<Emphasis Type="Italic">In vitro</Emphasis> regeneration of the tennessee coneflower (<Emphasis Type="Italic">Echinacea tennesseensis</Emphasis>)

Summary Tennessee coneflower [Echinacea tennesseensis (Beadle) Small] was regenerated from flower stalks, leaf sections from flowering plants, and hypocotyls and cotyledons from seedlings. Murashige and Skoog medium (MS) supplemented with naphthaleneacetic acid (NAA) at 0.54 μM and thidiazuron (TDZ) at 22.7 μM yielded the most shoots per leaf explant. NAA and 6-benzylaminopurine concentrations for optimal shoot regeneration from leaf, flower stalk, cotyledon and hypocotyl explants in MS media were 0.54 and 24.6μM, respectively. All explant types generated shoots; however, those derived from leaves and flower stalks produced the highest number of shoots per explant and highest percentage of explants with shoots. Explants cultured on media containing high levels of NAA (5.4–27 μM) formed calluses but no adventitious shoot. Leaf explants responded to a wider range of NAA concentrations than the other explant types but shoots generated from flower stalks grew the fastest. While all cytokinins tested increased the number of shoots per explant, the number of shoots in media containing TDZ was increased by nearly threefold. Regenerated shoots from all explant types cultured on MS medium supplemented with 0.25 μM indole-3-butyric acid initiated roots within 4 wk; NAA was not effective for root induction. All vernalized plantlets developed into plants that were morphologically identical to the source material.     

Influence of strobilurin compounds on the development of Puccinia horiana

The effectiveness of 5 strobilurin fungicides: Acanto 250 SC, Amistar 250 SC, Discus 500 WG, Signum 33 WG, Zato 50 WG and Score 250 EC (triazole-standard) in the control of Puccinia horiana was tested on chrysanthemum cv. Melba Blane. Number of pustules per leaf was observed before treatment, as well as 2 and 4 weeks after treatment. Additionally, after 4 weeks, their influence on plant growth, size of pustules and eventually phytotoxicity were assessed. Plants were sprayed preventively and curatively 4 times at weekly intervals. In preventive programme after 4 weeks of investigations, average of about 1.5 spot per leaf was recorded on control plants. Disease symptoms did not appear on chrysanthemums protected by fungicides Signum 33 WG at concentration 0.18% and Zato 50 WG at concentration 0.015%. In case of the other tested fungicides only sporadically pustules on single leaves were noticed (over 95% of them were browned, dried and crumbled). On control plants more than 46% of leaves was infected but in case of the other investigated fungicides it was only 3-7%. Diameter of spots on plants protected with: Score 250 EC, Acanto 250 SC and Discus 500 WG was similar as on the leaves of control plants. On plants protected with Amistar 250 SC the diameter of pustules was significantly lower than on control plants. In curative programme after 4 weeks of tests, leaves of control plants had about 4 spots per leaf. On leaves sprayed with Score 250 EC at concentration 0.05% there were 4 times less spots than on control plants. Chrysanthemums treated with tested strobilurin fungicides had about 2 times less pustules than on control plants. Diameter of spots on control plant leaves was 3.6 mm and was similar as on chrysanthemums protected with tested fungicides. On leaves of control plants all pustules were active without visible changes or damage but in case of the investigated fungicides almost 100% of them were browned, dried and crumbled. After 4 weeks of experiment, a measured height of control plants was about 125 mm and was similar to the height of plants protected with tested fungicides except Signum 33 WG, which stimulated plant growth. None of tested compounds showed phytotoxic effect.     

Phytotoxicity to blackcurrants of sprays containing sulphur

Studies in 1963–65 of the phytotoxic effects, on leaves, flowers and yields of blackcurrants, of sprays containing sulphur, particularly lime sulphur, showed that there was considerable variation in degree of effect between years and between experiments in the same year. It was difficult to damage flowers except at low temperatures, but if fruit set was affected then yield was depressed. Leaf scorching has to be very severe before yields are depressed. There was no evidence from preliminary experiments that sprays of seaweed extract reduced sulphur shock if used up to 3 days before lime sulphur application. The growth rate of shoots was reduced by 1/4–4% lime sulphur for short periods, dependent on concentration, but total bud numbers, flower/ vegetative bud ratios and yield were unaffected. It was found that no adverse effects of lime sulphur were carried over into the following year.     

The Dark Respiration of Sugar-cane and the loss of Photosynthate during the Growth of a Crop

The dark respiration of the whole shoots (stems and leaves)and stems only of plants of commercial sugar-cane cultivars(Saccharum hybrids) of different ages was measured in a largerespiration chamber. The respiration rates of all parts of the plants were closelyrelated to ambient temperature. On a unit dry-weight basis leavesrespire faster than stalks at the same temperature. However,as the stalks grow and their dry weight increases with age andgreatly exceeds that of the leaves the greatest loss of carbohydrateby respiration occurs from the stalks. The percentage loss of gross photosynthate due to respirationhas been estimated for different stages of growth. The lossdepends on the age of the plant and the relative proportionsof leaf and stalk. It can range from some 20 per cent in activelygrowing young plants to at least 50 per cent in 18-month-oldplants of an irrigated crop in Natal.     

The seasonal carry-over of Botrytis tulipae (Lib.) Lind., the cause of tulip fire

Damage done by Botrytis tulipae developed in a variety of ways after planting naturally and artificially inoculated bulbs, the fungus sometimes rapidly invading developing shoots, preventing their emergence. In other instances (a) leaves emerged above ground, but not before being severely infected (the traditional ‘primaries’), (b) leaves emerged uninfected but the flower stalks were attacked at a later stage causing mechanical weakness (and hence frequent snapping), or (c) leaves and flower stalks remained uninfected, with the development of B. tulipae being restricted to its spread from mother to daughter bulbs, which also occurred in (a) and (b). More emerging shoots were infected when inoculated bulbs were grown at 10° and 15.5° than at 4 °C—an effect suggesting that greater numbers of foliar primaries would develop in mild winters. The underground transmission of B. tulipae indicates the need for eradicating infections in the bulb, the primary sources of this pathogen.     

Plant critical levels for the evaluation of boron toxicity in spring barley (Hordeum vulgare L.)

Summary Pot experiments on B toxicity in spring barley (Hordeum vulgare L., cv. Trumpf) using sandy soils indicated that there are significant relationships between B content of the leaves and of the shoots respectively in the toxic range and degree of damage of the leaves at stage 7–8 of the Feekes scale, which may be used to derive plant critical levels of B toxicity. Symptoms due to B excess begin to develop on the leaves (leaf tip necroses) relatively independently of the ontogenetical stage of development as soon as the B content of the leaf tissue reaches 60–80 mg/kg DM.The corresponding symptom-related toxic plant critical level of shoots (i.e. the B content of the whole shoot at which the first damage in leaves begins to occur) ranges from 30 mg/kg shoot DM (related to older leaves) to 80 mg/kg shoot DM (related to younger leaves). Grain yield is significantly reduced only when the B content of shoots at Feekes stages 7–8 exceeds the yield-related toxic plant critical level (yield reduction to 90% of the optimum yield) of 120–130 mg/kg shoot DM.B contents of the shoots at Feekes stages 7–8 from 80–120 mg/kg shoot DM define the range at which plants have marked toxicity symptoms, but at which there are no yield reductions.     

Impact of the flower stalk-boring moth Neoschoenobia testacealis (Lepidoptera: Crambidae) and water-level fluctuations on the flower and fruit production of the yellow water lily Nuphar subintegerrima (Nymphaeaceae) in irrigation ponds of western Japan

The flower and fruit production of the yellow water lily Nuphar subintegerrima and the seasonal occurrence of the flower stalk-boring moth Neoschoenobia testacealis were surveyed in two irrigation ponds in western Japan. Water-level fluctuations at each pond were measured. Flowering was observed from late May to September, and fruiting from late May to October. The yellow water lily produced cumulative numbers of 189 and 181 flowers and 121 and 129 fruits in the two ponds’ quadrats. The fruit setting rates at the two ponds were 0.64 and 0.71, and decreased in the summer. The percentage of bored flower stalks was 16 and 5%. Mature larvae bored flower stalks severely during the summer. Whenever the boring larvae attacked the flower stalks, the flower buds and flowers were aborted. There was a significant negative correlation between the fruit setting rate and the boring rate per month (number of bored flower stalks/number of all flower stalks). Whenever abruptly rising water levels (about 10 cm) submerged the flowers, the flowers were aborted too and could not set fruits. The percentages of non-setting fruit due to the rising water levels at the two ponds were 6 and 8%. Overall, our results indicated that flower stalk boring was a more important factor than water-level fluctuation in the sexual reproduction of N. subintegerrima and that N. subintegerrima was well suited to small irrigation ponds.     

2个慈竹bZIP基因的克隆、生物信息学分析及其诱导表达

从慈竹笋转录组数据库中筛选并克隆出2个bZIP基因（BebZIP2和BebZIP6）进行生物信息学分析。分析结果表明,它们编码序列长度分别为504和720 bp,编码167个和239个氨基酸,BebZIP2和BebZIP6属于bZIP相关蛋白,与水稻OsbZIP52/RISBZ5蛋白聚在一枝。组织表达分析表明,这2个慈竹BebZIP基因在慈竹笋、茎、展开叶和未展开叶等部位均有表达,属于组成型表达,同一基因在不同组织中的表达量差异较大,表达量的大小为未展开叶 > 展开叶 > 茎 > 笋。对慈竹幼苗进行ABA、NaCl和PEG6000非生物胁迫处理,结果表明,BebZIP2和BebZIP6对盐、干旱和ABA胁迫均具有不同程度的响应。     

Herbicidal activity of the antibiotics geldanamycin and nigericin

Geldanamycin and nigericin, phytotoxic metabolites from a strain ofStreptomyces hygroscopicus, were tested for herbicidal activity and selectivity on a range of crop and weed species. In petri dish bioassays, geldanamycin reduced radicle growth of all species tested, whereas nigericin inhibited 7 of 10. The two compounds in mixture appeared to be additive rather than synergistic in effect. In assays with seeds and seedlings in field soil, geldanamycin showed significant preemergence activity on proso millet, barnyardgrass, garden cress, and giant foxtail. It had no postemergence herbicidal effect on any of the species tested. Nigericin had preemergence activity on garden cress and large crabgrass and postemergence activity on garden cress and velvetleaf. The postemergence effect of nigericin on velvetleaf was especially striking, with leaves showing symptoms of injury within 24–48 h of treatment. Doses as low as 0.3 kg/ha caused damage. The primary herbicidal effect of both compounds was slowing of seed germination or seedling growth, although some plants were killed, especially at higher rates of application. Herbicidal effects were most pronounced for 1 to 2 weeks after treatment and diminished thereafter.Michigan Agricultural Experiment Station journal article no. 13012.     

Effects of brassinosteroid, auxin, and cytokinin on ethylene production in Arabidopsis thaliana plants

Inflorescence stalks produced the highest amount of ethylene in response to IAA as compared with other plant parts tested. Leaf age had an effect on IAA-induced ethylene with the youngest leaves showing the greatest stimulation. The highest amount of IAA-induced ethylene was produced in the root or inflorescence tip with regions below this producing less. Inflorescence stalks treated with IAA, 2,4-D, or NAA over a range of concentrations exhibited an increase in ethylene production starting at 1 microM with increasingly greater responses up to 100 microM, followed by a plateau at 500 microM and a significant decline at 1000 microM. Both 2,4-D and NAA elicited a greater response than IAA at all concentrations tested in inflorescence stalks. Inflorescence leaves treated with IAA, 2,4-D, or NAA exhibited the same trend as inflorescence stalks. However, they produced significantly less ethylene. Inflorescence stalks and leaves treated with 100 microM IAA exhibited a dramatic increase in ethylene production 2 h following treatment initiation. Inflorescence stalks showed a further increase 4 h following treatment initiation and no further increase at 6 h. However, there was a slight decline between 6 h and 24 h. Inflorescence leaves exhibited similar rates of IAA-induced ethylene between 2 h and 24 h. Light and high temperature caused a decrease in IAA-induced ethylene in both inflorescence stalks and leaves. Three auxin-insensitive mutants were evaluated for their inflorescence's responsiveness to IAA. aux2 did not produce ethylene in response to 100 microM IAA, while axr1-3 and axr1-12 showed reduced levels of IAA-induced ethylene as compared with Columbia wild type. Inflorescences treated with brassinolide alone had no effect on ethylene production. However, when brassinolide was used in combination with IAA there was a dramatic increase in ethylene production above the induction promoted by IAA alone.     

Induction of Systemic Resistance in Pea to Pea Powdery Mildew by Exogenous Application of Salicylic Acid

Exogenous application of salicylic acid (SA) solutions to pea leaves induced systemic resistance to Erysiphe pisi. reducing by 20–30% the percentages of fungal germlings that successfully infected untreated leaves of SA-treated plants. SA concentrations of 1.5 and 15 mM were similarly effective, but 0.15 mM had no detectable effect. While 15 mM SA solutions were phytotoxic. 1.5 mM solutions caused no apparent damage indicating that resistance induction was not due to tissue damage. The induced resistance persisted for at least 13 days after treatment, but excision of treated leaves 1 day after SA application prevented full induction of systemic resistance, and the resistance was not expressed if untreated leaves were inoculated fewer than 3 days after SA application. The effect of SA was transmitted to leaves at nodes both above and below treated leaves. Chemical induction of systemic resistance may provide an additional means for controlling pea diseases.     

Oryzalin combined with adventitious regeneration for an efficient chromosome doubling of trihaploid kiwifruit

Summary Chromosome doubling of one parthenogenetic trihaploid from cultivar Hayward ofActinidia deliciosa was investigated. Two antimitotic agents, colchicine and oryzalin, appliedin vitro on shoots and leaves at different concentrations were compared with regard to their efficiency. Survival and regeneration rates were determined and ploidy level of regenerated plantlets was evaluated by flow cytometry. Differences were observed between the two antimitotic agents depending on whether shoots or leaves were treated. Hexaploid plantlets were obtained with highest efficiency by adventitious regeneration from leaves treated by oryzalin at 5 M, constituting an original and promising result which was corroborated for another trihaploid clone. Dodecaploid plantlets were also induced but only from oryzalin treated leaves. On the other hand, colchicine applied to leaves was very phytotoxic. This study demonstrates that oryzalin combined with adventitious regeneration is particularly efficient to induce chromosome doubling of trihaploid kiwifruit.Abbreviations MS Murashige and Skoog - IBA indole-3-butyric acid - DMSO dimethylsulfoxide - PBS phosphate buffer salin - DTT dithiothreitol     

Soil fumigation with methyl bromide: the phytotoxicity of inorganic bromide to carnation plants

Rooted carnation cuttings often developed phytotoxic symptoms when planted in soil previously fumigated with methyl bromide, and many died. Those which recovered suffered a marked check in growth and flower production was reduced. Plant injury and effects on flower yield were more severe at high rates of fumigant application, but were reduced by flooding the soil with water or by incorporating peat into the growing medium.
Plant survival and flower yield were inversely related to the concentration in soil of inorganic bromide formed by the breakdown of the fumigant. Injury to plants occasionally occurred in the presence of soil concentrations of inorganic bromide as low as 5 pglg. Flooding the soil or incorporating peat into it were beneficial because these treatments reduced the soil concentration of inorganic bromide.
Carnation plants which were grown in soil previously fumigated with methyl bromide or supplemented directly with potassium bromide accumulated bromide in their leaves, and a bromide gradient was eventually established, the concentrations decreasing from the bottom to the top of the plants.
The evidence that inorganic bromide is the cause of the injury to carnations is discussed, and the role of peat in alleviating the incidence and seventy of the injury is considered.     

Osmolytes in salinity-stressed Iris hexagona

We characterize the salinity stress response of Iris hexagona, a freshwater species, by measuring three putative osmolytes, betaine, proline, and dimethylsulphonio-propionate (DMSP) in plants after short (3 days) and long-term (4–5 months) exposure to NaCl. HPLC analyses show that untreated control leaves contained 2.1, 0.2 and 3.2 mg g⁻¹ DW of betaine, proline, and DMSP, respectively, and establish the presence of these compounds in the Iridaceae. Within 4 days of salinity stress (200 mM NaCl) betaine, proline and DMSP increased significantly. Among vegetative tissues, the highest level of proline occurred in roots; betaine and DMSP were highest in leaves. Analyses of generative tissue (flowers and flower stalks) after long-term exposure showed the highest levels (>10 mg g⁻¹ DW) of all examined compounds in petals but only proline and betaine increased with salinity. All three substances showed a basipetal gradient in flower stalks. Although the examined compounds responded to salinity, the osmometry of the sap indicated that they comprise less than 10% of the osmotically active solutes. The temporal and spatial changes in the distribution of the analyzed compounds indicate complex responses to salinity.     

Association of Eriophyes dimocarpi (Acari: Eriophyidae) with longan witches’ broom disease in Vietnam

Longan witches’ broom (LgWB) syndrome was observed in all longan-growing provinces of Vietnam. Key symptoms include: small, stunted shoots with curved, rolled up margins, deformed leaves with blisters and hairy patches on the underside; abnormal development of flower structures, flower abortion, failure to produce fruits or developing small fruits. During 2012–2015, field surveys and study of the relationship between LgWB symptoms and Eriophyes dimocarpi mites presence were carried out. Moreover, molecular analysis, electron microscopy observations, E. dimocarpi inoculations, pruning of affected spikelets and miticide experiments were performed. An average of 36.58% of longan seedlings inoculated with E. dimocarpi mites showed typical symptoms of LgWB at about 27.5 days after inoculation. The use of several pesticides in different combinations showed high efficacy on E. dimocarpi mites elimination and of symptomatology incidence reduction. These results suggest a significant association of E. dimocarpi with LgWB syndrome in Vietnam.     

Induced defences in the neotropical tree Bauhinia brevipes (Vog.) to herbivory: effects of damage-induced changes on leaf quality and insect attack

Induced defences to herbivory are physical, nutritional, and allelochemical traits that change in plants following damage or stress, and that reduce the performance and/or preference of herbivores. The aim of this study was to verify the occurrence and effect of induced responses in Bauhinia brevipes (Vog.) (Leguminosae) which defend it against herbivores, through the manipulation of its leaves, and their effects on herbivore foraging behaviour. We selected 15 plants in the field, and three shoots per plant were subjected to one of three treatments: (1) damaged shoots (simulation of the main types of foliar herbivory and insect exclusion); (2) damaged control shoots (insect exclusion); and (3) control shoots (not manipulated). Water and nitrogen content, tannin concentration, levels of herbivory, and shoot growth rates were compared among treatments. Leaf quality varied among treatments. Damaged leaves showed higher tannin concentration, and lower water and nitrogen content compared to undamaged leaves. On the other hand, they experienced higher rates of herbivory than leaves on control shoots. Moreover, shoots that were experimentally induced showed a higher increase in final shoot length. These results suggest that simulated herbivory on B. brevipes reduced the nutritional quality of its leaves and increased the amount of secondary compounds, therefore altering insect herbivore attack and increasing shoot performance.     

The impact of two gall-forming arthropods on the photosynthetic rates of their hosts

The impact of herbivores on host plant photosynthetic rates can range from negative to positive. While defoliation by chewing herbivores can result in increases in photosynthesis followed by compensatory growth, other herbivore guilds, such as mesophyll feeders which damage photosynthetic leaf tissues, almost always reduce photosynthetic rates. The impact of galling herbivores on host photosynthesis has rarely been examined, even though the limited tissue disruption and the strong metabolic sinks induced by gall-forming herbivores could potentially stimulate photosynthetic rates. I examined the hypothesis that gall-inducing herbivores could stimulate photosynthesis in neighboring leaves in response to increased sink-demand by the gall. To address this hypothesis, I measured photosynthetic rates of galled leaves or leaflets, neighboring ungalled leaves or leaflets, and ungalled leaves or leaflets on ungalled shoots on naturally growing Prunus serotina (wild cherry) and Rhus glabra (smooth sumac). The leaves of wild cherry were galled by an eriophyid mite, Phytoptus cerasicrumena; the leaves of smooth sumac by an aphid, Melaphis rhois. I found that both species reduced the photosynthetic rates of the leaves or leaflets they galled from 24 to 52% compared to ungalled leaves in ungalled areas of the plants. Contrary to my hypothesis, mite galls on wild cherry reduced photosynthesis of neighboring ungalled leaves within the same shoot by 24% compared to ungalled leaves on gall-free shoots. Aphid galls on sumac leaflets did not significantly alter the photosynthetic rates of neighboring leaflets relative to ungalled leaves on ungalled shoots. Although gall-formers would appear to have the potential to stimulate photosynthesis in the same manner as defoliating herbivores, i.e., by increasing sink demand relative to source supply, I found only negative impacts on photosynthesis. I suggest that sink competition for nutrients between developing leaves and growing gall tissue may account for the negative impacts of sink-inducing gallers on photosynthesis. Received: 17 October 1997 / Accepted: 2 February 1998     

Tissue-specific oxylipin signature of tomato flowers: allene oxide cyclase is highly expressed in distinct flower organs and vascular bundles

A crucial step in the biosynthesis of jasmonic acid (JA) is the formation of its correct stereoisomeric precursor, cis(+)12-oxophytodienoic acid (OPDA). This step is catalysed by allene oxide cyclase (AOC), which has been recently cloned from tomato. In stems, young leaves and young flowers, AOC mRNA accumulates to a low level, contrasting with a high accumulation in flower buds, flower stalks and roots. The high levels of AOC mRNA and AOC protein in distinct flower organs correlate with high AOC activity, and with elevated levels of JA, OPDA and JA isoleucine conjugate. These compounds accumulate in flowers to levels of about 20 nmol g-1 fresh weight, which is two orders of magnitude higher than in leaves. In pistils, the level of OPDA is much higher than that of JA, whereas in flower stalks, the level of JA exceeds that of OPDA. In other flower tissues, the ratios among JA, OPDA and JA isoleucine conjugate differ remarkably, suggesting a tissue-specific oxylipin signature. Immunocytochemical analysis revealed the specific occurrence of the AOC protein in ovules, the transmission tissue of the style and in vascular bundles of receptacles, flower stalks, stems, petioles and roots. Based on the tissue-specific AOC expression and formation of JA, OPDA and JA amino acid conjugates, a possible role for these compounds in flower development is discussed in terms of their effect on sink-source relationships and plant defence reactions. Furthermore, the AOC expression in vascular bundles might play a role in the systemin-mediated wound response of tomato.     

THE CONTROL OF CERTAIN PLANT DISEASES WITH SULPHONAMIDES

In in vitro tests, sulphanilamide was more toxic to plant pathogenic fungi than to bacterial plant pathogens, but sulphadiazine and other heterocyclic-ring substituted compounds were more toxic to plant pathogenic bacteria than to fungi. When tested in vivo against a number of facultative plant parasites the sulphonamides were without effect except in providing slight control of Pseudomonas coronafaciens on oats. Against a number of obligate parasites including Uromyces fabae on broad beans and Puccinia triticina on wheat, the sulphonamides gave effective control when applied either through the roots or leaves. The minimal effective concentrations in the leaves of the more active compounds varied between 100–200 μg./g. fresh weight of leaf tissue.
The sulphonamides are also toxic to higher plants and both the fungitoxic and phytotoxic effects could be reversed with p -aminobenzoic acid.
A number of sulphanilamides with acyl substituents on the p -amino-group were tested against P. triticina and were shown to control the disease with very slight phytotoxic damage. Control could be attributed to the release of 'free' sulphanilamide by hydrolysis within the plant.
Two factors appear to control the systemic action of sulphonamides: first, the movement in the plant which results in the accumulation of effective concentrations in the leaves, and secondly, the specificity of a sulphonamide for a particular host-parasite association.     

扁桃生理落果期不同组织激素浓度的动态变化及其对落果的影响

为探明扁桃幼果生理脱落与GA3、IAA和ABA等3种激素的关系,以新疆‘纸皮’扁桃为试材,分析新梢、结果枝组、幼果和果柄(包括正常发育幼果和果柄、即将脱落幼果和果柄)中3种内源激素浓度的动态变化规律,并分别涂抹3种外源激素调查其对坐果率的影响。结果表明:(1)‘纸皮’扁桃幼果脱落期和新梢生长期重合,扁桃生理落果期不同组织中3种内源激素浓度变化趋势与新梢生长期和幼果脱落期的动态特征基本一致。(2)扁桃生理落果期间,正常的和即将脱落的幼果及其果柄中内源激素浓度呈规律性变化,即:GA3和IAA浓度表现为正常果和正常果果柄始终大于相应的落果和落果果柄,而内源ABA浓度表现则与之相反,同时对应外源涂抹试验也印证了幼果和幼果果柄中高GA3和IAA浓度、低ABA浓度有利于扁桃坐果。(3)新梢和幼果中对应内源激素之间的浓度平衡关系也是调控扁桃幼果生理脱落的重要因素,即:新梢与幼果的GA3比值和IAA比值增大、而ABA比值减少将会促进幼果脱落,反之则减缓幼果脱落。