Local Trichoderma strains as a control strategy of complex black root rot disease of strawberry in Egypt

Enhanced activity of Trichoderma asperellum introduced in solarized soil and its implications on the integrated control of strawberry-black root rot

An effective method for maintaining the activity and longevity of microorganisms in adverse conditions is microencapsulation. In the present study, synthetic alginate pellets were developed as carriers for the biocontrol agent Trichoderma asperellum. In two field experiments, solarization was applied for three weeks to loamy clay soil that was naturally infested with strawberry-black root rot fungi (Fusarium solani, Rhizoctonia solani and Machrophomina phaseolina). Following solarization, T. asperellum-based alginate pellets or spore suspension were added to the soil. Data reveal that, three weeks solarization of irrigated soil increased its maximum temperature reached by 11-14.2 °C (1-10 cm depth), 11.6-13.1 °C (11-20 cm depth) and 10.1-12.2 °C (21-30 cm depth). In either trial, solarization also successfully lowers the vitality of strawberry-black root rot fungi directly after the solarization phase. When compared to controls, strawberry-black root rot was substantially less common in solarized plots. In two field trials, soil solarization followed by inoculation with alginate pellets based on T. asperellum led to the greatest reductions in black root rot incidence (59.3 and 74.1 %) and severity (72.5 and 75.2 %), as compared to un-solarized control plots. In vivo studies, this treatment dramatically increased the activity of defensive enzymes (peroxidase and chitinase) and strawberry yield (60.5 and 60.0 %, respectively), as compared to non-solarized control plots. In two field studies, the rhizosphere population of native Trichoderma spp. Developed more in solarized soils after the application of alginate pellets based on T. asperellum (86.5 and 83.6 %, respectively), compared to the non-solarized control.

Biological Control of Root Rot of Strawberry by Bacillus amyloliquefaciens Strains CMS5 and CMR12

Strawberry root rot caused by Fusarium solani is one of the main diseases of strawberries and significantly impacts the yield and quality of strawberry fruit. Biological control is becoming an alternative method for the control of plant diseases to replace or decrease the application of traditional chemical fungicides. To obtain antagonistic bacteria with a high biocontrol effect on strawberry root rot, over 72 rhizosphere bacteria were isolated from the strawberry rhizosphere soil and screened for their antifungal activity against F. solani by dual culture assay. Among them, strains CMS5 and CMR12 showed the strongest inhibitory activity against F. solani (inhibition rate 57.78% and 65.93%, respectively) and exhibited broad-spectrum antifungal activity. According to the phylogenetic tree based on 16S rDNA and gyrB genes, CMS5 and CMR12 were identified as Bacillus amyloliquefaciens. Lipopeptide genes involved in surfactin, iturin, and fengycin biosynthesis were detected in the DNA genomes of CMS5 and CMR12 by PCR amplification. The genes related to the three major lipopeptide metabolites existed in the DNA genome of strains CMS5 and CMR12, and the lipopeptides could inhibit the mycelial growth of F. solani and resulted in distorted hyphae. The inhibitory rates of lipopeptides of CMS5 and CMR12 on the spore germination of F. solani were 61.00% and 42.67%, respectively. The plant-growth-promoting (PGP) traits in vitro screening showed that CMS5 and CMR12 have the ability to fix nitrogen and secreted indoleacetic acid (IAA). In the potting test, the control efficiency of CMS5, CMR12 and CMS5+CMR12 against strawberry root rot were 65.3%, 67.94% and 88.00%, respectively. Furthermore, CMS5 and CMR12 enhanced the resistance of strawberry to F. solani by increasing the activities of defense enzymes MDA, CAT and SOD. Moreover, CMS5 and CMR12 significantly promoted the growth of strawberry seedlings such as root length, seedling length and seedling fresh weight. This study revealed that B. amyloliquefaciens CMS5 and CMR12 have high potential to be used as biocontrol agents to control strawberry root rot.

Soil bio-solarization and Trichoderma asperellum suppress black root rot disease and increase strawberry yield.. [DOI: 10.21203/rs.3.rs-3096529/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Trichoderma asperellum applied as pellets, disks, or spore suspension against the causal agents of strawberry-black root rot disease represented by three fungal species was tested. The pellets/disks could significantly reduce the growth area of the pathogenic fungi Rhizoctonia solani, Fusarium solani, and Macrophomina phaseolina in vitro. Solarization via mulching soil with transparent polyethylene sheets could affect these pathogens. It reduced the counts of the fungi buried in cloth bags at 1–10 cm of soil surface by 70, 65, and 65% for R. solani, F. solani, and M. phaseolina, respectively relative to unmulched soil. Yet, the more depths of bags in soil, the less the mulching affects the three pathogens. In two field experiments, the disease incidence and severity were more reduced when T. asperellum pellets/suspension was integrated with bio-solarization (mulching soon after bio-fumigation with Al-Abour Compost®)) than any single treatment. The highest reductions obtained by T. asperellum pellets combined with bio-solarization averaged 75 and 73.8%, respectively. Bio-solarization with Actamyl affected the disease incidence/severity to a lesser extent. All tested treatments significantly boosted yield of strawberry plants. Strawberry yield and activities of the pathogenesis-related proteins peroxidase and chitinase showed favorable responses almost parallel to the extent of reduction in the disease incidence and severity caused by all treatments. The highest yield increase achieved via combining T. asperellum pellets with bio-solarization was 160.8%. Our results support hypothetical biocontrol potential that T. asperellum and bio-solarization together with adequate phytosanitary measures can reliably control strawberry-black root rot disease and enhance strawberry yield.

Native bacteria for field biocontrol of black root rot in Egyptian strawberry

Background

Increasing cultivation of strawberry in Egypt has boosted efforts to increase its yield. Biocontrol agents (BCAs) may avoid side effects and health risks caused by chemical fungicides used to control black root rot disease in strawberry. Some BCAs control the disease and augment strawberry yield, but additional research is needed to fit BCAs into emerging control strategies. The impact of six bacterial isolates of Paenibacillus polymyxa and Bacillus brevis on this disease and on berry yield is reported and compared to a common chemical fungicide.

Results

The bacterial isolates reduced the growth of the black root rot causal agents Fusarium solani, Rhizoctonia solani, and Macrophomina phaseolina, in dual culture bioassays. The greatest fungal inhibition was caused by P. polymyxa isolates 1 and 2 and B. brevis isolate 2. They suppressed the growth of F. solani, R. solani, and M. phaseolina by more than 74, 76, and 79%, respectively. Disease severity and incidence were significantly reduced on naturally infected strawberry plants in the field by the six isolates. The best results were obtained by the superior bioassay isolates which suppressed the disease incidence by 73, 77, and 71%, and its severity by 72, 78, and 70%, respectively. Disease suppression by bacteria was comparable to that by fungicide Actamyl. Bacteria surpassed Actamyl with regard to strawberry yield and enhancement of peroxidase and chitinase activities in the leaves.

Conclusions

These isolates are potential benign alternatives to fungicides used against black root rot in strawberry in Egypt. More studies are needed to examine their economic use on a wider scale.

Application of Bacillus pumilus isolates for management of black rot disease in strawberry

Background

Black root rot of strawberry plants caused by Rhizoctonia solani, Fusarium solani, and Pythium sp. is a serious disease in Egypt. Biocontrol agents have frequently proved to possess paramount and safe tools against many diseases. The impact of soil treatments with 3 Bacillus pumilus isolates on black root rot disease of strawberry plants caused by R. solani, F., and Pythium sp. under laboratory and field conditions was examined herein on the commonly used ‘Festival’ strawberry cultivar. To increase the bacterial adhesion and distribution on the roots, each seedling was dipped in bacterial cell suspension at 1 × 108 colony-forming units/ml of each separate bacterial isolate for 30 min then mixed with 5% Arabic gum.

Results

The tested B. pumilus isolates significantly reduced the growth area of these 3 fungi. The two bacterial isolates Nos. 2 and 3 reduced the growth area by more than 85.2, 83.6, and 89.0% for R. solani, F. solani, and Pythium sp., respectively. Likewise, the 3 bacterial isolates significantly (P ≤ 0.05) inhibited the disease under field conditions. Isolates Nos. 2 and 3 suppressed the disease incidence by 64.4 and 68.9% and disease severity by 65.3 and 67.3%, respectively. The fungicide Actamyl had effect similar to that of the 2 isolates. B. pumilus isolates significantly enhanced growth parameters and yields of strawberry plants; isolates Nos. 2 and 3 raised the yield by 66.7 and 73.3%, respectively.

Conclusions

Bacillus pumilus isolates could effectively manage the black rot disease in strawberry herein. Due to the significant impact of the root rot disease on strawberry yield, B. pumilus should be further tested to manage the disease on strawberry on large scale in Egypt.