Increasing genotypic productivity in post Green Revolution durum wheat: the case of Spain

[eng] It is of strategic importance for Mediterranean agriculture to develop new varieties of durum wheat with greater production potential, together with a better adaptation to adverse environmental conditions and better quality of grain. While durum wheat, which is the most strategic crop in the south Mediterranean agriculture, has benefited as other cereals of the Green Revolution, genetic progress in recent decades has been less evident, partly masked by climate change, and the underlying physiological mechanisms are not evident. For this propose, the objective is to evaluate whether there have been agronomic and physiological changes associated with the genetic improvement of durum wheat grown in Spain after the Green Revolution and the environmental conditions where breeding gains have been higher. The study was based on a collection of 20 commercial varieties, grown in Spain between the beginning of the 70s of the last centuries and the present. The set was readapted during the last two cropping cycles and increased to a total of 23 cultivars, including more recent cultivars, released during the present decade. Cultivars were compared through consecutive years in wide range growing conditions secured by growing in three different sites differing in latitude and temperature, together with the implementation of support irrigation and different planting times. Changes in the genetic gain of the yield were evaluated between 2014 and 2016. Change in the agronomic and physiological parameters related to the genetic progress was evaluated between 2015- 2016, and the changes caused by the improvement in the adaptation patterns through the study of the genotype by environment (GE) interaction was evaluated between 2017 and 2018. It has been observed that the rate of genetic progress in the yield of durum wheat in Spain after the Green Revolution has been low it was estimated on 24 kg ha-1 y-1 (0.44% y-1 in term of relative gain) between 1980 and 2003 and has even stopped during the last decade until 2010. It was mainly due to increases in the number of kernels per spike (117 kernels m-2 y-1), and spikes per unit area (0.24 kernels spike-1 y-1), while no clear trend in some grain quality traits (TKW and grain N concentration). Moreover, areal biomass at harvest and grain nitrogen yield increased with the year of release of the cultivars for the entire period. In addition, it has been observed that the more productive genotypes were characterized by a plant height of around 85 cm, small erect flag leaves, more open stomata, a better balance between N sources and N sinks and a higher capacity to re-fix CO2 respired by the grain. Moreover, in general the non-laminar parts of the plants play a key role in providing assimilates during grain filling. Also, that the high heritability of most of the studied parameters allows their consideration as traits for phenotyping durum wheat better adapted to a wide range of Mediterranean conditions. On the other hand, an improvement in genetic yield has been reported in warm environments and under optimal water conditions, environments similar to those of from where the germplasm provenance release or origin. The adaptation of semi-dwarf durum in Spain has shown a tendency to specific adaptation rather than large-scale adaptation. Two different patterns of selection have been reported due the G×E interaction and change in the ranking of genotypes: in the high yielding environments, plant favors more water uptake, with more transpiration and more open stomata (more negative value of δ13C, whereas, in low yielding environments, plant close stomata and favors more water use efficiency (positive value of δ13C).[spa] El trigo duro, que es el cultivo más estratégico en la agricultura del sur del Mediterráneo, se ha beneficiado como otros cereales de la Revolución Verde, el progreso genético en las últimas décadas ha sido menos evidente, en parte enmascarado por el cambio climático, y los mecanismos fisiológicos subyacentes no son evidentes. Se ha observado que la tasa de progreso genético en el rendimiento del trigo duro en España después de la Revolución Verde ha sido baja, se estimó en 24 kg ha-1 año-1 entre 1980 y 2003 e incluso se detuvo durante la última década hasta 2010. Se debió principalmente al aumento en el número de granos por espiga, y espigas por unidad de área, aunque no hay una tendencia clara en algunos rasgos de calidad de grano (TKW y concentración de N de grano). Además, la biomasa área en la cosecha y el rendimiento de nitrógeno en grano aumentó con el año de liberación de los cultivares durante todo el período. Además, se ha observado que los genotipos más productivos se caracterizaron por una altura de planta de alrededor de 85 cm, pequeñas hojas de bandera erectas, estomas más abiertos, un mejor equilibrio entre las fuentes de N y los sumideros de N y una mayor capacidad para re-fijar CO2 Respirado por el grano. Además, en general, las partes no laminares de las plantas juegan un papel clave en el suministro de asimilados durante el llenado del grano. Por otro lado, se ha informado una mejora en el rendimiento genético en ambientes cálidos y en condiciones óptimas de agua, ambientes similares a los de donde se origina el germoplasma. La adaptación del durum semi-enano en España ha mostrado una tendencia a la adaptación específica en lugar de la adaptación a gran escala. Se han informado dos patrones diferentes de selección debido a la interacción G × E: en los entornos de alto rendimiento, la planta favorece una mayor absorción de agua, con más transpiración y más estomas abiertos, mientras que, en entornos de bajo rendimiento, planta estomas cercanos y favorece una mayor eficiencia en el uso del agua