BIOESTIMULANTES Y PRODUCTOS FITOSANITARIOS PARA SISTEMAS DE CÉSPED: TENDENCIAS DE USO ACTUALES Y FUTURAS

What are Biostimulants? In the purest sense the word, a biostimulant can be defined as any material when applied to a plant that stimulates “life” (e.g. bio). Numerous materials fall this simple definition and it could even be argued that applying water to a plant is one example of a biostimulant since it “promotes life”. Research and use of plant biostimulants in turf systems is nothing new and work has been ongoing for over three decades. An early pioneer in biostimulant research was Dr. Richard E. Schmidt from Virginia Tech. His program pioneered many basic and applied aspects of biostimulants for many plants. A great deal of that research focused on exogenous applications of various natural and synthetic plant hormones with the intent of helping to optimize rooting (Liu et al. 1998), superior tolerance to soil-borne pests like nematodes (Sun et al., 1997), mitigate the effects of stresses like intense ultra-violet light (Schmidt and Zhang, 2001), heat-drought (Wang et al., 2012, 2013, 2014; Zhang and Schmidt, 1999,2000; Zhang et al., 2012,2013), salinity (Yan, 1993; Nabati et al. 1994), improving winter survival (Schmidt and Chalmers. 1993; Zhang et al., 2013), optimizing nutritional efficiency (Schmidt et al., 1999; Wang et al., 2011), or enhancing recovery from routine stressful mechanical cultural management practices (Bigelow et al., 2010).
Dr. Schmidt and with Dr. Xunzhong Zhang coined an initial operating definition for describing these various plant growth substances they were exploring that promoted plant growth without being nutrients, soil improvers or pesticides. They defined biostimulants as “materials that, in minute quantities, promote plant growth”. The use of the word minute in this definition was important and intended to differentiate the fact that these substances compared to traditional nutrients and/or soil amendments elicited a measurable and beneficial response at much lower application rates. They explained the plant biostimulation by way of hormonal effects and often plant protection against abiotic stress through various antioxidant production. Later, the term “metabolic enhancers” was also used but the important aspect was that something positive was happening to the plant beyond what mineral nutrition supplied.
More recently, the definition of biostimulants has been continually refined. In 2015, Patrick duJardin published the paper, “Plant biostimulants: Definition, concept, main categories and regulation”. In this article a plant biostimulant is defined as “any substance or microorganism applied to plants with the aim to enhance nutritional efficiency, abiotic stress tolerance and/or crop quality traits, regardless of its nutrient content.” The main categories of biostimulants proposed were: Humic and fulvic acids, protein hydrolysates and other N-containing compounds, seaweed extracts and botanicals, chitosan and other biopolymers, inorganic compounds, beneficial fungi and bacteria. These categories were important to define not only traditional biostimulants but also including the beneficial organisms that may elicit a positive plant health response while also helping to guide policymakers who might want to regulate these materials.
In the turf market segment, particularly in the USA, research into the biostimulant was continued at a high level by Drs. Ervin and Zhang who explored numerous aspects of biostimulant materials and their effect on turf physiology from the 2000’s to present. These projects included previously explored materials while including an expanded view of how various synthetic, non-mineral nutritional materials might also promote growth. It was postulated that these materials when applied in conjunction to the naturally biostimulants may produce additive and/or synergistic effect on turf plant growth. In addition to the categories named previously, Ervin (2013) described and suggested mechanisms for a wider range of additional products and chemistries commonly being applied to turf. For example, secondary plant hormones (e.g. salicylic acid) which can induce systemic acquired resistance (SAR) in response to plant pathogens (e.g. fungi, bacteria, insects, nematodes), similarly compounds like phosphites (PO3) that may stimulate phytoalexins (stress induced antimicrobial compounds) for health/diseases suppression. Additional products that could protect tissues from ultra-violet light injury like green pigments or compounds containing titanium dioxide and zinc oxide. Acibenzolar, which mimics salicylic acid effects to induce SAR. Synthetic fungicides like propiconazole had been previously explored by Dr. Schmidt with positive plant responses, but newer chemistries like pyraclostrobin was shown in a number of University research trials to slow down plant respiration and boost antioxidants under heat and drought stress. One interesting find was that pyraclostrobin naturally degrades to the amino acid tryptophan which is a precursor to the plant rooting hormone auxin. Amino acids like proline and glycine-betaine are often suggested for use as osmoregulators or dehydration avoidance compounds. The practice of supplementing amino acids via foliar applications in summer months is a long-standing suggested approach to improve plant health that might be experiencing energy depletion during stressful environmental conditions (e.g. the aim of mitigating seasonal summer decline for cool-season grasses). Lastly, the long standing well researched biostimulants like humic substances, auxin, seaweed and cytokinins are listed. A large fraction of biostimulant products marketed to the turf industry contain seaweed extract (SWE), or seaplant/kelp extract. SWE is naturally high in cytokinin (Crouch and VanStaden, 1993) and research by Schmidt, Ervin and Zhang has shown that SWE was similar to a synthetic cytokinin applications and that monthly application of SWE boosted antioxidant levels, less loss of root viability and improved heat/drought tolerance. Further, Ervin and Zhang showed that combining HA + SWE can provide better plant health during stressful conditions than using either alone. The turf industry contains a vast array of products that claim positive plant or soil health benefits, particularly under stress conditions. Choosing the right material for the intended specific plant benefit is truly important.

Resumen: Gestionados correctamente, los sistemas de césped pueden ser un enorme activo medioambiental. Un césped denso y sano ofrece numerosas ventajas estéticas, recreativas y medioambientales, entre las que destacan la retención del suelo urbano y el filtrado de los contaminantes de las aguas de escorrentía. Sin embargo, se trata de sistemas vegetales perennes que requieren un cierto nivel de aportes nutricionales e hídricos para mantener su vigor y persistir. Si el objetivo es gestionarlas de forma más sostenible con menos insumos tradicionales y hacerlas más resistentes a las tensiones ambientales, los bioestimulantes y otros productos fitosanitarios son herramientas para alcanzar esta meta. La investigación de los efectos de los bioestimulantes en los céspedes permite avanzar hacia enfoques más sostenibles de la nutrición de los céspedes. Los aspectos orgánicos de la fisiología del césped son tan importantes como los aspectos minerales en la nutrición adecuada de las plantas. La diferencia en el contenido mineral entre plantas del mismo cultivar con diferentes respuestas de crecimiento es relativamente pequeña. Además, la nutrición mineral está poco correlacionada con la tolerancia al estrés. Sin embargo, conocer el impacto que los materiales biológicamente activos tienen en el metabolismo del césped permite a los gestores del césped acondicionarlo mejor para tolerar el estrés ambiental. El conocimiento de las funciones minerales y de los efectos metabólicos permitirá mejorar las mejores prácticas de gestión nutricional para mitigar numerosos estreses del césped. El uso de este conocimiento proporciona una herramienta adicional para producir césped de alta calidad y resistente cuando se cultiva en entornos adversos".
Con la atención y el escrutinio cada vez mayores sobre los aportes de nutrientes y agua para la gestión, junto con el estrés a veces severo del césped como la sequía prolongada debido a las condiciones climáticas cada vez más impredecibles, la aplicación de bioestimulantes a las áreas que tradicionalmente han recibido menos atención como el césped puede convertirse en una corriente más principal. Independientemente del producto o programa bioestimulante o fitosanitario, es importante señalar que los bioestimulantes no sustituyen a un buen programa de nutrición mineral de las plantas. Además, si el objetivo es incorporar bioestimulantes como parte de un programa holístico de sanidad vegetal, la investigación en sistemas de césped ha demostrado que deben aplicarse con antelación al estrés medioambiental, etc. para optimizar sus beneficios. Se avecinan innovaciones apasionantes en este ámbito y los esfuerzos basados en pruebas marcarán el camino hacia una mejor comprensión de cómo estos materiales ayudarán a mantener y mejorar la salud de las plantas.