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- Avoiding high relative air humidity during critical stages of leaf ontogeny is decisive for stomatal functioningPublication . Fanourakis, Dimitrios; Carvalho, Susana M. P.; Almeida, Domingos M. P.; Domingos, P.F.; Heuvelink, EpPlants of several species, if grown at high relative air humidity (RH >= 85%), develop stomata that fail to close fully in case of low leaf water potential. We studied the effect of a reciprocal change in RH, at different stages of leaf expansion of Rosa hybrida grown at moderate (60%) or high (95%) RH, on the stomatal closing ability. This was assessed by measuring the leaf transpiration rate in response to desiccation once the leaves had fully expanded. For leaves that started expanding at high RH but completed their expansion after transfer to moderate RH, the earlier this switch took place the better the stomatal functioning. Leaves initially expanding at moderate RH and transferred to high RH exhibited poor stomatal functioning, even when this transfer occurred very late during leaf expansion. Applying a daily abscisic acid (ABA) solution to the leaves of plants grown at continuous high RH was effective in inducing stomatal closure at low water potential, if done before full leaf expansion (FLE). After FLE, stomatal functioning was no longer affected either by the RH or ABA level. The results indicate that the degree of stomatal adaptation depends on both the timing and duration of exposure to high RH. It is concluded that stomatal functionality is strongly dependent on the humidity at which the leaf completed its expansion. The data also show that the effect of ambient RH and the alleviating role of ABA are restricted to the period of leaf expansion.
- QTL analysis for stomatal functioning in tetraploid Rosa × hybrida grown at high relative air humidity and its implications on postharvest longevityPublication . Carvalho, Dália R. A.; Koning-Boucoiran, Carole F. S.; Fanourakis, Dimitrios; Vasconcelos, Marta W.; Carvalho, Susana M. P.; Heuvelink, Ep; Krens, Frans A.; Maliepaard, ChrisHigh relative air humidity (RH >= 85 %) during leaf development disturbs stomatal functioning leading to excessive water loss in conditions of high evaporative demand, resulting in severe reduction in postharvest longevity. In roses, this effect depends on the genotype, opening the possibility for breeding cultivars with more responsive stomata. In this study, we aim at identifying genomic regions associated with the control of water loss following growth at high RH. The F1 generation (108 offspring) and the two parents (P540 and P867) of a tetraploid cut rose population grown at high (85 %) RH were phenotyped for stomatal control to water loss by assessing the relative water content after 4 h of leaflet desiccation (RWC_4 h). The RWC_4 h varied between 7 and 62 % across the 110 studied individuals, with parents P540 and P867 showing 51 and 20 % RWC_4 h, respectively. Based on these data, a quantitative trait locus (QTL) analysis was performed. The impact of the identified QTLs on postharvest longevity of ten selected offspring was further evaluated. Three QTLs were identified: two major [positioned on linkage group 5 of the integrated consensus map (ICM 5) of both parents and on ICM 2 of the parent P867] and one putative minor (mapped to ICM 6 of both parents), explaining 32 % of the variability in the RWC_4 h. Low RWC_4 h was found to be a good proxy for eliminating the offspring with short vase life. This study constitutes a first step toward identifying the most likely regions for genes of interest controlling stomatal functioning in high RH-grown plants.
- Melhoramento para elevada qualidade pós-colheita: validação do método de selecção de genótipos promissoresPublication . Carvalho, D.R.A.; Carvalho, S. M. P.; Fanourakis, D.; Heuvelink, E.; Almeida, Domingos P. F.
- Melhoramento para elevada qualidade pós-colheita: validação do método de selecção de genótipos promissoresPublication . Carvalho, D.R.A.; Carvalho, S. M. P.; Fanourakis, D.; Heuvelink, E.; Almeida, Domingos P. F.
- Genotypic variation in the stomatal characteristics of cut roses grown under high relative air humidityPublication . Fanourakis, Dimitrios; Tapia, Alejandra; Heuvelink, Ep; Carvalho, Susana M. P.
- Pre-harvest relative humidity level influences water uptake and transpiration during post-harvest phase of cut rosesPublication . Fanourakis, D.; Matkaris, N.; Heuvelink, E.; Carvalho, S. M. P.
- Genotypic variation of cut chrysanthemum response to high CO2 concentration: growth, time to flowering and visual qualityPublication . Fanourakis, D.; Heuvelink, E.; Maaswinke, R.; Carvalho, S. M. P.In this study sixteen cut chrysanthemum cultivars were used to evaluate the effects of high CO2 concentration (1500 μmol mol-1) on growth, time to flowering and visual quality as compared to the concentration used in commercial greenhouses (600 μmol mol-1). CO2 enrichment increased light use efficiency (11-41%) and total plant dry mass (TDM) (5-40%) in a cultivar dependent manner. This TDM increase was a result of: (i) higher relative growth rate during the long day period (i.e., 0 to 2 weeks; LD); and (ii) higher absolute growth rate both during the period between 2 to 6 weeks (SD1), and 6 weeks to final harvest (SD2). Cultivar differences in TDM at flowering between the two CO2 concentrations could be explained by differences in growth rate during the LD and SD2 periods. Furthermore, growing at high CO2 regime enhanced the number of flowers and flower buds per plant (NoF, 4-48%). Interestingly, the cultivars that showed the highest percentage of TDM increase, with CO2 enrichment, were not the ones that had the highest increase in the percentage of NoF. In contrast, high CO2 concentration had only a minor or no effect on the number of internodes on the main stem and on the reaction time in all the cultivars examined. From this research it is concluded that there is a large variation in the response of cut chrysanthemum cultivars to CO2 enrichment, in terms of TDM and NoF, which gives possibilities for breeding.
- Qualidade pós-colheita de rosas: efeitos da humidade relativa e da variação genotípicaPublication . Carvalho, Susana M.P.; Fanourakis, D.; Tapia, A.; Almeida, Domingos P. F.; Malcata, F. Xavier; Heuvelink, E.
- Cultivar differences in the stomatal characteristics of cut roses grown at high relative humidityPublication . Fanourakis, D.; Tapia, A.; Heuvelink, E.; Carvalho, S. M. P.High relative air humidity (RH>85%) during cultivation is known to reduce the vase life of cut roses, but the magnitude of such effect is cultivar dependent. The reasons behind this genotypic variation are not yet known. In this study, the stomatal density and stomatal responses to two closing stimuli (i.e. desiccation and abscisic acid (ABA) application) were evaluated using detached fully expanded leaves of two contrasting rose cultivars in their sensitivity to high RH (‘Frisco’ and ‘Prophyta’) which were grown at moderate (60%) and high (90%) RH. High RH significantly increased the stomatal density in both cultivars, but the effect was stronger in the tolerant cultivar (14% increase for ‘Frisco’, 8% increase for ‘Prophyta’). ‘Frisco’ also showed a higher stomatal density at moderate RH (53 stomata/mm2) as compared to the sensitive cultivar (43 stomata/mm2). Moreover, high RH decreased the speed and the degree to which stomata responded to different closing stimuli in both cultivars, resulting in higher transpiration rates. This effect was more pronounced in the sensitive cultivar. It was concluded that the tolerance to high RH during cultivation is related to more responsive stomata, while the stomatal density is apparently an irrelevant character. Furthermore, this study showed that the rose guard cell dimensions are not representative for the pore dimensions.
- Qualidade pós-colheita de rosas: efeitos da humidade relativa e da variação genotípicaPublication . Carvalho, Susana M. P.; Fanourakis, D.; Tapia, A.; Almeida, Domingos P. F.; Malcata, F. Xavier; Heuvelink, E.Elevada humidade relativa (i.e. HR > 85%) durante a produção de rosas de corte reduz a sua longevidade em jarra, mas a magnitude desse efeito depende em larga medida da cultivar em causa. Na tentativa de compreender melhor os mecanismos ligados à sensibilidade a valores de HR elevada, foram analisadas folhas completamente desenvolvidas de quatro cultivares de rosas de corte: as tolerantes ‘Frisco’ e ‘Dream’, e as sensíveis ‘Vendela’ e ‘Prophyta’; tais plantas foram produzidas em ambiente de HR moderada (60%) e elevada (90%). As plantas produzidas em ambiente de HR elevada apresentaram, em média, uma maior densidade estomática (14% mais estomas por mm2), estomas de maior dimensão (8% mais compridos) e com maior abertura (15% de aumento) comparativamente a plantas produzidas sob HR moderada. Esta tendência foi observada em todas as cultivares, embora a intensidade do efeito dependesse da cultivar. Paralelamente, o grau e a rapidez do fecho dos estomas, quando submetidos a estímulos apropriados, diminuíram significativamente em plantas produzidas sob HR de 90%, resultando num acentuado aumento da taxa de transpiração. Contudo, tal efeito foi mais pronunciado nas cultivares sensíveis. Conclui-se, assim, que a sensibilidade à HR elevada durante a produção está relacionada com uma menor capacidade de resposta dos estomas (i.e. dependente da fisiologia estomática), enquanto que a morfologia dos mesmos é aparentemente pouco relevante.