Andrés Alberto Rodríguez

Stress caused by suboptimal temperatures (ST) represents a stress that limits growth in all grasses without inhibiting their activity and induces alterations in photosynthetic performance. We evaluated the responses of photosynthetic parameters and leaf elongation between two groups of grass genotypes with different levels of tolerance to ST, belonging to phylogenetically distant species. Responses to ST depended on the type of parameter and on the genotypic group. Leaf elongation traits showed discriminatory power, especially the area under the leaf elongation curve, which integrated the early and transient effects of stress over time. The photosynthetic parameter PI_ABS showed lower discriminatory power compared with the area under the leaf elongation curve. However, a deeper analysis of other photosynthetic parameters revealed an increase in energetic connectivity between Photosystem II centers in tolerant, but not in sensitive, genotypes. A subsequent analysis of leaf and cellular parameters of early leaf elongation dynamics indicated that ST reduced meristematic activity in all genotypes, but the tolerant genotype group maintained a greater accumulation of mature cells compared with the sensitive genotype group. Overall, the results suggested a response to ST in tolerant genotypes, but not in sensitive genotypes, related to the early dynamics of leaf and cellular growth parameters to partially compensate for the restrictive effect of ST on leaf elongation not recorded. In parallel, they also indicated a response of the tolerant genotypes to ST in terms of photosynthetic parameters, probably as a pathway to maintain cellular homeostasis, to prevent photooxidative damage in PSII under stress. However, the relationship between both responses does not appear to be strictly linear, but rather would be mediated by coordinated adjustments in the temporal dynamics of growth, suggesting a functional integration between photosynthetic performance and the cellular mechanisms that regulate leaf expansion under ST stress.

Previous studies in the Salado River Basin (Argentina) demonstrated that the introduced forage species, Lotus tenuis Waldst. & Kit. ex Wild. (Fabaceae), possesses high tolerance to abiotic stresses—including flooding, alkalinity, salinity, and drought. The efficient biological fixation of nitrogen in a region with a scarce presence of native legumes is one of its advantages. Despite these qualities, a year-long characterization of cell wall (CW) polysaccharides in Lotus tenuis and their relationship with the high nutritional quality is missing. In this study, seasonal parametric investigations of L. tenuis, regarding its photosynthetic and ionic status, modifications in CW composition, and concomitant nutritional quality, were performed. Our results demonstrate the high plant digestibility and protein content of this legume, even in summer, when most accompanying species reduce their forage quality. Regarding gas production kinetics (in vitro production is a proxy for the animal rumen’s output), spring biomass had the highest values. The CW material yields are similar throughout the year, but with differences in polysaccharide composition. In summer and winter, pectins predominate, while in the regrowth periods (spring and autumn), pectins and β-glucans are found in similar amounts. This work confirms that Lotus tenuis can help optimize grassland productivity in challenging mesophytic terrains to increase livestock productivity through environmentally friendly services.

In this study, the first aim was to develop a rapid and non‐destructive method for analysing rice genotypes' tolerance to low temperatures (LT) during the seedling stage. Using a growth parameter and a physiological parameter, a discriminant formula was developed to differentiate between tolerant and sensitive genotypes based on their LT tolerance score. The study identified several benefits of the discriminant formula, including its low classification error rate, scalability, and ability to be used in controlled and reduced environments. Additionally, a second study was conducted, which found a strong correlation between the LT tolerance score during the seedling stage and plant yield at the ripening stage in plants grown under field LT during the vegetative stage. Panicle weight was the main mediator of the effect of the LT tolerance score on plant yield, but the number of panicles per plant also played a role. Overall, the results suggest that the LT tolerance score can serve as an indirect selection factor for plants for both LT tolerance and plant yield. This is especially relevant for rice‐growing regions with temperate climates and LT at the beginning of the cultivation season.

The first rice phenological stages are commonly subjected to low temperatures (LT) in temperate crop areas. Here, plants of rice genotypes were analyzed according to their LT tolerance at seedling stage, using a realistic experimental temperatures range, and measuring quantitative and operator-independent parameters, fast-obtainable by non-invasive techniques. The ratios between values of these parameters determined in plants under LT condition with respect to the control condition were statistically analyzed. We have found a discriminant formula based on two parameters that allowed to differentiate between genotypes previously described as tolerant and sensitive to LT, with a very low general classification error. The application of the discriminant formula to score plants under LT, using all genotypes from the Rice Diversity Panel 1 which comprehensively represents the genetic variability of the O. sativa species, resulted in LT tolerance levels of its subspecies and subpopulations consistent with previous reports. In turn, a strong association between the LT tolerance score at the seedling stage and the panicle weight in plants under field LT during the vegetative stage, suggested that this scoring could be used as an indirect selection factor of genotypes with good yield traits and suited to LT prone environments.

The effective increase of the rice breeding process for grain yield could be sustained by developing efficient tools to accelerate plant selection through the rapid determination of reliable predictors. Here, we have described different associations between grain yield and photosynthetic parameters simply and fast obtainable by a non-invasive technique in flag leaf during the anthesis stage. Among the analyzed photosynthetic parameters, the photosynthetic performance index (PI _ABS ) stood out for its strong association with grain yield. A genome-wide association analysis determined in plants from a rice diversity panel at tillering stage indicated the presence of a quantitative trait locus on chromosome 9 characterized by a set of candidate chloroplastic genes with contrasting haplotypes for PI _ABS . An analysis of these haplotypes indicated a separation into two groups. One with haplotypes linked to high values of PI _ABS , which were associated almost exclusively with Japonica spp. subpopulations, and another with haplotypes linked to low values of PI _ABS , which were associated exclusively with Indica spp. subpopulations. Genotypes of the Japonica spp. subpopulations showed high values in panicle weight, a yield components parameter, compared with the Indica spp. subpopulations genotypes. The results of this work suggested that PI _ABS could be an early predictor of grain yield at the tillering stage in rice breeding processes.

El arroz (Oryza sativa L.) es uno de los cereales de mayor importancia económica debido a que provee alimento a más de la mitad de la población mundial. El mejoramiento de este cultivo mediante ingeniería genética requiere poner a punto procesos como el cultivo de tejidos y la transformación. En este trabajo se optimizaron los métodos de cultivo in vitro y transformación de la variedad local de alto rendimiento Don Justo FCAyF. Con respecto al cultivo de tejidos se determinó que la concentración óptima de 2,4D para la callogénesis fue de 3 mg.l^-1 con un 42%. La regeneración de parte aérea mostró un 77% de eficiencia con una combinación de 4 mg.l^-1 BAP y 0,8 mg.l^-1 ANA. En relación a la transformación mediante Agrobacterium tumefaciens se obtuvieron diferentes porcentajes de eficiencia dependiendo del plásmido utilizado para transformar como también del explanto. En el caso de la transformación in vitro de callos embriogénicos se obtuvieron valores entre 14-29% dependiendo del plásmido. Mientras que el método in planta de transformación de embriones presentó una eficiencia entre 3-28%. En conclusión, en este trabajo se puso a punto los métodos de cultivo y transformación de una variedad local de arroz que facilitará el mejoramiento genético de la misma mediante distintas técnicas como transgénesis convencional o edición génica.