Vegetative Shoot Growth Research Articles

Summer pruning effect on tree growth and fruit production of persimmon

This paper reviews the effect of summer pruning in persimmon (Diospyros kaki Thunb.) with regard to its positive and negative aspects on tree growth and fruit production. In order for this practice to be of a significant value, a clear understanding is needed to appreciate the fact that so many variables are involved and much remains to be substantiated. Major reasons for summer pruning of persimmon are to improve fruit quality by enhancing light penetration into the tree canopy and to restrict vegetative shoot growth. Summer pruning generally suppresses tree growth even though it elevates leaf activity. Positive effects of summer pruning on skin color, soluble solids, and appearance of fruits are observed mainly in those orchards where the trees are heavily dormant-pruned to lower tree height and to secure space in high density plantings. Secondary shoot pruning and topping could also improve fruit quality, increasing flower bud formation of remaining shoots. Summer-pruning effects are highly dependent on its severity and timing to affect tree growth, shoot regrowth, reserve accumulation, and fruit quality.

Development of transplantation method for the restoration of surfgrass, Phyllospadix japonicus, in an exposed rocky shore using an artificial underwater structure

The surfgrass Phyllospadix japonicus is an abundant seagrass on the exposed rocky shores of the Korean peninsula. Many surfgrass meadows on the coasts of Korea have been adversely affected by anthropogenic activities and natural phenomena such as “rock whitening,” which is caused by overgrowths of crustose coralline algae. Few attempts have been made to develop transplanting techniques for surfgrass, owing to the difficulty of transplant survival on exposed rocky shores. We developed a new Phyllospadix Transplant System (PTS), which was an artificial underwater structure constructed of a 4:5:1 ratio of cement, sand, and water. In January 2005, we transplanted P. japonicus shoots using the newly developed PTS. P. japonicus shoots were tied together at the lower part of the sheaths to iron screws, which were placed in a hollow part of the PTS, with latex elastic. To evaluate the feasibility of this transplantation technique, we compared vegetative and reproductive shoot densities, growth, and morphological characteristics in transplants to those of shoots in nearby natural beds over a 2-year period. Transplant density increased gradually without significant initial shoot loss. Approximately 6 months after transplantation, leaf growth of transplants was similar to that of naturally growing shoots. The shoot heights and sheath lengths of transplants were similar to those of naturally growing shoots at 10–15 months post-planting. Approximately 50 mm of rhizome elongation was detected in P. japonicus transplants over the 2-year period. Since P. japonicus transplants attached to the PTS successfully established at the test area, the transplantation of surfgrass using the PTS may be an effective approach to restoring the habitat of P. japonicus.

Plum pox virus as a stress factor in the vegetative growth, fruit growth and yield of plum (Prunus domestica) cv. ‘Cacanska Rodna’

During 2005–2007, under the environmental conditions of Cacak (43°53’N; 20°21’E), western Serbia, the effect of Plum pox virus (PPV) on the phenology of vegetative shoot and fruit growth was investigated in a plum orchard of cv. ‘Cacanska Rodna’ including trees non-infected with PPV and those with infection and clearly visible symptoms, as verified by RT-PCR. The results showed that PPV did not affect the growth phenology of the vegetative shoot (length and thickness) and the fruit growth. However, it caused negative effects on the average length (22.31 ± 0.28 cm in non-infected trees, 18.35 ± 0.07 cm in infected trees) and thickness (4.21 ± 0.03 mm in non-infected trees, 4.01 ± 0.02 mm in infected trees) of vegetative shoots as well as on the average fruit weight (20.43 ± 0.16 g in non-infected fruits, 17.58 ± 0.18 g in infected fruits) and fruit dimensions. The greatest effect of PPV during the trial was the induction of a massive premature fruit drop and, consequently, a 52.94% decrease in total yields per tree (18.0 ± 1.10 kg) and unit area (12.0 ± 0.89 t ha-1) in infected vs non-infected trees.

Growth Characteristics of a Small-fruit Dwarf Mutant Arising from Bud Sport Mutation in Japanese Persimmon (Diospyros kaki Thunb.)

Fruit size is one of the most important traits that affect the economic value of fruit. In persimmon (Diospyros kaki Thunb.), somatic and bud-sport mutations that affect the fruit traits are frequently observed. Recently, a small-fruit mutant, ‘Totsutanenashi’ (TTN), was discovered in Japan as a bud-sport mutant of the leading cultivar Hiratanenashi (HTN). In this study, we investigated the morphological and physiological characteristics of TTN and HTN focusing on the tree architecture, fruit size, and the fruit flesh chemical composition. The objectives of the study were to evaluate the potential horticultural use of TTN and to characterize the differences between HTN and TTN. Both TTN and HTN are nonaploid plants, indicating that a difference in ploidy is not the cause of the small-fruit mutation. The vegetative growth of trees and tissue-cultured shoots of TTN was more compact than that of HTN. The floral organs of TTN appeared similar to those of HTN before flowering, but the TTN flowers opened earlier, resulting in smaller ovaries than in HTN flowers. The fruit size of TTN was consistently lower than that of HTN at all fruit developmental stages. TTN fruit had a higher sugar content and a higher proportion of sucrose to total sugars than HTN fruit. TTN fruits contained lower levels of secondary metabolites such as soluble tannins and ascorbate than HTN fruits. These results suggest that the fruit size mutation also affects the fruit biochemistry, leading to alterations in the fruit flesh composition. TTN may be a valuable genetic resource because compact trees require less labor and maintenance, and small, sweeter fruits may meet the various needs of consumers. The use of TTN in studies of the genetic control of fruit size is also discussed.

Dynamics of flower development and vegetative shoot growth in the high mountain plant Saxifraga bryoides L.

Saxifraga bryoides L. is an abundant species in the subnival and nival zone of the European mountains. First flowering occurs, at the earliest, 6 weeks after snowmelt. This is a remarkably long prefloration period in an environment with a short growing season. To gain more information about the developmental strategies of this species, the timing and the dynamics of flower bud formation and vegetative shoot growth were studied at sites with growing seasons of different lengths at two subnival locations (2650 and 2880 m a.s.l.) in the Tyrolean Alps. At an early, mid and late thawing site, individuals emerging from the winter snow were labelled. Reproductive and vegetative shoots were sampled at regular intervals throughout the growing season and analysed, using different microscopic techniques. Flower buds of S. bryoides develop in three cohorts. Provided the growing season is long enough, cohorts 1 and 2 come into flower, whereas cohort 3 buds remain primordial and continue to develop after winter. New flower primordia appear as day-length decreases from August on, which suggests a short-day requirement for floral initiation. At the end of the growing season, flower buds of different stages are present, but only primordial stages survive winter. Thus, flower buds of S. bryoides develop largely or even completely in the year of anthesis. Developmental dynamics were quite similar at the different sites. Time from flower initiation until anthesis took about 2 months, independently of whether flowers were formed within one or two seasons. All of the leaves on vegetative short-stem shoots turnover within a growing season. Leaves having passed winter continuously decline and are replaced by newly formed ones (21±3 at the mid-thawing site and 18±1 leaves at the short-season site). An individual leaf functions therefore, on average, about 12 months. In most years the seed crop of S. bryoides results mainly from the first cohort of flowers in an individual. In a changing climate with a prolonged growing season, the chance of two cohorts to develop mature seeds from flower cohorts 1 and 2 would increase.

SUITABILITY OF SOME AGAR SUBSTITUTES FOR THE PROPAGATION OF SPATHIPHYLLUM AND ANTHURIUM BY TISSUE CULTURE TECHNIQUE IN MULTIPLICATION STAGE

This study was carried out in a trial to find out a cheaper substitute for agar. Different substrates were tested as support matriceswith MS solution and compared with agar-gelled MS medium. Aseptic explants of two aroids, Spathiphyllum wallisii and Anthurium scherzerianum were cultured on these media under aseptic conditions. The highest records of total number of shoots, shoot length, total number of leaves, diameter of vegetative growth and total fresh weight of Spathiphyllum were observed in shoots grown on agar medium. Results of Anthurium shoots grown on agar medium did not differ significantly from the highest levels of shoot length and total fresh weight. Agar also achieved the second rank in total number of shoots, total number of leaves and the diameter of vegetative growth of Anthurium shoots. Length of Spathiphyllum and Anthurium shoots grown on cotton medium was not significantly different from the highest level. Cotton also achieved the second rank in total number of shoots, total number of leaves, diameter of vegetative growth and total fresh weight of Spathiphyllum and Anthurium shoots. In case of Spathiphyllum, perlite medium achieved the second rank in total fresh weight, and was not significantly lower than this category in total number of leaves. Records of Spathiphyllum shoots grown on perlite were lowered to the third rank in total number of shoots, shoot length and diameter of vegetative growth. On the other hand, the highest significant levels in total number of shoots, shoot length, total number of leaves, diameter of vegetative growth and total fresh weight of Anthurium were observed in shoots grown on perlite. Value of the total fresh weight of Spathiphyllum shoots grown on bagasse medium significantly occupied the second rank in a descending order compared to the corresponding character in other media. The bagasse medium reached the third category in shoot length and total number of leaves, and the fourth one in total number of shoots and diameter of vegetative growth of Spathiphyllum. In case of Anthurium, values of all characters measured of shoots grown in the bagasse medium significantly reached the third rank in a descending order. The longest shoots were those grown on straws of rice or wheat in case of Spathiphyllum, and on rice straw in case of Anthurium. Parameters of the photosynthetic pigments, i.e. chlorophyll a, chlorophyll b, total chlorophyll and carotenoids, were not influenced significantly by media substrate in case of Spathiphyllum. On the contrary, the highest significant values of these characters were observed in Anthurium shoots grown on bagasse medium, followed without any significant difference by those grown on the cotton one. Corresponding values of Anthurium shoots grown on perlite medium were not significantly different from those grown on agar medium. However, values of the two later media were significantly lower than those of the two former ones. The use of cheaper substrates such as cotton, perlite or bagasse could be recommended as a replacement for agar, especially in commercial tissue culture labs.

Effects of ulvoid ( Ulva spp.) accumulation on the structure and function of eelgrass ( Zostera marina L.) bed

The objective of this study is to clarify the effect of ulvoid ( Ulva spp.) accumulation on the structure and function of an eelgrass bed by the coast of Iwakuni, Seto Inland Sea, Japan. We monitored eelgrass shoot density and volume of ulvoid accumulation in the study site and evaluated effects of the accumulated ulvoid canopy on the percent survival, seedling density, growth rates, photosynthetic photon flux density (PPFD) and carbon contents of eelgrass. Eelgrass shoot density decreased by the accumulation of ulvoid. Also, seedling density decreased by the increase in the ulvoid volumes. Shoot density, seedling density and leaf elongation were negatively correlated with ulvoid volume. Carbon contents in eelgrass decreased by the accumulation of ulvoid (canopy height: 25 cm). These results suggest that accumulation of ulvoid bloom has significant negative impacts on the structure and function of eelgrass bed, i.e. decreases in vegetative shoot density, seedling density, shoot height and growth rate.

Cold Hardiness of the Rare Dirca occidentalis: Comparisons to Dirca palustris from Disparate Provenances

Abstract We determined the cold hardiness of Dirca occidentalis (western leatherwood) within its restricted natural distribution in northern California and made comparisons to Dirca palustris (eastern leatherwood) from northern (Iowa) and southern (Florida) provenances. Stems of western leatherwood were sampled twice while all or some plants were dormant (October 27 and December 8, 2004, respectively) and again on January 19, 2005, when flowering and incipient vegetative shoot growth of most plants had begun. Stems of D. palustris were sampled on the same schedule and on March 2, 2005 (Iowa and Florida) and April 13, 2005 (Iowa) such that the last sampling date coincided with flowering and incipient vegetative shoot growth. Lowest survival temperature was determined based on visual assessments of the viability of cambium and phloem of stems exposed to progressively lower temperatures in a freezer. Lowest survival temperature of western leatherwood was −6 to −3C (21 to 27F) regardless of date. Eastern leatherwood accrued hardiness through mid-winter and then deacclimated; minimal lowest survival temperature of eastern leatherwood was −33C (−27F) in Iowa and −17C (1F) in Florida. The minimal cold hardiness of western leatherwood is consistent with its natural distribution in specialized niches within a Mediterranean climate. Unless western leatherwood accrues increased hardiness when planted where winters are harsh, its horticultural use will be restricted to areas with mild winters. In contrast, widespread use of eastern leatherwood is feasible if production challenges are resolved and selections from climatically appropriate provenances are used.

The Alternative Oxidase of Plant Mitochondria Is Involved in the Acclimation of Shoot Growth at Low Temperature. A Study of Arabidopsis AOX1a Transgenic Plants

The alternative oxidase (AOX) pathway of plant mitochondria uncouples respiration from mitochondrial ATP production and may ameliorate plant performance under stressful environmental conditions, such as cold temperatures, by preventing excess accumulation of reactive oxygen species. We tested this model in whole tissues by growing AtAOX1a-transformed Arabidopsis (Arabidopsis thaliana) plants at 12 degrees C. For the first time, to our knowledge, in plants genetically engineered for AOX, we identified a vegetative shoot growth phenotype. Compared with wild type at day 21 after sowing, anti-sense and overexpressing lines showed, on average, 27% reduced leaf area and 25% smaller rosettes versus 30% increased leaf area and 33% larger rosette size, respectively. Lines overexpressing a mutated, constitutively active AOX1a showed smaller phenotypic effects. These phenotypic differences were not the result of a major alteration of the tissue redox state because the changes in levels of lipid peroxidation products, reflecting oxidative damage, and the expression of genes encoding antioxidant and electron transfer chain redox enzymes did not correspond with the shoot phenotypes. However, the observed phenotypes were correlated with the amount of total shoot anthocyanin at low temperature and with the transcription of the flavonoid pathway genes PAL1 and CHS. These results demonstrate that (1) AOX activity plays a role in shoot acclimation to low temperature in Arabidopsis, and that (2) AOX not only functions to prevent excess reactive oxygen species formation in whole tissues under stressful environmental conditions but also affects metabolism through more pervasive effects, including some that are extramitochondrial.

Shoot regeneration, re-flowering and post flowering survival in bamboo inflorescence culture

In vitro grown inflorescences of Bambusa edulis were used to investigate the process of vegetative shoot growth in detail. The findings revealed that auxins and ACC could be significant growth regulators in this process. Overall, auxins [NAA, indolebutyric acid (IBA), and 2,4-dichlorophenoxyacetic acid (2,4-D)] induced inflorescences to grow vegetative shoots. However, the efficiency of shoot regeneration varied. A greater percentage (27.3–34.5) of inflorescences in the 5 mg l−1 NAA, 10 mg l−1 NAA, and 1 mg l−1 2,4-D treatments formed more vegetative shoots than those exposed to other treatments. IBA promoted shoot regeneration less effectively than NAA and 2,4-D. Fifty percent of regenerated vegetative shoots flowered after 2 months when the medium was supplemented with 5 mg l−1 NAA. All shoots that received 1 mg l−1 1-amino-cyclopropane-1-carboxylic acid (ACC) flowered in 5 mg l−1 NAA medium. Rooted plantlets were used to examine their survival following in vitro flowering. All plantlets with vegetative shoots, even those with inflorescences, survived and grew.

Mechanism and Underlying Physiology Perpetuating Alternate Bearing in Citrus

Alternate-bearing trees produce a heavy on-crop followed by a light off-crop. Whereas climatic events initiate alternate bearing, it is perpetuated by endogenous tree factors. For citrus, the mechanism and underlying physiology by which fruit influence floral intensity the next spring was unresolved. To determine whether reduced return bloom of on-crop trees was due to inhibition of vegetative shoot production and, thus, a lack of “wood” on which to bear next spring's inflorescences or, alternatively, to inhibition of phase transition and inflorescence development on an adequate number of vegetative shoots, fruit were removed from individual shoots monthly or from entire on-crop `Pixie' mandarin trees during periods critical to shoot initiation (summer) and phase transition (winter). Fruit removal provided clear evidence that the on-crop exerted a significant effect on return bloom during the summer by reducing summer–fall shoot growth and, hence, the number of flowers borne on these shoots as well as on old wood of fruit-bearing shoots. The on-crop had less effect in winter on phase transition and return bloom. Buds collected during the summer from on-crop `Pixie' mandarin trees were characterized by high indoleacetic acid and low isopentenyladenosine concentrations compared to buds from off-crop trees. The starch level of the buds was not affected. No differences in hormone concentrations were detected for buds collected during winter from on- and off-crop trees, but buds of on-crop trees had less starch. The results demonstrate that the on-crop reduces return bloom predominantly by inhibiting summer-fall vegetative shoot growth by a mechanism similar to apical dominance, not a lack of available carbohydrate.

Indirect effects of ant predation (Hymenoptera: Formicidae) on bilberry Vaccinium myrtillus

Bilberry (Vaccinium myrtillus L.) is one of the dominant plants of the Fennoscandian boreal coniferous forest and consti- tutes a major food source for many insect herbivores. A common ant species in these forests is the wood ant Formica (Formica) aquilonia Yarrow, which preys heavily on other invertebrates within its territories. The aim of this study was to investigate whether aquilonia's predation on the insect herbivores may have indirect positive or negative effects on bilberry. Damage to the bilberry, its vegetative growth and reproduction were quantified in order to contrast localities close to (2 m) and far away from (50 m) ant nests. Close to ant nests, herbivore damage to the bilberry was significantly lower and reproductive success, i.e. proportion of flowers succeeding to berries, significantly higher. The results of this study therefore suggest that distance to aquilonia nests, and thus preda- tion from ants, can significantly affect herbivore damage to the bilberry and its reproductive success (supporting the hypothesis of a top down effect in this three-trophic-level system). Vegetative growth, i.e., density and biomass of current year shoots, and reproduc- tive investment, i.e., proportion of current year shoots with flower, of the bilberry was, however, not affected by distance to ant nests, indicating that the bilberry can also compensate for losses due to herbivory.

Contrôles épigénétiques, développement et variation génétique naturelle chez les plantes

Plant life strategies differ radically from those of most animals. Plants are not motile, and can only face stress by developing appropriate physiological responses. In addition, many developmental decisions take place during post-embryonic life in plants, whereas vertebrate and invertebrate development is nearly complete by the time of birth. For instance, while the germ line is typically set aside early during embryogenesis in animals, plants produce gametes from stem cell populations that were previously used for the vegetative growth of shoots. Nevertheless, plants and animals have similar nuclear organization, chromatin constitution and gene content, which raises the question as to whether or not fundamental differences in the use of genetic information underlie their distinct life strategies. More specifically, we would like to know if chromatin and the epigenetically defined, heritable cell fates that it can confer play comparable roles in plants and animals. Here we review our current knowledge on chromatin-mediated epigenetic processes in plants. Based on available evidence, we argue that epigenetic regulation of gene expression plays a relatively minor role in plants compared to mammals. Conversely, plants appear to be more prone than other multicellular organisms to the induction of chromatin-based, epigenetically modified gene activity states that can be transmitted over many generations. These so-called "epimutations" may therefore represent a significant proportion of the natural genetic variation seen in plants. In humans, epimutations are frequently observed in cancers, and given their metastable nature, they could also play an important role in familial disorders that do not demonstrate clear Mendelian inheritance.

Gender effects on the post‐facilitation performance of two dioecious Juniperus species

Summary Plant facilitation usually changes to competition as plants age. In dioecious plants, females should be affected more negatively than males by stressful conditions because of the greater costs of female reproduction. We investigated the gender effects on the post‐facilitation performance of adult plants of two dioecious Juniperus species from the high mountains of eastern Spain: J. sabina L. acts as a nurse plant for J. communis L. We compared physiological (water potential, carbon isotope discrimination and nitrogen concentration), vegetative (shoot growth) and reproductive (number of male flowers, and number of fruits and seeds) characters of associated and non‐associated plants of both species, to test the hypothesis that this association represents a more stressful condition for females than for males because of the greater costs of female reproduction. Despite their close phylogenetic relatedness, both species showed a distinct performance pattern after the facilitation phase. Association with the nurse plant reduced the growth and reproductive capacity of both genders in J. communis, the facilitated species. In contrast, the association with J. communis did not affect the fitness of the nurse plant, J. sabina, although in accordance with our hypothesis a gender effect was found on several physiological parameters. Thus J. sabina‐associated females had a more negative water potential and carbon isotope discrimination than the associated males, but there were no differences between genders when growing in isolation. The consequences of the post‐facilitation interaction between the two long‐lived woody Juniperus species are asymmetrical: harmful for the facilitated species, but harmless for the nurse. Gender had also asymmetrical consequences on some functional traits of the nurse – but not the facilitated – species.

The effects of Apogee® on shoot growth, secondary flowering, fire blight, fruit quality, yield and return bloom in ‘Bartlett’ pear growing in California

SummaryApogee® sprays were applied to mature ‘Bartlett’ pear (Pyrus communis L.) trees as single or multiple sprays during the growing seasons of 1999 to 2003 at concentrations of 420 g ha–1 (125 mg –1) or 840 g ha–1 (250 mg–1): both reduced vegetative shoot growth. Two sprays of 840 g ha–1 applied 3–3.5 weeks apart were most effective and reduced shoot growth by approximately 40%. An application made 2 d after fall bloom was ineffective and led to more vegetative shoot growth. Single sprays of Apogee® made within 9–28 d after full bloom (DAFB) were equally effective in reducing vegetative shoot growth. Bourse shoot growth was reduced 43% by 3 April, 2001 (8 DAFB) treatment of 840 g ha–1 when bourse and vegetative shoots ranged from 2.5 to 7.5 cm in length. Subsequent single applications of 840 g ha–1 Apogee® (on April 12 or 23, 2001) did not reduce bourse shoot growth significantly. Vegetative shoot growth was also reduced by 12% (9 d after treatment) and by 38% (approximately one month after treatment) by 840 g ha–1 Apogee® applied on 3 April, 2001, (8 DAFB). In 2002, bourse shoot growth was controlled most effectively by split applications (840 + 420 g ha–1 or 840 2 g ha–1, 9 April and 24 May) and by 840 g ha–1 Apogee®, applied at 2.5 to 7.5 cm shoot growth (9 April). These split applications, as well as girdling, decreased shoot strikes in 2002, the year after treatment. Split applications of 840 g ha–1 Apogee® made in April to early May were most effective in controlling both vegetative and bourse shoot growth in most years, although single applications of Apogee® were effective in some years. Subsequent flushes of shoots tended to be controlled by split applications with the second application timed to the emergence of new shoots. Apogee® was not consistently effective in reducing the incidence of Type I or Type V secondary flowers in these trials. Single or multiple sprays of Apogee® had no measurable or consistent effect on return bloom, fruit size or shape, firmness, percentage soluble solids, or yield per tree over the period of these experiments. Apogee® appears to have promise as a shoot growth control agent in ‘Bartlett’ pear growing in California, USA, without deleterious effects.

Comparative Vegetative Growth Responses of Two Peach Cultivars Grown on Size-controlling versus Standard Rootstocks

Vegetative growth of two peach (Prunus persica L. Batsch) cultivars Flavorcrest and Loadel growing on six different rootstocks (`Nemaguard', `Hiawatha', K-146-43, K-146-44, P-30-135, and K-119-50) was analyzed during the third season of growth in an experimental orchard at the University of California Kearney Agricultural Center near Parlier, California. Seasonal trunk cross-sectional area, shoot and internode growth, diurnal stem extension growth rate and summer and dormant pruning weights were measured to determine extent of size-control imparted by the experimental rootstocks compared to the trees on the `Nemaguard' control and to characterize the nature of the sizecontrolling response. Trunk cross-sectional area growth of trees on the two smallest rootstocks (K-146-43 and K-146-44) was only 25% to 37% of the growth of trees on `Nemaguard', while trees on the other three rootstocks provided an intermediate level of size control. Generally, the seasonal patterns of shoot growth did not vary substantially among trees on the different rootstocks, but average shoot and internode lengths did correspond with tree size. Vigorous watersprout growth was decreased by more than 80% in the trees on the least vigorous rootstocks compared to trees on `Nemaguard' resulting in major reductions in the extent of summer and winter pruning weights. Variations in vegetative shoot growth appeared to correspond to variations in daily shoot extension growth rates but more research is needed to explore these relationships.

Leaf potassium concentration, CO 2 exchange and light interception in almond trees ( Prunus dulcis (Mill) D.A. Webb)

The goal of this study was to determine the effect of tree potassium status on CO 2 exchange and light interception of field-grown almond trees ( Prunus dulcis (Mill) D.A. Webb). Treatments consisted of four levels of potassium fertilization applied for three consecutive seasons. Potassium deficiency negatively affected tree light interception. Defoliation after mechanical harvesting indicated that potassium deficiency accelerated premature leaf senescence and premature leaf abscission. CO 2 exchange rates were curvilinearly related to leaf potassium concentration during mid-summer after most vegetative shoot growth was completed. Leaf potassium concentrations less than 0.5–0.6% appeared to limit leaf CO 2 exchange rate. Large variations in leaf potassium concentration were found in the non-fertilized trees. Indeed, most of the response curve of leaf CO 2 exchange rate to leaf potassium concentration could be described by analyzing the leaves of non-fertilized trees. Stomatal conductance was not affected significantly by leaf potassium concentration and leaves with low potassium concentration had the highest calculated internal CO 2 concentrations. Thus it appears that potassium deficiency in almond affected the leaf photosynthetic capacity via biochemical limitations and not through an effect on stomatal conductance.

'BARBARA' AND 'DANIELA': TWO CULTIVARS FOR MYRTLE BERRIES PRODUCTION

'BARBARA' AND 'DANIELA': TWO CULTIVARS FOR MYRTLE BERRIES PRODUCTION

Effects of leader pruning on vine architecture, productivity and fruit quality in kiwifruit ( Actinidia deliciosa cv. Hayward)

The effects of two summer pruning strategies on vine architecture, fruit yield and quality were compared over three growing seasons. With ‘leader pruning’, all vigorous vegetative shoot growth close to the central leader zone was removed continually through the growing season. With ‘conventional pruning’, this new shoot growth was left virtually un-pruned over summer with only summer pruning to shorten fruiting laterals in the fruiting zone to three to four leaves past the last fruit. Leader pruning resulted in significant increases in the ratio of second year wood to first year wood, and in the number of self-terminating canes per vine. The basal diameter of canes was significantly reduced in leader pruned vines. Leader pruning was associated with an increase in total fruit yield. This increase was a result of increased fruit size on leader pruned vines, coupled with a small increase in the number of fruits per unit area. The number of winter buds per square metre did not differ from that of control vines, suggesting that the slight increases in fruit number could be attributed to an increased number of flowers per winter bud. Changes in vine composition as a result of leader pruning included a decrease in leaf number, particularly in the upper zone of the canopy, and these changes were associated with significant changes in fruit quality, with fruits from the upper zones being larger, and having a higher soluble solids content after storage than fruits from lower parts of the vines in the same treatment. The effects of pruning strategy on vine resource balance allocation are discussed.

EMBRYONIC FLOWER2, a novel polycomb group protein homolog, mediates shoot development and flowering in Arabidopsis.

In higher plants, developmental phase changes are regulated by a complex gene network. Loss-of-function mutations in the EMBRYONIC FLOWER genes (EMF1 and EMF2) cause Arabidopsis to flower directly, bypassing vegetative shoot growth. This phenotype suggests that the EMF genes play a major role in repression of the reproductive program. Positional cloning of EMF2 revealed that it encodes a zinc finger protein similar to FERTILIZATION-INDEPENDENT SEED2 and VERNALIZATION2 of Arabidopsis. These genes are characterized as structural homologs of Suppressor of zeste 12 [Su(z)12], a novel Polycomb group gene currently identified in Drosophila. In situ hybridization studies have demonstrated that EMF2 RNA is found in developing embryos, in both the vegetative and the reproductive shoot meristems, and in lateral organ primordia. Transgenic suppression of EMF2 produced a spectrum of early-flowering phenotypes, including emf2 mutant-like phenotype. This result confirms the role of EMF2 in phase transitions by repressing reproductive development.