Chitin and Laminarin Trigger Plant Defense Responses Against Soybean Rust Caused by Phakopsora pachyrhizi

Soybean (Glycine max) is one of the most economically important crops in the world. Production of soybean can be severely impacted by many diseases, including soybean rust. Elicitor treatments have been utilized to enhance plant resistance against multiple diseases. To investigate whether elicitor treatment can induce soybean resistance, pilot experiments were conducted to test the effects of elicitors (chitin, laminarin, and co-treated with both) on the reactive oxygen species (ROS) burst in five soybean genotypes. We discovered that all elicitor treatments induced an ROS burst with different levels. The expression of several plant defense genes was upregulated in soybean Williams 82 following elicitor treatments. GmCERK1, GmRbohD, GmPR1, GmPR2, GmPAL, and GmCHS exhibited the highest expression at 3 h post-elicitor treatments. Interestingly, co-treatment with chitin and laminarian significantly enhanced the expression of GmPAL and GmCHS. Soybean rust severity was evaluated on plants with elicitor treatment prior to Phakopsora pachyrhizi inoculation. A 5-point scale, with 5 as the highest, was used. With chitin treatment, the severities were reduced to 2.0 and 1.9 in Williams 82 and PI 200526, respectively. Controls without elicitor treatments had severities of 4.2 and 3.8, which were significantly (P < 0.001) higher than the severities in the genotypes with elicitor treatments. To the best of our knowledge, this is the first demonstration of the effects of elicitors chitin and laminarin on inducing resistance in soybean against P. pachyrhizi infection. The information from this research will be useful for development of an alternative method to control soybean rust or other diseases in crops.