Temporal variability and scaling behaviour in the fine-root system of kiwifruit (Actinidia deliciosa)

We show that temporal variability in root populations can depend upon the scale of measurement (particularly the sampled soil volume). The presence of roots in a range of volumes of soil was studied using perspex tubes installed horizontally into the soil around three mature kiwifruit vines. Roots intercepting lines scored on the tubes were counted using a periscope. For small volumes of soil (c. 2–4 cm³) the root counts varied with time in a very irregular manner, and as the interval between measurements increased the autocorrelation between the measurements decayed rapidly. At about half of the locations monitored there was no significant autocorrelation between measurements 27 d apart. Linear interpolation in these time series was unreliable, and where the correlation dimension could be resolved it was usually non-integer (suggesting chaotic behaviour). The time series measured at different locations were poorly correlated, indicating weak coordination. As the observed soil volume increased, the coordination between locations improved, the autocorrelation function increased, and linear interpolation errors decreased (although these remained substantial). Clearly there are considerable fundamental constraints on our ability to predict the root behaviour of kiwifruit vines at scales that are appropriate for mechanistic models of nutrient and water uptake. We discuss the need for a new conceptual model of the fine-root systems of kiwifruit and similar species.     

Pollen-pistil interaction in kiwifruit (Actinidia deliciosa; Actinidiaceae)

The pollen-pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life-span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.     

Magnesium deficiency of kiwifruit (Actinidia deliciosa)

Magnesium deficiency was associated with large yield reductions in a five-year-old commercial kiwifruit (Actinidia deliciosa) orchard. The effect on yield resulted primarily from a reduction in fruit numbers, there being no difference in mean fruit weight between fruit harvested from affected and unaffected vines. Magnesium deficiency had no deleterious effect on postharvest storage characteristics of fruit stored at 0.5–1°C for 18 weeks; fruit from deficient vines were firmer but had slightly lower soluble solids than fruit from control vines. Although deficiency symptoms were first observed on the basal leaves of the non-fruiting shoots mid season, indications of the impending deficiency could be established very early in the season using foliar analysis. Magnesium concentrations in youngest fully expanded leaves (YFEL) on the affected vines were less than 2.0 g kg⁻¹ DM four weeks after budbreak and remained below this value for the rest of the season; concentrations in YFEL on unaffected vines did not decrease below this value and gradually increased after fruitset to 4.5 g kg⁻¹ DM at harvest. To avert potential production losses, it is suggested that soluble magnesium fertilizers (containing at least 200 kg ha⁻¹ Mg) should be broadcast early in the season if foliar magnesium concentrations less than 2.0 gkg⁻¹ DM are measured four–six weeks after budbreak.     

A genome-specific repeat sequence from kiwifruit (Actinidia deliciosa var. deliciosa)

Summary Six members of a family of moderately repetitive DNA sequences from kiwifruit (Actinidia deliciosa var. deliciosa) have been cloned and characterized. The repeat family is composed of elements that have a unit length of 463 bp, are highly methylated, occur in tandem arrays of at least 50 kb in length, and constitute about 0.5% of the kiwifruit genome. Individual elements diverge in nucleotide sequence by up to 5%, which suggests that the repeat sequence is evolving rapidly. Homologous sequences were found in A. deliciosa var. chlorocarpa. The repeat sequence was not found under low stringency hybridization conditions in the diploid A. chinensis, the species most closely related to the hexaploid kiwifruit, or in eight other Actinidia species. However, homologous repeats were detected in a tetraploid species, A. chrysantha. The results provide the first molecular evidence to suggest that kiwifruit may be an allopolyploid species.     

Light enhances differentiation of the vascular system in the fruit of Actinidia deliciosa

Light is recognized as crucial in determining high quality of fleshy fruits, for example, kiwifruit [Actinidia deliciosa var. deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson]. Among the possible mechanisms through which light improves the quality of kiwifruit berry, there may be a direct morphogenic role on the differentiation of the fruit's vascular system, though this has not yet been investigated. The present study's aim was to determine (1) whether light positively affects the differentiation of the vascular system of the fruit and/or the pedicel, and, if so, (2) which component (xylem, phloem, or both) is more affected, and (3) in which period of the berry's development the improvement of the vascular differentiation (if any) occurs. To this end, fruit morphogenesis of kiwifruit was studied in two developmental environments (i.e., in full sunlight and in paper bags that reduced the full sunlight to 10%), and in two phases of fruit development (i.e., 1 and 5 months [harvest] after anthesis). During the growth period, the type of environment did not affect the differentiation pattern of the vascular system in the three types of bundles present in the fruit. However, in comparison with shade, light improved the vasculature in the fruit pericarp and pedicel, inducing a consistently higher extent of the xylary component in the main bundles of the fruit and pedicel, principally due to an increase in the number of xylem elements. The phloic component was also increased by light, but to a much lesser extent than that of the xylary. During the entire period of development, light-grown fruits contained higher concentrations of calcium and magnesium, as compared with shade-grown fruits. In conclusion, in the berry of Actinidia deliciosa, light enhances the differentiation of the vascular system, in particular the xylary component. The hypothesis that fruit quality is improved through a more efficient translocation of specific mineral nutrients (e.g., calcium) via the xylem is presented.     

The development and effects of nitrogen deficiency in field-grown kiwifruit (Actinidia deliciosa) vines

The development and effects of nitrogen (N) deficiency in kiwifruit (Actinidia deliciosa Hayward) vines planted at three densities (25.0, 12.5 and 8.33 m² vine^–1) were examined in a long term (1982 to 1989) field experiment in which N was applied at rates from 0 to 200 kg N ha^–1 year^–1. The rate of applied N significantly affected leaf N concentrations every year from 1985 onwards, and the average leaf N concentrations declined throughout the experiment. Fruit N concentrations varied significantly with the level of applied N as early as 1986. The average fruit N concentrations varied strongly between years, and were inversely proportional to the fruit number (per m²), indicating that, after fruit set, growth of individual fruit was relatively insensitive to the vine N status. Effects of N supply on fruit yields resulted mostly from changes in fruit number (per m²). For vines planted at the high density, fruit yields responded significantly to the level of applied N each season from 1986 onwards. In any year, maximum fruit yields for vines planted at the high density were associated with leaf N concentrations (20 weeks after bud burst) of at least 1.8 mmol g^–1. For vines planted at low density, significant yield responses to the level of applied N were not recorded until 1988, and maximum yields in that year were associated with leaf N concentrations of at least 1.4 mmol g^–1. The delayed expression of effects of N deficiency on fruit yields for vines planted at low density appeared to follow a shift in partitioning of resources in favour of fruit growth. This shift in partitioning did not appear to be sustainable, and by 1989 the fruit yield response to applied N continued to the highest N level tested. In that year, the leaf N concentration associated with maximum yield was 1.8 mmol g^–1, the same as that recorded throughout the experiment for the vines planted at high density. In the last two seasons of the experiment, leaf necrosis developed extensively on vines receiving less than the highest rate of N. This necrosis appeared to be premature senescence resulting from N deficiency. Leaf chloride (Cl) concentrations increased significantly with increasing severity of N deficiency, but were never more than those associated with Cl toxicity. While N supply significantly affected fruit firmness immediately post-harvest, there were no significant effects on fruit firmness after 12–20 weeks storage.     

Independent control of organogenesis and shoot tip abortion are key factors to developmental plasticity in kiwifruit (Actinidia)

BACKGROUND AND AIMS: In kiwifruit (Actinidia), the number of nodes per shoot is highly variable and is influenced by genotype and environmental conditions. To understand this developmental plasticity, three key processes were studied: organogenesis by the shoot apical meristem during shoot growth; expansion of phytomers; and shoot tip abortion. METHODS: Studies were made of organogenesis and shoot tip abortion using light and scanning electron microscopy. The effect of temperature on shoot growth cessation was investigated using temperature indices over the budbreak period, and patterns of shoot tip abortion were quantified using stochastic modelling. KEY RESULTS: All growing buds began organogenesis before budbreak. During shoot development, the number of phytomers initiated by the shoot apical meristem is correlated with the number of expanding phytomers and the mean internode length. Shoot tip abortion is preceded by growth cessation and is not brought about by the death of the shoot apical meristem, but occurs by tissue necrosis in the sub-apical zone. For most genotypes studied, the probability of shoot tip abortion is higher during expansion of the preformed part of the shoot. Lower temperatures during early growth result in a higher probability of shoot tip abortion. CONCLUSIONS: Organogenesis and shoot tip abortion are controlled independently. All buds have the potential to become long shoots. Conditions that increase early growth rate postpone shoot tip abortion.     

Effect of the physical nature of the culture medium on the metabolism of benzyladenine and endogenous cytokinins in Actinida deliciosa tissues cultured in vitro

Endogenous cytokinin and benzyladenine (BA) metabolites were studied in kiwifruit explants grown on solidified and liquid Murashige and Skoog media supplemented with BA. The same proliferation rate was observed in both media. However, in the liquid medium the release from apical dominance was faster and the growth rate was higher than on solid medium. At the same time the number of vitrified shoots increased considerably in the liquid cultures. Exogenous BA was transformed into 9-β-D-glucopyranosyl-BA ([9G]BA), 7-β-D-glucopyranosyl-BA ([7G]BA). 7-β-D-ribofura-nosyl-BA ([9R]BA) and the 5¹-monophosphate of [9R]BA ([9R-5¹P]BA). The proportion of active forms (BA, [9R-5¹P]BA and [9R]BA) in respect to total BA metabolites, was generally higher in shoots from liquid than from solid media. An exception was found at day 20 when this balance was inverted. Endogenous cytokinins in kiwifruit shoots were measured by enzyme-linked immuno sorbent assay (ELISA). The content of natural cytokinins was influenced by the levels of active forms of BA.     

Influence of anions on the potassium status and productivity of kiwifruit (Actinidia deliciosa) vines

The effects of K fertiliser (160 kg ha^-1) applied with Cl^- or SO₄ ^2- as the accompanying anion on the K nutrition of kiwifruit (Actinidia deliciosa var. deliciosa) were assessed in a field experiment, using vines with varying degrees of K deficiency. Leaf K concentrations in spring were significantly higher for vines receiving KCl, compared to those receiving K₂SO₄. This effect did not interact significantly with the degree of K deficiency, and persisted for about 6 weeks. Subsequently there was no significant difference between the leaf K concentrations for the vines receiving KCl or K₂SO₄. Applying K as KCl increased the leaf Cl concentration, especially in spring, while applying K as K₂SO₄ had no significant effect on the leaf S concentration at that time. These results implied a greater requirement for organic acid anions for K⁺ uptake from K₂SO₄ than from KCl, and the importance of organic acid anions for K⁺ uptake from different sources of K fertiliser is discussed. This transient effect of the accompanying anion on leaf K status was associated with large effects on flowering, and fruit yields were about 28% higher for plants receiving KCl rather than K₂SO₄.The effects on growth and tissue nutrient composition of varying the concentrations of Cl^-, NO₃ ^-, SO₄ ^2- and H₂PO₄ ^- around the roots of kiwifruit vines were examined in a solution culture experiment. For H₂PO₄ ^-, plant growth was very similar over a wide range of rates of addition. For the other anions, the range between deficiency and toxicity was clearly delineated. For Cl^- and NO₃ ^-, toxicity was associated with high tissue concentrations of Cl and N, respectively, and was consistent with competition for uptake between Cl^- and NO₃ ^-. However, for SO₄ ^2-, toxicity was associated with only a small increase in the tissue S concentration relative to that associated with maximum growth, and appeared to result more from effects on uptake of other anions and cations rather than from direct effects of high tissue S concentrations.It is concluded that the sensitivity of kiwifruit to the anion accompanying K⁺ in fertiliser may be related to the unusually high requirement for Cl previously reported for this species.     

Fate of 15N-labelled nitrogen fertilizer applied to kiwifruit (Actinidia deliciosa) vines

The fate of ¹⁵N-labelled ammonium fertilizer applied once to six-year-old field-grown kiwifruit (Actinidia deliciosa Hayward) vines was measured over three years. The three main treatments were nitrogen (N) applied singularly at 100 or 200 kg N ha^–1 in early spring (two weeks before bud burst) or split with 100 kg N ha^–1 (unlabelled) in early spring and 100 kg N ha^–1 (¹⁵N-labelled) ten weeks later. All N treatments were applied to vines with a history of either 50 or 200 kg N ha^–1 yr^–1. For three years after ¹⁵n application, components of the vines and soil (0–600 mm depth) were sampled at harvest in late autumn and the N and ¹⁵N contents determined.By the first harvest, all plant uptake of ¹⁵N had occurred and this represented 48–53% of the ¹⁵N applied. There was no significant effect of current N fertilizer treatment or of N history on ¹⁵N recovery by vines. Removal of ¹⁵N in harvested fruit was small at 5–6% in the first year and 8% over 3 years. After 2–3 years, most plant ¹⁵N occurred in the roots and this component declined only slowly over time. In contrast, there was a large temporal decline in ¹⁵N in above-ground plant components due to the annual removal in leaf fall and pruning. An associated experiment showed that when ¹⁵N-labelled prunings and leaves were mulched and returned to the soil, only about 9% was recovered by plants within 2 years. Almost all remaining mulched material had been immobilised into the soil organic N.In all treatments, about 20% of the added ¹⁵N remained in soil at the first harvest. This was almost entirely in organic fractions (<0.4% in inorganic N) and mostly in the surface 150-mm layer. The ¹⁵N content in soil changed little over time (from 20 to 17% between the first and third harvests respectively) and indicated that most of the N had been immobilised into stable humus forms.     

Temporal expression of effects of varying nitrogen supply on canopy growth, photosynthesis and fruit production for Actinidia deliciosa vines in the field

The effects of varying nitrogen supply on canopy leaf area, response of leaf net photosynthesis (A_n) to quantum flux density (Q), and fruit yields of kiwifruit vines (Actinidia deliciosa var. deliciosa) were examined in a two-year field experiment. Vines were grown with 0, 250 or 750 kg N ha^?1 year^?1. The responses to nitrogen supply were compared with responses to shade, to examine the impact of reduced carbon assimilation on canopy leaf area and fruit yields. Nitrogen supply did not affect significantly any of the measured variables during the first season of the experiment. In the second season, canopy leaf area was reduced significantly where nitrogen supply was limited. The quantum efficiency of photosynthesis (φ_q) increased from 0. 03 mol CO₂ mol^?1 Q soon after leaf emergence to more than 0. 05 mol CO₂ mol^?1 Q during the middle of the growing season. The quantum saturated rate of A_n (A_sat) also increased during the season, from 7–10 μmol CO₂ m^?2 s^?1 soon after leaf emergence, to 15–20 (μmol CO₂ m^?2 s^?1 during the middle of the growing season. φ_q and A_sat increased significantly with nitrogen supply at all measurement times during the second season. For vines with high nitrogen, fruit yields in both seasons were similar, averaging 3. 05 kg m^?2. Fruit yields in the second season were reduced significantly where nitrogen supply was limited, due to reduced fruit numbers. The relative effects of reduced leaf area and reduced leaf photosynthesis for carbon assimilation by nitrogen deficient vines were examined using a mathematical model of canopy photosynthesis for kiwifruit vines. Simulations of canopy photosynthesis indicated that effects on leaf area and on leaf photosynthesis were of similar importance in the overall effects of nitrogen deficiency on carbon assimilation. The effects of nitrogen supply on fruit numbers (i. e. flower development) preceded the measured effects on carbon assimilation, indicating that the nitrogen supply affected carbon partitioning to reserves in the first season.     

Anti-hyperglycemic activity of kiwifruit leaf (Actinidia deliciosa) in mice

The methanol extract of kiwifruit leaf suppressed the postprandial blood glucose level after an oral administration of soluble starch or sucrose in mice. The mechanism of action is proposed to be due to the alpha-amylase-inhibiting activity in the 90% aqueous methanol fraction and alpha-glucosidase-inhibiting activity in the n-buthanol fraction, based on the results of in vitro experiments.     

Gender variation in Actinidia deliciosa,the kiwifruit

Summary Flower and fruit characters were measured in ten female, five male and five fruiting male selections of A. deliciosa var deliciosa (A. Chev) Liang and Ferguson. Flowers from female vines had functional pistils, which contained many ovules. Stamens appeared to be fully developed but produced only empty pollen grains. Flowers from male vines had functional stamens that produced high percentages of pollen grains with stainable cytoplasmic contents. Pistils did not contain ovules and were generally small with vestigial styles. Fruiting male vines had both staminate and bisexual flowers. Staminate flowers were similar to those found on strictly male vines. Bisexual flowers produced ovules and stainable pollen. Pistils were smaller than in pistillate flowers. Although the three flower sexes differed in style length, ovary dimensions and ovules per carpel, staminate and bisexual flowers were similar in number of flowers per inflorescence, stamen filament length, pollen stainability, inflorescence rachis length and carpel number, and differed from pistillate flowers in these characters. The three flower sexes had similar sepal and petal numbers. The fruit of fruiting males were considerably smaller than those of females. Low ovule number appears to be the major factor limiting fruit size in the fruiting males studied. Prospects for developing hermaphroditic kiwifruit cultivars through breeding are discussed.     

The allopolyploid origin of kiwifruit,Actinidia deliciosa (Actinidiaceae)

The genetic origin of kiwifruit (Actinidia deliciosa var.deliciosa) was studied using phylogenetic analysis of DNA sequences derived from the polygalacturonase gene. Results indicate that hexaploid kiwifruit had an allopolyploid origin with the diploidA. chinensis contributing one genome (genome A) and another (as yet unidentified) diploid species contributing a second genome (genome B). The results leave open the question of whether a third, distinct species contributed to the hexaploid kiwifruit genome. A tetraploid race ofA. chinensis is also suggested to be allopolyploid containing genomes A and B.