LCO Applications Provide Improved Responses with Legumes and Nonlegumes

Abstract

Lipochitooligosaccharides (LCOs), including Nod factors and Myc factors, are signal molecules produced by rhizobia and arbuscular mycorrhizae, respectively, that are essential for plant infection by these symbiotic microorganisms. Basic research has identified the structure of these LCO molecules and the mechanisms by which they bind to specific root hair receptors activating plant genes. A common plant gene pathway for both Nod factors, leading to nodule formation in legumes, and Myc factors, essential for plant root mycorrhization, has been extensively reported. Applied research investigating LCO direct plant growth responses in greenhouse and field trials has been less common and will be reported in this review. Nod factors, combined with the host-specific rhizobium and applied to legume seeds, or in-furrow with seeds at planting, have led to improved seed germination, enhanced lateral root development, and better early season growth, which lead to frequent greater crop yields. The benefits of combining Nod factors with the rhizobial inoculant in field studies have been observed in studies with soybeans (Glycine max (L.) Merrill] and peas (Pisum sativum). Further field studies with LCOs alone, both as a seed treatment and in-furrow, with legumes (soybeans) and nonlegumes [corn (Zea mays L.) and cotton (Gossypium hirsutum)] also frequently demonstrate enhanced growth parameters and yield increases. In addition, foliar applications of LCOs on legumes (soybeans) and nonlegumes (corn) in greenhouse and field trials improved various plant growth parameters, including grain yields. LCO applications with legumes and nonlegumes applied as seed treatments, as in-furrow, and as a foliar spray have provided improved plant growth and yield increases with important agronomic crops in both North American and South American field trials.