Type-B cytokinin response regulators link hormonal stimuli and molecular responses during the transition from endo- to ecodormancy in apple buds.

KEY MESSAGE: Cytokinin together with MdoBRR1, MdoBRR8 and MdoBRR10 genes participate in the downregulation of MdoDAM1, contributing to the transition from endo- to ecodormancy in apple buds. The final step of cytokinin (CK) signaling pathway culminates in the activation of type-B response regulators (BRRs), important transcriptional factors in the modulation of CK-responsive genes. In this study, we performed a genome-wide analysis aiming to identify apple BRR family members and understand their involvement in bud dormancy control. The investigation identified ten MdoBRR protein-coding genes. A higher expression of three MdoBRR (MdoBRR1, MdoBRR9 and MdoBRR10) was observed in dormant buds in comparison to other developmental stages. Interestingly, in ecodormant buds these three MdoBRR genes were upregulated in a CK-dependent manner. Transcription profiles, determined during dormancy cycle under field and artificially controlled conditions, revealed that MdoBRR1 and MdoBRR8 played important roles in the transition from endo- to ecodormancy, probably mediated by endogenous CK stimuli. The expression of MdoBRR7, MdoBRR9, and MdoBRR10 was induced in ecodormant buds exposed to warm temperatures, indicating a putative role in growth resumption after chilling requirement fulfillment. Contrasting expression patternsin vivo between MdoBRRs and MdoDAM1, an essential dormancy establishment regulator, were observed during dormancy cycle and in CK-treated buds. Thereafter, in vivo transactivation assays showed that CK stimuli combined with transient overexpression of MdoBRR1, MdoBRR8, and MdoBRR10 resulted in downregulation of the reporter gene gusA driven by the MdoDAM1 promoter. These pieces of evidences point to the integration of CK-triggered responses through MdoBRRs that are able to downregulate MdoDAM1, contributing to dormancy release in apple.

Characterization of the nucellus-specific dehydrin MdoDHN11 demonstrates its involvement in the tolerance to water deficit.

KEY MESSAGE: MdoDHN11 acts in the nucellus layer to protect the embryo and the endosperm from limited water availability during apple seed development. Dehydrins (DHNs) are protective proteins related to several plant developmental responses that involve dehydration such as seed desiccation and abiotic stresses. In apple (Malus × domestica Borkh.), the seed-specific MdoDHN11 was suggested to play important roles against dehydration during seed development. However, this hypothesis has not yet been evaluated. Within this context, several experiments were performed to functionally characterize MdoDHN11. In situ hybridization analysis during apple seed development showed that MdoDHN11 expression is confined to a maternal tissue called nucellus, a central mass of parenchyma between the endosperm and the testa. The MdoDHN11 protein was localized in the cytosol and nucleus. Finally, transgenic Arabidopsis plants expressing MdoDHN11 were generated and exposed to a severe water-deficit stress, aiming to mimic a situation that can occurs during seed development. All transgenic lines showed increased tolerance to water deficit in relation to wild-type plants. Taken together, our results provide evidences that MdoDHN11 plays important roles during apple seed development by protecting the embryo and the endosperm from limited water availability, and the mechanism of action probably involves the interaction of MdoDHN11 with proteins and other components in the cell.

Budburst and flowering intensity by the spraying of dormancy-breaking products in 'Eva' apple trees / Brotação e intensidade de floração pela aplicação de indutores de brotação em macieiras 'Eva'

Spraying of dormancy-breaking chemicals is a mandatory procedure to produce temperate fruits in low-chill regions. Although hydrogen cyanamide (HC) + mineral oil (MO) show efficiency enhancing budburst, the usage of HC is restricted in some countries due to its toxicity. Therefore, this research aimed to evaluate the efficiency of spraying different dormancy-breaking agents on ‘Eva’ apple tree buds, under the conditions of the Depressão Central of Rio Grande do Sul, Brazil. Different doses of Erger® (0, 2, 3, 4, 5%) + 3% Ca(NO3)2 were tested and compared with MO (4%) or MO (4%) + HC (0.6%). Budburst rate of apical and axillary buds, physiological alterations in buds, return bloom, yield and fruit weight were evaluated. Erger® treatments efficiently enhanced budburst, with a result equivalent to HC + MO treatment. The budburst rate increased as the Erger® dose increased, also causing the increment of the return bloom in the following year. However, doses of 4 and 5% caused the death of shoots. The activity of the peroxidases and the content of H2O2 in the buds were affected by the treatments. Yield and fruit mass were different in response to treatments, although the effect varied between years. Erger® + Ca(NO3)2 spraying increase budburst in apical and axillary buds of ‘Eva’ apple tree in low-chill conditions and doses up to 3% of the commercial product do not cause toxicity.

A aplicação de indutores de brotação é uma prática fundamental para a produção de frutíferas temperadas em regiões com menor quantidade de horas de frio. Apesar de cianamida hidrogena (CH) + óleo mineral (OM) apresentarem eficiência na indução da brotação de gemas de macieira, a toxicidade de CH ao aplicador resultou em restrições ao seu uso em alguns países. Assim, o objetivo do trabalho foi avaliar a eficiência da aplicação de diferentes indutores de brotação de gemas na macieira ‘Eva’, nas condições da Depressão Central do RS. Testaram-se diferentes doses de Erger® (0, 2, 3, 4, 5%) + 3% Ca(NO3)2, comparados com OM (4%) ou OM (4%) + CH (0,6%). Foram avaliados a taxa de brotação de gemas apicais e axilares, alterações fisiológicas nas gemas, o retorno floral, a produção e a massa dos frutos. Os tratamentos de Erger® foram eficientes em aumentar a brotação de gemas, com resultados equivalentes ao tratamento CH + OM. A taxa de brotação de gemas aumentou em resposta ao aumento na dose de Erger®, provocando também incremento no retorno floral no ano seguinte, no entanto doses de 4 e 5% provocaram morte de ramos. A atividade de peroxidases e os teores de peróxidos de hidrogênio nas gemas apicais foram afetadas pelos tratamentos. A produção e a massa média dos frutos diferiram entre tratamentos, porém o efeito variou entre as safras. A aplicação de Erger® + Ca(NO3)2 aumenta a brotação de gemas apicais e axilares em macieiras ‘Eva’ em condição de baixo acúmulo de frio e doses de até 3% do produto comercial não causam toxidez.

Budburst and flowering intensity by the spraying of dormancy-breaking products in 'Eva' apple trees / Brotação e intensidade de floração pela aplicação de indutores de brotação em macieiras 'Eva'

Spraying of dormancy-breaking chemicals is a mandatory procedure to produce temperate fruits in low-chill regions. Although hydrogen cyanamide (HC) + mineral oil (MO) show efficiency enhancing budburst, the usage of HC is restricted in some countries due to its toxicity. Therefore, this research aimed to evaluate the efficiency of spraying different dormancy-breaking agents on ‘Eva apple tree buds, under the conditions of the Depressão Central of Rio Grande do Sul, Brazil. Different doses of Erger® (0, 2, 3, 4, 5%) + 3% Ca(NO3)2 were tested and compared with MO (4%) or MO (4%) + HC (0.6%). Budburst rate of apical and axillary buds, physiological alterations in buds, return bloom, yield and fruit weight were evaluated. Erger® treatments efficiently enhanced budburst, with a result equivalent to HC + MO treatment. The budburst rate increased as the Erger® dose increased, also causing the increment of the return bloom in the following year. However, doses of 4 and 5% caused the death of shoots. The activity of the peroxidases and the content of H2O2 in the buds were affected by the treatments. Yield and fruit mass were different in response to treatments, although the effect varied between years. Erger® + Ca(NO3)2 spraying increase budburst in apical and axillary buds of ‘Eva apple tree in low-chill conditions and doses up to 3% of the commercial product do not cause toxicity.(AU)

A aplicação de indutores de brotação é uma prática fundamental para a produção de frutíferas temperadas em regiões com menor quantidade de horas de frio. Apesar de cianamida hidrogena (CH) + óleo mineral (OM) apresentarem eficiência na indução da brotação de gemas de macieira, a toxicidade de CH ao aplicador resultou em restrições ao seu uso em alguns países. Assim, o objetivo do trabalho foi avaliar a eficiência da aplicação de diferentes indutores de brotação de gemas na macieira ‘Eva, nas condições da Depressão Central do RS. Testaram-se diferentes doses de Erger® (0, 2, 3, 4, 5%) + 3% Ca(NO3)2, comparados com OM (4%) ou OM (4%) + CH (0,6%). Foram avaliados a taxa de brotação de gemas apicais e axilares, alterações fisiológicas nas gemas, o retorno floral, a produção e a massa dos frutos. Os tratamentos de Erger® foram eficientes em aumentar a brotação de gemas, com resultados equivalentes ao tratamento CH + OM. A taxa de brotação de gemas aumentou em resposta ao aumento na dose de Erger®, provocando também incremento no retorno floral no ano seguinte, no entanto doses de 4 e 5% provocaram morte de ramos. A atividade de peroxidases e os teores de peróxidos de hidrogênio nas gemas apicais foram afetadas pelos tratamentos. A produção e a massa média dos frutos diferiram entre tratamentos, porém o efeito variou entre as safras. A aplicação de Erger® + Ca(NO3)2 aumenta a brotação de gemas apicais e axilares em macieiras ‘Eva em condição de baixo acúmulo de frio e doses de até 3% do produto comercial não causam toxidez.(AU)

Yield efficiency for nine apple cultivars grafted on two rootstocks / Eficiência produtiva de nove cultivares de macieira sobre dois porta-enxertos

Currently, using smaller trees is one of the most important trends in apple cultivation. It is expected that reduced size plants produce lower amount of fruit, but with high yield and yield efficiency. The aim of this study was to evaluate the yield efficiency (YE) of nine apple tree cultivars, grafted on two rootstocks, from the second to the seventh year after planting. The YE indexes oscillated from one to the other year, regardless of rootstock. Correlations between YE and yield per tree and between YE and trunk cross sectional area (TCSA) confirmed that efficiency can be increased by the production increment or by the plant's vigor reduction. The usefulness of cumulative YE (YE) is highlighted to compare apple tree cultivars after the third year of production. The highest YE indexes were observed for 'Royal Gala' and 'Baigent', on M-9 rootstock, and for 'Gala Real' and 'Maxi-Gala', on Marubakaido/M-9 rootstock.(AU)

A utilização de árvores de pequeno porte é uma das mais importantes tendências na cultura da macieira na atualidade. É esperado que plantas de tamanho reduzido produzam menor quantidade de frutos, mas exibam produtividade e eficiência produtiva elevadas. O objetivo do trabalho foi avaliar a eficiência produtiva (EP) de nove cultivares de macieira, enxertadas sobre dois porta-enxertos, do segundo ao sétimo ano após o plantio. Os índices de EP oscilaram de um ano para outro, independentemente do porta-enxerto utilizado. As correlações entre EP e produção por planta e entre EP e a área da secção transversal do tronco (ATC) confirmam que a eficiência pode ser incrementada pelo aumento da produção ou pela redução do vigor da planta. É ressaltada a validade do uso da eficiência produtiva acumulada (EPA) para comparação de cultivares de macieira após o terceiro ano de produção. Os maiores índices de EPA foram determinados para 'Royal Gala' e 'Baigent', no porta-enxerto M-9, e para 'Gala Real' e 'Maxi-Gala', no porta-enxerto Marubakaido/M-9.(AU)

Functional diversification of the dehydrin gene family in apple and its contribution to cold acclimation during dormancy.

Dehydrins (DHN) are proteins involved in plant adaptive responses to abiotic stresses, mainly dehydration. Several studies in perennial crops have linked bud dormancy progression, a process characterized by the inability to initiate growth from meristems under favorable conditions, with DHN gene expression. However, an in-depth characterization of DHNs during bud dormancy progression is still missing. An extensive in silico characterization of the apple DHN gene family was performed. Additionally, we used five different experiments that generated samples with different dormancy status, including genotypes with contrasting dormancy traits, to analyze how DHN genes are being regulated during bud dormancy progression in apple by real-time quantitative polymerase chain reaction (RT-qPCR). Duplication events took place in the diversification of apple DHN family. Additionally, MdDHN genes presented tissue- and bud dormant-specific expression patterns. Our results indicate that MdDHN genes are highly divergent in function, with overlapping levels, and that their expressions are fine-tuned by the environment during the dormancy process in apple.

Digital cover photography for estimating leaf area index (LAI) in apple trees using a variable light extinction coefficient.

Leaf area index (LAI) is one of the key biophysical variables required for crop modeling. Direct LAI measurements are time consuming and difficult to obtain for experimental and commercial fruit orchards. Devices used to estimate LAI have shown considerable errors when compared to ground-truth or destructive measurements, requiring tedious site-specific calibrations. The objective of this study was to test the performance of a modified digital cover photography method to estimate LAI in apple trees using conventional digital photography and instantaneous measurements of incident radiation (Io) and transmitted radiation (I) through the canopy. Leaf area of 40 single apple trees were measured destructively to obtain real leaf area index (LAI(D)), which was compared with LAI estimated by the proposed digital photography method (LAI(M)). Results showed that the LAI(M) was able to estimate LAI(D) with an error of 25% using a constant light extinction coefficient (k = 0.68). However, when k was estimated using an exponential function based on the fraction of foliage cover (f(f)) derived from images, the error was reduced to 18%. Furthermore, when measurements of light intercepted by the canopy (Ic) were used as a proxy value for k, the method presented an error of only 9%. These results have shown that by using a proxy k value, estimated by Ic, helped to increase accuracy of LAI estimates using digital cover images for apple trees with different canopy sizes and under field conditions.