Biofertilization with Macrocystis pyrifera algae extracts combined with PGPR-enhanced growth in Lactuca sativa seedlings
To improve crop yields the application of fertilizers to provide nutrients to soils is recommended. An alternative option to substitute nutritional supplements of chemical origin is the use of biofertilizers. This study evaluated the effectiveness of a biofertilizer of natural origin, Macrocystis pyrifera algal extracts and its combination with the plant growth–promoting bacterium Azospirillum brasilense, on the germination and establishment of lettuce seedlings (Lactuca sativa) under two different water irrigation treatments. Results demonstrated that germination energy and germination power improved upon inoculation of lettuce seeds with the seaweed extract. After 7 days of culture, seedlings showed increased root growth which would help to ensure their establishment. The application of bacteria and algae individually or in combination exerted a positive effect on lettuce plant growth compared with controls (without applications). In addition, treatments with the brown seaweed extract favoured seedlings adaptation to an unfavourable environment (water deficit) by increasing their root mass and protecting them from the negative effects imposed by stress. These results suggest that the use of M. pyrifera extract to improve plant growth and to provide stress protection may be considered an interesting tool for agricultural purposes. Nevertheless, when A. brasilense (whose plant growth–promoting properties are largely known) is combined with the brown seaweed extract, a new biofertilizing formula is obtained and proposed for future seed inoculation technology, based on the promising effects observed in this work.