Abstract
Soybean cyst nematode (SCN), Heterodera glycines, is one of the most destructive soybean pests worldwide. Unlike many diseases, SCN doesn't show above ground evidence of disease until several weeks after infestation. Knowledge of Volatile Organic Compounds (VOCs) related to pests and pathogens of foliar tissue is extensive, however, information related to above ground VOCs in response to root damage is lacking. In temporal studies, gas chromatography-mass spectrometry analysis of VOCs from the foliar tissues of SCN infested plants yielded 107 VOCs, referred to as Common Plant Volatiles (CPVs), 33 with confirmed identities. Plants showed no significant stunting until 10 days after infestation. Total CPVs increased over time and were significantly higher from SCN infested plants compared to mock infested plants post 7 days after infestation (DAI). Hierarchical clustering analysis of expression ratios (SCN: Mock) across all time points revealed 5 groups, with the largest group containing VOCs elevated in response to SCN infestation. Linear projection of Principal Component Analysis clearly separated SCN infested from mock infested plants at time points 5, 7, 10 and 14 DAI. Elevated Styrene (CPV11), D-Limonene (CPV32), Tetradecane (CPV65), 2,6-Di-T-butyl-4-methylene-2,5-cyclohexadiene-1-one (CPV74), Butylated Hydroxytoluene (CPV76) and suppressed Ethylhexyl benzoate (CPV87) levels, were associated with SCN infestation prior to stunting. Our findings demonstrate that SCN infestation elevates the release of certain VOCs from foliage and that some are evident prior to symptom development. VOCs associated with SCN infestations prior to symptom development may be valuable for innovative diagnostic approaches.
Highlights
As one of the major nutritional foods in human diets that provides high quality proteins and oil, soybeans are one of the most economically important agricultural crops globally (Whitham et al, 2016; Liu et al, 2020)
Our work reveals that infestation of soybean roots with Soybean cyst nematode (SCN) results in the elevated release of Volatile Organic Compounds (VOCs) from foliar tissues and that this rise occurs prior to symptom appearance (Figures 3, 4)
One such example is the herbivory of Brassica nigra roots by Delia radicum which affects the behavior of Cotesia glomerata, a parasitoid of the leaf herbivore Pieris brassicae through alteration of the VOC bouquet
Summary
As one of the major nutritional foods in human diets that provides high quality proteins and oil, soybeans are one of the most economically important agricultural crops globally (Whitham et al, 2016; Liu et al, 2020). H. glycines commonly referred to as the soybean cyst nematode (SCN) is responsible for SCN VOCs causing upwards of $1.2 billion of yield loss each year in the USA (Davis et al, 2004). The extensive root damage leads to the aboveground symptoms of plant stunting and yellowing These aboveground indicators are difficult to visualize until late infestation and there has been extensive root damage leading to significant yield loss (Niblack et al, 2006). SCN has been managed through a combination of nematicides, SCN-resistant soybean varieties, and crop rotation (Niblack, 2005). Some of these current practices are losing their effectiveness or being phased out. The detection of SCN prior to symptom development would likely be of practical value
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