Bio-management of nematode-fungus disease complex

Introduction

Sustainable agriculture is critical to meet the growing global food needs. However, crop productivity is declining as a result of the risk posed by a wide range of pathogens. When these pathogens co-infect, disease complex is developed which is challenging to manage. 

When two organisms interact synergistically, a disease complex is created. Positive synergistic interactions are defined as those in which the combined effects of the fungus and nematode cause more plant damage than the total of the individual damages caused by the pathogens. Atkinson (1892) reported the first instance of nematode–fungus interaction when he noted that the severity of cotton fusarium wilt, which is caused by Fusarium oxysporum f.sp. vasinfectum, increased when root-knot nematodes (Meloidogyne spp.) were present. Later, field tests using 1,3-dichloropropene or ethylene dibromide to sterilize soil provided more proof of the relationship between Fusarium spp. and root-knot nematodes in cotton (Smith, 1948; Newson and Martin, 1953). The frequency of wilting cotton plants was greatly decreased in areas where soil sterilant was applied. Since the compounds are thought to have minimal fungicidal effect, it was suggested that by lowering the densities of nematodes, they interact with, they indirectly decreased pathogen infection.

Nematode-fungus disease complex is a major constraint in majority of crops grown worldwide. Generally, chemical fungicides and nematicides are employed to counteract the harm that diseases inflict, however biological control is environmentally friendly option that is necessary because of the health and environmental hazards associated with chemicals. 

Occurence 

The development of diseases in cultivated crops has long been known to depend on the complex interrelationship between host, pathogen, and prevailing environmental conditions. Additional potential for interactions with other microorganisms sharing the same ecological niche exists in the case of soilborne diseases. Nematodes have a major role in the development of diseases caused by soilborne pathogens, as evidenced by numerous crops worldwide. For most crops, the nematode-fungus disease combination is a significant hindrance, as shown below.

Nematode-fungus disease complexes in crops

 Bio management

Using beneficial bacteria and fungi, is a key component of biocontrol techniques. These helpful bacteria are naturally environmentally benign. Use of these advantageous microorganisms in a long run can control plant diseases just as chemical methods.

Trichoderma harzianum and Pseudomonas fluorescens were effective bioagents in the management of disease complex caused by Meloidogyne incognita and Rhizoctonia solani on Okra. The bioagents were tested in conjunction with nematicide (Carbosulfan 25 ST) and fungicide (Carbendazim 50% WP) as a single or combined seed treatment and soil application resulted in a significant reduction in the disease complex coupled with improved plant growth traits. However, seed treatment of either or both of the bioagents was more effective than soil application in decreasing pre- and post-emergence damping off due to fungus, and nematode population, besides increasing the growth parameters of the plants (Bhagawati et al.,2009).

In order to manage the disease complex caused by R. reniformis and F. oxysporum f.sp. vasinfectum in cotton, the biocontrol agents, Glomus mosseae, P. fluorescens, and T. viride, were applied as seed treatment and soil application. Application of P. fluorescens as seed treatment and G. mosseae as soil application were successful in reducing nematode multiplication and wilt incidence with an increase in plant growth. Hence, G. mosseae and P. fluorescens can be used in the management of disease complex of cotton on the long run (Seenivasan and Murugan, 2011).

In another study, using bacterial, fungal, and chemical biocontrol agents to manage the castor wilt disease complex caused by F. oxysporum f. sp. ricini and Rotylenchulus reniformis, it was recorded that the most successful method for lowering the incidence of wilt and the population of reniform nematode was to apply a combination of carbofuran (2 g/kg soil) and carbendazim (1 g/kg soil) followed by Trichoderma viride (4 g/kg seed) and Pseudomonas fluorescens (10 g/kg seed) (Shalini et al.,2014).

To control the disease complex in tuberose caused by root knot nematode, Meloidogyne incognita and the fungus, Fusarium oxysporum it was recorded that among the combined application of Bacillus subtilis Bbv 57 and Pseudomonas fluorescens Pfbv 22 (each at 500 ml/ha) at monthly interval recorded maximum efficacy against the disease complex with the induction of high level of defense enzymes over other strains (Meena et al., 2016).        

Bacillus subtilis strain Bbv 57 (KF718836) was shown to be efficient for managing the wilt nematode complex in Gerbera caused by Fusarium oxysporum f. sp. gerberae and Meloidogyne incognita (Ramyabharathi et al, 2018). About 10 and 100 μl of culture filtrate of the strain significantly reduced the mycelial growth of F. oxysporum f. sp. gerberae (KM523669) by 44.33 and 63.33%, respectively in vitro. The culture filtrate at 100% concentration killed nematode eggs (7.0 hatched) and juveniles (87% mortality). Strain Bbv 57 showed significant potential for use as biocontrol against Fusarium wilt-root knot nematode disease complex in gerbera under greenhouse conditions, as shown by its reduced wilt incidence of 15.33% and its capacity to produce antifungal and nematicidal activities.

In another study, to evaluate the efficacy of 108 rhizobacterial isolates collected from different Oilseed rhizospheres against the wilt pathogen, Fusarium oxysporum f.sp. ricini and reniform nematode, Rotylenchulus reniformis under in vitro conditions it was recorded that among the 108 isolates tested, four isolates were reported to inhibit the radial growth of Fusarium oxysporum f.sp. ricini by more than 50% and caused more than 80% of juvenile (J4) mortality of reniform nematode (Fathima et al., 2024a). 

A novel lipopeptide producing rhizobacteria, Bacillus spizizenii proved to be effective against wilt pathogen, Fusarium oxysporum f.sp. ricini and reniform nematode, Rotylenchulus reniformis under in vitro conditions. The 100% concentration of the lipopeptide extract was recorded to reduce the mycelial growth of F. oxysporum f.sp. ricini up to 77.36% and also caused 92% juvenile mortality of R. reniformis at 96h of exposure of the extract to juveniles. From pot culture studies, it was recorded, that plants treated with B. spizizenii significantly reduced the wilt incidence up to 78.17% and nematode soil population up to 209 /200 cc soil and increased plant growth parameters, which confirmed the efficacy of B. spizizenii against the fungus and nematode (Fathima et al., 2024b).

References

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Content contributors

• Sk. Menaaz Fathima, Department of Plant Pathology, College of Agriculture, Rajendranagar, Professor Jayashankar Telangana State Agricultural University, Hyderabad, Telangana, India.
• K. Sankari Meena, Indian Institute of Oilseeds Research, PJTSAU, Hyderabad, Telangana, India
• B. Vidya Sagar,  Department of Plant Pathology, College of Agriculture, Rajendranagar, Professor Jayashankar Telangana State Agricultural University, Hyderabad, Telangana, India.