Impact of Wheat on Soybean Cyst Nematode Population Density in Double-Cropping Soybean Production

Double-cropping is defined as producing more than one crop on the same parcel of land in a single growing season. It is reported to have many benefits when incorporated in cropping systems, including improving soil health. In some double-cropping systems, soybean is planted following winter wheat. The soybean cyst nematode (SCN) (Heterodera glycines Ichinohe) is a major soybean pathogen, and several reports suggest suppressive effects of wheat on SCN populations. Field trials were conducted from 2017 to 2018 to investigate the effect of wheat on SCN populations in double-cropping soybean. Nine fields with three levels of initial SCN populations (low, moderate, and high) were selected in Illinois. Wheat was planted in strips alternating with strips-maintained weed-free and under fallow over winter and early spring. Soybean was planted in all strips after wheat harvest. SCN egg densities were acquired at four time points: wheat establishment, post-wheat/pre-soybean, mid-soybean (R1 growth stage or beginning of flowering), and post-soybean harvest. Wheat strips reduced SCN egg densities compared with fallow strips at the R1 stage (−31.8%) and after soybean harvest (−32.7%). Double-cropping soybean with wheat has the potential to suppress SCN field populations and is a system with the potential to provide additional farm income. This study is meant to be a first step toward a better understanding of the mechanisms that govern the suppression of SCN by wheat.

Interaction between mycorrhizal fungi and Meloidogyne javanica on the growth and essential oil composition of basil (Ocimum basilicum)

Plant-parasitic nematodes and arbuscular mycorrhizal fungi (AMF) have been reported to alter the yield and chemical composition of basil (Ocimum basilicum) essential oil. The aim of this study was to evaluate the effectiveness of AMF to control the root-knot nematode Meloidogyne javanica in basil and to investigate the effects of nematode-AMF interactions on plant growth, phosphorus (P) absorption, and essential oil composition. The experiment was conducted under greenhouse conditions following a completely randomized 3 × 2 factorial (two fungal species and an uninoculated control × inoculated and uninoculated seedlings) arrangement with 10 replicates. Substrates were inoculated with Claroideoglomus etunicatum, Rhizophagus clarus, or no fungi (control) and sown with basil seeds. After 20 days, half of the seedlings were inoculated with 4,000 M. javanica eggs. After 60 days, the vegetative parameters, P absorption, essential oil composition, nematode population density, AMF root-colonization efficiency, and AMF spore density were determined. The presence of AMF increased the basil’s fresh weight and ability to absorb P, while reducing the M. javanica reproduction. In total, 21 compounds were identified in basil essential oil, the concentrations of which varied according to the treatments. The major components were eucalyptol, linalool, eugenol, β-elemene, trans-α-bergamotene, and τ-cadinol. Inoculation with AMF decreased the linalool levels but increased the amount of eucalyptol. Mycorrhizal plants showed increased shoot height, P uptake, and essential oil yield and a decreased nematode population density in their roots

Mineral composition of beetroot treated with potential elicitors and inoculated with Meloidogyne javanica

Background The root-knot nematode Meloidogyne javanica can infect beetroots, causing extensive damage to this food crop. As chemical and genetic control tactics have shown limited efficacy, new strategies are needed to improve the integrated management of this parasite. This study assessed the influence of potential defence elicitors and M. javanica infection on the mineral composition of beetroot. Plants were treated with acibenzolar-S-methyl (ASM), citrus biomass, or a mannanoligosaccharide-based product (MOS) and inoculated with 1000 eggs and second-stage juveniles of M. javanica. At 60 days after inoculation, beetroot plants were harvested and evaluated for nematode population density, vegetative growth, and mineral content. Results All potential elicitors reduced nematode population density in beetroots (p ≤ 0.10) and improved the vegetative parameters of inoculated plants (p ≤ 0.05), except shoot fresh weight. Some minerals were found to be negatively affected by treatments, particularly calcium, whose levels were consistently lower in treated plants. On the other hand, M. javanica inoculation increased magnesium, iron, manganese, zinc, and copper contents in beetroots. However, the latter mineral (Cu content) of inoculated plants was positively influenced by MOS and ASM. Conclusion Potential elicitor treatments did not improve the mineral composition of beetroot, but were effective in reducing nematode population density. Plants inoculated with M. javanica had higher mineral levels. However, gall formation decreases the commercial value of the crop and might render it unsuitable for commercialisation. M. javanica-infected beetroots may be used for nutrient extraction or sold to food processing industries.

ACTIVITY OF RUTA GRAVEOLENS L. AGAINST ROOT-KNOT NEMATODES (MELOIDOGYNE spp.)

Two in vitro experiments and two open field trials were carried out to investigate the nematicidal effect of Ruta graveolens on the root-knot nematode Meloidogyne incognita. In the first in vitro experiment the nematode egg masses were immersed for 3 weeks in aqueous leaf extract of rue plants and then subjected to an hatching test in distilled water for five more weeks. In the other in vitro experiment M. incognita egg masses were exposed to the rue extract for 4, 8 and 16 hours and then incubated in distilled water for 8 weeks. Distilled water and a 5 μg/mL an aqueous solution of Fenamiphos or only distilled water were used as controls in the first and second in vitro experiment, respectively. Both hatching tests were carried out in a growth cabinet at 25±2 0C, providing four replicates for each treatment. In the first experiment the hatching from the egg masses treated with rue extracts and Fenamiphos solution resulted significantly lower than that in the untreated control. In the second in vitro experiment, a 8-hour immersion of the egg masses in the rue extract resulted in a final hatch significantly lower than that in distilled water. The nematicidal effect of R. graveolens green manure was investigated in open field condition on tomato and tobacco. Plots amended with rue plant biomass were compared with untreated and Fenamiphos treated plots (3 t/ha). Four replications were provided for each treatment. Crop yield, root gall index and soil nematode population density were recorded at the end of each crop cycle. Soil incorporation with R. graveolens plant materials significantly increased both tomato and tobacco yield and reduced root gall index and soil nematode population density in comparison to the untreated controls. These experiments demonstrated a high suitability of R. graveolens for the development of new sustainable nematicidal products.

Yield losses caused by plant parasitic nematodes graphical estimation

Curves for graphical estimation of yield losses caused by plant parasitic nematodes were calculated on the basis of the relationship between soil nematode population density and damage to plants as described by the Seinhort’s equation y = m + (1 – m) z(P-T). By a logarithmic transformation this equation was transformed as y = m + (1 – m) 1.05[(P/-T) + 1] and solved considering values of tolerance limit (T) and the minimum relative yield (m) from the literature. The obtained curves that can be defined “Curves of nematode-pathogenicity” allow a quick and easy evaluation of yield losses for each known crop-nematode relationship.

Meloidogyne hapla development on growing legume plants – Short Communication

The legume genus lupine, pea, faba bean and common vetch were cultivated under natural conditions in pots filled with soil naturally infected with Meloidogyne hapla Chitwood, 1949. The nematode population density increased relevantly in the soil planted with the faba bean (cultivars (cvs.) Bobas, Amulet, Albus) and the pea cv. Lasso, in which numerous root galls and egg masses appeared. The narrow-leaved lupine (cvs. Karo, Zeus), yellow lupine (cvs. Parys, Lord) and white lupine (cv. Boros) cultivation decreased the nematode population density and these were not statistically significant when compared with the nematode density in a fallow soil.

Identification of Chili Pepper Genotypes (Capsicum spp.) Resistant to Meloidogyne enterolobii

Chili pepper has economic importance and is the dominant Solanaceae in the market of spicy spices. Among the pathogens that affect this crop, Meloidogyne enterolobii is one of the most important because it presents a wide range of hosts and there are no resistance genes identified that are efficient against this species. The present study aimed to evaluate the reaction of chili pepper genotypes (Capsicum spp.) to M. enterolobii in order to identifify genetic resistance. Three experiments were conducted in a completely randomized design under greenhouse conditions: Experiment I, with 53 genotypes with ten replications; Experiment II, with twenty genotypes with ten replications; Experiment III in a 16 × 4 factorial scheme, with sixteen Capsicum spp. genotypes and four inoculum concentrations of M. enterolobii and eight replications. Inoculation was performed seven days after transplanting the Capsicum spp. seedlings into 2L plastic bags filled with sterilized soil and sand (2:1), using 4,000 eggs + J2/plant. Ninety days after inoculation (DAI) (Experiments I and II) and 60 DAI (Experiment III) nematode population density, reproduction factor (RF), fresh root mass, egg mass index (EMI) and gall index (GI) were evaluated. Genotypes with RF < 1.0 were considered resistant according to Oostenbrink (1966). Thirty one genotypes of Capsicum spp. showed resistance to M. enterolobii with RF ranging from 0.87 to 0.08. Seventeen resistant genotypes of C. chinensis presented RF lower than 0.85, ten genotypes of C. annuum had the RF lower than 0.75, three genotypes of C. frutescens had the RF lower than 0.87 and only one genotype of C. baccatum was resistant to M. enterolobii, presenting RF = 0.6. EMI and GI weren’t considered reliable variables to determine resistance and susceptibility. Fourteen genotypes rated as resistant in Experiments I and II were submitted to increasing concentrations of inoculum and, nevertheless, remained resistant.