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Robert Savé, Josep Peñuelas, Oriol Marfà, and Lydia Serrano

Field-grown strawberry (Fragaria × annanasa Duch. cv. Chandler) plants were subjected to two irrigation regimes from Nov. 1989 to July 1990 to evaluate the physiological and morphological effects of mild water stress. Irrigation was applied when soil matric potential reached -10 and-70 kPa for the wet and dry treatments, respectively. During the spring, these regimes did not promote significant changes in plant water relations, transpiration rates, plant morphology, or canopy architecture. However, during the summer, after several stress cycles, significant differences between treatments were observed. Pressure-volume curves of dry-treatment plants indicated that leaf osmotic potentials, measured at full and zero turgor, decreased 0.2 to 0.4 MPa. This decrease in osmotic potential also was accompanied by a 50% increase in the modulus of elasticity for these water-stressed plants compared to well-watered plants. Dry-treatment plants also showed stress avoidance mechanisms in changes of whole-plant morphology and canopy architecture, from monolayer to polylayer leaf distribution and leaf orientation from south to north. Despite what would appear to be useful drought-resistance strategies, there was significantly lower fruit production by plants grown under the dry treatment.

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Javier Polo, Rubén Barroso, Jesús Ródenas, Joaquín Azcón-Bieto, Rafaela Cáceres, and Oriol Marfà

The effects of different kinds of biotic and abiotic stress on crops can be lessened through exogenous application of different biostimulant products. Although some of these products come from enzymatic hydrolysates derived from animal remains, the literature does not contain references to the use of enzymatic hydrolysates obtained from animal hemoglobin, specifically porcine blood. With the aim of evaluating the effectiveness of a product obtained from the enzymatic hydrolysis of porcine hemoglobin (PHH) as a biostimulant that lessens the effects of thermal stress, two experiments were carried out in which lettuce plants (Lactuca sativa) were subjected to short-term episodes of intense cold and heat. After these episodes, different doses of the PHH product were administered into the growing medium. Moreover, in the heat episode experiment, one group of plants was first subjected to a heat episode and then administered a commercial biostimulant with the aim of comparing its efficacy with the PHH product. The biometric measurements carried out on the lettuce plants several days after being subjected to the episodes of cold and heat and then either administered or not administered the indicated treatments show that at the highest tested dose, the PHH product promoted a reaction that lessened the harmful effects caused by the intense cold and heat treatments.