​Antagonistic Activity of Panchagavya and Trichoderma spp. against Wilt Complex causing Pathogens of Chickpea (Cicer arietinum L.)

Background: Chickpea wilt complex caused by several soil-borne pathogens is the major yield-reducing malady worldwide. Biological control is one of the best, low-cost and ecologically sustainable method for managing plant diseases caused by soil-borne pathogens. Methods: In this present investigation Panchagavya and Trichoderma spp. were evaluated by following poisoned food technique and dual culture technique against wilt complex causing pathogens i.e. Fusarium oxysporum f. sp. ciceri, Fusarium solani and Macrophomina phaseolina. Result: Among the different isolates of Trichoderma spp. evaluated, Trichoderma viride (AAU isolate) was highly antagonistic to F. oxysporum f. sp. ciceri (52.78%) and F. solani (65.37%) whereas, Trichoderma asperellum (AAU isolate) was highly antagonistic to M. phaseolina (65.93%). Panchagavya at the highest concentration (50%) showed significantly higher efficacy (80.74, 66.62 and 49.67%) in inhibiting the mycelial growth of all three pathogens and at the lowest concentration it was moderately effective.

Effect of Plant Growth Promoting Bacillus spp. on Germination and Seedling Growth of Soybean

Background: Bacillus spp., known to promote growth and reduce disease of various field and vegetable crops, are frequently found in soils. The objective of the study was to select effective Bacillus spp. isolates with multiple plant growth properties and antifungal activities and to examine their effect on germination of soybean. Methods: Bacterial isolates were screened for production of indole-3-acetic acid (IAA) and siderophores and solubilization of phosphate. The ability of bacterial isolates to inhibit the growth of seven phytopathogenic fungi affecting soybean was determined using a dual plate assay. Bacillus spp. were further selected and examined in a seed germination test. Result: All Bacillus spp. isolates were positive for IAA production, while siderophore production and P-solubilization were observed in 80% and 20% bacterial isolates, respectively. Bacillus spp. exhibited the highest antifungal activity against Diaporthe caulivora, followed by Diaporthe sojae, Diaporthe eres, Diaporthe longicolla and Macrophomina phaseolina and the least antagonistic effect toward Fusarium graminearum and Fusarium subglutinans. Selected isolates of B. subtilis significantly affected final germination, shoot length, root length, shoot dry weight and root dry weight of two soybean cultivars. The most effective Bacillus spp. isolates could be used as potential inoculants for improving soybean productivity.

Determination of Biocontrol Potential of Bacillus spp. and Stenotrophomonas sp. against Macrophomina phaseolina in Sunflower

Macrophomina phaseolina is a soil pathogen known as charcoal rot and can cause up to 90% yield loss in sunflower under suitable conditions. The serious damage caused by chemicals used in the control of soil-borne pathogens to the environment and health has become one of the most important concerns in agriculture. Therefore, in our study, it was aimed to determine the in vitro antagonistic effects of various bacterial species against M phaseolina. A total of 38 bacterial strains were isolated from soil samples in the rhizosphere of Malva sylvestris (hibiscus), Vicia sativa (vetch), Cicer arietinum (chickpea), Papaver rhoeas (weasel), Carlina marianum (thistle), Glebionis coronaria (crown daisy) and Vicia faba collected from Urla district of İzmir. All bacterial strains exhibited antibiosis effect under in vitro conditions, but it was determined that 5 bacterial isolates among them showed a high inhibition zone and showed an average inhibition potential ranging between 55% and 74%. The most effective bacteria identified at species and genus level by Maldi biotyping (MALDI-TOF MS) were identified as Bacillus amyloliquefaciens, Stenotrophomonas sp. and Bacillus cereus (3 isolates), and these species showed that they can be important biocontrol agents in biological control against M. phaseolina.

Determination of the Antagonistic Effects of Some Rhizospheric Bacteria against Macrophomina phaseolina under In Vitro Conditions

Macrophomina phaseolina (Tassi) Goid. is a fungal pathogen causes charcoal rot disease (Sin: Rhizoctonia bataticola) and is responsible for significant yield losses in many plants. In our study, we aimed to evaluate the antagonistic ability of 39 different bacteria, isolated from the fields of sugar beet in 2019, against the pathogen Macrophomina phaseolina isolated from sugar beet, beans and chickpeas. Approximately 31% of the bacteria showed antibiosis effect against the pathogen. It was determined that the effectiveness level of Lelliottia amnigena, Bacillus atrophaeus, B.pumilus and B. cereus (7 isolates) was moderate to high against Macrophomina phaseolina. Bacillus atrophaeus (PTo15-1a) showed the highest efficacy of 80%, 72.94% and 82.35% against Macrophomina phaseolina of chickpea, bean and sugar beet respectively. Lelliottia amnigena (Pto 14-1b) was moderately effective (57.78%) against the chickpea isolate of the pathogen. It was observed that of the seven Bacillus cereus isolates used in the experiment, three isolates (Pto14-1a, Pto12-1b, Pto17-1b) were highly effective against the chickpea pathogen, two (Pto12-1b, Pto14-2b) against bean pathogen, and one (Pto15-1b) against sugar beet isolate. Results have shown varied level of antagonism by different test bacterial against different Macrophomina phaseolina isolates, while the highest level of antibiosis shown by Bacillus atrophaeus against all pathogenic isolates indicated that it can be a potential future bioagent in managing the disease.

Feeding selectivity of Aphelenchoides besseyi and A. pseudogoodeyi on fungi associated with Florida strawberry

Aphelenchoides besseyi and A. pseudogoodeyi are foliar nematodes associated with commercial strawberry production in Florida, USA. The reproductive and feeding habits of these two nematode species were assessed on Florida isolates of the fungi Botrytis cinerea, Colletotrichum gloeosporioides, Macrophomina phaseolina, and Neopestalotiopsis spp. pathogenic to strawberry, and the non-pathogenic isolates of Fusarium oxysporum and Monilinia fructicola grown on PDA in petri dishes. Each culture was inoculated with six specimens with mix life stages of either A. besseyi and A. pseudogoodeyi and incubated at 24°C under axenic and non-axenic conditions 23 and 31 days after inoculation, respectively. Aphelenchoides besseyi reproduction rates were significantly higher on strawberry pathogenic isolates of B. cinerea, C. gloeosporioides, and Neopestalotiopsis rosae than on the non-pathogenic isolates of F. oxysporum and M. fructicola. In contrast, reproductive rates of A. pseudogoodeyi did not significantly vary across the fungi cultures. For both nematode species, Macrophomina phaseolina was a poor host because it did not produce mycelium on the media used. Our findings indicate that A. besseyi is more selective in its fungal-feeding preference than A. pseudogoodeyi. Additionally, A. pseudogoodeyi eggs and juveniles were significantly higher than adults. Yet, for A. besseyi, adult stages were more common. Fungi aid in the maintenance of soil-dwelling populations of these two nematode species. Removing fungi-infected strawberry plant residues is both a desirable and effective management practice to limit A. besseyi in central Florida commercial strawberry fields.

First report of Macrophomina phaseolina causing charcoal root rot of Hebe (Veronica cupressoides, V. ochracea, and V. pinguifolia) in Oregon, U.S.A.

Hebes (Veronica spp. in the section Hebe) are ornamental perennials and shrubs grown for their flowers and symmetric, evergreen leaves. They are uncommon in U.S. horticulture and are only produced by a few nurseries regionally (Oregon and Washington). In June, July, and August (2016 to 2021), stems on 1 to 5-year-old Veronica cupressoides, V. ochracea, and V. pinguifolia in five landscape plantings around Benton County, OR (17 plants total, locations 2 to 37 km apart) began to wilt, turn brown, and die. At least nine of the plants originated from a single nursery. Initially, just one or two stems/plant were affected, but eventually the entire plant died. Stem tissues were discolored brown to black internally and the roots were dry and necrotic. Leaves turned brown and brittle, but remained attached. Stems from each plant were disinfested in 0.5% NaOCl (1 min), rinsed in 70% ethanol, and dried (2 min). Pieces (5 mm2) were then plated onto 1/2 strength potato dextrose agar amended with streptomycin (50 mg/liter) and incubated in the dark at 20°C. Three to five days later, greyish-white cultures producing black microsclerotia (75 × 110 µm, n = 50) grew out of all samples. No spores were produced. All isolates were identified as Macrophomina phaseolina by morphology and by ≥99% homology (566-570/571 nt) to the internal transcribed spacer sequence (primers ITS1 and ITS4) from the type specimen (GenBank KF766195) (Hyde et al. 2014). Three representative sequences were deposited in GenBank (MZ726450 to MZ726452). Inoculum was prepared from these isolates by growing cultures in 250 ml of potato dextrose broth on a shaker (125 rpm at 25°C). After 2 weeks, the broth was decanted and the fungal biomass was air dried for 3 days at 25°C before grinding into a powder with a mortar and pestle. Three plants each of 6-month-old V. ochracea 'James Stirling', V. cupressoides 'McKean', and V. pinguifolia 'Sutherlandii' were inoculated with each isolate by rinsing the soil off of the roots with tap water, trimming off 0.5 cm of the roots, and then soaking the rootball in a slurry of 1 g dried inoculum in 500 ml of 0.2% water agar (WA) for 10 minutes (Reyes Gaige et al. 2010). Three plants of each species that were soaked in plain 0.2% WA served as negative controls. Afterwards, plants were potted into soilless media (Metro-Mix 840, Sun Gro Horticulture, Agawam, MA) in 3.5 inch square pots and arranged in a completely randomized design in a greenhouse set at 28/24°C day/night. The experiment was conducted three times. One to three months later, inoculated plants began to turn yellow, wilt, and die whereas all control plants remained healthy. The same pathogen was reisolated from 90% of the inoculated plants, but never from negative controls. M. phaseolina was reported on strawberry in southern Oregon in 2014 (Pscheidt and Ocamb 2021), but has not been reported from locations further north in the state where soil temperatures are cooler. It is unusual that M. phaseolina was isolated from an uncommon host at five different locations in an area of the state where the pathogen was not known to occur. Based on this, and on the number of infected plants originating from a single source, it seems likely that M. phaseolina was accidentally spread on contaminated plants produced by the nursery industry, where the warmer temperatures in production greenhouses would provide a more conducive environment for the pathogen's growth and spread. Growers should keep watch for symptoms of this pathogen in their nurseries.