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- 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.
- 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.Breeding for better keeping quality: validation of the selection method of promising genotypes. Water stress is one of the most important postharvest quality problems, resulting in shorter vase life and reduced consumer‟s satisfaction. This problem is enhanced in plants grown at high RH (RH > 85%) due to stomatal malfunctioning leading to shorter postharvest longevity. Previously, a subset of a segregating tetraploid population (60 genotypes) cultivated in a greenhouse under noncontroled RH was characterized for stomatal responsiveness to water stress (i.e. desiccation). The population screening revealed extreme differences of relative water content (RWC) after 4 h leaf desiccation. This study aims at the validation of a selection method for promising genotypes with good stomatal responsiveness to desiccation (i.e. high RWC after 4 h desiccation) when grown under contrasting HR conditions. Therefore, five genotypes with expected good stomatal response to desiccation were selected for this study. These genotypes were grown under moderate RH (60%) and high RH (90%). The RWC was significantly different within the five studied genotypes. K099 was the most tolerant genotype to desiccation, with a RWC after 4 h desiccation 19% higher than the least tolerant genotype. Genotypes cultivated at high RH had on average only 10% lower RWC, as compared to genotypes grown at moderate RH, confirming a good stomatal response. The postharvest longevity varied between 12 (K119) and 25 (K099) days and it was not significantly affected by the two different RH during growth. It is concluded that the analysis of the stomatal responsiveness in leaves of cut roses is an efficient method that allows, in the early stages of the selection process, to identify tolerant genotypes to high RH.