BIOSTIMOLANTI E PRODOTTI FITOSANITARI PER I SISTEMI DI TAPPETI ERBOSI: TENDENZE D'USO ATTUALI E FUTURE

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.

Sintesi: gestiti correttamente, i sistemi di tappeti erbosi possono essere un'enorme risorsa ambientale. Un manto erboso denso e sano offre numerosi vantaggi estetici, ricreativi e ambientali, in particolare il mantenimento del suolo urbano e il filtraggio dei contaminanti dal deflusso delle acque urbane. Tuttavia, si tratta di sistemi vegetali perenni che richiedono un certo livello di apporti nutrizionali e idrici per mantenere il vigore e la persistenza. Se l'obiettivo è quello di gestirle in modo più sostenibile con meno input tradizionali e di renderle più resistenti agli stress ambientali, i biostimolanti e altri prodotti fitosanitari sono strumenti per raggiungere questo obiettivo. La ricerca sugli effetti dei biostimolanti sui tappeti erbosi consente di progredire verso approcci più sostenibili alla nutrizione dei tappeti erbosi. Gli aspetti organici della fisiologia dei tappeti erbosi sono importanti quanto gli aspetti minerali per una corretta nutrizione delle piante. La differenza di contenuto minerale tra piante della stessa cultivar con risposte di crescita diverse è relativamente piccola. Inoltre, la nutrizione minerale è scarsamente correlata alla tolleranza agli stress. Tuttavia, conoscere l'impatto che i materiali biologicamente attivi hanno sul metabolismo dei tappeti erbosi consente ai gestori dei tappeti erbosi di condizionarli meglio per tollerare gli stress ambientali. La comprensione delle funzioni dei minerali e degli effetti metabolici consentirà di migliorare le migliori pratiche di gestione nutrizionale per mitigare numerosi stress del tappeto erboso. L'utilizzo di queste conoscenze fornisce un ulteriore strumento per produrre tappeti erbosi di alta qualità e resilienti anche quando vengono coltivati in ambienti avversi".
Con l'attenzione e il controllo sempre maggiore sugli apporti nutritivi e idrici per la gestione dei tappeti erbosi, abbinati a stress talvolta gravi come la siccità prolungata dovuta a condizioni climatiche sempre più imprevedibili, l'applicazione di biostimolanti ad aree che tradizionalmente hanno ricevuto meno attenzione, come i prati, potrebbe diventare una pratica più diffusa. Indipendentemente dal prodotto o dal programma di biostimolanti e fitosanitari, è importante sottolineare che i biostimolanti non sostituiscono un valido programma di nutrizione minerale delle piante. Inoltre, se l'obiettivo è quello di incorporare i biostimolanti come parte di un programma olistico per la salute delle piante, la ricerca nei sistemi di tappeti erbosi ha dimostrato che devono essere applicati in anticipo rispetto agli stress ambientali, ecc. per ottimizzare i loro benefici. In questo settore si profilano innovazioni interessanti e gli sforzi basati sull'evidenza apriranno la strada a una migliore comprensione del modo in cui questi materiali contribuiscono a mantenere e migliorare la salute delle piante.