Plant-parasitic nematodes represent a substantial constraint on global food security by reducing the yield potential of all major crops, including soybean (Glycine max L.). The soybean cyst nematode (SCN) (Heterodera glycines I.) is widely distributed across all soybean production areas of the US, and is the major yield-limiting factor, especially in the Midwestern US. Double cropping (DC) is defined as producing more than one crop on the same parcel of land in a single growing season. Compared to conventional single annual crops, DC provides many advantages, including improving soil health, enhanced nutrient provisioning to plants, improvement of soil physical properties, control of erosion, decrease in tillage requirements, and enhanced profitability. In some double-cropping systems, soybean is planted following winter wheat (Triticum aestivum L.), and several reports suggest the potential of wheat to suppress SCN populations. Field trials were conducted from 2017 to 2018 to investigate the effect of wheat on SCN populations in double-cropping soybean. Nine fields with three levels of initial SCN populations (low, moderate, and high) were selected in Illinois. Wheat was planted in strips alternating with strips-maintained weed-free and under fallow over winter and early spring. Soybean was planted in all strips after the wheat harvest. Soybean cyst nematode egg densities were acquired at four time points: wheat establishment, post-wheat/pre-soybean, mid-soybean (R1 growth stage or beginning of flowering), and post-soybean harvest. Wheat strips reduced SCN egg densities compared with fallow strips at the R1 stage (−31.8%) and after soybean harvest (−32.7%). Field locations with noted SCN suppression were selected for a metagenomics study. The structure of fungal communities differed significantly between DC and fallow plots at soybean planting and after harvest (P<0.001). Fungal populations were affected by location at all sampling times and by treatments before planting and after soybean harvest. Several enriched fungal and bacterial taxa in wheat plots, including Mortierella, Exophiala, Conocybe, Rhizobacter spp., and others, were previously reported to parasitize SCN and other plant-parasitic nematodes. Knowing that phytocompounds with potential nematicidal activity are released via the root system of plants, we implemented a gas chromatography–mass spectrometry (GC-MS) pipeline to investigate the profile of phytochemicals in soil samples collected from these fields and reviewed the potential nematicidal activity of compounds with higher concentration in double cropping fields. A total of 51 compounds were detected with the GSMS analysis, 8 with unknown identification. Several compounds, including multiple fatty acids, had greater relative peak areas in double-cropping samples compared to fallow. This multi-approach study provides a better understanding of the mechanisms governing wheat's effect on SCN populations. Rather than a single mechanism, the suppression of SCN in soybean fields double-cropped with winter wheat is potentially linked to enriched microbial communities, increased populations of beneficial organisms, and higher concentrations of phytochemicals with nematicidal activity. This is the first study implementing metagenomics and GCMS to characterize soil microbial and chemical profiles in soybean fields double-cropped with winter wheat. Finally, a set of studies were conducted to evaluate the effect of two seed-applied succinate dehydrogenase inhibitors (SDHI) compounds, fluopyram and pydiflumetofen, on SCN population densities, plant injury, and plant growth. Next-generation sequencing was later employed to identify transcriptomic shifts in gene expression profiles of soybean seedlings treated with fluopyram and pydiflumetofen. Fluopyram reduced both SCN egg and cyst counts in comparison to pydiflumetofen and the untreated control. RNA expression patterns of seed treatments clustered by sampling time (5 DAP vs 10 DAP). Multiple DEGs identified in soybean seedlings treated with fluopyram are reported to be linked to systemic resistance, suggesting a role of systemic resistance on the suppression of SCN by fluopyram. The non-target inhibition of soybean succinate dehydrogenase genes by fluopyram may be the origin of the phytotoxicity symptoms observed and potentially the cause of the systemic resistance activation reported in the current study. To our knowledge, this is the first report of systemic resistance being activated by fluopyram in addition to the suppression of soybean succinate dehydrogenase (SDH) and ubiquinone oxidoreductase genes. This work helps to elucidate the mechanisms of suppression of SCN by fluopyram

Forty lines, 20 determinate and 20 indeterminate, from four soybean (Glycine max L. Merrill) crosses were evaluated under full-season and double cropping conditions to compare the performance of the two plant types under both cropping systems. The parents and selected lines were in the range of Maturity Groups IV and V. In 1980, the lines were planted 1 July in a replicated test at Warsaw, VA while in 1981 these lines were planted in three replicated tests on 11 June and 8 July at Warsaw and on 12 June at Orange, VA. Both June plantings were considered full-season. Standard cultivars in 1980 included 'Essex', 'Williams', and 'Crawford'. 'Bay' and 'Will' were added in 1981. Yields were similar in 1980 for both plant types with the determinates yielding 10.1 q/ha and the indeterminates yielding 9.9 q/ha. In 1981, the yields were similar for both types at Orange with the determinates and indeterminates yielding 26.4 and 26.5 respectively. The types were significantly different in the 11 June planting at Warsaw, with yields of 28. 6 and 28. 0 q/ha for the determinate and indeterminate lines, respectively. The opposite was observed for the 8 July planting in which the indeterminates yielded 21.2 q/ha and the determinates yielded 20.8 q/ha. A comparison of the two determinate and indeterminate lines with the highest yields in both 1981 Warsaw plantings showed that indeterminates were more adaptable to double cropping, though high yielding lines of both types were present. The high yielding indeterminates of the 8 July planting had a tendency to be taller and more erect than the determinates, an attribute desirable for double cropping. Lines that were highest yielding in the 11 June planting were ranked lower in the 8 July planting and vice versa. Spearman' s rank correlation for yield in the two Warsaw plantings had a coefficient of 0. 23, indicating a high degree of specific adaptation to the two environments. Selection of better adapted lines for double cropping appears feasible. The indeterminate trait appears to make some contributions to this adaptation. / Ph. D.

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Call number: LD2668 .T4 1985 E39 / Master of Science

Call number: LD2668 .T4 1985 L435 / Master of Science

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.

The 1985 and 1986 Cotton Reports have the same publication and P-Series numbers.