Use of sugarcane bagasse as an alternative low-cost support material during the rooting stage of apple micropropagation

Summary Studies were carried out to evaluate sugarcane bagasse as an alternative to agar for micropropagation of apple clones to reduce the cost of micropropagation and improve the quality of the propagules. Significant improvement in the in vitro rooting process, coupled with cost reduction, were obtained by the use of sugarcane bagasse as a substitute for the traditionally used agar-gelled medium. The tests were undertaken with micro-cuttings of the apple rootstock Marubakaido (Malus prunifolia Borkh.) using a rooting medium composed of half-strength Murashige and Skoog salts and vitamins, 3% (w/v) sucrose, and 0.49 μM indole-3-butyric acid. The plants grown on sugarcane bagasse yielded a 22% increase in root length, 20% increase in plant length, and 63% increase in the number of roots, compared with agar-grown micro-cuttings. Particle size of the sugarcane bagasse had a significant impact on all those parameters, and the best results were obtained with bagasse comprising particles smaller than 0.18 mm. The results demonstrated that the sugarcane bagasse could be used effectively as a substitute for agar during rooting of apple shoots.     

Physical mapping of three fruit ripening genes：Endopolygalacturonase,ACC oxidase and ACC synthase from apple（Malus x domestica） in an apple rootstock A106（Malus sieboldii

The apple rootstock,A106(Malus sieboldii),had 17 bivalents in pollen mother cells at meiotic metaphase 1,and 17 chromosomes in a haploid pollen cell.Karyotypes were prepared from root-tip cells with 2n=34 chromosomes,Seven out of 82 karyotypes(8.5%) showed one pari of satellites at the end of the short arm of chromosome 3.C-bands were shown on 6 pairs of chromosomes 2,4,6,8,14,and 16 near the telomeric regions of short arms.Probes for three ripening-related genes from Malus x domestica:endopolygalacturonase(EPG,0.6kb),ACC oxidase(1.2kb),and ACC synthase(2kb)were hybridized in situ to metaphase chromosomes of A106.Hybridization sites for the EPG gene were observed on the long arm of chromosome 14 in 15 out of 16 replicate spreads and proximal to the centromere of chromosomes 6 and 11.For the ACC oxidase gene,hylridization sites were observed in the telomeric region of the short arm of chromosomes 5 and 11 in 87% and 81% of 16 spreads respectively,proxiaml to the centromere of chromosome 1 in 81% of the spreads,and on the long arm of chromosome 13 in 50% of the spreads. Physical mapping of three fruit ripening genes in an apple rootstock A106.Twenty five spreads were studied for the ACC synthase gene and hybridization sites were observed in the telomeric region of the short arm of chromosome 12 in 96% of the spreads.chromosomes 9 and 10 in 76% of the spreads,and chromosome 17 in 56% of the spreads.     

Chromosomal localization of ribosomal DNA sequences in an apple rootstock using a digoxygenin detection system

A 6kb rDNA probe comprising the 18S coding plus spacer sequences has been hybridized to the metaphase chromosomes of apple rootstock cultivar MM106 demonstrating the localization of ribosomal gene arrays in the vicinity of the telomeric regions of the short arms of chromosomes 6 and 14.The in situ results using digoxygenin labelling coupled to an alkaline phosphatase immunoassay were confirmed by silver staining for NORs and nucleoli.This study demonstrates the feasibility of molecular cytogenetic analysis of very small chromosomes(1.0-2.7μm） of apple.     

Drought stress of apple trees alters leaf emissions of volatile compounds

Actively growing potted apple trees ( Malus domestica [L.] Borkh. ev. Delicious) unacclimated to drought stress were subjected to drought to determine changes in emissions of leaf volatile compounds. Drought stress was imposed over a 2-week period by weighing pots every 2 or 3 days and adding water hack to an arbitrary and decreasing traction of the original pot weight. Stem water potential was -2.7. -2.0 and -0.8 MPa for the severely stressed, moderately stressed and control trees, respectively. 13 days alter watering treatments were begun. Water use the last 4 days of the experiment was about one-half for the moderately and severely stressed trees compared to that of the controls Twenty-nine volatile compounds were identified by using gas chromatography and mass spectroscopy. Emission rates of hexanal, (E)-2-hexenal, (E)-2-hexen-1-ol, 1-hexenol, hexyl acetate and (E)-2-hexenyl acetate were 5 to 310 times higher for severely stressed trees compared to those of the controls with the moderately stressed trees intermediate. The large increases in hexanal. (E)-2-hexenal and l-hexanol may be related. In enhanced lipoxygenase activity. Volatile compounds are products of metabolism and measurement of their changes after biotic or abiotic stresses will increase understanding of the relationship of changes in plant metabolism by those stresses.     

Changes of inositol phosphates during decapitation-induced lateral bud break of Malus domestica

An increase in phosphatidylcholine (PC), phosphatidyl-ethanolamine (PE), phosphatidylglycerol (PG), and phosphatidylinositol (PI) occurred during bud break induced by decapitation. Inositol-1-phosphate [Ins(l)P₁], inositol-1,4-bisphosphate [Ins(1,4)P₂], and inositol-1,4,5-triphosphate [Ins(1,4,5)P₃] were found in apple buds and increased progressively following decapitation. Ins(1)P₁ and Ins(1,4)P₂ peaked 48 h after decapitation and Ins(1,4,5)P₃ peaked 72 h after decapitation during the metabolic transition when buds emerged from dormancy. Ins(1,4)P₂ and Ins(1,4,5)P₃ levels declined there after. The lateral buds on shoots with intact terminals and decapitated shoots treated with indole-3-acetic acid (IAA) in the terminals tip remained dormant and there were no significant changes in phospholipid and inositol phosphate contents.     

MDH1: an apple homeobox gene belonging to the BEL1 family

Differential display was used to isolate genes differentially expressed early in fruit development of apple (Malus domestica Borkh.). This approach resulted in the isolation of MDH1, a homeobox gene with a homeodomain similar to that of BELL1 (BEL1), which is involved in regulation of ovule development in Arabidopsis. However, outside the homeodomain MDH1 is quite different from BEL1. In apple, MDH1 mRNA was predominantly found in flowers, expanding leaves and expanding fruit. In pre-anthesis flowers, in situ hybridization showed that MDH1 mRNA accumulated in ovules. To further investigate the function of this new homeobox gene, MDH1 was transformed into Arabidopsis thaliana under the control of the cauliflower mosaic virus 35S promoter. The transgenic Arabidopsis plants showed dwarfing, reduced fertility and changes in carpel and fruit (silique) shape. The size and shape of the cells in the transgenic fruit was irregular. Both the transgenic phenotypes in Arabidopsis and the expression pattern of this gene in apple are consistent with the idea that MDH1 is likely to play an important role in control of plant fertility.     

Biological Control of Postharvest Diseases of Apple and Pear under Semi-commercial and Commercial Conditions Using Three Saprophytic Yeasts

The yeastsCryptococcus laurentii(strain HRA5),Cryptococcus infirmominiatus(strain YY6), andRhodotorula glutinis(strain HRB6) were tested as biocontrol agents of postharvest diseases of apple and pear in semi-commercial and commercial trials. The yeasts effectively controlled decay when applied in a drench or line spray. The yeasts were not adversely affected when treated fruits were stored in a controlled atmosphere consisting of 1% oxygen and 99% nitrogen. In a commercial trial, the most effective treatments for control of blue mold of pear were a combination ofC. laurentiiandC. infirmo-miniatus(91% control) and the commercially recommended high rate (528 μg/ml) of thiabendazole (88% control). In the commercial apple trial, the most effective treatments for blue mold wereC. infirmo-miniatuscombined with 264 μg/ml thiabendazole (91% control),C. infirmo-miniatuscombined withC. laurentii(84% control), and thiabendazole alone at 528 μg/ml (79% control). The combination ofC. laurentiiwith 264 μg/ml of thiabendazole was significantly more effective for control of blue mold on pear than thiabendazole at 528 μg/ml whenever any thiabendazole-resistant spores were present in the inoculum.     

Effect of fruiting and drought or flooding on carbon balance of apple trees

The response of fruiting or deblossomed trees to water stress such as drought or flooding was investigated in six semi open-top cuvettes each containing one apple (Malus domestica Borkh. cv. Golden Delicious) tree. Xylem water potentials of leaves dropped from -1.2 to -4.1 MPa within 7 d of drought, the effect being enhanced by fruiting. Apple trees without fruits showed smaller reductions in net photosynthetic rate (P _N ) and dark respiration rate (R _D ) after 2 d of drought and hence more positive carbon balances relative to fruiting trees. Flooding for 4 d had a more pronounced effect on P _N than on transpiration, resulting in a reduced water use efficiency (WUE). This reduction in WUE was greater in the non-fruiting trees. Flooding reduced P _N of the whole apple canopies irrespective of fruiting; aple trees without fruits increased R _D resulting in a less positive carbon balance relative to fruiting trees. Fruiting increased the sensitivity to drought of apple trees (R _D and P _N ), but decreased their sensitivity to flooding (R _D and WUE), suggesting different adaptation mechanisms for the two forms of water stress. This revised version was published online in August 2006 with corrections to the Cover Date.     

Changes in jasmonic acid concentration during early development of apple fruit

Apple fruits ( Malus domestica Borkh.) were harvested from 24 to 136 days after full bloom (DAFB) and endogenous jasmonic acid was analyzed by GC-MS. There were two isomers of jasmonic acid in apple fruit with a ratio of 37:63 ( cis:trans ). The cis:trans ratio remained relatively constant throughout this period of fruit development. The endogenous jasmonic acid concentration was 138 ng g⁻¹ fresh weight 24 DAFB and decreased as fruit developed. Changes in jasmonic acid concentration were coincident with those of respiration, ethylene production, and anthocyanin accumulation in patterns consistent with the reported responses to exogenous jasmonates. Possible roles for jasmonic acid during early fruit development are discussed.     

Quantification of endogenous gibberellins in exudates from fruits of Malus domestica

In exudates from developing apple fruits GA₁, GA₃, GA₄, GA₇, GA₂₀ and GA₃₄ could be identified and subsequently quantified by LC-ESI-MS selected-ion-monitoring analyses on the basis of internal standards. This is the first evidence obtained by mass spectrometrical analysis which demonstrates export of endogenous GAs from the fruits during the period when flower induction occurs. The observed differences in GA₄ export are discussed in connection with biennial bearing.