Excessive rainfall provides a favorable condition for field mold infection of plants, which triggers field mold (FM) stress.  If FM stress occurs during the late maturation stage of soybean seed, it negatively affects seed yield and quality.  To investigate the responses of soybean seed against FM stress and identify the underlying biochemical pathways involved, a greenhouse was equipped with an artificial rain producing system to allow the induction of mold growth on soybean seed.  The induced quality changes and stress responses were revealed on the levels of both transcriptome and metabolome.  The results showed that soybean seeds produced under FM stress conditions had an abnormal and inferior appearance, and also contained less storage reserves, such as protein and polysaccharide.  Transcriptional analysis demonstrated that genes involved in amino acid metabolism, glycolysis, tricarboxylic acid, β-oxidation of fatty acids, and isoflavone biosynthesis were induced by FM stress.  These results were supported by a multiple metabolic analysis which exhibited increases in the concentrations of a variety of amino acids, sugars, organic acids, and isoflavones, as well as reductions of several fatty acids.  Reprogramming of these metabolic pathways mobilized and consumed stored protein, sugar and fatty acid reserves in the soybean seed in order to meet the energy and substrate demand on the defense system, but led to deterioration of seed quality.  In general, FM stress induced catabolism of storage reserves and diminished the quality of soybean seed in the field.  This study provides a more profound insight into seed deterioration caused by FM stress.

Soybean is one of the major oil seed crops, which is usually intercropped with other crops to increase soybean production area and yield.  However, soybean is highly sensitive to shading.  It is unclear if soybean morphology responds to shading (i.e., shade tolerance or avoidance) and which features may be suitable as screening materials in relay strip intercropping.  Therefore, in this study, various agronomic characteristics of different soybean genotypes were analyzed under relay intercropping conditions.  The soybean materials used in this study exhibited genetic diversity, and the coefficient of variations of the agronomic parameters ranged from 13.84 to 72.08% during the shade period and from 6.44 to 52.49% during the maturity period.  The ratios of shading to full irradiance in stem mass fraction (SMF) were almost greater than 1, whereas opposite results were found in the leaves.  Compared with full irradiance, the average stem length (SL), leaf area ratio (LAR) and specific leaf area (SLA) for the two years (2013 and 2014) increased by 0.78, 0.47 and 0.65 under shady conditions, respectively.  However, the stem diameter (SD), total biomass (TB), leaf area (LA), number of nodes (NN) on the main stem, and number of branches (BN) all decreased.  During the shady period, the SL and SMF exhibited a significant negative correlation with yield, and the SD exhibited a significant positive correlation with yield.  The correlation between the soybean yield and agronomic parameters during the mature period, except for SL, the first pod height (FPH), 100-seed weight (100-SW), and reproductive growth period (RGP), were significant (P<0.01), especially for seed weight per branch (SWB), pods per plant (PP), BN, and vegetative growth period (VGP).  These results provide an insight into screening the shade tolerance of soybean varieties and can be useful in targeted breeding programs of relay intercropped soybeans.