Wilt Severity Research Articles

Assessment of postharvest soil fungal population with special reference to Trichoderma in eggplants

The research work was done to assess the postharvest soil fungal population and to find out the relation between population dynamics of Trichoderma and soil borne disease of 41 eggplant cultivars. Soil samples collected from IPM lab germplasm maintenance field at post-harvest stage were analyzed for microbes in dilution plate technique. Fungal colonies appeared in each plate were counted and made their average. Incidence and severity of Fusarium wilt and Sclerotium collar rot in the plot of 41 eggplant varieties were recorded at flowering-fruiting stage. The highest total soil fungal population was estimated from the plot soil of eggplant var. Singnath S (IPM- 42) that was 40.75×104. The var. Bijoy had the lowest fungal population that was 7.5×104. A comparison between Trichoderma population and other fungal population was made. Different eggplant cultivars had variation in the population of two important soil fungi- Trichoderma and Fusarium. The total populations of Trichoderma and Fusarium in the plot soil of 41 eggplant varieties were 129.75 and 348.75 × 104 per gram of soil, respectively. The average number of colonies of Trichoderma varied with the range (1-8.25) per plate. Fusarium varied with the range from (2-22.50). In 20 important eggplant varieties out of 41, both Fusarium wilt and Sclerotium collar rot incidence ranged between 0.00 to 40.00%. The variety Puta begun had the highest incidence of Fusarium wilt with the highest soil population of Fusarium oxysporum against the absence of Trichoderma harzianum. The disease incidence at flowering-fruiting stage was negatively correlated with the population of Trichoderma. Disease severity decreased with the increase in Trichoderma population. Increase of Trichoderma population, decreased the population of other fungi (Fusarium oxysporum and Sclerotium rolfsii). These results are clearly indicating that Trichoderma might have the antagonistic potential and might contribute to the reduction of incidence of soil-borne diseases.
 Progressive Agriculture 32 (1): 31-42, 2021

In vitro inhibition attempts and bio-elicitation of Solanum lycopersicum L. by chitin and chitosan against Ralstonia solanacearum, the causal agent of bacterial wilt

Ralstonia solanacearum is one of the most destructive pathogens of vegetables causing very important economic losses. In 2019, 20 strains of R. solanacearum were collected from potato tubers in Morocco. After their identification, the inhibitory effect of colloidal solutions of chitin and/or chitosan was evaluated in vitro on a solid medium (Mueller Hinton) supplemented with these biopolymers. The concentrations (25, 50, or 100 mg L-1) contributed to significant inhibition of the growth of the isolated strains that led to an inhibition of 45.04% with the combination of chitin-chitosan (100 mg L-1), 58.92% with the addition of 100 mg L-1 of chitin, and 68.74% in the presence of chitosan at 25 mg L-1. Likewise, in experiments with Solanum lycopersicum L. seedlings, chitin derivatives significantly promoted stem and root growth. Stem length increased by 54.95% when chitin was added at 25 mg L-1, while soil amendment with 100 mg L-1 of chitosan increased root length by 82.55% compared to the control. The severity of bacterial wilt due to R. solanacearum was reduced by 117.02% when we added 100 mg L-1 of chitosan to the soil. However, the severity of this disease decreased by 142.86% when the soil was amended with chitin at 50 mg L-1. These findings are consistent with prior research that suggests using this technique to manage bacterial wilt caused by R. solanacearum.

Molecular identification and biological control of Ralstonia solanacearum from wilt of papaya by natural compounds and Bacillus subtilis: An integrated experimental and computational study

Ralstonia solanacearum is a harmful pathogen that causes severe wilt disease in several vegetables. In the present study, we identified R. solanacearum from wilt of papaya by 16S rRNA PCR amplification. Virulence ability of R. solanacearum was determined by amplification of approximately 1500 bp clear band of hrpB gene. Further, in-vitro seed germination assay showed that R. solanacearum reduced the germination rate up to 26.21%, 34% and 33.63% of cucumber, bottle guard and pumpkin seeds, respectively whereas shoot and root growth were also significantly decreased. Moreover, growth inhibition of R. solanacearum was recorded using antibacterial compound from medicinal plant and antagonistic B. subtilis. Petroleum ether root extract of Rauvolfia serpentina showed highest 22 ± 0.04 mm diameter of zone of inhibition where methanolic extract of Cymbopogon citratus and ethanolic extract of Lantana camara exhibited 20 ± 0.06 mm and 20 ± 0.01 mm zone of inhibition against R. solanacearum, respectively. In addition, bioactive compounds of B. subtilis inhibited R. solanacearum growth by generating 17 ± 0.09 mm zone of inhibition. To unveil the inhibition mechanism, we adopted chemical-protein interaction network and molecular docking approaches where we found that, rutin from C. citratus interacts with citrate (Si)-synthase and dihydrolipoyl dehydrogenase of R. solanacearum with binding affinity of −9.7 kcal/mol and −9.5 kcal/mol while quercetin from B. subtillis interacts with the essential protein F0F1 ATP synthase subunit alpha of the R. solancearum with binding affinity of −6.9 kcal/mol and inhibit the growth of R. solanacearum. Our study will give shed light on the development of eco-friendly biological control of wilt disease of papaya.

Effect of soil drenching with humic acid, L-methionine and phosphoric acid on Fusarium wilt and induction of enzymes related to oxidative stress and defense in tomato plants

The main objective of the present study was to evaluate the efficacy of humic acid, L-methionine and phosphoric acid as a soil application for controlling Fusarium wilt disease of tomato and their effect on gene expression alterations using protein and isozyme profiling. Two isolates from each of Fusarium oxysporum f. sp. lycopersici (FOL) and F. solani (FS) were obtained from diseased tomato plants. According to pathogenicity tests, all tested isolates were able to infect tomato cultivars; cv. Super Jackal and cv. 745 under greenhouse conditions. In in vitro studies, the addition of humic acid, L-methionine and phosphoric acid to the medium at different concentrations reduced the growth of the tested isolates of the pathogens. Under greenhouse conditions, the addition of humic acid at 2%, 2 g/L of L-methionine and 0.6% of phosphoric acid to infested soil after sowing significantly decreased percentage disease severity of Fusarium wilt at both seasons (2016/17 and 2017/18). Protein bands at molecular weight 47.2 KD, 38.2 KD, 16.3 KD and 15.6 KD appeared only in treated plants. New esterase, peroxidase, chitinase and superoxide dismutase isozyme bands were detected in all treatments while not appear in the control. This results revealed that these treatments were able to induced new protein which increases resistance in tomato plants to Fusarium wilt disease.

The identification and pathogenicity of Fusarium oxysporum causing acacia seedling wilt disease

Wilt disease with unknown etiology causes mass mortality in commercial Acacia mangium nurseries in South Sumatra. This pathogen induces symptoms of chlorosis in the lower leaves and develops into the shoots; subsequently, the plants wither and die. This research identifies the pathogenic species causing this wilt disease and to assess its pathogenicity or virulence. Fifteen isolates of Fusarium oxysporum with varying colony sizes and color pigments were recovered from symptomatic A. mangium seedlings. The pathogenicity test showed that all isolates could infect plants with wilt severity reaching 80%, and the pathogen was verified as causing vascular disease. Koch’s postulate was verified by re-isolating the F. oxysporum isolates. The pathogen was confirmed by observing the morphological characters and elongation factor 1-α (tef1-α) gene sequences as F. oxysporum.

Evaluation of Hararge coffee (Coffea arabica L.) landraces for moisture stress tolerance

Arabica Coffee is an important export commodity for Ethiopia, contributing 25 to 30 % of the country’s total foreign exchange earnings. Moisture stress is one of the major constraints of coffee production in Hararge, Eastern Ethiopia. Moisture stress affects the growth, yield and quality of coffee. Local coffee landraces are source of desirable traits including moisture stress tolerance. Accordingly, this study was conducted to evaluate Hararge coffee landraces for moisture stress tolerance. Treatments consisted of 200 coffee landraces (178 from seven districts of east Hararge Zone and 22 from two districts of west Hararge Zone). The coffee landraces were field planted in July 2005 at Mechara Agricultural Research Center using augmented design with six trees per plot or accessions. Moisture stress tolerance was recorded from three randomly selected coffee trees per plot, three times a day (in the morning, noon and night) from January 05 to 25, 2014. The stress tolerance was determined using 1-5 scale by visual scoring (1- all leaves green and turgid, 2- most leaves still turgid but younger leaves show leaf folding; 3- all leaves wilt or fold, 4- Leaves partially turning pales, and partly shed showing severe wilting and 5-leaves completely turning brown and dry, mostly dropping). The collected data were analyzed using descriptive statistics. The result of this study revealed that the coffee landraces varied in their level of tolerance to moisture stress. The 200 coffee landraces were grouped into seven clusters based on their level of tolerance to moisture stress. Nine coffee landraces (4.5%) were highly tolerant to moisture stress, 25 (12.5%) were tolerant, and 36 (18%) were moderately tolerant. On the other hand, 60 coffee landraces (30%) were less tolerant; while 57 (28.5%), 11(5.5%) and 2 (1%) were moderately sensitive, sensitive and highly sensitive to moisture stress, in that order. There was variation in coffee landraces for moisture stress tolerance both between and within areas of the collection. Hence, it is advisable to maintain and use promising coffee landraces in coffee breeding. Screening of the landraces under controlled conditions like green house and studying of mechanisms of moisture stress is also the way forward.

EVALUATION OF GRAFTING USING CUCURBIT INTERSPECIFIC HYBRIDS TO CONTROL FUSARIUM WILT IN CUCUMBER

Grafting is a safe agro-technique used to boost tolerance against biotic and abiotic stresses and increase crop yield and quality. This study was undertaken to control cucumber Fusarium wilt through grafting onto novel Cucurbit interspecific hybrids and assess their effect on nutrients, defense enzymes in cucumber, and root characteristics. Four crosses were done between two lines of each of Bottle Gourd (Lagenaria siceraria), Winter squash (Cucurbita maxima), Winter squash (C. moshata), and Wild cucumber (C. zambinus). The commercial hybrid rootstock Supper Shintosa was also considered. Results indicated that all hybrid rootstocks, except Bottle Gourd, exhibited a significant decrease in Fusarium wilt severity compared with non-grafted control. Plant height and shoot dry weight of grafted plant were higher than those of the nongrafted control with best results for grafting onto C. moshata. The macro (N, P, K, Ca, and Mg%) and micro (Fe and Zn ppm) nutrient contents in the leaf of grafted plants were more than those of the nongrafted control. The highest macro and micronutrient contents were observed due to grafting onto C. moshata followed by C. maxima. Grafting of cucumber onto resistant rootstocks exhibited a significant increase in activity of peroxidases and polyphenoloxidase enzymes. Furthermore, grafting onto all rootstocks, except C. zambinus, caused an increase in root diameter more than the nongrafted control. Grafted cucumber onto C. maxima rootstock showed the best values in terms of diameter of the root, thickness of the cortex, dimension of vascular bundle, mean diameter of the vessel, and the pith over the nongrafted control.

Lateral Flow Immunoassay Detection of Ralstonia syzygii subsp. celebensis Causing Banana Blood Disease in Symptomatic and Asymptomatic Banana Plants

Banana blood disease caused by Ralstonia syzgii subsp. celebensis (Rsc) is one of the most well-known and most critical phytopathogenic bacteria which causes severe bacterial wilt in banana and considerable economic losses to the growers. Unlike common bacterial wilt caused by R. solanacearum, Rsc did not cause infection in solanaceous plant. The banana blood disease caused by the bacteria is fatal to the banana industry in Malaysia and other parts of the world. In an effort to better control the disease, a swift, sensitive, and user-friendly method for routine diagnostics is essential. This study aimed to raise polyclonal antibodies (pAb) from rabbit against whole cells of Rsc and to develop a lateral flow immunoassay (LFIA) strip utilising the purified IgG to detect the pathogen. We have developed the Rsc LFIA strips and obtained the sensitivity limit of 104 CFU/mL Rsc. The strip performance in real samples were performed using samples from symptomatic and asymptomatic banana plants consisting of samples from the pseudostems, petioles and leaves. The LFIA results were validated using polymerase chain reaction (PCR) with 100% correlation. The results showed that the strips were able to detect Rsc in all symptomatic samples. Additionally, positive result was obtained from the pseudostem of the asymptomatic samples. This study indicated the capability of the LFIA strips to detect Rsc not only in symptomatic plants but also before visible symptom appearance was observed which offered the potential for the LFIA strip to be used as a handy screening tool to detect Rsc.

Eucalyptus cloeziana mulch suppresses Fusarium wilt of banana

Fusarium wilt of banana, caused by Fusarium oxysporum f.sp. cubense, is a serious threat to banana production, with no effective treatment. Mulches and oils from Eucalyptus have been shown to inhibit the growth of F. oxysporum, and reduce the severity of Fusarium wilt. Eucalyptus cloeziana leaves contain many compounds commonly found in Eucalyptus as well as a very high concentration of the uncommon compound tasmanone. We applied E. cloeziana mulch, fresh or partially steam distilled, or no mulch as a control, to potted soil, inoculated the soil with F. oxysporum f.sp. cubense and grew susceptible banana plants to test the capacity of the mulch to reduce the severity of Fusarium wilt of banana. Disease severity, analysed by internal corm discoloration, was reduced from 90% in the control to 37% in the treatment with steam distilled mulch.In another experiment, comparison of steam distilled with fresh mulch showed no difference between the two, with a disease severity of 13%, compared to 49% in the control. Mulch (fresh or steam distilled) had no detrimental effects on plants grown without F. oxysporum inoculation. We propose that disease suppression was likely due to tasmanone, as it was the primary oil constituent of the mulches.

Spatial distribution and characterization of Fusarium wilt (Fusarium oxysporum f.sp. ciceris) of chickpea in Northern Shoa, Ethiopia

A field survey was conducted to determine the distribution and association of biophysical factors with chickpea Fusarium wilt (CFW), and to characterize CFW isolates from Northern Shoa, Ethiopia, in 2018/19. A total of 63 fields were inspected from major chickpea growing districts, and found 100% prevalence. Wilt incidence and severity were variable (34.3–50.2%) across districts. Logistic regression was used to analyze association of CFW with biophysical factors. High (>40%) incidence and severity were strongly associated with district, grey soil, pod setting, low to medium plant population, and dry soil moisture condition. Twenty six Fusarium oxysporum f.sp. ciceris isolates were identified and were highly variable in colony texture, sporulation capacity, conidial shape and size, septation character, and chlamydospore types. Most of the isolates were highly pathogenic, causing ≥50% wilting. It is confirmed that CFW is important and the pathogen is highly variable, implying for designing of effective management options.

Current progress on pathogenicity-related transcription factors in Fusarium oxysporum.

Fusarium oxysporum is a well‐known soilborne plant pathogen that causes severe vascular wilt in economically important crops worldwide. During the infection process, F. oxysporum not only secretes various virulence factors, such as cell wall‐degrading enzymes (CWDEs), effectors, and mycotoxins, that potentially play important roles in fungal pathogenicity but it must also respond to extrinsic abiotic stresses from the environment and the host. Over 700 transcription factors (TFs) have been predicted in the genome of F. oxysporum, but only 26 TFs have been functionally characterized in various formae speciales of F. oxysporum. Among these TFs, a total of 23 belonging to 10 families are required for pathogenesis through various mechanisms and pathways, and the zinc finger TF family is the largest family among these 10 families, which consists of 15 TFs that have been functionally characterized in F. oxysporum. In this review, we report current research progress on the 26 functionally analysed TFs in F. oxysporum and sort them into four groups based on their roles in F. oxysporum pathogenicity. Furthermore, we summarize and compare the biofunctions, involved pathways, putative targets, and homologs of these TFs and analyse the relationships among them. This review provides a systematic analysis of the regulation of virulence‐related genes and facilitates further mechanistic analysis of TFs important in F. oxysporum virulence.

Multifaceted intervention of Bacillus spp. against salinity stress and Fusarium wilt in tomato.

This study aimed to screen halotolerant Bacillus strains able to promote growth and protect tomato plants against salt stress and Fusarium wilt (Fusarium oxysporum f. sp. lycopersici). We evaluated some halotolerant strains of Bacillus spp. (Bacillus velezensis (AP-3) and Bacillus spp. (AP-6, AP-85 and AP-100)) to promote growth of tomato plants grown under salinity stress conditions and to protect them against Fusarium wilt disease. Such strains had been previously selected among 154 bacterial strains through biochemical tests (siderophores and indoleacetic acid productions, cellulase and catalase activity, nitrogen fixation and phosphate solubilization) in the presence of 100-mmoll-1 NaCl. Besides the above-mentioned strains, B.subtilis QST-713 (SerenadeTM ) was also evaluated. Compared to control plants, aboveground dry weight increased in plants inoculated with AP-6, AP-85, AP-3, AP-100 and QST-713 strains developed in the absence of salt stress. The same tendency occurred for root dry weight; however, AP-3 strain was more effective, promoting an increase of 163%, when compared to control. Chlorophyll index and height increased >40 and 53%, respectively, for all Bacillus strains. Saline stress reduced plant growth regardless of the presence of Bacillus. Height, stem diameter, and aboveground and root dry weights increased in plants treated with Bacillus strains grown under saline conditions when compared to control. Bacillusvelezensis AP-3 reduced the severity of Fusarium wilt in tomato by 50% when compared to control. Halotolerant Bacillus strains controlled tomato Fusarium wilt, increased growth as well as tolerance to salt stress. We demonstrated the efficacy of halotolerant Bacillus strains to control Fusarium wilt and improve tomato growth. We also demonstrated that these Bacillus strains protect tomato plants against salt stress. Bacillus can be used in an eco-friendly way because they are considered Generally Recognized As Safe.

Soil amendments and fumigation for the management of Fusarium wilt of bunching spinach in Ontario, Canada

Fusarium wilt, caused by Fusarium oxysporum f. sp. spinaciae, is a significant constraint to the summer production of bunching spinach in Ontario, Canada. Trials were conducted to assess soil amendments (limestone) and fumigants (metam sodium, chloropicrin and dazomet) for the suppression of Fusarium oxysporum f. sp. spinaciae. Dolomitic limestone applied at a rate of 10 and 20 t ha−1 reduced the incidence of fusarium wilt by 10 and 47%, respectively, even though there was little change in soil pH (7.4–7.5) or soil calcium concentration (1598 vs 1483 in 20 t lime vs control, respectively. Fusarium wilt severity was lower in the 2013 than in the 2014 growing season. In 2014, the fumigants metam sodium, chloropicrin and dazomet reduced the population of Fusarium spp. propagules in the soil by 84, 93 and 100%, respectively. Chloropicrin provided the best control of the spinach fusarium wilt pathogen compared to the other fumigants but was only assessed one year. Chloropicrin was the only treatment to truly reduced spinach Fusarium wilt by preventing vascular discolouration. Brassica juncea and calcium cyanamide were not effective at suppressing the disease. A high rate of nitrogen, consisting of polymer coated sulphur coated urea, was applied to provide the same rate of nitrogen as the Brassica juncea and calcium cyanamide treatments. Applying nitrogen in this formulation was as effective as metam sodium in reducing the incidence and severity of Fusarium wilt and should be evaluated further to determine the economics and environmental impact of this approach.

Iron chelates have little to no effect on the severity of Fusarium wilt of bananas in soils of the humid tropics

Previous research has shown that application of iron chelates to soil reduces Fusarium wilt in several crop species. The aim of this work was to test the effect for bananas grown in tropical soils. Disease severity and plant characteristics were measured in banana plants (cv. Ducasse, Musa ABB) grown in pots inoculated with Fusarium oxysporum f. sp. cubense, Race 1 in two experiments. Experiment 1 compared amendment with iron chelates (with ligands of differing iron binding stability) with water, plus an uninoculated unamended control, in two tropical Australian soils. Experiment 2 examined the effect of Fe-HBED application rate with high or low calcium addition. In Experiment 1, iron-saturated chelate application did not significantly affect disease severity or plant tissue iron concentration, irrespective of the iron binding stability of the chelate. In Experiment 2, disease severity was not affected by Fe-HBED or calcium application rate. The concentrations of iron and aluminium in plants were both somewhat affected by the addition of Fe-HBED, calcium and their interaction. Fusarium wilt of bananas was not affected by addition of iron chelates to these soils. The lack of effect was likely due to high iron availability in the soils overwhelming the capacity of the treatments to alter iron availability to the host plant and pathogen. Application of strong chelating ligands increased the concentration of aluminium and decreased the concentration of manganese in plant tissue, with possible detrimental effects.

Biocontrol agent, biofumigation, and grafting with resistant rootstock suppress soil-borne disease and improve yield of tomato in West Virginia

Organic tomato growers in West Virginia and neighboring states suffer serious economic losses each year due to soil-borne wilt diseases caused by fungal pathogens including Verticillium dahliae. This study determined the efficacies of biological control agents (BCAs – Serenade SOIL and Prestop), bio-fumigants and transplants grafted to a resistant rootstock in suppressing wilt disease in heirloom tomato cv. Mortgage Lifter in a certified organic production system in West Virginia in two consecutive years. Prestop and Serenade treatments resulted in higher seedling vigor at the early stage. However, within 40 days of field set in the fungal pathogen infested soil, grafted transplants (on resistant rootstock Maxifort) had the highest vigor followed by BCA treatments, biofumigation with mustard cover crop and mustard meal and was lowest in nontreated control. All treatments showed significantly lower Verticillium wilt severity index than control except mustard cover crop and Prestop in 2015 and 2016, respectively. Total fruit harvested over a six-week period indicated that yield from all but mustard cover crop treatment were significantly (P < 0.001) higher compared to the nontreated control in 2015. However, results from 2016 indicated that mustard cover crop would work best for both disease suppression and yield enhancement when tissues were well macerated and incorporated immediately in the soil and covered with impervious plastic for up to 10 days. In 2016, all treatments except Prestop produced higher tomato yield than the nontreated control. In general, yield advantage over nontreated were in the order of grafted > bio-fumigation > BCA treatments > nontreated check. Between two BCAs, Bacillus subtilis (Serenade) consistently provided better disease suppression and improved yield compared with Gliocladium catenulatum (Prestop) in both years. Grafted plants produced 9.1 and 10.0 kg tomatoes/plant in 2015 and 2016, respectively, compared with only 5.0 kg in nontreated control. Our results suggest that grafted transplants, biofumigation and selected BCA should be useful for sustainable management of tomato wilt disease in organic production systems. An economic analysis indicated that grafted tomato can provide the greatest net revenue followed by mustard meal biofumigation in farms infested with wilt causing pathogen.

Influence of Single and Combined Mixtures of Metal Oxide Nanoparticles on Eggplant Growth, Yield, and Verticillium Wilt Severity.

Verticillium wilt, caused by Verticillium dahliae, is one of the major diseases of eggplants. Nanoparticles (NPs) of CuO, Mn2O3, and ZnO were sprayed alone onto leaves of young eggplants and in different combinations and rates, and then seedlings were transplanted into soil infested with V. dahliae in the greenhouse and field between 2015 and 2018. All combinations of NPs were consistently less effective than CuO NPs applied alone at 500 µg/ml at increasing disease suppression, biomass, and fruit yield. CuO NPs were associated with an increase in fruit yield (17 and 33% increase) and disease suppression (28 and 22% reduction) in 2016 and 2017, respectively, when compared with untreated controls. However, this effect was negated in the greenhouse and field experiments when CuO NPs were combined with Mn2O3. Combining NPs of CuO with ZnO resulted in variable effects; amendments increased growth and suppressed disease in greenhouse experiments, but results were mixed in the field. Leaf tissue analyses from the greenhouse experiments showed that Cu concentration in leaves was reduced when CuO NPs were combined with other NPs, even when application rates were the same amount. A simple competition for entry sites may explain why combinations of CuO NPs and Mn2O3 NPs reduced efficacy but does not explain the lack of inhibition between Cu and Zn. NPs of CuO performed better than their larger bulk equivalent, and studies on application rate found 500 µg/ml was optimal. No phytotoxicity, as determined, by leaf burning, necrotic spots, or dead apical buds was noted even at the highest combined rates of 1,500 µg/ml.

Palmitic acid mediated change of rhizosphere and alleviation of Fusarium wilt disease in watermelon.

Palmitic acid (PA) in root exudates or decaying residues can reduce the incidence of soil-borne diseases and promote the growth of some crop plants. However, the effects of PA on soil-borne pathogens and microbial communities are poorly understood. Here, we investigate the effects of PA on overall watermelon microbial communities and the populations of Fusarium oxysporum f.sp. niveum (Fon). The effects of PA on the mycelial growth and spore production of Fon were tested in vitro, while its effects on Fon, total bacteria and total fungi populations, and microbial communities were evaluated in a pot experiment. The results revealed that all test concentrations of PA inhibited Fon mycelia growth and spore production. The pot experiment showed that 0.5 mM and 1 mM PA reduced Fon but increased total bacteria populations, and 0.5 mM and 1 mM PA 0.5 mM and 1 mM PA promoted the change to a soil type of bacteria soil. Meanwhile, 0.5 mM PA and 1 mM PA altered the community composition of the rhizosphere microorganisms and reduced the relative abundance of two bacterial operational taxonomic units (OTUs) and the two fungal OTUs that were significantly (p < 0.01) related with disease severity and increased that of four bacterial OTUs and the two fungal that were highly significantly (p < 0.01) negatively correlated with the disease severity. These results suggest that application of PA decreased the populations of Fon, changed the rhizosphere microbial composition, reduced the disease severity of Fusarium wilt, and promoted the growth of watermelon.

Biological Control of Collar Rot on Passion Fruits Via Induction of Apoptosis in the Collar Rot Pathogen by Bacillus subtilis.

The seedlings and fresh fruits of passion fruits are of high value in local and global trade. Fusarium solani is a main disease-causing agent affecting passion fruits. The objectives of this study were to develop Bacillus-based biocontrol agents for the management of Fusarium diseases on passion fruits and to investigate their putative control mechanisms. Our studies indicated that B. subtilis YBC and 151B1 show antagonistic activity to F. solani PF7 from passion fruits and inhibited the conidial germination of strain PF7. The application of broth cultures from B. subtilis 151B1 and YBC in SYB medium reduced disease severity of Fusarium wilt on the leaves of passion fruits and enhanced the survival rates of passion fruit seedlings challenged with F. solani PF7. With regard to the putative mechanisms of disease control, the results indicated that treatments consisting of the respective culture filtrates from B. subtilis 151B1 and YBC broths caused aberrant conidial morphology and loss of cell membrane integrity. Additionally, the treatments caused reductions in mitochondrial membrane potential and interfered with the energy metabolism of F. solani PF7. The treatments also enhanced reactive oxygen species accumulation and resulted in the externalization of phosphatidylserine, chromatin condensation, and DNA fragmentation, suggesting their function in triggering apoptotic-like cell death. In conclusion, B. subtilis 151B1 and YBC are potential biocontrol agents for passion fruit disease caused by F. solani. Their control efficacy may result from the surfactins produced to trigger apoptotic-like cell death, reducing mitochondrial membrane potential and interfering with the energy metabolism of the pathogen.[Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Copy Number Variations of Glycoside Hydrolase 45 Genes in Bursaphelenchus xylophilus and Their Impact on the Pathogenesis of Pine Wilt Disease

The pine wood nematode Bursaphelenchus xylophilus parasitizes millions of pine trees worldwide each year, causing severe wilt and the death of host trees. Glycoside hydrolase 45 genes of B. xylophilus are reported to have been acquired by horizontal gene transfer from fungi and are responsible for cell wall degradation during nematode infection. Previous studies ignored the possibility of copy number variations of such genes. In this study, we determined that two of the glycoside hydrolase 45 genes evolved to maintain multiple copies with distinct expression levels, enabling the nematode to infect a variety of pine hosts. Additionally, tandem repeat variations within coding regions were also detected between different copies of glycoside hydrolase 45 genes that could result in changes in protein sequences and serve as an effective biological marker to detect copy number variations among different B. xylophilus populations. Consequently, we were able to further identify the copy number variations of glycoside hydrolase 45 genes among B. xylophilus strains with different virulence. Our results provide new insights into the pathogenicity of B. xylophilus, provide a practical marker to genotype copy number variations and may aid in population classification.

Evaluation of chickpea (Cicer arietinum L.) accessions for Fusarium wilt resistance

Aim: The present study was conducted to evaluate chickpea breeding lines and popular varieties for Fusarium wilt resistance through multi-location field evaluation in major chickpea growing states of India. Methodology: Forty-five chickpea accessions were evaluated for Fusarium wilt resistance in field sick plots at Kanpur, Junagadh, Sehore and Rahuri in India during 2016 and 2017. Each accession was planted in three replications in a randomized block design. The data was subjected to analysis of variance (ANOVA) for testing the significance of variation due to accessions, environments and their interaction. GGE biplots analysis were constructed from the first two principal components (PC1 and PC2) using 45 genotypes and 8 environments using statistical software R, versions 2.15. Results: The effects of genotype, environment and G x E interaction for wilt incidence were highly significant with maximum variation caused by G x E interaction effect (50.42%), followed by genotypic (46.92 %) and environmental effect (2.24%). GGE biplot analysis revealed that Rahuri and Junagadh locations were most discriminating locations and could differentiate the wilt resistant and susceptible chickpea accession, while Kanpur was least discriminating. Junagadh was most representative followed by Sehore and Kanpur while Rahuri was least representative of the average environment. On an average, the most severe wilt incidence was observed at Junagadh, followed by Sehore, Kanpur and Rahuri over the years. Interpretation: Elite chickpea accessions possessing high level of fusarium wilt resistant at each location can be utilized for region specific breeding.The accessions IPC 2008-11, H 2010-05, GNG 1581, JG 24, SCGP-WR 28, H 2010-01 and IPC 2008-69 exhibited stable resistance over locations. These possessed resistance against multiple races of Fusarium wilt prevailing in the country and can be utilized as donors for disease resistance breeding. Key words: Chickpea, Fusarium wilt, GGE biplot, Multi-location evaluation, Stable resistance