Algal compounds exhibit great potential to enhance plant growth and resistance to abiotic and biotic stresses. This review focuses on aspects concerning the physical-chemical properties, function and biological activity of macroalgae polysaccharides. Updated results of the main poly- and oligosaccharides studied for the control of plant diseases are discussed and summarized. The carrageenans from red algae have a well-established obtaining system, but its high market value discourages its use in plant protection. The fucans found in the cell walls of brown algae are present in several fertilizers and accounted for the benefits of such commercial products on plant physiology. The laminarans, from brown algae mainly Laminaria digitata, are currently the main algal polysaccharides on the phytosanitary market. The ulvans, from cell the walls of Ulva spp., open new ways to obtain polysaccharides able to induce resistance due to its abundance worldwide. All these algal polysaccharides show ability to activate multiple plant defense mechanisms against a broad spectrum of plant pathogens. Taking into account the promising results reported in the literature and the enormous biochemical diversity of these biopolymers, it is likely that they will provide new types of resistance inducers in a near future.

O presente trabalho objetivou avaliar a eficácia da ulvana, um polissacarídeo proveniente de alga, em induzir resistência em Phaseolus vulgaris contra Colletotrichum lindemuthianum, quando formulada sozinha ou com caulinita, sílica amorfa ou atapulgita e armazenada por 0, 4, 8 ou 12 meses. Após cada período de armazenamento, as formulações e água (controle) foram aplicadas à folhagem de plantas de feijão (cv. Uirapuru, estádio fenológico V4) aos 6 e 3 dias antes da inoculação com C. lindemuthianum. A severidade da antracnose foi estimada em intervalos de 2 dias, com o aparecimento dos primeiros sintomas até 13 dias após a inoculação. A partir dos dados de severidade calculou-se a Área Abaixo da Curva de Progresso da Doença (AACPD). A aplicação de ulvana (controle) ou de suas formulações com sílica amorfa ou caulinita, promoveu uma redução de cerca de 45% na severidade da antracnose. A eficiência da ulvana em controlar a antracnose foi mantida nas formulações com sílica amorfa ou caulinita, mas não naquela contendo atapulgita, durante o período de 12 meses.

The present work aimed to evaluate the effectiveness of ulvan, an algal polysaccharide, in inducing resistance of Phaseolus vulgaris against Colletotrichum lindemuthianum when formulated alone or with kaolinite, amorphous silica or attapulgite, and stored for 0, 4, 8, or 12 months. Following each storage period, the formulations and a water control were applied to the foliage of bean plants (cv. Uirapuru, growth stage V4) at 6 days, and again at 3 days, before the foliage was inoculated with C. lindemuthianum. Anthracnose severity was estimated at intervals of 2 days, beginning when the first symptoms appeared and continuing until 13 days after inoculation. The severity data were used to calculate values for Area Under the Disease Progress Curve (AUDPC). The application of ulvan (control) or its formulations with amorphous silica or kaolinite reduced anthracnose severity by 45%. The efficiency of ulvan in controlling anthracnose was maintained throughout 12 months of storage when it was formulated with amorphous silica or kaolinite, but not with attapulgite.