Phytonematodes as a limiting biotic factor of agricultural production in the world (review)

Purpose. To analyze domestic and foreign scientific literature on the species composition and harmfulness of the world's most dangerous parasitic species of phytonematodes in crops. Results. Today, according to the available literature, the most dangerous species of phytonematodes include: gall nematode (Meloidogyne spp.), cyst-forming nematode (Heterodera spp. and Globodera spp.), root lesion nematode (Pratylenchus spp.), banana drill nematode (Radoholus similis), stem nematode (Ditylenchus dipsaci), pine stem nematode (Bursaphelenchus xylophilus), reniform nematode (Rotylenchulus reniformis), xiphinema index (Xiphinema index), false head nematode (Nacobbus aberrans), and rice leaf nematode (Aphelenchoides besseyi). Conclusions. The results of research on the prevalence and harmfulness of parasitic nematode species in crops convince us of the need for a more detailed study of this group of microorganisms. Due to the rapid development of molecular genetic methods in the last decade, scientists have been able to expand and improve their knowledge of identifying species, races and pathotypes of phytonematodes, their biological and environmental characteristics, and most importantly, to discover and understand extremely complex mechanisms of parasite and host plants. Nematologists are confident that further research in these and other areas in the future will create a basis for developing a new strategy for long-term and environmentally safe control of these dangerous plant parasites.

Freshwater crabs could act as vehicles of spreading avian influenza virus

Avian influenza virus (AIV) possessed significant risk to various animals and human health. Wild birds, especially waterfowls are considered to be the natural reservoir of AIVs. The ecology of AIV is still far from being fully understood. Freshwater crabs are nonnegligible biotic factor in AIV ecosystem. We analyzed the ability of freshwater crabs accumulate and spread AIV. We found that AIV remain infectious in water only for 36 h but persist in crabs for 48 h. Crabs could accumulate AIV in their gills and gastrointestinal tracts. The AIV titers in crabs were higher than the surrounding contaminated water. Crabs could accumulate AIV from contaminated water, carry the virus and spread to naïve crabs via surrounding water. Our study identified freshwater crab as a novel transmission vehicle in AIV ecosystem.

Chinese Mitten Crabs (Eriocheir Sinensis) Could Act As Vehicles of Spreading Avian Influenza Virus

Avian influenza virus (AIV) possessed significant risk to various animals and human health. Wild birds, especially waterfowls are considered to be the natural reservoir of AIVs. The ecology of AIV is still far from being fully understood. Chinese mitten crabs are nonnegligible biotic factor in AIV ecosystem. We analyzed the ability of Chinese mitten crabs accumulate and spread AIV. We found that AIV remain infectious in water only for 36 hours but persist in crabs for 48 hours. Crabs grills and gastrointestinal tracts accumulated AIV with higher titers than viral water. Crabs could accumulate AIV from contaminated water, carry the virus and spread to naïve crabs via surrounding water. Our study identified Chinese mitten crab as a novel transmission vehicle in AIV ecosystem.

Efficient Biocontrol of Gaeumannomyces graminis var. Tritici in Wheat: Using Bacteria Isolated from Suppressive Soils

“Take-all” disease is the most important biotic factor affecting cereal productivity, causing 30–50% of crop losses. The causal agent is the ascomycete soil-borne pathogen Gaeumannomyces graminis var. tritici (Ggt). Current control measures are ineffective, because Ggt can remain saprophytic in soils for long periods. Therefore, the study of the microbiome residing in suppressive soils (SS) is a promising niche of Ggt biocontrol. Here, we evaluated the efficiency of Serratia sp., Bacillus sp., and Acinetobacter sp. isolated from SS against the incidence of Ggt on wheat. Our results demonstrated that plants inoculated with the bacterial consortium in both greenhouse and field conditions were highly efficient in Ggt biocontrol, more so than individual strains. The disease reduction was evidenced by higher biomass production, fewer copies of the Ggt genome with a concomitant curtailment of blackening of roots, a decrease of lipid peroxidation, and an increase of superoxide dismutase activity. The ability of the microbial consortium over that of single strains could be attributable to interspecies communication as a strategy to biocontrol; i.e., higher chitinase activity. In conclusion, bacterial consortia from SS are an important niche of Ggt biocontrol, serving as a model for other soil-borne pathogens.

Sodium Hydrosulfide Induces Resistance Against Penicillium expansum in Apples by Regulating Hydrogen Peroxide and Nitric Oxide Activation of Phenylpropanoid Metabolism

As a multifunctional signaling molecule, hydrogen sulfide (H2S) has been reported to induce plant responses to a variety of abiotic stresses. However, there are no reports on H2S treatment inducing resistance in apples against Penicillium expansum, a biotic factor, and its possible mechanism of action. In this study, fumigating apples with 5 mM sodium hydrosulfide (NaHS), the exogenous donor of H2S, for 12 h reduced the diameter of lesions in fruit colonized by P. expansum. NaHS treatment markedly promoted the synthesis of endogenous H2S, hydrogen peroxide (H2O2), and nitrogen oxide (NO). In vivo NaHS treatment enhanced the activities of phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, p-coumarate:coenzyme A ligase isoenzymes, caffeoyl-CoA-O-methyltransferase, caffeic acid-O-methyltransferase, ferulic acid-5-hydroxylase, cinnamyl-CoA reductase, and cinnamyl-alcohol dehydrogenase. The treatment also facilitated the production of specific phenolic acids, such as cinnamic acid, p-coumaric acid, caffeic acid, ferulic acid, and sinapic acid; total phenolic compounds; p-coumaryl alcohol; coniferyl alcohol; sinapyl alcohol; and lignin. NaHS treatment induced resistance against P. expansum in apples through H2O2- and NO-mediated activation of phenylpropanoid metabolism.

Carbon and Oxygen Gas Exchange in Woody Debris: The Process and Climate-Related Drivers

The carbon-to-oxygen relationship and gas exchange balance, organic carbon to CO2 conversion intensity and efficiency, and their relevance to climate parameters and wood decay fungi were investigated for birch woody debris (WD) in the Mid-Urals mixed pine and birch forests. It was shown that, within the range of temperatures from 10 to 40 °C and relative moisture (RM) of wood of 40% and 70%, aerobic gas exchange was observed in the WD, encompassing the physiologically entwined processes of CO2 emission and O2 uptake. Their volumetric ratio (0.9) confirmed that (1) the WD represents a globally significant CO2 source and appropriate O2 consumer and (2) the oxidative conversion of organic carbon is highly efficient in the WD, with an average ratio of CO2 released to O2 consumed equal to 90%. The balance of carbon-to-oxygen gas exchange and oxidizing conversion efficiency in the WD were not affected by either fungal species tested or by moisture or temperature. However, the intensity of gas exchange was unique for each wood decay fungi, and it could be treated as a climate-reliant parameter driven by temperature (Q10 = 2.0–2.1) and moisture (the latter induced a corresponding trend and value changes in CO2 emission and O2 uptake). Depending on the direction and degree of the change in temperature and moisture, their combined effect on the intensity of gas exchange led to its strengthening or weakening; otherwise, it was stabilized. Aerobic respiration of wood decay Basidiomycetes is an essential prerequisite and the major biotic factor in the WD gas exchange, while moisture and temperature are its climatic controllers only.

Insights Into Natural Genetic Resistance to Rice Yellow Mottle Virus and Implications on Breeding for Durable Resistance

Rice is the main food crop for people in low- and lower-middle-income countries in Asia and sub-Saharan Africa (SSA). Since 1982, there has been a significant increase in the demand for rice in SSA, and its growing importance is reflected in the national strategic food security plans of several countries in the region. However, several abiotic and biotic factors undermine efforts to meet this demand. Rice yellow mottle virus (RYMV) caused by Solemoviridae is a major biotic factor affecting rice production and continues to be an important pathogen in SSA. To date, six pathogenic strains have been reported. RYMV infects rice plants through wounds and rice feeding vectors. Once inside the plant cells, viral genome-linked protein is required to bind to the rice translation initiation factor [eIF(iso)4G1] for a compatible interaction. The development of resistant cultivars that can interrupt this interaction is the most effective method to manage this disease. Three resistance genes are recognized to limit RYMV virulence in rice, some of which have nonsynonymous single mutations or short deletions in the core domain of eIF(iso)4G1 that impair viral host interaction. However, deployment of these resistance genes using conventional methods has proved slow and tedious. Molecular approaches are expected to be an alternative to facilitate gene introgression and/or pyramiding and rapid deployment of these resistance genes into elite cultivars. In this review, we summarize the knowledge on molecular genetics of RYMV-rice interaction, with emphasis on host plant resistance. In addition, we provide strategies for sustainable utilization of the novel resistant sources. This knowledge is expected to guide breeding programs in the development and deployment of RYMV resistant rice varieties.

Impact of Competition on the Growth of Pinus Tabulaeformis in Response to Climate on the Loess Plateau of China

With climate change, understanding tree responses to climate is important for predicting trees’ growth, and plant competition as a nonnegligible biotic factor plays a key role in such response. However, few studies have investigated how competition affects the response of Pinus tabulaeformis plantations to climate . In our study, we investigated nine 29-year-old P. tabulaeformis plantation plots (three density gradients). The dendroecological method was used to analyze the impact of competition on trees response to drought and interannual climate variation. Stand density index was used to indicate the intensity of competition. The results showed that competition modified the climate-growth relationship. Competition increased trees’ sensitivity to drought but the relationship between competition and sensitivity to drought was nonlinear. The competition effect slightly increased under intense competition conditions. Additionally, competition reduced trees’ sensitivity to interannual climate variation. After 1999, the effect of competition was obvious. The sensitivity of small-diameter trees, especially those in middle- and high-density stands, declined. Thus, in the future these trees presumably may exhibit a reduced sensitivity to interannual climate variation and a greater sensitivity to drought.

Aboveground and Belowground Plant Traits Explain Latitudinal Patterns in Topsoil Fungal Communities From Tropical to Cold Temperate Forests

Soil fungi predominate the forest topsoil microbial biomass and participate in biogeochemical cycling as decomposers, symbionts, and pathogens. They are intimately associated with plants but their interactions with aboveground and belowground plant traits are unclear. Here, we evaluated soil fungal communities and their relationships with leaf and root traits in nine forest ecosystems ranging from tropical to cold temperate along a 3,700-km transect in eastern China. Basidiomycota was the most abundant phylum, followed by Ascomycota, Zygomycota, Glomeromycota, and Chytridiomycota. There was no latitudinal trend in total, saprotrophic, and pathotrophic fungal richness. However, ectomycorrhizal fungal abundance and richness increased with latitude significantly and reached maxima in temperate forests. Saprotrophic and pathotrophic fungi were most abundant in tropical and subtropical forests and their abundance decreased with latitude. Spatial and climatic factors, soil properties, and plant traits collectively explained 45% of the variance in soil fungal richness. Specific root length and root biomass had the greatest direct effects on total fungal richness. Specific root length was the key determinant of saprotrophic and pathotrophic fungal richness while root phosphorus content was the main biotic factor determining ectomycorrhizal fungal richness. In contrast, spatial and climatic features, soil properties, total leaf nitrogen and phosphorus, specific root length, and root biomass collectively explained >60% of the variance in fungal community composition. Soil fungal richness and composition are strongly controlled by both aboveground and belowground plant traits. The findings of this study provide new evidence that plant traits predict soil fungal diversity distribution at the continental scale.

Use of multispectral images to evaluate the efficacy of pre-emergent herbicides in peas under greenhouse conditions

In Colombia, peas are the second most important legume after the bean, and weeds are the main biotic factor that limits production, causing losses of up to 100%. Manual control can represent up to 40% of the labor force. The critical period in the crop-weed competition is the first third of the crop cycle; therefore, pre-emergent herbicide applications are a cost-effective way to control weeds. Common variables for assessing weed-control efficacy include, weed density (individuals/area), which is precise but time consuming, and weed coverage (%), which is faster but very subjective. Therefore, pre-emergence herbicides and a weed-control evaluation method that standardizes, facilitates, and provides greater precision are needed for peas cultivation and experimentation. Five pre-emergent herbicides (linuron, S-metolachlor, metribuzine, oxifluorfen and pendimetalin) were evaluated at two doses in a greenhouse pea crop. Also, two methods (quantification process of multispectral images and conventional human visual) for assessing weed coverage and control efficacy were compared. The best herbicide treatment for the dry grain yield was metribuzine (2.36 t ha-1). Furthermore, the effectiveness of the weed control was 88% at 36 days after sowing, which is optimal. Finally, there was agreement between the weed assessment methods (human vs. machine). The intraclass correlation coefficient was over 0.95, which validates the use of machine quantification for weed coverage.