Biomedical Physics and Engineering Express

Abstract Phenolic compounds, known for their antioxidant and antifungal properties may be connected to infection processes of Cronartium rusts in alternate host plants. We studied changes in leaf chemistry after Cronartium inoculation on susceptible alternate hosts of C. pini and C. ribicola. Impatiens balsamina and Paeonia lactiflora were inoculated with C. pini, and R. nigrum with C. ribicola in the greenhouse. Leaves of the inoculated plants were harvested 3 and 6 days after inoculation for chemical analysis, which was done using LC–MS (liquid chromatography mass spectrometry). Species-specific differences were found in dominant phenolics ferulic acid, hyperoside, quercitrin, and rutin. Rust inoculation produced limited changes in phenolic concentrations, with significant increases only in p-coumaric acid in I. balsamina and rutin in R. nigrum. Significant post-inoculation decrease was found in several cases. While phenolic fluctuations varied by species and incubation time, there was no significant interaction between inoculation and incubation time, suggesting the absence of induced phenolic accumulation during early infection stages. The results support the hypothesis that susceptible alternate hosts exhibit weak, delayed phenolic defenses, possibly due to rust virulence factors suppressing these responses. Indirectly, they provide support for the defensive role of phenolics in resistant congeneric hosts, emphasizing also the importance of further molecular studies to explore plant defense mechanisms against rust pathogens.

Abstract Root-knot nematodes (RKN) cause extensive damage to grapevine cultivars. RKN-resistant grapevine rootstocks remain vulnerable to biotic and abiotic stresses. This study aimed to determine the influence of composted animal manures (CAMs) [chicken manure (CM), cow manure (CowM), and sheep manure (SM)] with or without plant growth-promoting rhizobacteria (PGPR) on the population of Meloidogyne incognita, free-living nematodes (FLNs) and predaceous nematodes (PNs) residing in the soils of vineyard cultivars (Flame, Superior and Prime). The nematodes were isolated from grapevine roots and rhizosphere soils, then the absolute frequency of occurrence (FO), relative FO, prominence value (PV), and population density (PD) were assessed. The impact of CAMs and PGPR on the growth parameters, fruit output, and quality of three grapevine varieties was subsequently evaluated. Eight treatments included a control without CAMs or PGPR amendments, the CAMs alone, or CAM treatments combined with PGPR. The results showed that FLNs and PNs were more abundant in Prime than Flame or Superior cultivars when poor sandy loam soils were supplied with CAMs. Among all tested manures, CM was the best treatment as a nematicide. This was evident from the decreased numbers of M. incognita and increased numbers of FLNs and PNs in grapevine fields. Compared to the soil-applied oxamyl (a systemic nematicide), which was efficiently suppressive on M. incognita for two months, CM significantly (P < 0.05) decreased PD of the phytonematodes for five months, improved soil structure and enhanced the soil biological activities. There were significant (P < 0.05) increases in the number of leaves/vines by 79.9, 78.8, and 73.1%; and total fruit weight/vine by 76.9, 75.0, and 73.0% in Flame, Superior, and Prime varieties, respectively, compared to untreated vines. Regardless of the cultivar, soils amended with CM + PGPR achieved the lowest number of M. incognita among all other treatments, followed by SM + PGPR and CowM + PGPR. It was concluded that CAMs amendment, mainly CM, along with PGPR in poor sandy soils of temperate areas, is considered a sustainable approach for reducing parasitic nematodes and improving agricultural management.

Bacterial leaf blight (BLB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most destructive bacterial diseases of rice world wide. In the present study, five fungal endophytes isolated from rice leaves were tested for their antagonistic potential against Xoo. The endophyte isolate viz., KTD-2 inhibited the bacterial pathogen. The antagonism was visualized as overgrowth of the endophyte on the pathogen followed by degradation of its yellow pigmentation. The isolate could also successfully colonize the roots of rice plants within two weeks of inoculation. Phylogenetic analysis based on ITS and LSU sequences revealed that the endophyte belonged to the Xylariaceae family. Further characterization clustered the endophyte to the Xylaria genus with 95.35 and 94.04 per cent sequence similarity to Xylaria sicula f. major when sequenced with the btub and rpb-2 genes respectively. This is the first report of endophytic Xylaria sp. isolated from rice antagonistic to Xoo. Endophyte application as seed treatment and foliar application significantly reduced disease severity to 28.89% compared to 79.26% in the control at 90 days after transplanting (DAT). Seed treatment significantly enhanced seed germination to 94.31 per cent compared to 88.46 per cent in untreated control. The in vitro study revealed that the germination percentage, seedling length as well as the seedling vigour index were the highest in endophyte treated seedlings compared to untreated seeds. This strongly suggests that the identified endophyte, KTD-2 is a potential candidate for biological control for the management of BLB along with plant growth promoting activities.

Abstract The pangenome of lactic acid bacteria (LAB) was constructed with five bacterial strains isolated from oat silage produced by smallholder farmers from a region in the highlands of the Colombian Andes. The goal of this work was to use genome mining to elucidate some potential mechanisms of action associated with plant growth promotion and biocontrol in LAB. Multiple genes were uncovered, including those associated with antibiosis and antimicrobial compound production, genes that induce plant defense and phytohormone activation. Additionally, genome sequencing suggested mechanisms for LAB to protect against abiotic and biotic stress. Furthermore, genes that may improve phosphorus availability and those that might stimulate root growth were present. We then tested some of these findings in vitro. For instance, the biocontrol activity of these strains was evaluated against the fungal pathogens Fusarium oxsyporum f. sp. cubense (Foc R1 and Foc TR4) and the bacterial pathogen Ralstonia solanacearum (Rs). All tested strains showed the ability to significantly inhibit pathogen growth in vitro. The capability of LAB to grow at high concentrations of fusaric acid was demonstrated, suggesting that LAB might have detoxification mechanisms to compete with other microorganisms. Also, the ability of LAB to solubilize phosphate and produce IAA was demonstrated. These two properties might be involved in plant-growth promotion. Here we show that genomic sequencing can be an efficient tool to identify putative biocontrol or plant-growth promoting related sequences for genome mining.

Abstract The increasing use of bacterial biocontrol agents in agriculture raises concerns about their potential impact not only on the environment of infected plants but also on that of healthy plants. This study investigated the effects of introducing the endophytic bacterium Frateuria defendens, a potential biocontrol agent against phytoplasma diseases, on melon (Cucumis melo) as a model plant. Different isolates of F. defendens were screened for their in vitro and in planta antimicrobial activity, as well as their ability to colonize and influence the plant microbiome. Only one isolate, designated KT11, successfully colonized the melon shoot and was found in the plant sap. The antimicrobial activity of this isolate was retained in the plant sap and was confirmed in a biological test on Spiroplasma melliferum. The presence of KT11 in the plant tissue induced distinct shifts in the overall structure and diversity of the endophytic microbial populations. These significant findings emphasize the need for a comprehensive understanding of the ecological implications of introducing exogenous microbes into plant systems. This study contributes to the growing body of knowledge on the intricate interactions between plants, their microbiomes, and introduced biocontrol agents, towards performing sustainable agricultural practices.

Fusarium fujikuroi is a pathogenic fungus, causing bakakae disease in rice, known for its detrimental impact on aromatic rice, causing significant yield losses. This study intended to investigate the efficacy of seed priming with salicylic acid (SA) for the induction of systemic acquired resistance (SAR) against bakanae infection in two aromatic rice cultivars, PB 1121 and PB 1509, under field conditions. Seed priming was done with SA at 10 mg/l for 6 h, followed by inoculation with pure cultures of F. fujikuroi for 24 h. Seed priming with salicylic acid effectively reduced disease incidence as compared to positive controls. The tissues of the positive control of both cultivars showed severe structural deformities, with evident pathogenic structures in roots, stems, and leaves. Priming with SA strengthened rice seedlings against pathogen progression by having higher lignin content, peroxidase activity, net photosynthetic rate, stomatal conductance, and photosynthetic pigments while reducing hydrogen peroxide content, endogenous levels of GA3 and IAA, and increasing endogenous ABA levels as compared to both positive and negative controls. The knowledge gained from studying the histological and biochemical changes in infected and un-infected plant components post-SA priming can lead to the development of sustainable management of bakanae disease in rice. This study holds significant implications for understanding SA-induced systemic acquired resistance against bakanae disease in rice.

Abstract This study evaluates the susceptibility of various hop varieties to three viroids: Hop Latent Viroid (HLVd), Hop Stunt Viroid (HSVd), and Citrus Bark Cracking Viroid (CBCVd), all of which pose significant threats to Slovenian hop production. The experiment was conducted under in vitro conditions, involving the cultivation of 13 different hop varieties in tissue cultures, alongside the in vitro synthesis of viroid transcripts and subsequent inoculation of the plants. The plants were then monitored for growth, development, and their responses to viroid infection. The findings reveal the complex interactions between hops and viroids, with successful inoculation observed in all varieties. However, infection rates varied, with HSVd showing the highest rates of infection, followed by CBCVd and HLVd. This research enhances the understanding of viroid dynamics in hop plants, which is crucial for developing effective disease management strategies. Despite the insights gained, no resistance or tolerance to the viroids was identified in any of the tested hop varieties.

Abstract Macadamia is an Australian native tree grown for its edible kernel in tropical and subtropical regions worldwide. However, there is limited knowledge about the fungal leaf pathogens that can infect macadamia nursery plants and potentially reduce productivity. To address this gap, we surveyed major commercial nurseries in Australia to identify leaf diseases affecting macadamia plants in different growing seasons. We identified four main leaf diseases: yellow halo leaf blight, brown leaf blight, anthracnose, and black leaf blight, each caused by multiple fungal species. Leaf anthracnose was the most prevalent disease observed in all the nurseries across the four seasons. From mature leaves with anthracnose symptoms, we isolated eight Colletotrichum spp., but only C. siamense and C. gloeosporioides sensu lato were found to cause infection in pathogenicity assays. In addition, we isolated eleven Neopestalotiopsis and two Pestalotiopsis spp. from yellow halo leaf blight lesions and found that N. clavispora and N. maddoxii were capable of causing disease. We also determined that the A. alternata and A. tenuissima in the Alternaria alternata species complex caused black leaf blight only in non-suberised new leaf flush. For brown leaf blight, Neofusicoccum parvum and Ne. luteum were isolated from symptomatic leaves, both of which caused similar levels of disease. Our findings indicate that several pathogen species are responsible for at least four leaf diseases in macadamia nurseries, suggesting a potential productivity risk when affected plants are planted in the field.

Abstract Laserine-type phenylpropanoids are a main group of natural bitter compounds synthesized in carrot taproots and putatively contribute to defence mechanisms against soil-borne pathogens. In this study, we analysed the relationships between the constitutive levels of two laserine compounds present in mature taproots and the extent of root infection by the two main carrot storage fungal pathogens Mycocentrospora acerina and Botrytis cinerea. Taproots of eight carrot cultivars exhibiting different levels of laserine and its isomer 2-epilaserine in the taproot periderm were inoculated with the two fungi and evaluated for diseased area with a digital image analysis system after 6 weeks incubation in a cold storage facility. The concentrations of the two phenylpropanoids showed a significant negative correlation with M. acerina and B. cinerea disease severity. We present, to our knowledge for the first time, novel insights about putative effects of laserine compounds against soil-borne fungal carrot pathogens.

Passion fruit (Passiflora spp.) is an important crop with increasing yields in recent years. However, its expansion in Brazil faces challenges, including diseases affecting the crop. The main disease is passion fruit woodiness, caused by cowpea aphid-borne mosaic virus (CABMV), which leads to leaf and fruit symptoms, compromising both quality and production. Viral infections directly affect plant physiology and often disrupt gas exchange by impacting leaf function. In this study, our aim was to analyze gas exchange caused by CABMV and to estimate genetic parameters to aid in the selection of genotypes with superior physiological performance. Gas exchange measurements were performed on passion fruit leaves from full-sib families showing varying symptoms of infection, as well as on leaves from resistant (P. setacea) and susceptible (P. edulis) individuals. Disease severity was assessed on a rating scale associated with the SPAD index. The estimation of genetic parameters facilitated the determination of variances, heritability and accuracy for each physiological variable examined. Our results confirmed that the presence of CABMV in leaves reduces photosynthetic rates and stomatal conductance, especially in the face of moderate and severe symptoms. Furthermore, genotypic variation played a more significant role in the photosynthetic rate, intercellular CO2 concentration and transpiration rate compared to phenotypic variation. Heritability values ranged from moderate to high, and accuracy values were high, validating the reliability of the analyses. In conclusion, the study demonstrates, for the first time, the negative impact of CABMV infection on gas exchange in passion fruit leaves. In addition, it highlights the potential use of physiological variables, such as photosynthesis, in the selection of individuals with superior physiological performance in passion fruit breeding programs.

The major disease of the common bean, anthracnose, is caused by the hemibiotrophic fungus Colletotrichum lindemuthianum and results in significant economic losses. In the present study, we evaluated: (i) the antifungal activity of 26 essential oils (EOs) in the germination and mycelial growth of two isolates of C. lindemuthianum, one of race 65 (LV 136) and the other of race 73 (LV 99), (ii) ultrastructural changes of Cymbopogon citratus, Eugenia caryophyllata and Cymbopogon martini EOs in fungal conidia, (iii) the effect of these EOs on anthracnose control, applied before and after inoculation, and (iv) the effect of C. citratus EOs on the activity of defense enzymes Chitinase (CHI), Polyphenol oxidase (PPO), Guaiacol peroxidase (POX) and Phenylalanine ammonia-lyase (PAL) on bean plants. Of the 26 EOs, 95% of the conidial germination was inhibited by C. citratus, C. martini, Cinnamomum sp., T. vulgaris, E. caryophyllata, and M. recutita at concentrations lower than 0.1%. Mycelial growth was completely inhibited by C. citratus, E. caryophyllata and C. martini at 0.1% for both races. There was little mycelial growth in the fungicide treatment 4 day after infection, DAI. Transmission electron microscopy (TEM) ultrastructure showed that C. citratus, C. martini and E. caryophyllata had direct antifungal action against C. lindemuthianum. These EOs damaged the conidia's ultrastructure by causing vacuolization, cytoplasmic leakage, and plasma membrane invagination. The activity of plant defense enzymes increased in the treatment with C. citratus. Moreover, Cymbopogon citratus and E. caryophyllata decreased anthracnose severity in both the preventive and the curative experiment by 29% and 21%, respectively. Essential oils demonstrated potential for the management of anthracnose in bean crops caused by C. lindemuthianum.