Histopathology of the Plasmodiophora brassicae-Chinese Cabbage Interaction in Hosts Carrying Different Sources of Resistance

Clubroot is a serious soil-borne disease of crucifers caused by the obligate parasite Plasmodiophora brassicae. The genetic basis and histopathology of clubroot resistance in two Chinese cabbage (Brassica rapa ssp. pekinensis) inbred lines Bap055 and Bap246, challenged with pathotype 4 of P. brassicae, was evaluated. The Chinese cabbage cultivar “Juxin” served as a susceptible check. The resistance in Bap055 was found to be controlled by the CRa gene, while resistance in Bap246 fit a model of control by unknown recessive gene. Infection of the roots by P. brassicae was examined by inverted microscopy. Despite their resistance, primary and secondary infection were observed to occur in Bap055 and Bap246. Primary infection was detected at 2 days post-inoculation (DPI) in “Juxin,” at 4 DPI in Bap055, and at 6 DPI in Bap246. Infection occurred most quickly on “Juxin,” with 60% of the root hairs infected at 10 DPI, followed by Bap055 (31% of the root hairs infected at 12 DPI) and Bap246 (20% of the root hairs infected at 14 DPI). Secondary infection of “Juxin” was first observed at 8 DPI, while in Bap055 and Bap246, secondary infection was first observed at 10 DPI. At 14 DPI, the percentage of cortical infection in “Juxin,” Bap055 and Bap246 was 93.3, 20.0, and 11.1%, respectively. Although cortical infection was more widespread in Bap055 than in Bap246, secondary infection in both of these hosts was restricted relative to the susceptible check, and the vascular system remained intact. A large number of binucleate secondary plasmodia were observed in “Juxin” and the vascular system was disrupted at 16 DPI; in Bap055 and Bap246, only a few secondary plasmodia were visible, with no binucleate secondary plasmodia. The defense mechanisms and expression of resistance appears to differ between Chinese cabbage cultivars carrying different sources of resistance.

Effect of pyrene-induced changes in root activity on growth of Chinese cabbage (Brassica campestris L.), and the health risks caused by pyrene in Chinese cabbage at different growth stages

Background Polycyclic aromatic hydrocarbons (PAHs) pose a potential risk to ecological safety and human health. They have a range of effects on plant growth and there have been few reports on the health risks associated with ingestion of vegetable crops at different growth stages. Methodology In this study, a pot experiment in which Chinese cabbage (Brassica campestris L.) were grown in a greenhouse for 75 days was used to investigate the dose–effect relationship of pyrene with plant growth and also the exposure risk for adults of ingestion of Chinese cabbage at different growth stages. Results The results showed that low doses of pyrene (5–45 mg kg−1) promoted plant growth (20–220% and 55–97% higher than control treatment for the root biomass and shoot biomass, respectively), but significant inhibition was observed at a high dose (405 mg kg−1) (41–66% and 43–91% lower than control treatment for the root biomass and shoot biomass, respectively). High doses of pyrene reduced soil bacterial abundance and diversity during the growth of Chinese cabbage, and increased malondialdehyde (MDA) levels in the plant. The effects of pyrene on plant biomass were mainly attributed to changes in root activity induced by pyrene, as the relationship between soil pyrene concentration and biomass was similar to that between soil pyrene concentration and root activity. Furthermore, structural equation modeling analysis showed that pyrene altered growth of the vegetable by directly affecting root activity. The incremental lifetime cancer risk for adults is highest for ingestion of Chinese cabbage at the seedling stage, followed in decreasing order by the rosette stages and heading stages. Conclusions The health risk of consumers who have the possibility to ingest the Chinese cabbage planted in pyrene-contaminated soil would be decreased with the increasing growth periods. However, further studies are required to confirm the dose–effect relationship between pyrene concentration and Chinese cabbage growth on a field scale. Graphical Abstract

Chinese Cabbage Changes Its Release of Volatiles to Defend against Spodoptera litura

Plants respond to herbivorous insect attacks by releasing volatiles that directly harm the herbivore or that indirectly harm the herbivore by attracting its natural enemies. Although the larvae of Spodoptera litura (the tobacco cutworm) are known to induce the release of host plant volatiles, the effects of such volatiles on host location by S. litura and by the parasitoid Microplitis similis, a natural enemy of S. litura larvae, are poorly understood. Here, we found that both the regurgitate of S. litura larvae and S. litura-infested cabbage leaves attracted M. similis. S. litura had a reduced preference for cabbage plants that had been infested with S. litura for 24 or 48 h. M. similis selection of plants was positively correlated with the release of limonene; linalool and hexadecane, and was negatively correlated with the release of (E)-2-hexenal and 1-Butene, 4-isothiocyanato. S. litura selection of plants was positively correlated with the release of (E)-2-hexenal, 1-Butene, 4-isothiocyanato, and decanal, and was negatively correlated with the release of limonene, nonanal, hexadecane, heptadecane, and octadecane. Our results indicate that host plant volatiles can regulate the behavior of S. litura and M. similis.

Series-Spatial Transcriptome Profiling of Leafy Head Reveals the Key Transition Leaves for Head Formation in Chinese Cabbage

Chinese cabbage is an important leaf heading vegetable crop. At the heading stage, its leaves across inner to outer show significant morphological differentiation. However, the genetic control of this complex leaf morphological differentiation remains unclear. Here, we reported the transcriptome profiling of Chinese cabbage plant at the heading stage using 24 spatially dissected tissues representing different regions of the inner to outer leaves. Genome-wide transcriptome analysis clearly separated the inner leaf tissues from the outer leaf tissues. In particular, we identified the key transition leaf by the spatial expression analysis of key genes for leaf development and sugar metabolism. We observed that the key transition leaves were the first inwardly curved ones. Surprisingly, most of the heading candidate genes identified by domestication selection analysis obviously showed a corresponding expression transition, supporting that key transition leaves are related to leafy head formation. The key transition leaves were controlled by a complex signal network, including not only internal hormones and protein kinases but also external light and other stimuli. Our findings provide new insights and the rich resource to unravel the genetic control of heading traits.

Mitigation of Commercial Food Waste-Related Salinity Stress Using Halotolerant Rhizobacteria in Chinese Cabbage Plants

The use of commercial food waste in the Korean agricultural industry is increasing due to its capacity to act as an ecofriendly fertilizer. However, the high salt content of food waste can be detrimental to plant health and increase salinity levels in agricultural fields. In the current study, we introduced halotolerant rhizobacteria to neutralize the negative impact of food waste-related salt stress on crop productivity. We isolated halotolerant rhizobacteria from plants at Pohang beach, and screened bacterial isolates for their plant growth-promoting traits and salt stress-mitigating capacity; consequently, the bacterial isolate Bacillus pumilus MAK9 was selected for further investigation. This isolate showed higher salt stress tolerance and produced indole-3-acetic acid along with other organic acids. Furthermore, the inoculation of B. pumilus MAK9 into Chinese cabbage plants alleviated the effects of salt stress and enhanced plant growth parameters, i.e., it increased shoot length (32%), root length (41%), fresh weight (18%), dry weight (35%), and chlorophyll content (13%) compared with such measurements in plants treated with food waste only (control). Moreover, relative to control plants, inoculated plants showed significantly decreased abscisic acid content (2-fold) and increased salicylic acid content (11.70%). Bacillus pumilus MAK9-inoculated Chinese cabbage plants also showed a significant decrease in glutathione (11%), polyphenol oxidase (17%), and superoxide anions (18%), but an increase in catalase (14%), peroxidase (19%), and total protein content (26%) in comparison to the levels in control plants. Inductively coupled plasma mass spectrometry analysis showed that B. pumilus MAK9-inoculated plants had higher calcium (3%), potassium (22%), and phosphorus (15%) levels, whereas sodium content (7%) declined compared with that in control plants. Similarly, increases in glucose (17%), fructose (11%), and sucrose (14%) contents were recorded in B. pumilus MAK9-inoculated plants relative to in control plants. The bacterial isolate MAK9 was confirmed as B. pumilus using 16S rRNA and phylogenetic analysis. In conclusion, the use of commercially powered food waste could be a climate-friendly agricultural practice when rhizobacteria that enhance tolerance to salinity stress are also added to plants.

Isolation of a Leuconostoc mesenteroides ssp. jonggajibkimchii strain from Parona leatherjacket (Parona signata): behavior in vegetal matrices fermentation

A Gram-positive, facultatively anaerobic, gas-forming, catalase-negative, nonmotile, non-sporeforming, vancomycin-resistant, and ovoid-shaped bacterium, designated strain Tw234, was isolated from the intestinal tract of Parona leatherjacket (Parona signata). The strain grew in the presence of 0–6% (w/v) NaCl, at pH 3.5–8.5 and 8–40 °C; optimum growth was achieved at 1% (w/v) NaCl, at pH 6.0 and 30–32 °C. Exopolysacharides production was detected by the solidification test of skim milk supplemented with sucrose in the temperature range of 8 to 30 °C. Results of phylogenetic analysis based on the 16S rRNA gene sequence similarity indicated that strain Tw234 was closed related to the genus Leuconostoc and 100% homology with the type strain Ln. mesenteroides ssp. jonggajibkimchii DRC1506 (KCCM 43249, JCM 31787). The evaluation of growth and acidification rates were carried out in white cabbage and Chinese cabbage and compared with the strain Ln. mesenteroides ssp. jonggajibkimchii RCTw1.1, isolated from the spontaneous fermentation of red cabbage. No significant differences were observed between the behaviors of the two strains. The strain Tw234 displayed higher growth and acidification rates in controlled fermentation of white cabbage compared with those obtained in Chinese cabbage. New trends are targeted on the isolation and selection of strains to achieve controlled fermentation of vegetables that may ensure uniform quality. The results obtained in this work suggest that strain Tw234 harbored technological useful properties for its potential use as a starter in controlled vegetable fermentations.