Apple production depends on the fulfilment of a chilling requirement for bud dormancy release. Insufficient winter chilling results in irregular and suboptimal bud break in the spring, with negative impacts on apple yield. Trees from apple cultivars with contrasting chilling requirements for bud break were used to investigate the expression of the entire set of apple genes in response to chilling accumulation in the field and controlled conditions. Total RNA was analysed on the AryANE v.1.0 oligonucleotide microarray chip representing 57,000 apple genes. The data were tested for functional enrichment, and differential expression was confirmed by real-time PCR. The largest number of differentially expressed genes was found in samples treated with cold temperatures. Cold exposure mostly repressed expression of transcripts related to photosynthesis, and long-term cold exposure repressed flavonoid biosynthesis genes. Among the differentially expressed selected candidates, we identified genes whose annotations were related to the circadian clock, hormonal signalling, regulation of growth, and flower development. Two genes, annotated as FLOWERING LOCUS C-like and MADS AFFECTING FLOWERING, showed strong differential expression in several comparisons. One of these two genes was upregulated in most comparisons involving dormancy release, and this gene's chromosomal position co-localized with the confidence interval of a major quantitative trait locus for the timing of bud break. These results indicate that photosynthesis and auxin transport are major regulatory nodes of apple dormancy and unveil strong candidates for the control of bud dormancy.
The molecular control of bud dormancy establishment and release is still not well understood, although some genes have already been demonstrated to play important roles in this process. The dormancy-associated MADS-box (DAM) genes were first identified in the peach EVERGROWING locus and are considered the main regulators of bud dormancy control. In this work, the apple (Malus × domestica Borkh.), a perennial plant adapted to temperate climates that displays cycles of growth and bud dormancy, was screened for the presence of DAM genes. The candidate genes retrieved were characterized in comparison to DAM genes from other species. Four of them (MdDAM1-4) are structurally very similar to the reported DAM genes. When apple genomic segments containing these candidates were compared to the peach EVERGROWING locus, a highly conserved noncoding region was detected inside their largest intron. Similar sequences were also identified inside introns of apricot and pear DAM genes. Organ expression patterns revealed that MdDAM1-4 are mainly expressed in dormant buds and seeds, with low transcript accumulation in vegetative structures. In addition, the MdDAM genes showed seasonally oscillating patterns of steady-state messenger RNA (mRNA) levels and were downregulated by artificial chilling. Motif analyses in the promoter and in the intronic conserved region of the MdDAM genes disclosed some clues to the regulation of the expression patterns observed. Possible roles for the conserved intronic sequence in dormancy regulation are discussed.
Fluctuations in winter chilling availability impact bud dormancy and budburst. The objective of this work was to determine chilling requirements to induce and overcome endodormancy (dormancy controlled by chilling) of buds in different grape cultivars. ‘Chardonnay’, ‘Merlot’ and ‘Cabernet Sauvignon’ shoots were collected in Veranópolis-RS vineyards in 2010, and submitted to a constant 3 °C temperature or daily cycles of 3/15 °C for 12/12h or 18/6h, until reaching 1120 chilling hours (CH, sum of hours with temperature ≤ 7.2 °C). Periodically, part of the samples in each treatment was transferred to 25 °C for budburst evaluation (green tip). Chilling requirements to induce and overcome endodormancy vary among cultivars, reaching a total of 136 CH for ‘Chardonnay’, 298 CH for ‘Merlot’ and 392 CH for ‘Cabernet Sauvignon’. Of these, approximately 39, 53 and 91 CH are required for induction of endodormancy in the three cultivars, respectively. The thermal regimes tested (constant or alternating) do not influence the response pattern of each cultivar to cold, with 15 °C being inert in the CH accumulation process. In addition, time required to start budburst reduces with the increase in CH, at a rate of one day per 62 CH, without significant impacts on budburst uniformity.
-The objective of this work was to evaluate the effect of heat waves on the evolution of bud dormancy, in apple trees with contrasting chilling requirements. Twigs of 'Castel Gala' and 'Royal Gala' were collected in orchards in Papanduva, state of Santa Catarina, Brazil, and were exposed to constant (3°C) or alternating (3 and 15°C for 12/12 hours) temperature, combined with zero, one or two days a week at 25°C. Two additional treatments were evaluated: constant temperature (3°C), with a heat wave of seven days at 25°C, in the beginning or in the middle of the experimental period. Periodically, part of the twigs was transferred to 25°C for daily budburst evaluation of apical and lateral buds. Endodormancy (dormancy induced by cold) was overcome with less than 330 chilling hours (CH) of constant cold in 'Castel Gala' and less than 618 CH in 'Royal Gala'. A daily 15°C-temperature cycle did not affect the endodormancy process. Heat waves during endodormancy resulted in an increased CH to achieve bud requirements. The negative effect of high temperature depended on the lasting of this condition. Chilling was partly cancelled during dormancy when the heat wave lasted 36 continuous hours or more. Therefore, budburst prediction models need adjustments, mainly for regions with mild and irregular winters, such as those of Southern Brazil.
RESUMOO manejo adequado da poda permite alterar a fenologia da videira, modificando os períodos de colheita, inclusive com potencial de obtenção de mais de uma safra por ciclo vegetativo. Diante desse potencial avaliou-se uma época de poda seca no inverno (08/08/05) e duas épocas de poda verde (04/11/05 e 02/12/05) nas cultivares Niagara Branca e Concord, ambas Vitis labrusca, visando obter duas safras no mesmo ciclo vegetativo. O experimento foi realizado na safra 2005/2006 em videiras cultivadas em sistema de espaldeira, localizadas em Eldorado do Sul -RS. Variáveis associadas à fenologia, produção por planta, peso dos cachos, sólidos solúveis totais (SST), acidez total titulável (ATT) e relação SST/ATT foram analisadas para as safras obtidas. O ciclo fenológico das plantas podadas no inverno foi de 156 dias para a 'Niagara Branca' e 161 dias para a 'Concord', com colheita realizada em meados de janeiro. Por sua vez, o ciclo fenológico das brotações oriundas das podas verdes realizadas em 04/11/2005 e 02/12/2005 foi, respectivamente, de 127 e 113 dias, para a 'Niagara Branca', e 134 e 120 dias para a 'Concord', com colheitas realizadas em meados do mês de abril. A época de poda verde realizada em 04/11/05 permitiu maior produção por planta e cachos de maior peso, independentemente da cultivar, comparativamente à 02/12/05. A qualidade dos frutos foi semelhante entre as safras, mostrando apenas diferenças significativas entre cultivares, expressa numa menor ATT e maior relação SST/ATT para a 'Niagara Branca'.Palavras-chave: Vitis labrusca; fenologia; manejo da poda; segunda colheita. ABSTRACTThe adequate pruning management of grapevine permits to change its fenology, modifying the crop periods and creating conditions for two annual harvests. A winter pruning period (08/08/05) and two periods of summer pruning (04/11/ 05 and 02/12/05) were evaluated in order to obtain two annual harvests, using Niagara Branca and Concord grape varieties (both Vitis labrusca). This experiment was performed during the 2005/2006 season in grapevines conducted by cordon training in Eldorado do Sul county, Rio Grande do Sul, Brazil. Variables associated to fenology, plant production, weight of grapes, total soluble solids, total titratable acidity and ratio total soluble solids by total titratable acidity related to harvests were analyzed. The fenology of plants pruned in winter was 156 days for 'Niagara Branca' and 161 days for 'Concord', and the harvest was performed around January, 15th. Regarding the summer pruning performed on 04/11/05 and 02/12/05, fenology cycle of shoots was 127 and 113 days for the 'Niagara Branca' and 134 and 120 days for the 'Concord', respectively. Harvest was realized in middle April, 15th. The summer pruning realized in 04/11/05 provided higher production per plant and grapes of higher weight, independent of cultivar, when compared to the 02/12/05 pruning. Fruit quality was similar among the harvests, with significant differences between cultivars expressed by smaller total titratable acidity and higher ...
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