergence damping-off and postemergence seedling blight of sweet corn, While seed infection and infestation by P. oxalicum is common, the amount of injury observed in the field is variable. Our objective was to determine factors influencing the occurrence and severity of disease due to P. oxalicum. Inoculation of sh-2 sweet corn seeds with conidia of P. oxalicum reduced seedling emergence and resulted in seedling mortality. Disease severity in the greenhouse and the field was greater as inoculum density increased from ≈ 102 to 106 conidia per seed. Increasing soil temperatures after planting inoculated seed resulted in more preemergence damping-off. Penicillium oxalicum is capable of growth and sporulation in soil that is too dry for seed germination. Nontreated (naturally infected) sh-2 sweet corn seeds or seeds inoculated with P. oxalicum were incubated in pasteurized soil that had been adjusted to various moisture levels-all too low for seed germination. Increasing soil moisture was associated with visible growth of Penicillium spp. on seed after incubation, and greater levels of damping-off and seedling blight when the seed was planted.
Disease management is an important step in any crop establishment system. Emergence of field-seeded crops may take several weeks for many species and represents a vulnerable stage of plant growth. This paper considers various biological, chemical, and physical seed treatments for improved seed performance. The role of seed quality and cultural practices in seedling establishment also is reviewed. Multidisciplinary approaches to improving horticultural crop establishment are promising.
Foliar applications of growth regulators (GR) in early autumn induced leaf retention (LR) on peach [Prunu,s persica (L.) Batsch.] and `Montmorency' tart cherry (Prunus cerasus L.) trees. In `Johnson Elberta' peach, the relative effectiveness of GRs on LR was NAA = Promalin (BA + GA4+7) > GA4+7 > GA3 > BA > control, and on leaf detachment pull force (PF) NAA > BA + GA4+7 > GA4+7 = GA3 > BA3 > BA > control. Relative GR-induced chlorophyll (CL) content in retained leaves was BA + GA4+7 > GA4+7 > GA3 > BA > control > NAA. Relative xanthophyll (XN) content of retained leaves was NAA > control > BA > GA3 = GA4+7 = BA + GA4+7. Treating only half of a peach tree with NAA did not affect LR on the untreated side. NAA decreased subsequent bud and flower size in peach. Bud hardiness was enhanced by NAA in `Johnson Elberta' peach but not in `Redhaven' peach or in `Montmorency' tart cherry. NAA increased hardening on both the leafy treated (foliated) and untreated (defoliated) sides of half-treated `Johnson Elberta' trees. Increased endodormancy duration, as measured by GA3 forcing of terminal leaf buds, was proportional to LR. Chemical names used: N-(phenylmethyl)- 1H-purin-6-amine (BA); (1a,2ß,4bß,10ß)-2,4a,7-trihydroxy-l-methyl-8-methylenegibb-3-ene-l,lO-dicarboxylic acid,l,4a-lactone (GA3, GA4+7); l-naphthaleneacetic acid (NAA).