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Plasmodiophora brassicae , an obligate biotrophic pathogen-causing clubroot disease, can seriously affect Brassica crops worldwide, especially Chinese cabbage. Understanding the transcriptome and metabolome profiling changes during the infection of P. brassicae will provide key insights in understanding the defense mechanism in Brassica crops. In this study, we estimated the phytohormones using targeted metabolome assays and transcriptomic changes using RNA sequencing (RNA-seq) in the roots of resistant (BrT24) and susceptible (Y510-9) plants at 0, 3, 9, and 20 days after inoculation (DAI) with P. brassicae . Differentially expressed genes (DEGs) in resistant vs. susceptible lines across different time points were identified. The weighted gene co-expression network analysis of the DEGs revealed six pathways including “Plant–pathogen interaction” and “Plant hormone signal transduction” and 15 hub genes including pathogenic type III effector avirulence factor gene ( RIN4 ) and auxin-responsive protein ( IAA16 ) to be involved in plants immune response. Inhibition of Indoleacetic acid, cytokinin, jasmonate acid, and salicylic acid contents and changes in related gene expression in R-line may play important roles in regulation of clubroot resistance (CR). Based on the combined metabolome profiling and hormone-related transcriptomic responses, we propose a general model of hormone-mediated defense mechanism. This study definitely enhances our current understanding and paves the way for improving CR in Brassica rapa .

Plasmodiophora brassicae (P. brassicae) is a soil-born pathogen worldwide and can infect most cruciferous plants, which causes great yield decline and economic losses. It is not well known how microbial diversity and community composition change during P. brassicae infecting plant roots. Here, we employed a resistant and a susceptible pakchoi cultivar with and without inoculation with P. brassicae to analyze bacterial and fungal diversity using 16S rRNA V3-V4 and ITS_V1 regions, respectively. 16S rRNA V3-V4 and ITS_V1 regions were amplified and sequenced separately. Results revealed that both fungal and bacterial diversity increased, and composition was changed in the rhizosphere soil of the susceptible pakchoi compared with the resistant cultivar. In the four groups of R_mock, S_mock, R_10d, and S_10d, the most relatively abundant bacterium and fungus was Proteobacteria, accounting for 61.92%, 58.17%, 48.64%, and 50.00%, respectively, and Ascomycota, accounting for 75.11%, 63.69%, 72.10%, and 90.31%, respectively. A total of 9488 and 11,914 bacteria were observed uniquely in the rhizosphere soil of resistant and susceptible pakchoi, respectively, while only 80 and 103 fungi were observed uniquely in the correlated soil. LefSe analysis showed that 107 and 49 differentially abundant taxa were observed in bacteria and fungi. Overall, we concluded that different pakchoi cultivars affect microbial diversity and community composition, and microorganisms prefer to gather around the rhizosphere of susceptible pakchoi. These findings provide a new insight into plant–microorganism interactions.

Pieris brassicae (Linn.) is a destructive cosmopolitan pest of cruciferous crops. It is present wherever its host plants occur, and it is considered to be one of the most widely distributed of all the Lepidoptera. We investigated the affect of various host plants on the food consumption and utilization by P. brassicae. We quantified consumption of food, larval duration, pupal duration and weight on cabbage (Brassica oleracea var. capitata), cauliflower (Brassica oleracea var. botrytis), radish (Raphanus sativus), broccoli (Brassica oleracea var. italica) and mustard (Brassica campestris) under laboratory conditions. Insect-host relationships can be better understood by knowing the rate of food consumption, its digestibility and conversion of food eaten to body tissue. The consumption of food generally increased with the advancement of larval age. In our study we found that consumption of food was highest on radish and lowest on broccoli. The highest consumption of a particular host does not always indicate greater suitability of that host, until and unless other factors like consumption index (CI), relative growth rate (RGR), efficiency of conversion of ingested food (ECI), approximate digestibility (AD) and efficiency of conversion of digested food (ECD) are also considered. In the current investigation, factors like CI, RGR, ECI and ECD were highest on cabbage. Low body weight of pupa is associated with rapid development. On cabbage, the weight of pupa of both sexes was found lowest. Thus, from the present study, it can be concluded that cabbage is a more suitable host for P. brassicae than other host plants evaluated. Hence, on cabbage, the values of Waldbauer indices were highest and P. brassicae developed with a faster rate.

Climate change has direct influence on the development and survival of herbivores in addition to indirect effects through trophic interactions. The present studies were carried out to observe the effect of increase in minimum temperature on development and food consumption of Helicoverpa armigera Hubner, Pieris brassicae Linnaeus and Spodoptera litura Fabricius. The mean food consumptionincreased by 12.78 and 32.64 per cent with increase in minimum temperature of 30C and 60C, respectively accompanied by decrease in larval duration by 10.37 and 27.97 per cent. Similarly, observations on P. brassicae larvae at four temperature ranges indicated that the mean food consumption increased by 4.87 with rise in minimum temperature by 30C accompanied by faster development. Likewise, effect of temperature ranges viz. 21°C: 7°C and 21°C: 10°C for 16: 8 hrs on biology of S. litura was estimated. The observations revealed faster growth when the mean minimum temperature was raised from 7 to 10°C. The rise in minimum temperature by 3°C resulted in decrease in larval and pupal duration by 5.36 and 10.43 per cent, respectively. The survival per cent was also increased by 1.44 per cent when rise in minimum temperature by 3°C.

• Plants respond to phosphorus (P) limitation through an array of morphological, physiological and metabolic changes which are part of the phosphate (Pi) starvation response (PSR). This response influences the establishment of the arbuscular mycorrhizal (AM) symbiosis in most land plants. It is, however, unknown to what extent available P and the PSR redefine plant interactions with the fungal microbiota in soil. • Using amplicon sequencing of the fungal taxonomic marker ITS2, we examined the changes in root-associated fungal communities in the AM nonhost species Arabidopsis thaliana in response to soil amendment with P and to genetic perturbations in the plant PSR. • We observed robust shifts in root-associated fungal communities of P-replete plants in comparison with their P-deprived counterparts, while bulk soil communities remained unaltered. Moreover, plants carrying mutations in the phosphate signaling network genes, phr1, phl1 and pho2, exhibited similarly altered root fungal communities characterized by the depletion of the chytridiomycete taxon Olpidium brassicae specifically under P-replete conditions. • This study highlights the nutritional status and the underlying nutrient signaling network of an AM nonhost plant as previously unrecognized factors influencing the assembly of the plant fungal microbiota in response to P in nonsterile soil.

Secondary plant metabolites such as polyphenols and flavonols play an important role in plant defense and host–pathogen interaction. In this study, metabolomics and quantitative gene expression analysis was used to identify the polyphenols and flavonols, and the genes involved in resistance to clubroot disease in Brassica napus. For this, a set of clubroot susceptible and resistant canola lines, carrying resistance of the rutabaga cv. Polycross was inoculated with a virulent Plasmodiophora brassicae pathotype 3A to examine disease progression at 7-, 14- and 21 days after inoculation (DAI). The root samples collected at these time points were used for metabolomics and quantitative gene expression analyses. An increased concentration of several metabolites such as caffeic acid, protocatechuic aldehyde, vanillin and kaempferol, derived from phenylpropanoid and flavonoid biosynthesis pathways, were observed in roots of the resistant lines in response to P. brassicae infection implying that they might play a role in clubroot resistance. The higher expression of the genes C4H-A, C4H-B, CCR, CHI, CHS and F3H involved in the biosynthesis of these compounds substantiated the metabolomics analysis results. Conversely, significantly greater contents of ferulic acid and 3,4-hydroxybenzoic acid were found in roots of the susceptible lines indicating their possible role in disease susceptibility. Thus, the results from this study provide an insight into Brassica-P. brassicae interaction and the molecular basis of clubroot resistance.

Insect eggs represent a threat for the plant as hatching larvae rapidly start with their feeding activity. Using a whole-genome microarray, we studied the expression profile of Arabidopsis (Arabidopsis thaliana) leaves after oviposition by two pierid butterflies. For Pieris brassicae, the deposition of egg batches changed the expression of hundreds of genes over a period of 3 d after oviposition. The transcript signature was similar to that observed during a hypersensitive response or in lesion-mimic mutants, including the induction of defense and stress-related genes and the repression of genes involved in growth and photosynthesis. Deposition of single eggs by Pieris rapae caused a similar although much weaker transcriptional response. Analysis of the jasmonic acid and salicylic acid mutants coi1-1 and sid2-1 indicated that the response to egg deposition is mostly independent of these signaling pathways. Histochemical analyses showed that egg deposition is causing a localized cell death, accompanied by the accumulation of callose, and the production of reactive oxygen species. In addition, activation of the pathogenesis-related1::β-glucuronidase reporter gene correlated precisely with the site of egg deposition and was also triggered by crude egg extract. This study provides molecular evidence for the detection of egg deposition by Arabidopsis plants and suggests that oviposition causes a localized response with strong similarity to a hypersensitive response.

Insect population count and yield were used to determine the effectiveness of two bio-rational pesticides -a commercial formulation of Pieris rapae granulosis virus and Bacillus thuriengensis, Bypel 1® (PrGV + Bt) (1.5 g/l w/v) and aqueous neem kernel extract (ANKE) (50 g/l w/v), on the insect pests complex of two cabbage varieties, KK cross and Oxylus for two consecutive cropping seasons of 2016/2017. The experiment was laid in a split-plot design with three replications, with the cabbage varieties as main plots and the bio-rational pesticides as subplots. Cabbage plots treated with Bypel 1® and ANKE had the lowest population of Plutella xylostella, Brevicoryne brassicae, Hellula undalis, Bemisia tabaci and Thrips tabaci for both seasons. The control plot consistently had higher pest population in both seasons. There was no detrimental effect of bio-rational pesticides on natural enemies. The bio-rational pesticides-treated plots produced higher yield than control plots. Mean numbers of P. xylostella was higher on KK (0.61, 1.46) compared to Oxylus (0.65, 1.70) in both seasons, respectively. The yield between the cabbage varieties was not significantly different in both seasons, although Bypel 1® and ANKE treated plots generally produced significantly higher yields than the control plot. Yield between both cropping seasons was significantly different (p = 0.039). These findings provide evidence that bio-rational pesticides may offer effective management of the pest complex of cabbage and may be successfully used as an integral part of IPM in Africa as a means to curb the abuse of synthetic insecticides.

The composition of secondary metabolites and the nutritional value of a plant both determine herbivore preference and performance. The genetically determined glucosinolate pattern of Barbarea vulgaris can be dominated by either glucobarbarin (BAR-type) or by gluconasturtiin (NAS-type). Because of the structural differences, these glucosinolates may have different effects on herbivores. We compared the two Barbarea chemotypes with regards to the preference and performance of two lepidopteran herbivores, using Mamestra brassicae as a generalist and Pieris rapae as a specialist. The generalist and specialist herbivores did not prefer either chemotype for oviposition. However, larvae of the generalist M. brassicae preferred to feed and performed best on NAS-type plants. On NAS-type plants, 100% of the M. brassicae larvae survived while growing exponentially, whereas on BAR-type plants, M. brassicae larvae showed little growth and a mortality of 37.5%. In contrast to M. brassicae, the larval preference and performance of the specialist P. rapae was unaffected by plant chemotype. Total levels of glucosinolates, water soluble sugars, and amino acids of B. vulgaris could not explain the poor preference and performance of M. brassicae on BAR-type plants. Our results suggest that difference in glucosinolate chemical structure is responsible for the differential effects of the B. vulgaris chemotypes on the generalist herbivore.

It has been suggested that the white coloration of Pieridae butterflies is a warning signal and therefore all white Pieridae could profit from a mimetic resemblance. We tested whether green-veined white (Pieris napi) and orange-tip (Anthocharis cardamines) butterflies benefit from white coloration. We compared their relative acceptability to wild, adult pied flycatchers (Ficedula hypoleuca) by offering live A. cardamines and P. napi together with two non-aposematic butterflies on the tray attached to birds' nesting boxes. Experienced predators equally attacked white and non-white butterflies, and the order of attack among the Pieridae was random. If anything, there was a slight indication that the female A. cardamines was the least favoured prey. Since birds did not avoid white coloration, we compared the palatability of these two species against known palatable and unpalatable butterflies by presenting them to great tits (Parus major). Pieris brassicae, which has been earlier described as unpalatable, was also included in the palatability test. However, there were no significant differences in the palatability of the butterflies to birds, and even P. brassicae was apparently palatable to the great tits. Our results do not unambiguously support the hypothesis that the white coloration of Pieridae would signal unpalatability. Nevertheless, in our last experiment, pied flycatchers often rejected or left untouched free flying P. napi and A. cardamines. This suggests that other features in a more natural situation, such as the agile flight pattern or odours might still make them unprofitable to birds.