Response of secondary bloom of ‘Bartlett’ pear (Pyrus communis L.) to pruning

Summary

Type V secondary bloom of pear (Pyrus communis L.) is associated with pruning and is frequently infected by fire blight (Southwick et al., 2000). The goal of this research was to determine which pruning practices would most likely be associated with subsequent Type V secondary bloom. Pruning date, shoot age, type of pruning cut and shoot orientation were varied and effect on Type V secondary bloom assessed. In both 1998 and 1999, dormant pruning was more likely to result in Type Vs than summer pruning or pruning one month after harvest. Pruning one week after harvest in 1998 was as likely to lead to Type Vs as dormant pruning, but was less likely in 1999. The likelihood that Type Vs would occur was lowest from 49 to 89.d from full bloom (DFB) and at 175 DFB in 1998. The lowest likelihood of Type Vs in 1999 was found on shoots pruned at 83 or 185 DFB. The likelihood for Type Vs rose with increasing shoot age from one to four years, but there was no difference between three- and four-year old shoots. In 1998, stub cuts (severe heading) were more likely to have Type Vs than head cuts when pruning two year old shoots, but not for one year old shoots. In 1999, type of pruning cut had an inconsistent effect on the likelihood for Type Vs and was not the same for each shoot age. NAA applied to summer pruned shoots completely prevented Type Vs from occurring and almost completely stopped Type Vs when applied to dormant pruning cuts. Summer pruning from 50 to 90 DFB or pruning one month after harvest and the application of NAA to pruning wounds may be strategies for reducing the occurrence of Type V secondary bloom.     

In vitro colchicine-induced polyploid plantlet production and regeneration from leaf explants of the diploid pear (Pyrus communis L.) cultivar, ‘Fertility’

Summary

Polyploid plantlets, including triploid, tetraploid, and mixoploid, were induced from the European pear (Pyrus communis L.) cultivar ‘Fertility’ by in vitro colchicine treatment of leaf explants. The leaf explants were incubated in 0.4% (w/v) colchicine for 24, 48, or 72 h, then transferred to adventitious shoot-induction medium. Regenerated shoots were pre-selected according to their morphological characteristics when compared to control shoots from untreated shoot proliferation cultures. Shoots with putative polyploid morphological characteristics were maintained and proliferated. The ploidy levels of all putative polyploid individuals were analysed by flow cytometry and identified by chromosome counts of shoot tip tissue squashes. Polyploid shoots were rooted, and the resulting plantlets were transferred to the field. Polyploid plantlets had a higher specific leaf mass and larger stomata than those of diploid plantlets.     

Performance of ‘Coscia’ pear (Pyrus communis) on seven rootstocks in a warm climate

Summary

The vegetative and reproductive performance of ‘Coscia’ pear (Pyrus communis L.) growing on seven rootstocks [OHF 69, OHF 97, OHF 513 and BP 1 (P. communis), clonal seedling (Davis AxB) of P. betulifolia, and quince BA 29 and EMA (Cydonia oblonga)] were compared over an 8-year period. The trial was conducted at the Experimental Orchard Farm Station in northern Israel, on a well-drained soil with pH 7.5. Trees were planted in December 1998 at a distance of 4.0 m 2.0 m, and trained with a central axis. The most vigorous trees were on P. betulifolia seedling, followed by BP 1 and the three OHF rootstocks (69, 97, 513). All the above rootstocks demonstrated greater vigour than quince BA 29 or EMA. The reason for this effect, at least in part, appeared to be the excellent water status (high midday stem water potential values) of trees on P. betulifolia in comparison with the other rootstocks. The highest cumulative yields per tree were harvested from trees on P. betulifolia and BP 1, followed by the three OHF rootstocks (69, 97, 513). However, the highest cumulative yield of large fruit (> 60 mm) was obtained from trees on P. betulifolia, followed by the OHF series and BP 1. The two quince rootstocks had the lowest cumulative yield, and the lowest yield of large fruit. A positive correlation was found between the vigour of the tree, as affected by the rootstock, and both total yield and fruit size. We conclude that, in a warm climate, yield efficiency is not the only parameter that should be taken into account, and building a strong tree for the weak scion cultivar is the first requirement for establishing an orchard. Fruit quality at harvest and during cold storage were examined for fruit from three rootstocks only. The highest soluble solids content values at harvest were obtained in fruit grown on quince EMA, compared to values for BP 1 and P. betulifolia fruit.     

梨(Pyrus communis L.)多倍体新种质表型变异多样性研究

【目的】为选育梨(Pyrus communis L.)突破性品种提供新种质。【方法】以二倍体梨品种‘丰产’及其衍生的系列多倍体无性系为研究试材,对其在试管内及移出试管外在田间生长的自根苗植株的表型变异进行了观测。【结果】多倍体植株比二倍体茎粗、节间短;四倍体的叶色比二倍体深,厚度比二倍体大;多倍体和二倍体的叶形指数差异显著,叶缘差异明显。不同倍性无性系的叶缘变异表现多样性,有全缘变异,也有锐锯齿变异。试管繁殖条件下,混倍体叶片形状不一,有大量畸形叶片产生,而二倍体、三倍体和四倍体很少观察到畸形叶片产生。移栽入田间生长后,相对于二倍体,多倍体植株的株高显著变矮、节间长显著变短、地面以上30 cm处的树干直径显著变小。混倍体对自然环境条件适应性差,没有获得在试管外正常生长的植株。【结论】相同环境条件下,梨体细胞染色体加倍衍生的多倍体植株,比二倍体对照生长慢,且株高明显矮于二倍体。     

Fate of photosynthates from spur leaves of ‘Nijisseiki’ pear during the period of rapid fruitgrowth

Summary

Spurs of ‘Nijisseiki’ pear (Pyrus pyriflora Nakai) were allowed to assimilate _10033;CO₂ at 87.d after anthesis (DAA) and at 108 DAA during the period of rapid fruit growth. Then the spurs were sampled periodically until fruit harvest time to trace the time course and amount of movement of assimilates from spur leaves to individual organs in the spur. The amount of _10033;C absorbed by fruit within 3.d after labelling was constant until harvest, regardless of the labelling date. However, the total amount of _10033;C in the spur decreased continually until harvest.Of the total amount of _10033;C recovered in the spur labelled at 87 DAA, by harvest, 43.2% of 13C was found in the fruit flesh (cortex of receptacle), 5% in the core (pith of receptacle 1 pericarp 1 seeds), 5.6% in spur stem, 5.4% in the source leaves, and 40.8% was respired and exported from the spur. Of total amount of initial _10033;C labelled at 108 DAA, at harvest, the proportion of _10033;C translocated to flesh, core, stem, respired, and remaining in leaves was 61%, 6.1%, 3.0%, 24% and 5.4%, respectively. Photosynthates fixed by the spur early in the rapid growth stage of the fruit contribute more to the formation of starch and structural materials and less to solublecarbohydrates in fruit than do those fixed later.     

Effects of nitric oxide fumigation on post-harvest core browning in ‘Yali’ pear (Pyrus bretschneideri Rehd.) during cold storage

Summary

Core browning often occurs as a physiological disorder in ‘Yali’ pear (Pyrus bretschneideri Rehd.) and results in a high losses during storage. In this study, the effects of fumigation with nitric oxide (NO) gas on the incidence of core browning in ‘Yali’ pears during cold storage were investigated. ‘Yali’ pear fruit were treated with 0, 10, 20, or 30 µl l^–1 NO at 25º ± 2ºC for 3 h under anaerobic conditions, then stored at 0º ± 1ºC under normal air for up to 120 d. The data showed that fumigation with 20 µl l^–1 NO was most effective at suppressing core browning. Thereafter, treatment with 20 µl l^–1 NO was used for comparisons with untreated control fruit in experiments to measure changes in total phenolics contents, polyphenol oxidase (PPO) activities, and the contents of glutathione (GSH), ascorbic acid (AsA), and NO in fruit core tissue during storage. The results showed that NO-fumigated fruit had lower PPO activity, but higher GSH and AsA contents in their core tissue compared with untreated control fruit. NO fumigation also maintained higher endogenous NO levels in core tissue after 60 d in storage, while the total phenolics contents of fruit remained at lower levels until day-100 of storage. These results indicate that the inhibitory effect of fumigation with

20 µl l^–1 NO on core browning was associated with its effects on reducing PPO activity and total phenolics contents, while maintaining the contents of GSH and AsA in core tissue of ‘Yali’ pear during cold storage.     

Somatic embryogenesis and plant recovery from callus of ‘Nabali’ Olive (Olea europea L.)

Regeneration via somatic embryogenesis from callus was studied in ‘Nabali’ olive (Olea europea L.). Among different explant sources (leaf blades, leaf petioles, hypocotyls of germinated seeds and roots of germinated seeds), roots gave the highest (46%) callus induction. Somatic embryogenesis was induced from root callus on embryogenesis induction medium (EIM) containing 5.0 μM 2,4-D, 0.5 μM kinetin and 5.0 μM NAA in darkness. Embryo regeneration was studied by transferring the callus from EIM to embryogenesis expression medium (EEM) containing different concentrations (0.0, 5.0, 10.0 and 15.0 μM) of 2-isopentenyladenine (2iP), BA, thiadiazuron (TDZ), zeatin or kinetin. Among the tested concentrations, 2iP at 10.0 μM outperformed the other growth regulators. 2,4-D at 5.0 μM in the EIM was satisfactory for embryogenesis induction. Sucrose at 0.2 M evoked higher embryogenesis than any other concentration of fructose and glucose in EIM, while sorbitol and mannitol at 0.1, 0.2 or 0.3 M reduced embryogenesis significantly and inhibited it totally at 0.4 M. Somatic embryos were rooted by transferring them to hormone-free medium (HFM). About 85% of embryos converted to rooted plantlets, 5% showed secondary embryogenesis and 10% were not developed and died. Rooted plantlets gave 95% survival when acclimatized ex vitro. Acclimatized plantlets developed into whole plants in the greenhouse and they were phenotypically similar.     

Studies on the hawthorn (Crataegus azarolus L.): III. A potential rootstock for ‘Golden Delicious9 apple and ‘Williams’ pear

Seedlings of the hawthorn Crataegus azarolus L. were budded with ‘Williams’ pear and ‘Golden Delicious’ apple and followed for compatibility, growth control, precocity and suckering. Four years of observations indicated that the hawthorn is compatible with ‘Williams’ and ‘Golden Delicious’, conferring growth control and precocity; and producing suckers profusely. On the other hand, bud break in ‘Williams’ started 10 d earlier and gave longer shoots than ‘Golden Delicious’. Delayed symptoms of incompatibility and long-term reciprocal influences require further study.     

Rejuvenation influences indirect organogenesis from leaf explants of Pomegranate (Punica granatum L.) ‘Kandhari Kabuli’

Sequential subculturing leads to a gradual physiological change in cells that may be termed ‘rejuvenation’. The effect of repetitive subculturing on callus induction and shoot regeneration from leaf explants of Punica granatum L. ‘Kandhari Kabuli’ were investigated. Surface-sterilised leaves were cultured on 1.0× Murashige and Skoog (MS) medium supplemented with 4.0 mg l^–1 α-naphthaleneacetic acid (NAA) and 2.0 mg l^–1 6-benzyladenine (BA) for callus induction. Shoots were regenerated from callus on 1.0× MS medium supplemented with 1.5 mg l^–1 BA, 0.5 mg l^–1 kinetin, and 0.25 mg l^–1 NAA. Subculturing of callus onto fresh medium maintained the rate of shoot formation and substantially increased the production of shoot buds up to the second subculture. Following further subculture passages, a lower shoot regeneration potential from callus was observed. A maximum shoot bud induction from callus of 63.9% was observed at the second subculture passage. The rate of multiplication of in vitro shoots increased until the fourth subculture, then became constant. Similarly, in vitro rooting of micro-shoots increased up to the third subculture, followed by a decline during further subculturing.     

In vitro propagation of olive (Olea europea sativa L.) ‘Kalamon’

A micropropagation method is described for olive (Olea europea sativa L.) ‘Kalamon’ using single-node explants collected from shoots produced from olive ovules grown in a growth chamber. Shoot proliferation was obtained on OM modified medium supplemented with 0.5 mg r¹ cystine, 10 mg I^-1 pantothenic acid calcium, 0.5 mg I^-' gibberel- lic acid (GA₃), 0.1 mg T¹ indole-3-acetic acid (IAA) and 10 mg I^-1 zeatin riboside, or 7.5 mg I^-1 benzyladenine (BA), or 10 mg I^-1 N⁶-2-isopentenyladenine (2ip). Explants were rooted on a medium similar to that for shoot development, but without cytokinins and with a-naphthaleneacetic acid (a-NAA), and indole-3-butyric acid (IBA) at 1, 2 and 3 mg I^-1 for both auxins. a-NAA at all concentrations was more effective than IBA. Shoot proliferation and rooting were improved by the addition to the nutrient media of 20 mg I^-1 and 50 mg I^-1 crude extract from olive ovules, respectively. Rooted explants were transferred to pots containing equal volumes of peat and vermiculite; about half survived.     

Preliminary studies on the use of (2RS, 3RS)-paclobutrazol for fruitlet thinning and growth control of ‘Conference’ pear

Summary

Single foliar sprays of paclobutrazol (PP333) at 300, 1000 or 3000 mg H applied at three different stages from full bloom to petal-fall in a year of average initial sets . and fruit size were equally effective in thinning ‘Conference’ pear, increasing the proportion of large fruits at harvest, but decreasing their absolute numbers. Sprays applied nine days after petal-fall reduced initial sets less effectively and, applied 21 days after petal-fall, were ineffective. Thinning was completed within 25 days after petal-fall. Shoot extension was initially retarded at all three concentrations, but later increased, so that the total growth made during the season was not reduced. Single foliar sprays at 300 or 1000 mg l^?1 applied at 70% full bloom in a year of heavy set and small fruit size increased the numbers of large fruits in the >55 mm size category by 66% and decreased those of fruits <55 mm by a similar amount. The increase in the yield of fruits >55 mm and decrease of unsaleable <45 mm fruits was equivalent to about 3 and 2 t ha^?1 respectively from a total average yield of about 17.5 t ha^?1. In the same experiment, similar sprays counteracted the stimulation in the production of small fruits by sprays of gibberellic acid (GA) applied on the same day, but did not increase the harvest of large fruits. Sprays of paclobutrazol at 30 or 100 mg l^?1 applied two weeks after petal-fall and then on three successive occasions at two-week intervals inhibited total extension growth per shoot during the season without affecting initial or final sets, fruit size or flower bud production. Single sprays applied at 100 mg l?1 in July reduced total extension per shoot almost as effectively as the repeated sprays. For more effective control of ‘Conference’ shoot growth, paclobutrazol may have to be sprayed later in the season than commercially recommended. Applied as a blossom thinner, paclobutrazol may increase the yield of large fruits only in years of heavy set and small fruit size, requiring that applications be delayed until set can be judged.     

Pollen-tube growth behaviour in ‘Chanee’ and ‘Monthong’ durians (Durio zibethinus L.) after selfing and reciprocal crossing

Summary

Two durian cultivars, ‘Monthong’ and ‘Chanee’, were investigated with respect to post-pollination processes in the pistil and the percentages of fruit set after self-pollination or reciprocal crossing. Pollen grains from each cultivar germinated normally on both stigmas and grew downwards healthily. The percentage of penetrated ovules exceeded 40% in all treatments. However, fruit set after self-pollination in ‘Chanee’ was extremely low. The percentage of fruit set in ‘Chanee’ 35 d after self-pollination (DAP) was 0% in 2002 and 2003, while that of ‘Monthong’ was 6.9% in 2002, and 23.6% in 2003. The percentage of fruit-set after cross-pollination was significantly higher. On the basis of pollen-tube growth behaviour and the non-synchronisation of fruit drop between self-pollination and the two cross combinations, it may be that ‘Monthong’ and ‘Chanee’ durians possess post-zygotic barriers to selfing, especially in ‘Chanee.’     

Abscisic acid alleviates the deleterious effects of cold stress on ‘Sultana’ grapevine (Vitis vinifera L.) plants by improving the anti-oxidant activity and photosynthetic capacity of leaves

The effects of exogenous application of abscisic acid (ABA) on anti-oxidant enzyme activities and photosynthetic capacity in ‘Sultana’ grapevine (Vitis vinifera L.) were investigated under cold stress. When vines had an average of 15 leaves, 0 (control), 50, 100, or 200 µM ABA was sprayed to run-off on all leaves of each plant. Twenty-four hours after foliar spraying with ABA, half (n = 5) of the water-only control vines and half (n = 5) of each group of ABA-treated plants were subjected to 4°C for 12 h, followed by a recovery period of 3 d under greenhouse conditions (25°/18°C day/night). The remaining plants in each treatment group were kept at 24°C. Cold stress increased H₂O₂ and malondialdehyde (MDA) concentrations in vine leaves, whereas all foliar ABA treatments significantly reduced their levels. Chilled plants showed marked increases in their total soluble protein contents in response to each ABA treatment. ABA significantly increased the activities of superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase in cold-stressed grapevine leaves. In contrast, cold stress markedly decreased the rates of leaf photosynthesis (A) and evaporation (E), stomatal conductance (g_s), and chlorophyll concentrations in leaves, but increased intercellular CO₂ concentrations (C_i) in leaves. Treatment with all concentrations of ABA resulted in lower leaf A, E, and g_s values, but higher C_i values at 24°C. However, following cold stress, ABA-treated vines showed higher leaf A, E, and g_s values, but lower C_i values compared to control vines without ABA treatment. The application of 50–200 µM ABA allowed chilled vines to recover more quickly when re-exposed to normal temperatures, enabling the vines to resume their photosynthetic capacity more efficiently following cold stress. These results showed that, by stimulating anti-oxidant enzyme systems and alleviating cold-induced stomatal limitations, ABA reduced the inhibitory effect of cold stress on the rate of CO₂ fixation in ‘Sultana’ grapevine plants.     

Effect of agar,galactomannan and indole-butyric acid on in vitro rooting of the pear cultivar ‘Durondeau’ and apple rootstock cultivar ‘Marubakaido’

Summary

The influence of partial substitution of agar by galactomannans in culture media supplemented with different concentrations of indole-3-butyric acid (IBA) was studied on in vitro rooting of pear (Pyrus communis L.) cultivar ‘Durondeau’ and apple rootstock (Malus prunifolia Borkh.) cultivar ‘Marubakaido’. The galactomannans applied were obtained from Cassia fastuosa (cassia) and Cyamopsis tetragonolobus (guar gum) seeds. The results obtained with mixtures of agar and galactomannan (3 g l^–1 each) were compared with those from media solidified with a standard concentration of agar (6 g l^–1). The rooting of pear shoots was enhanced significantly in the presence of a mixture of agar plus cassia galactomannan compared to medium solidified with agar only. The modified media promoted a higher number of roots than the control, and increased the percentage of rooted shoots. A maximum of 84.8% rooting was obtained on half-strength MS medium (¹?2MS) supplemented with 0.49 µM IBA and solidified with a blend of agar plus cassia galactomannan. For the apple rootstock, only the number of roots per shoot was influenced significantly by the addition of galactomannan to the rooting medium. The highest number of roots per shoot was 16.67 on ¹?2MS medium gelled with a mixture of agar plus guar galactomannan supplemented with 4.90 µM IBA. The behaviour of the agar-galactomannan gel and the possibility of reduced costs when compared with systems containing only agar, suggest new biological and commercial applications for galactomannans.     

Post-harvest putrescine treatments extend the storage-life of apricot (Prunus armeniaca L.) ‘Tokhm-sefid’ fruit

Summary

The aim of this study was primarily to increase the storability of apricot which is normally a very short storage-life stone fruit. Polyamines are well-known to improve the storability of many horticultural crops. The effect of exogenously applied putrescine on the post-harvest storage-life of apricot (Prunus armeniaca L.) ‘Tokhm-sefid’ fruit at 2°C was therefore investigated. The rate of ethylene production, fresh weight (FW) loss, tissue firmness, soluble solids content (SSC), titratable acidity (TA), and the pH of fruit were determined 5, 10, 15, 20 and 25 d after the beginning of storage. Overall, the application of putrescine caused a reduction in ethylene production, as well as an increase in fruit flesh firmness. SSC and pH were reduced, and TA was increased in putrescine-treated fruits. The loss of fruit FW was affected by putrescine in a concentration-dependent manner. Thus, fruit treated with higher concentrations of putrescine showed lower FW loss.     

‘Chambourcin’ grapevine (Vitis vinifera Vitis L.) berries display sustained post-veraison accumulation of oxalic acid

SUMMARY

A substantial accumulation of organic acids (OAs) occurs during pre-veraison grape berry development, which results in low pH conditions and contributes to the organoleptic properties of the fruit. The main OAs in most grape berries are tartaric acid (TA) and malic acid (MA). MA is accumulated via a primary metabolic shunt, whereas TA is accumulated via ascorbic acid (AA; vitamin C) metabolism. Oxalic acid (OX) is also derived from AA in competition with TA, and results from a cleavage between the second and third carbon atoms. Oxalic acid is subsequently biomineralised as calcium oxalate crystals in idioblast cells. We have examined the biosynthesis of TA, MA, and OX during grape berry development in four grapevine cultivars. We show that in the Vitis vinifera L. Vitis L. complex inter-specific hybrid, ‘Chambourcin’, there is a high capacity to accumulate OX during post-veraison fruit development. OX content increased from approx. 1 mg g^–1 to 3 mg g^–1 berry fresh weight between 14 and 16 weeks post-anthesis, resulting in OX levels that were similar to the MA levels in mature fruit. Whether OX accumulation occurs due to increased biomineralisation or biosynthesis, our results show that ‘Chambourcin’ grape berries represent the only documented case of post-veraison accumulation of OX.     

Foliar Spray with Different Agrochemicals on Fruit Quality and Exportability of ‘Washington’ Navel Orange Fruit (Citrus sinensis L.)

The present study was carried out to improve fruit set, yield, quality, marketability, and exportability of ‘Washington’ Navel orange. Pre-harvest foliar sprays of GA₃, K, and Ca, either alone or combined, were applied at full bloom. The following treatments were applied: {control (T₁), 25 mg/L GA₃ (T₂), 2% K₂SO₄ (T₃), 25 mg/L GA₃ + 2% K₂SO₄ (T₄), 25 mg/L GA₃ + 2% Ca Cl₂ (T₅), 2% K₂SO₄ + 2% Ca Cl₂ (T₆), and 25 mg/L GA₃ + 2% K₂SO₄ + 2% Ca Cl₂ (T₇). All treatments improved fruit set, yield, physical and chemical characteristics, mineral content of leaves and fruit rind, and the percentage of exportable fruit in comparison to the control. Fruit set, fruit detachment force, peel firmness, and the mineral content of leaves and fruit rind were enhanced significantly with the combination of GA₃ + K₂SO₄ + Ca Cl₂ (T₇) in comparison to all other treatments and the control. Results indicated that all foliar combination treatments improved fruit quality and marketability, and increased the percentage of exportable fruit and reduced the defects of non-exportable fruit.