First record of damage and reproduction of Helicotylenchus dihystera on barleyABSTRACT:
Barley (Hordeum vulgare L.) is one of the most important cereals in Brazil and is affected by several pathogens, including plant-parasitic nematodes. Our objective was to estimate the damage caused by Helicotylenchus dihystera and its reproduction on barley. To this end, an experiment was carried out with a completely randomized design, with two barley cultivars (BRS Cauê and BRS Brau) and six selected population densities (0, 639, 1,278, 1,917, 2,556 and 3,195 individuals per 250 cm³ of soil). We used generalized linear models with Gaussian and Poisson distributions to analyses the data of shoot height, number of tillers, aerial dry mass (ADM), root dry mass (RDM), and reproduction factor (RF). The results showed that the density of H. dihystera had a significant negative effect on ADM and RDM (P < 0.05). However, the variables shoot height, and the number of tillers showed no significant effect of density or cultivar (P > 0.05). The ‘BRS Cauê’ (RF = 1.45 ± 0.08) and ‘BRS Brau’ (RF = 0.97 ± 0.04) showed a significant difference for RF (P < 0.05). These results will provide useful information and highlight the importance of H. dihystera in barley production systems. To the best of our knowledge, this is the first time that damage caused by H. dihystera has been recorded in barley.
Key words:
spiral nematode; cereals; Hordeum vulgare L.
RESUMO:
A cevada é um dos cereais de maior importância econômica no Brasil, sendo afetada por diversos patógenos, incluindo os fitonematoides. O objetivo deste estudo foi estimar os danos e reprodução de Helicotylenchus dihystera na cevada. Para isto, foi realizado um experimento com delineamento completamente aleatorizado, com duas cultivares de cevada (BRS Cauê e BRS Brau) e seis densidades selecionadas (0, 639, 1.278, 1.917, 2.556 e 3.195 indivíduos por 250 cm³ de solo). Foram aplicados modelos lineares generalizados com distribuição Gaussiana e Poisson para analisar dados de altura, número de perfilhos, massa seca da parte aérea (MSPA), massa seca de raízes (MSR) e fator de reprodução (FR). Os resultados mostraram que as densidades de H. dihystera tem efeito negativo sobre MSPA e MSR (P < 0.05). Ademais, não foram observados efeitos para altura e número de perfilhos (P > 0.05). A cultivar BRS Cauê (FR = 1.45 ± 0.08) foi estatisticamente diferente de ‘BRS Brau’ (FR = 0.97 ± 0.04) para FR (P < 0.05). Estes resultados fornecem informações úteis e destacam a importância de H. dihystera, as quais devem ser consideradas em sistemas de produção de cevada. Conforme levantamento bibliográfico realizado, este é o primeiro registro de dano de H. dihystera em cevada.
Palavras-chave:
nematoide espiralado; cereais; Hordeum vulgare L
The spiral nematodes (Helicotylenchus spp.) are ubiquitous, globally distributed parasites that pose a threat to crop production by feeding on the plant roots, causing damage and losses (SUBBOTIN et al., 2011). Several studies in different locations and on different hosts have highlighted the presence of Helicotylenchus species in Brazil, such as H. dihystera (Coob, 1893) Sher, 1961, H. californicus (Steiner, 1932) Sher, 1961, H. multicinctus (Cobb, 1893) Golden, 1956, and H. pseudorobustus (Steiner, 1914) Golden, 1956 (KIRSCH et al., 2016; RIASCOS-ORTIZ et al., 2020; SEVERINO et al., 2010).
Studies carried out in Rio Grande do Sul have revealed the presence of Helicotylenchus spp. in several important crops (BELLE et al., 2014; RAMOS et al., 2024). Intensive agricultural land use favors the emergence of new diseases or the re-emergence of previously secondary pathogens (MACHADO et al., 2019). In this context, H. dihystera is one of the most frequently detected spiral nematodes in surveys of soybean fields in the region (CAMERA et al., 2019; KIRSCH et al., 2016). Greenhouse experiments have shown that H. dihystera can multiply and cause lesions on soybean roots, suggesting its potential as an emerging pathogen (MACHADO et al., 2019) and, by extension, to crops associated with these systems, such as barley. There are few records of the occurrence of the Helicotylenchus associated to barley fields, without evidence of damage and/or reproduction. Furthermore, the Helicotylenchus species was not always identified (DUGGAL & MANN, 2019; FEYISA, 2022), except in records surveyed by SIDDIQUI et al. (1973) <http://nemaplex.ucdavis.edu/Nemabase2010/PlantNematodeHostStatusDDQuery.aspx>, who identified it as H. dihystera. Recently, we obtained sixteen soil samples from commercial and experimental areas in the state of Rio Grande do Sul (Passo Fundo, Tapejara, Água Santa, Vila Langaro, Estação, Coxilha, and Ipiranga do Sul) and found a higher incidence of Helicotylenchus, similar morphologically to H. dihystera, on barley, with 50% of the samples showing more than 350 specimens per 250 cm3 of soil (unpublished data).
The present study involved an experiment carried out under greenhouse conditions with two cultivars (BRS Cauê and BRS Brau) and six selected initial population densities (P i ) (0, 639, 1,278, 1,917, 2,556, and 3,195 specimens per 250 cm3 of soil). The experiment was conducted using a completely randomized design with four replicates. The first and control density (0 specimens per 250 cm3 of soil) consisted of autoclaved soil only (120 oC/2 h), while the other consisted of a mixture of diluted infested soil and autoclaved soil. An aliquot was sampled from each mixture at the end of the process to check the density of each one. No other plant-parasitic nematodes were found at the sampling point. The soil infested with H. dihystera was obtained from the Palma Agricultural Center (31°48’08”S 52°29’49”W) in Capão do Leão, Rio Grande do Sul. The population densities used in this research are close to being representative of those found in areas planted with soybean (MÁRQUEZ et al., 2021). It should be noted that the Pi in the barley crop is theoretically the residue from the previous soybean crop, which reinforces our choice.
To identify the used inoculum, the morphological characteristics and morphometric data were performed of ten fixed females on temporary slides were examined. Each specimen was photographed using a camera attached to a microscope (20x, 40x and 100x objectives), and the software BEL VIEW 7.1. The following measurements were taken: L = 706.04 µm (525.60 - 848.30 µm), St = 22.73 µm (18.70 - 24.84 µm), maximum body diameter of 26.70 µm (21.10 - 29.69 µm), V% = 61 (52 - 65) and a = 26.39 (23.61 - 29.23). The populations of this species showed a post-mortem habitus with a spiral shape, a female tail with a short ventral projection and a narrow tail projection. The spiral nematode was then identified as H. dihystera, showing traits and measurements that were similar to those described by RIASCOS-ORTIZ et al. (2020).
The experiment was carried out from June 6 to October 7, 2024, under greenhouse conditions at the Faculdade de Agronomia “Eliseu Maciel”, Universidade Federal de Pelotas. During the experimental period, the temperature ranged from 8.90 to 14.06 oC (mean of 11.48 oC). The seeds were sown in 5-liter plastic pots containing four liters of infested soil with H. dihystera. The seedlings were thinned to leave one per pot, watered as needed and fertilized according to the Manual de calagem e adubação para os estados do Rio Grande do Sul e de Santa Catarina (CQFS, 2016). The variables final nematode population (Pf), shoot height (cm), number of tillers, aerial dry mass (ADM) (g), and root dry mass (RDM) (g) were obtained 122 days after planting. The Pf values for H. dihystera on barley were obtained through the extraction of nematodes from 250 cm3 of homogenized soil from each replicate (JENKINS, 1964), followed by quantification on Peters’ slide under a light microscope. The values of the reproductive factor (RF = Pf/Pi) were then estimated.
A statistical analysis was performed using generalized linear models (GLM) with a Gaussian or Poisson distribution (number of tillers), followed by analysis of variance (ANOVA). The dependent variables included shoot height, the number of tillers, RDM, ADM and RF. All analyses and graphics were performed using R version 4.4.2 (R DEVELOPMENT CORE TEAM, 2024) and the function glm used to build the GLMs. Models were built and the simpler model (s) and/or those with the lowest AIC (Akaike information criterion) values were chosen. For graphics, we used ChatGPT <https://chatgpt.com/> to help prepare the scripts, as well as the ggplot2 package. For the ADM, we selected a model with only the effects of cultivars and densities, since the interaction between cultivars and densities was not significant. For the RDM, we selected a model that included cultivar, densities and the cultivar-density interaction. We used the DeepL Tools <https://www.deepl.com> to improve the English in the text.
There was no significant difference in shoot height or number of tillers between cultivars, nor was there an effect of density (P > 0.05). Shoot height ranged from 63.96 (± 1.59) for ‘BRS Brau’ to 69.08 (± 2.52) for ‘BRS Cauê’. The number of tillers ranged from 11.79 (± 0.60) for ‘BRS Cauê’ to 12.5 (± 0.74) for ‘BRS Brau’. To ADM and RDM variables, values did not differ significantly between cultivars (P > 0.05), but decreased significantly with increasing population density (P < 0.05) (Figures 1A and 1B). The ADM values ranged from 10.82 (± 0.42) for ‘BRS Cauê’ to 11.29 (± 0.74) for ‘BRS Brau’, while the RDM values ranged from 1.21 (± 0.14) for ‘BRS Cauê’ to 1.51 (± 0.26) for ‘BRS Brau’. Reductions of 31% for ADM and of 65% for RDM were observed for ‘BRS Brau’. Despite the significant decrease, the reductions were less evident for cultivar BRS Caue due to the dispersion observed in the first class. For ADM, it is important to mention that the value of β for densities was -0.00111 (P = 0.00394), demonstrating a strongly negative effect of increasing densities. Similarly, for RDM, the value of β for densities was of -0.0005 (P = 0.00716).
Generalized linear models of areal dry mass [ADM (A)] and root dry mass [RDM (B)] as a function of population density. The reproduction factor (RF) of two cultivars of barley (‘BRS Brau’ and ‘BRS Caue’) inoculated with Helicotylenchus dihystera (C). ADM and RDM are expressed in grams while the population density is expressed in specimens per 250 cm3 of soil. The colored bands in figures A and B, and the bars in C represent 95% confidence intervals. In the figures A and B, the lines represent the predicted values for ADM and RDM, respectively.
On the other hand, RF was significantly higher in ‘BRS Cauê’ (RF = 1.45 ± 0.08) than in ‘BRS Brau’ (RF = 0.97 ± 0.040) (P < 0.001; Figure 1C), through it did not increase significantly with higher initial densities (P > 0.05). Alongside observations of barley and other crops grown in the same system (e.g., soybean), and the widespread distribution of this nematode, the findings obtained from our greenhouse experiment suggest that H. dihystera is a potential pathogen not only in barley but also in crops grown in the same area. It should be noted that the population was practically maintained in both cultivars. This resulted in unsuitable conditions for the subsequent crop. It is important to note that other winter crops also may be susceptible to H. dihystera, including oats (Avena sativa L.) and wheat (Triticum aestivum L.) cultivars. Indeed, PEDERSEN & RODRÍGUEZ-KABANA (1987) evaluated the response of winter crops to H. dihystera, including oat and wheat cultivars, concluding that all studied wheat cultivars were susceptible.
ACKNOWLEDGMENTS
This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001. J.V. Araujo Filho (grant number 317495/2021-6) is supported by fellowships from the Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq).
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