Onions

A list of all retail food stores and their postcodes in six council boundaries (Southampton, Eastleigh, Fareham, Gosport, Havant, Portsmouth) within Hampshire, UK, was compiled in July and August 2010. Store information was obtained from council Food Safety Registers and on-line business directories (yellow-pages and yell.com). Between July 2010 and June 2011 trained fieldworkers ‘ground-truthed’ the study area and collected data in 601 of the 606 retail food stores.
A consumer nutrition environment tool was designed to measure nine factors that can affect consumer’s food choices. Data on number of varieties, price, promotion, shelf placement and store placement were collected on seven healthy and five less healthy products. In addition, information on the type of nutrition information and availability of a healthier alternative were collected for less healthy products. The quality of two fruits and four vegetables and opportunity for single sale of the two fruits were also measured. Table 
1 describes the definitions and measurement scales of the variables included in the tool. Information on fruit and vegetable quality was collected using a published quality indicator
[18 (link)]. Data on the remaining variables were collected using novel measures. The tool and survey protocol are available in the Additional file
1. The median time taken to complete the survey across the 601 stores was 11 minutes (IQR: 7, 15).
The 12 food products were: peppers, tomatoes, lettuce, onions, apples, bananas, wholemeal bread, oven chips, sausages, crisps, sugar and white bread. Products were selected because they discriminate between better or poorer dietary patterns, are frequently consumed in England
[27 ] and could be measured in a large survey. The food products selected represent items from short and long food frequency questionnaires (FFQ) used to determine differences in dietary quality among a number of populations including young women, young children and older adults
[28 (link)-31 (link)]. These foods represent the UK Department of Health’s dietary recommendations and foods known to contribute to nutrition-related chronic diseases
[29 (link)].
The level of agreement between fieldworkers was assessed by the Kappa statistic on a sample of 14 stores (large supermarket (n = 2), discount supermarket (n = 1), small supermarket (n = 4), ‘world’ store (n = 1), convenience store (n = 5), petrol store (n = 1)). The relative consistency of price responses was assessed using the coefficient of variation: the standard deviation of difference divided by the mean (%). Cronbach’s alpha was used to assess the internal consistency of all nine components of the healthfulness score.

To visualize nuclei, the epidermis was stained with DAPI (5 µg/mL, sigma, USA). Materials were soaked in the dye liquid phosphate buffer solution (PBS) (pH 7.0; DAPI: PBS (v/v) = 1∶1000) and kept in darkness for 20 min. Pieces of onion epidermis were arranged on slides to make wet mounts, the made slides were observed and photographed in dark-field of fluorescence microscope (Olympus BX 61, Japan).

Polythene foam boxes (1, 36 × 25 × 22cm) containing 20 kg of soil each were used. At two cotyledons, tomato seedlings were transferred to experimental boxes (one seedling per box), and simultaneously potato onions were planted (three bulbs per box). There were five types of plantations, i.e., (i) tomato monoculture, (ii) S-potato onion monoculture (iii) N-potato onion monoculture (since the root distribution result of N-potato onion monoculture is very similar to S, the result of N-potato onion monoculture was not list), and tomato cocultured with (iv) S-potato onion and (v) N-potato onion (Figure 7). Each type of plantation had four boxes and was repeated three times. Boxes were placed randomly without any order and their placement was randomized once a week. Water was applied regularly to maintain 55 ± 5% of the water holding capacity. No fertilizers were applied and weeds were uprooted manually. After 20 days of tomato transplantation, tomato seedling root length density was measured.
Root length density was measured by the Monolith method (Li et al., 2006 (link); Wang et al., 2014 (link); Yu et al., 2017 (link)). The experimental boxes were cut horizontally and soil samples of the middle 5 cm thick soil layer were taken up to 20 cm of soil depth using an iron box (6 cm × 5 cm × 4 cm), and numbered according to the section sequence (six pieces horizontally and five pieces vertically; 30 pieces in total per box). Since the roots mixed together in the companion cropping system, the tomato and potato onion roots were distinguished by differences in color, smell, and fiber characteristics. For example, tomato roots are yellowish and hairy, whereas potato onion roots have a smooth surface with white coloration and some degree of transparency. The separated root fractions were then scanned with an image scanner analyzer (LA-S2400), yielding data from each soil core in terms of total root length. Root length density was calculated by combining root length and soil volume.

The odor-collection method was adapted from previous studies on human body odor^{28 (link),29 (link),38 (link)}. Human axillary sweat odor was collected from 24 adult participants (6 males and 18 females) who volunteered to take part in the experiment. They were recruited through an e-mail sent to all personnel of our research facility (660 people). Participants were asked to abstain from consuming products known to influence body odors (i.e., chili pepper, spices, blue cheese, onion, garlic, cabbage, tobacco, and alcohol), abstain from use of deodorant, perfume or scented lotion, and to wash with a perfume-free soap provided by the experimenters for 2 days before their sweat was collected. The morning before participants donated their sweat, they were asked to wash their armpits with clear water only. Given the small number of participants, the menstrual cycle of females was not discriminated.
Each participant took part in two individual sessions separated by at least 24 h, during which they watched a 20-min video meant to provoke fear or joy. The clip selected for the fear condition was an excerpt from the movie Sinister³⁹ (judged as the most frightening horror movie in 2020—https://www.broadbandchoices.co.uk/features/science-of-scare). The clips selected for the joy condition were adapted from those used by de Groot et al.^{28 (link)}: “Bare Necessities” from The Jungle Book, Kurt Kuene’s short movie Validation, and the dance scene from the film The Intouchables. The order of the conditions was chosen randomly for each participant and counterbalanced among participants (half of participants watched the fear-inducing video first and the other half watched the joy-inducing video first).
Immediately before watching the video, participants were required to wash their armpits with wet unscented cotton pads and dry them with an unscented paper towel. Then, they placed under each armpit two cotton pads (7.5 × 7.5 cm, Euromedis, Neuilly-sous-Clermont, France) that had been previously folded together and secured them in place with unscented surgical tape. They wore a provided unscented cotton t-shirt that was previously washed without detergent and did not wear any other clothes over it. After each session, participants placed the cotton pads and t-shirts in airtight sealed bags, which were stored in a freezer at − 20 °C for a maximum of six weeks. Participants rated their extent of fear and joy while watching the videos on 7-point Likert scales^{28 (link)}.
Participants also indicated in a questionnaire whether they had thoroughly followed the dietary and hygienic instructions. The samples from nine participants had to be excluded from the experiment due to lack of compliance with the instructions. The samples from the remaining 15 participants were used as stimuli presented to horses.