Dormant Pear Research Articles

The identification of pathogens associated with dead dormant pear buds

The identification of pathogens associated with dead dormant pear buds

The Survival of Pear Dormant Buds at Ultra-Low Temperatures.

Currently, there is a varietal diversity decline in pear orchards of the Czech Republic. Thus, the safe storage of their gene pool collections is becoming increasingly important. Therefore, the ultra-low temperature survival after two-step cryopreservation treatment of dormant buds was tested for a safe and rapid way to conserve pear germplasm in a broader range of varieties. The following varieties crucial for cultivation in the Czech Republic were tested; ‘Amfora’, ‘Beurré Hardy’, ‘Bosc’, ‘Clapp’s Favourite’, ‘Conference’, ‘Dicolor’, ‘Erika’, ‘Lucas’, ‘Williams’ and ‘Williams Red’. In 2011 and 2012, dormant pear buds were dehydrated to 40.1% and 36.0% water content, respectively, before cryopreservation. The average regeneration of the dormant pear buds after cryopreservation by the two-step cryoprotocol in 2011 and 2012 was 54.3% and 16.1%, respectively. The mentioned cryopreservation procedure is suitable for the safe storage of dormant buds in most tested pear varieties.

Alternative splicing of the dormancy-associated MADS-box transcription factor gene PpDAM1 is associated with flower bud dormancy in ‘Dangshansu’ pear (Pyrus pyrifolia white pear group)

Alternative splicing (AS) plays a crucial role in plant growth, development and response to various environmental changes. However, whether alternative splicing of MADS-box transcription factors contributes to the flower bud dormancy process in fruit trees still remains unknown. In this work, the AS profile of genes in the dormant flower buds of ‘Dangshansu’ pear tree were examined. A total number of 3661 alternatively spliced genes were identified, and three mRNA isoforms of the dormancy associated MADS box (DAM) gene, PpDAM1, derived by alternative splicing, designated as PpDAM1.1, PpDAM1.2 and PpDAM1.3, were characterized. Bimolecular fluorescence complementation (BiFC) analysis indicated that AS of PpDAM1 didn't affect the nucleus localization and homo-/heterodimerization of PpDAM1.1, PpDAM1.2 and PpDAM1.3 proteins, but disturbed the translocation of PpDAM1.1/PpDAM1.1, PpDAM1.3/PpDAM1.3, PpDAM1.1/PpDAM1.3, and PpDAM1.2/PpDAM1.3 dimers to the nucleus. Constitutive expression of PpDAM1.2, but not PpDAM1.1 and PpDAM1.3, in Arabidopsis retarded the growth and development of transgenic plants. Further comparative expression analyses of PpDAM1.1, PpDAM1.2 and PpDAM1.3 in the flower buds of ‘Dangshansu’ and a less dormant pear cultivar, ‘Cuiguan’, exhibited that the expression of all the three isoforms in ‘Dangshansu’ were significantly higher than in ‘Cuiguan’, especially PpDAM1.2, which showed a predominantly higher expression than PpDAM1.1 and PpDAM1.3 in both cultivars. Our results suggest that alternative splicing of PpDAM1 could play a crucial role in pear flower bud dormancy process.

Expression and genomic structure of the dormancy-associated MADS box genes MADS13 in Japanese pears (Pyrus pyrifolia Nakai) that differ in their chilling requirement for endodormancy release

We isolated three dormancy-associated MADS-box (DAM) genes (MADS13-1, MADS13-2 and MADS13-3) and showed regulated expression concomitant with endodormancy establishment and release in the leaf buds of Japanese pear 'Kosui'. Comparative analysis between 'Kosui' and Taiwanese pear TP-85-119 ('Hengshanli'), a less dormant pear cultivar, showed reduction of MADS13-1 expression level in 'Hengshanli' earlier than in 'Kosui' towards endodormancy release, suggesting the possible relationship between chilling requirement and MADS13-1 expression. Application of hydrogen cyanamide accelerated endodormancy release with a reduction in MADS13 expression, whereas heat treatment in autumn inhibited endodormancy establishment without induction of MADS13 expression, indicating a close relationship between the MADS13 expression pattern and endodormancy phase transitions. Moreover, both the cis-acting regulatory elements and the methylation status in the 5' upstream region of the MADS13-1 gene were not largely different between 'Kosui' and 'Hengshanli'. Genomic structures of MADS13-1 from 'Kosui' and 'Hengshanli' revealed a 3218 bp insertion in the first intron of 'Hengshanli' that might be ascribed to the lower expression of MADS13-1tw; however, this insertion was also found in pear genotypes with a high chilling requirement. These results indicated that the low expression of MADS13-1 in 'Hengshanli' towards endodormancy release could not be explained by the identified cis-acting regulatory elements, the methylation status of the putative promoter or by intron insertion.

Oviposition by Summer and Winter Forms of Pear Psylla (Homoptera: Psyllidae) on Dormant Pear Budwood

The winter form of pear psylla, Psylla pyricola Foerster, readily oviposited on pear budsticks and leaves; the summer form had a strong preference for leaves and was reluctant to oviposit on budsticks.

Effect of Prebloom Oil Applications on Pear Fruit Set and the Possible Mode of Action1

Abstract Dilute sprays of 4, 8 and 16% Volck Supreme oil at dormant and repeated at delayed dormant to mask pear trees against psylla, Psylla pyricola (Foerster), oviposition delayed bloom slightly, while 2% applications in the Meld advanced bloom less than 1 day. Dormant pear branches dipped under laboratory conditions in oil at concentrations of 8% and higher caused injury to vegetative buds and slight injury to flowering buds. Single and repeat field applications of oil at 2, 4 and 8% caused no reduction of fruit set or cropping of ‘Anjou’, ‘Bartlett’, ‘Cornice’, ‘Bose’, and ‘Seckel’ pear trees, and in some cases increased fruit set on ‘Anjou’ trees. Hormonal analysis of oil-treated buds indicated a slight increase of gibberellin (GA) and a reduction of abscisic acid (ABA) levels.

Changes in Isoperoxidases during Cold Treatment of Dormant Pear Embryo

The number of isoperoxidases and the intensity of certain isozymes increased with increasing periods of stratification of pear (Pyrus communis cv. Bartlett) embryos. The presence of GA(3) or kinetin during stratification enhanced the activity of certain isoperoxidases, and these enhancements were blocked in the presence of ABA which by itself had an inhibitory effect. Enhancement in isoperoxidases of pear embryos during stratification was inhibited by 6-methylpurine and cycloheximide; and in the presence of either of these two inhibitors, stratification failed to release the dormancy. Pear embryos germinated for 3 days showed changes in the pattern of isoperoxidases depending on the length of stratification.

Increases in activities of aminoacyl-tRNA synthetases during cold-treatment of dormant pear embryo

Aminoacyl-tRNA synthetases from a pH 5 enzyme fraction from dormant or non-dormant pear embryos were studied by the pyrophosphate exchange assay. Synthetases from dry embryos exchanged 18.6 n mol/min/mg protein. This value was slightly increased by the moist treatment, however a greater increase was obtained by cold-treatment. The activity of individual synthetases was generally higher after cold-treatment. The rate of pyrophosphate exchange was enhanced by kinetin or gibberellic acid treatment of dormant embryos and additional enhancement was observed when both hormones were used in combination. Abscisic acid inhibited synthetase activity in non-dormant embryos. The presence of 6-methylpurine during a 5 day cold-treatment resulted in a 50% decrease in enzyme activity compared to the control.

Selective effect of hormones on nucleic acid metabolism during germination of pear embryos.

1. The effect of hormones on (32)P incorporation into various RNA fractions in germinating pear embryos was studied by fractionation on methylated albumin-kieselguhr columns. Abscisic acid inhibited labelling of soluble RNA, DNA-RNA hybrid and light-ribosomal RNA fractions with (32)P and this effect was reversed by both kinetin and gibberellic acid. 2. Kinetin reversed the inhibition by abscisic acid of (32)P incorporation into total ribosomal RNA and appeared to promote labelling of heavy-ribosomal RNA. Gibberellic acid was more active than kinetin in reversing the inhibition by abscisic acid of labelling of the DNA-RNA hybrid fraction with (32)P, but in contrast with kinetin appeared to increase further the inhibition by abscisic acid of labelling of total ribosomal RNA. 3. The percentage of radioactivity in various RNA fractions showed marked variation in response to hormones. 4. The pattern of labelling of RNA in pear embryos during reversal of inhibition by abscisic acid with a combination of kinetin and gibberellic acid was similar to that after cold-treatment of dormant pear embryos. This is suggestive of hormonal interplay in dormancy release by cold-treatment in pear embryos.

Increase in nucleic acid synthesizing capacity during cold treatment of dormant pear embryos

Increase in nucleic acid synthesizing capacity during cold treatment of dormant pear embryos

Axillary buds in normal and irradiated apple and pear

Dormant buds of apple and pear are convenient material to irradiate for the production of mutations or chimeral rearrangements. The sites of action of ionizing radiation are the apical meristem and the secondary bud primordia of the dormant bud. Such buds and growing shoot tips of normal and irradiated McIntosh (2×) and Northern Spy (2×) apples, their cytochimeras Kimball McIntosh (2-4-4-4) and Loop Spy (2-2-4-4), and Bartlett pear (2×) were sectioned or dissected. Apple scions received 0 to 2850 rad of X-rays and pear scions were exposed to 0, 2000, 4000 or 6000 rad of γ-rays. Dormant pear buds had seven bud primordia which would normally continue growth while those of apple had only three. No bud primordium in a dormant bud had reached the mound stage. After irradiation of apple and pear radiation-damaged cells were found in the subsurface central region of both apical and axillary meristems. Greatest damage occurred in layers II and III. Cells adjacent to the damage, notably those surrounding the damaged area of the shoot between the youngest three leaves and those adaxial to the older bud primordia, became meristematic. One or more secondary buds developed from the axils of pre-irradiation leaves 1–5 in apple and 1–10 in pear. In older recovering shoots an adventitious bud might arise on the stem, as suggested by one cauline bud.