We evaluated lignin profiles and pulping performances of 2-yearold transgenic poplar (Populus tremula ؋ Populus alba) lines severely altered in the expression of caffeic acid/5-hydroxyferulic acid O-methyltransferase (COMT) or cinnamyl alcohol dehydrogenase (CAD). Transgenic poplars with CAD or COMT antisense constructs showed growth similar to control trees. CAD downregulated poplars displayed a red coloration mainly in the outer xylem. A 90% lower COMT activity did not change lignin content but dramatically increased the frequency of guaiacyl units and resistant biphenyl linkages in lignin. This alteration severely lowered the efficiency of kraft pulping. The Klason lignin level of CAD-transformed poplars was slightly lower than that of the control. Whereas CAD down-regulation did not change the frequency of labile ether bonds or guaiacyl units in lignin, it increased the proportion of syringaldehyde and diarylpropane structures and, more importantly with regard to kraft pulping, of free phenolic groups in lignin. In the most depressed line, ASCAD21, a substantially higher content in free phenolic units facilitated lignin solubilization and fragmentation during kraft pulping. These results point the way to genetic modification of lignin structure to improve wood quality for the pulp industry.

Selecting for improved growth in drought-prone environments may lead to a trade-off between traits related to both growth and drought resistance. This paper provides a review of the use of physiological traits in breeding for yield improvement in water-limited environments. Plant responses to water stress can be grouped into strategies, which are species-specific. Once a species drought resistance strategy is known, several physiological traits can be selected to be used in the species breeding program. Despite there are multiple physiological traits involved in plant responses to drought, only a few of them have been actually used to improve both growth and drought resistance. This review highlights the relevance of stomatal conductance and water-use efficiency as well as hydraulic traits in breeding for improved growth in drought-prone environments. It is illustrated with unpublished results obtained in several research programmes that share a common objective: improving Eucalyptus globulus growth and survival in south-western Spain throughout early selection based on morpho-physiological traits.Key words: Drought tolerance strategies, stomatal conductance, water use efficiency, hydraulic conductivity, xylem vulnerability, Tasmanian blue gum. ResumenUtilización de parámetros fisiológicos en programas de mejora del crecimiento bajo déficit hídrico La selección de genotipos con el objetivo de mejorar el crecimiento bajo suministro hídrico limitante exige buscar un equilibrio entre aquellos caracteres que permiten optimizar el crecimiento y los que confieren mayor resistencia a la sequía. En el presente artículo se realiza una revisión del uso de parámetros fisiológicos en programas de mejora establecidos para zonas donde el agua es factor limitante. Las plantas muestran un amplio abanico de respuestas frente al déficit hídrico, que se pueden agrupar en estrategias. Una vez conocida la estrategia de respuesta al estrés hídrico en una especie, se puede abordar la selección parámetros fisiológicos a utilizar como herramientas de mejora. Entre estos parámetros destacan por su interés la conductancia estomática, la eficiencia en el uso del agua y parámetros hidráulicos. La revisión del uso de estos parámetros se ha ilustrado con datos bibliográficos y datos obtenidos en el marco de varios proyectos de investigación, establecidos con un objetivo primordial: mejorar la productividad de las plantaciones de Eucalyptus globulus en el suroeste español, mediante programas de mejora que incorporen criterios de selección precoz basados en parámetros morfo-fisiológicos.Palabras clave: Estrategias de tolerancia a la sequía, conductancia estomática, eficiencia en el uso del agua, conductividad hidráulica, vulnerabilidad a la cavitación, eucalipto.

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& Key message Pinus pinaster Ait. susceptibility to pinewood nematode significantly differed among provenances, and the two Atlantic provenances of the Iberian Peninsula being the most affected. However, significant provenance × environment interaction was found. Provenance susceptibility was related to basal diameter, number of branches and oleoresin flow, and some climatic parameters. & Context The pinewood nematode Bursaphelenchus xylophilus, native to North America, is an important pest affecting pine forests throughout Eurasia. In Europe, it has been detected in Portugal and Spain and is primarily associated with Pinus pinaster, an important Mediterranean tree species. & Aims We have investigated the differences in susceptibility among several P. pinaster provenances in the Iberian Peninsula and France, as well as their relationship to certain growth traits and physiological parameters. & Methods Three independent inoculation tests were performed on 3 to 4-year-old trees, followed by assessment of growth traits and physiological variables, along with time course destructive sampling for nematode quantification. & Results The results showed significant differences among provenances for almost all growth traits, wilting, and mortality, though a significant provenance × environment interaction was also detected. Two Atlantic provenances, Noroeste-Litoral and Leiria, displayed the largest susceptibility to pinewood nematode. Changes in susceptibility to B. xylophilus between experiments were influenced by temperature and seasonality. Autumn precipitation and mean maximum temperature during summer at the original provenance sites could be related to provenance susceptibility. & Conclusion Noroeste-Litoral and Leiria were the most disease-affected provenances. This study emphasizes the need for further research on how tree growth stage influences susceptibility and on the possibility of cross-breeding among provenances.