Over the past decade, we have seen an increasing market for biopesticides and an increase in number of microbial control studies directed towards plant‐parasitic nematodes. This literature survey provides an overview of research on biological control of two economically important plant‐parasitic nematodes, Meloidogyne incognita (Kofoid & White) Chitwood (southern root‐knot nematode) and Heterodera glycines Ichinohe (soybean cyst nematode) using spore‐forming plant growth‐promoting rhizobacteria (PGPR). In this review, the current biological control strategies for the management of those cotton and soybean nematodes, the mechanism of using BacillusPGPR for biological control of plant‐parasitic nematode including induced systemic resistance and antagonism and the future of biological control agents on management of plant‐parasitic nematodes are covered.

Plant-parasitic nematodes (PPN) are among the most economically and ecologically damaging pests, causing severe losses of crop production worldwide. Chemical-based nematicides have been widely used, but these may have adverse effects on human health and the environment. Hence, biological control agents (BCAs) have become an alternative option for controlling PPN, since they are environmentally friendly and cost effective. Lately, a major effort has been made to evaluate the potential of a commercial grade strain of plant growth-promoting rhizobacteria (PGPR) as BCAs, because emerging evidence has shown that PGPR can reduce PPN in infested plants through direct and/or indirect antagonistic mechanisms. Direct antagonism occurs by predation, release of antinematicidal metabolites and semiochemicals, competition for nutrients, and niche exclusion. However, the results of direct antagonism may be inconsistent due to unknown endogenous and exogenous factors that may prevent PGPR from colonizing plant’s roots. On the other hand, indirect antagonism may occur from the induced systemic resistance (ISR) that primes whole plants to better fight against various biotic and abiotic constraints, actuating faster and/or stronger defense responses (adaption), enhancing their promise as BCAs. Hence, this review will briefly revisit (i) two modes of PGPR in managing PPN, and (ii) the current working models and many benefits of ISR, in the aim of reassessing current progresses and future directions for isolating more effective BCAs and/or developing better PPN management strategy.

Heterodera glycines, the soybean cyst nematode, is the most economically important plant-parasitic nematode on soybean production in the U.S. The objectives of this study were to evaluate the potential of plant growth-promoting rhizobacteria (PGPR) strains for mortality of H. glycines J2 in vitro and for reducing nematode population density on soybean in greenhouse, microplot, and field trials. The major group causing mortality to H. glycines in vitro was the genus Bacillus that consisted of 92.6% of the total 663 PGPR strains evaluated. The subsequent greenhouse, microplot, and field trials indicated that B. velezensis strain Bve2 consistently reduced H. glycines cyst population density at 60 DAP. Bacillus mojavensis strain Bmo3 suppressed H. glycines cyst and total H. glycines population density under greenhouse conditions. Bacillus safensis strain Bsa27 and Mixture 1 (Bve2 + Bal13) reduced H. glycines cyst population density at 60 DAP in the field trials. Bacillus subtilis subsp. subtilis strains Bsssu2 and Bsssu3, and B. velezensis strain Bve12 increased early soybean growth including plant height and plant biomass in the greenhouse trials. Bacillus altitudinis strain Bal13 increased early plant growth on soybean in the greenhouse and microplot trials. Mixture 2 (Abamectin + Bve2 + Bal13) increased early plant growth in the microplot trials at 60 DAP, and also enhanced soybean yield at harvest in the field trials. These results demonstrated that individual PGPR strains and mixtures can reduce H. glycines population density in the greenhouse, microplot, and field conditions, and increased yield of soybean.

During 2017, virus-like symptoms were observed in cotton fields in six counties in coastal Alabama infested by the whitefly Bemisia tabaci (Genn.) and cotton aphid Aphis gossypii (Glover). Symptoms consisted of foliar distortion, curling, rolling, and bluish-green discoloration, vein-clearing, and shortened internodes that resulted in dwarfing of plants, and reduced boll set. Disease incidence ranged from 3-30% per field, resulting in ~560 kg/ha loss, and affecting 25% of the 50,585 ha cotton crop in Alabama, with a loss of ~50,000 bales valued at $19 million dollars. Leaves were collected from symptomatic cotton plants, Gossypium hirsutum L., in Barbour County, Alabama during late August and mid-September 2017. Total DNA and RNA were purified and subjected to DNA and RNAseq Illumina Hi-Seq 2500 (paired-end reads, 150 bp) shotgun sequencing. The de novo-assembled DNA contigs yielded no match to viral sequences available in the GenBank database. However, one RNA de novo assembled contig (103 reads) of 1143...

Due to increased restrictions on the use of chemical nematicides, alternative nematode management strategies, including biocontrol, are needed. The objectives of this study were to evaluate the potential of Bacillus firmus GB-126 and Paecilomyces lilacinus 251 in commercial formulations applied separately or concomitantly to manage Rotylenchulus reniformis in cotton grown under greenhouse, microplot, and field conditions. In the greenhouse, seed treated with B. firmus (1.4 × 10⁷ CFU/seed), an application of P. lilacinus (0.3% vol/vol of water), or the combination of B. firmus and P. lilacinus reduced the number of females, eggs, and vermiforms of R. reniformis (P ≤ 0.02) and increased populations of free-living nematodes (P ≤ 0.01). In microplots and field conditions, populations of R. reniformis vermiforms decreased when exposed to B. firmus and P. lilacinus biocontrol agents at midseason (P ≤ 0.04). Furthermore, stem diameter and free-living nematode numbers increased (P ≤ 0.01) with the combination of B. firmus and P. lilacinus. In the field, numbers of females, eggs, and vermiform life stages at the end of the growing season decreased in the presence of the biocontrol agents applied individually or concomitantly (P ≤ 0.01). Cotton yields from the application of B. firmus GB-126 and P. lilacinus 251 were similar to those from aldicarb, the chemical nematicide standard.

Corynespora cassiicola (Berk. & Curt.) C.T. Wei is a fungus that occupies several diverse habits from a saprophyte to a parasite of plants, nematodes and humans. As a phytoparasitic fungus, C. cassiicola causes disease in a broad range of plant species worldwide. It causes target spot on cotton (Gossypium hirsutum L.) and Soya bean (Glycine max (L.) Merr.) and is a disease of economic importance. Increasing demand for food and fibre to supply a growing world population requires increasing yields of crops on existing agricultural land while protecting the environment, following the principles of integrated pest management (IPM) strategies. The current review provides a summary of research conducted on C. cassiicola with a special focus on target spot of cotton and Soya bean. The biology and diversity among C. cassiicola isolates are presented. A more detailed discussion on two essential IPM strategies is provided emphasizing their importance in disease management; the risk of fungicide resistance development with the use of fungicides to control target spot, and the need for genetic control with resistant cultivars.