Wheat (Triticum aestivum L.) grain yield response to plant density is inconsistent, and the mechanisms driving this response are unclear. A better understanding of the factors governing this relationship could improve plant density recommendations according to specific environmental and genetics characteristics. Therefore, the aims of this paper were to: i) execute a synthesis-analysis of existing literature related to yield-plant density relationship to provide an indication of the need for different agronomic optimum plant density (AOPD) in different yield environments (YEs), and ii) explore a data set of field research studies conducted in Kansas (USA) on yield response to plant density to determine the AOPD at different YEs, evaluate the effect of tillering potential (TP) on the AOPD, and explain changes in AOPD via variations in wheat yield components. Major findings of this study are: i) the synthesis-analysis portrayed new insights of differences in AOPD at varying YEs, reducing the AOPD as the attainable yield increases (with AOPD moving from 397 pl m -2 for the low YE to 191 pl m -2 for the high YE); ii) the field dataset confirmed the trend observed in the synthesis-analysis but expanded on the physiological mechanisms underpinning the yield response to plant density for wheat, mainly highlighting the following points: a) high TP reduces the AOPD mainly in high and low YEs, b) at canopy-scale, both final number of heads and kernels per square meter were the main factors improving yield response to plant density under high TP, c) under varying YEs, at per-plant-scale, a compensation between heads per plant and kernels per head was the main factor contributing to yield with different TP.

No abstract

No abstract

Recycling of carbon (C) and nitrogen (N) from plants into soils is decisive for maintaining soil organic matter and soil fertility. Therefore, we quantified plant biomass and C and N in the shoots and roots from the topsoil layer for a wide range of annual crops grown under subtropical conditions. We grew 26 species, 13 main crops, and 13 cover crops, in the field in standard sowing arrangements. Root biomass was recovered from the 0.00-0.20 m soil layer at flowering, and shoot biomass was measured at flowering for all crops and at maturity only for the main crops. Root dry matter (DM) exhibited an average of 14.9 ± 5.7 % of the total shoot biomass at flowering, and the mean shoot DM to root DM ratio was 6.9 (2.8-15.0) for the 26 crops considered. Leguminous species had less root DM (0.5 to 1.0 Mg ha-1) than grass species (1.1 to 2.3 Mg ha-1). The shoot C to root C ratio varied consistently with DM, while the root N to shoot N ratio varied considerably among species. Proportionally more biomass, C, and N was allocated to the root systems of grasses (Poaceae species) than non-grass species (especially Fabaceae species). The findings of this study contribute to designing rotations to include species that promote cycling of N and have high potential for adding C to the soil through roots. In this sense, the use of intercropped grasses and legumes is a promising strategy, especially for cover crops.

The lack of hygiene and sanitation practices and insufficient infrastructure in Cambodian informal markets may increase the risk of food contamination, specifically raw vegetables, which in turn may increase the chances of contracting a foodborne disease. The aims of this study were i) to quantify the prevalence of Salmonella enterica based upon seasonal differences (rainy and dry) between surface types (food contact surface [FCS] and non-food contact surface [NFCS]) and between location of vendors within the market (inside and outside), and ii) to characterize Salmonella enterica serotypes abundance in informal markets in Cambodia. A total of 310 samples were screened for Salmonella enterica prevalence following the U.S. Department of Agriculture guidelines and confirmed by PCR. Whole Genome Sequencing was performed and the serotype for each isolate was determined in-silico using SeqSero 1.0 on draft genomes. A total of 78 samples were confirmed positive for Salmonella enterica . During the dry season, Salmonella enterica was more prevalent on FCS compared to NFCS (estimated probability of detection [confidence interval]: 0.41 [0.25,0.59] and 0.17 [0.08, 0.32], respectively; P=0.002), though no differences were apparent during the rainy season. Further, there was no evidence of any differences in Salmonella enterica prevalence based on location within the market (P=0.61). Sixteen Salmonella enterica serotypes were detected across multiple surfaces. The most common serotypes were Rissen (n=18), Hvittingfoss (n=11), Corvallis (n=10), Krefeld (n=8), Weltevreden (n=6), and Altona (n=6). The availability of accurate data on the prevalence of Salmonella enterica in informal markets is crucial for the development of effective surveillance and implementation of suitable intervention strategies at the domestic level, thus preventing future foodborne illness.