Abstract
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.
Highlights
Heterodera glycines Ichinohe, the soybean cyst nematode, was first reported in the United States in North Carolina in 1954 [1]
Among all the plant growth-promoting rhizobacteria (PGPR) strains tested, 6.8% caused significantly greater level of mortality percentage than the biological standard Clothianidin plus B. firmus I-1582 (P 0.05); 7.9% caused significantly greater level of mortality percentage than the level caused by P. nishizawae (P 0.05); 5.6% caused statistically similar mortality percentage to the level caused by Aldicarb (P 0.05); and 13.2% caused significantly greater mortality percentage than the level caused by untreated control (P 0.05) (Table 1)
In vitro screening of the 663 PGPR strains indicated that 13 Bacillus species including B. altitudinis, B. aryabhattai, B. lentus, B. methylotrophicus, B. mojavensis, B. mycoides, B. pumilus, B. safensis, B. simplex, B. subtilis subsp. subtilis, B. toyonensis, B. velezensis, B. weihenstephanensis, and species of Fictibacillus and Paenibacillus caused greater than 50% mortality percentage of H. glycines J2 in vitro
Summary
Heterodera glycines Ichinohe, the soybean cyst nematode, was first reported in the United States in North Carolina in 1954 [1]. Biological control agents previously assessed for the management of H. glycines were nematophagous fungi, endoparasitic fungi, female and eggparasitic fungi, fungi producing antibiotic substances, vesicular-arbuscular mycorrhizal (VAM) fungi, Pasteuria spp., chitinolytic bacteria, and plant-growth-regulatory bacteria [5]. The fungal genera Exophiala, Fusarium, Gliocladium, Neocosmospora, Paecilomyces, Phoma, Stagonospora, and Pochonia were commonly recovered from females and cysts of H. glycines [5]. Isolates from those fungi could be female and/or eggparasitic fungi. Tylka et al [9] found that numbers of H. glycines in roots and soil were decreased by VAM fungi by as much as 73% at the highest H. glycines inoculum level through 49 days after planting in the greenhouse experiments
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