Research Article

Damage function model in two cucumber cultivars infected by Meloidogyne javanica under greenhouse conditions

Laleh,Rajabi¹, Zahra Tanha Maafi^2*, Naser Safaei³, Saeed Rezaei¹ and Farshad Rakhshandehroo¹

1. Department of Plant Protection, SR. C., Islamic Azad University, Tehran 14515-775, Iran.

2. Iranian Research Institute of Plant Protection, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran.

3. Department of Plant Pathology, Faculty of Agriculture, Tarbiat Modares University, Tehran, Iran.

Abstract: Root-knot nematodes (RKNs) hold global economic importance. Predicting the potential crop damage caused by a specific level of nematode population is crucial for developing effective nematode management strategies. This study aimed to investigate the effect of increasing the initial population density (Pi) of Meloidogyne javanica on the final population densities of the nematode and its impact on cucumber yield, to determine the damage functions for shoot fresh and dry weight as well as fruit weight in two selected cucumber cultivars (IRQS-22 and WGR-225) in response to the nematode. For this purpose, cucumber seedlings were inoculated with a specific density of J2s of M. javanica (0, 2, 4, 8, 16 J2s g^-1 soil), and the mentioned parameters were investigated. The findings indicated a negative correlation between the initial nematode inoculum level, the height and weight of the plant shoot, and the yield. However, the root response varied in relation to the level of nematode inoculum. The Pearson correlation coefficients among gall index and egg mass with plant growth parameters were negatively related. The yield responses to Pi were fitted properly by polynomial regression equations and Seinhorst’s model. The tolerance limits were estimated at 5.708 and 1.808 J2s g^-1 soil for the WGR225 and IRQS22 cultivars for shoot fresh weight. The shoot dry weight tolerance limits were calculated as 2.107 and 3.081 J2s g^-1 soil for the WGR225 and IRQS22 cultivars. The maximum nematode reproduction factor was 12.55 and 23.03 in the WGR225 and IRQS22 cultivars, respectively, at an initial population density of 2 J2s g^-1 soil. These results can be used as a basis for the efficient management of the nematode.

Keywords: Cucumis sativus, Damage function, Host-parasitic relationship, Inoculum Levels, Seinhorst model

Introduction[1][2]

Plant-parasitic nematodes are significant pests that cause substantial economic and social impacts by damaging crops (Nicol et al., 2011). Root-knot nematodes (RKNs), Meloidogyne spp., are the most destructive plant-parasitic nematodes. Their annual losses are around $173 billion for planted crops worldwide (Gamalero and Glick, 2020). The reduction of crop yields due to root-knot nematodes has been frequently reported in various plants, for example, in bell peppers (Moosavi, 2015), finger millet (Waweru et al., 2023), watermelon, and zucchini (Giné et al., 2014; López-Gómez et al., 2015). Nematode invasion disrupts root tissues, including the epidermis, cortex, endodermis, pericycle, and vascular cylinder, during penetration, female establishment, and giant cell formation (Anwar and McKenry, 2012). In addition, the feeding activities of nematodes interfere with plant physiological functions, such as photosynthesis, as well as increase the respiratory rate and disrupt the balance between catabolism and anabolism in the plant (Paez et al., 1976; Carneiro et al., 2002). The mentioned waste, as well as toxic enzymes, is sequestered by nematodes in the roots (Ami and Shingaly, 2020), resulting in a decrease in plant growth parameters. The reduction in plant yield depends on the Meloidogyne species and strains, the initial nematode population density at planting, and the host plant species and cultivar (Gullino et al., 2019; Chen et al., 2022). Understanding soil biology and nematode population dynamics at the time of sowing is critical for developing effective management strategies. Accurate prediction of damage levels is essential for deciding whether to cultivate specific crops or cultivars. Therefore, it is essential to investigate the response of major plant cultivars of each area to indigenous populations of nematodes to obtain the most precise correlation (Nadeem et al., 2023).

Models of nematode populations and crop yields are derived from the integration of mathematical theories and computer programs that represent a portion of the presumptive actuality. These models rely on historical data to forecast future outcomes, with the primary goal of estimating crop yield based on nematode population density and other relevant factors (Jamali et al., 2012). Previous studies have been conducted to determine the correlation between nematode-plant interactions and the loss threshold or tolerance limit. The results of these studies provided several experimental models for nematode population dynamics and yield loss in crops, and specific predictive models for estimating nematode damage in different crops were developed (Seinhorst, 1965; Jamali et al., 2012; Karimipour Fard et al., 2018).

The Seinhorst's model provided valuable insights into the correlation between crop yield and nematode population (Seinhorst, 1965). Based on the Nicholson competition curve (Nicholson, 1933), this model predicts crop yield in nematode-affected fields by analyzing data on nematode population densities. The model has two components: tolerance limit (T) and minimum yield (m). The 'tolerance limit' is defined as a population density of nematodes below which no crop loss occurred, and 'm' is the minimum relative yield when nematode population density is at its highest level (Seinhorst, 1965). The Seinhorst model has been widely applied to plant parasitic nematodes, including root-knot nematodes (Melodogyne spp.), potato cyst nematode (Globodera pallida), and Aphelenchoides besseyi (Phillips et al., 1991; Ehwaeti et al., 2000; Poudyal et al., 2005; Norshie et al., 2011; Jamali et al., 2012; Sasanelli et al., 2013; Heve et al., 2015; Moosavi, 2015). Despite its widespread use, some studies have reported inconsistencies between observed data and the Seinhorst model’s predictions (Gharabadiyan et al., 2013). Alternative models, such as linear or sigmoid functions, have been proposed as suitable in some instances, depending on the nature of nematode damage, initial population density, crop tolerance, and environmental conditions (Haji-Hassani et al., 2010; Karimipour Fard et al., 2018; Gharabadiyan et al., 2013).

In Iran, greenhouse cucumbers play a crucial role in the agricultural economy, contributing significantly to food production, employment, and export income. However, root-knot nematodes represent a serious biotic threat to the sustainability and profitability of this industry. Therefore, the present study aimed to: i) investigate the relationships between the population density of M. javanica and the growth and yield of the two commonly cultivated cultivars WGR-225 and IRQSP22 in Iran; ii) compare the damage functions of M. javanica on the cucumber cultivars to develop a predictive model for crop losses based on nematode population density; iii) evaluate the tolerance limit using the Seinhorst model study.

Materials and Methods

Nematode inoculum

In this study, M. javanica RKN was used. A single egg mass was selected from a tomato greenhouse in the Varamin district of Tehran, Iran, to establish a pure culture of the nematode. The species was identified using morphological approaches based on females and J2s (Jepson, 1987; Eisenback and Triantaphyllou, 1991) and confirmed species-specific primers (Zijlstra et al., 2000). A mass population of the nematode was propagated by inoculating the Rutgers tomato cultivar. Egg suspension was prepared by soaking infected tomato roots with 0.05% (v/v) NaOCl for 3 min (Hussey and Barkers, 1973). The eggs were incubated at 25 °C in Baermann trays, and hatched J2s were collected for use in the experiment.

Plant culturing

Seeds of two cucumber (Cucumis sativus) cultivars, IRQS-22 and WGR-225 were planted in the seedling tray containing cocopeat. At the 2–4 leaf stage, seedlings were transferred to 2 kg plastic pots containing a sterile mixture of sand, soil, and leaf mold (2:1:1). Each pot contained one seedling. Plants were grown in a phytotron (Noor Sanat Ferdous Co., Iran) with a 16-h light and 8-h dark photoperiod at a temperature of 25 °C.

Nematode inoculation to plants

Cucumber seedlings were inoculated with a specific density (Pi) of J2s of M. javanica (0, 2, 4, 8, 16 J2s g^-1 soil) by making holes around the plant. The J2s nematode inoculum was added to the soil and then covered with sterilized soil. For each initial population level, four replications were considered, and the experiment was repeated twice. The pots were kept in the phytotron under the specified conditions. The pots were watered gently to avoid washing away the J2s, and the moisture level was maintained at a constant level throughout the experiment. To record the data, plants were carefully uprooted four months after sowing. The harvested roots were washed to remove adhered soil, and plant growth parameters, as well as pathological parameters, were recorded.

Data collection

Plant growth and nematode pathological parameters were recorded. Growth parameters included shoot length, fresh weight of shoot, dry weight of shoot, fresh weight of root, number of fruits, and fruit weight. Pathological parameters included the number of galls, egg masses, eggs, and juveniles in the root system, as well as eggs and juveniles in the soil, final nematode population density (Pf), and reproduction factor (RF). For estimating the final nematode population (Pf), eggs and other developmental stages were extracted from the roots of individual plants (Hussey and Barker, 1973). The J2s were extracted from the soil of each pot using the Whitehead and Hemming tray method (Whitehead and Hemming, 1965). The Pf in each pot was determined by summing nematodes recovered from soil and roots. The reproduction factor (RF) was calculated by dividing the final population (Pf) by the initial one (Pi) (Sasser et al., 1984).

Statistical analysis and modeling

The experiment was conducted using a completely randomized factorial design with two factors: cultivars (WGR225 and IRQS22) and nematode density (with five levels: 0, 2, 4, 8, and 16 J2s g^-1 soil). There were 10 treatments in total, each with four replicates. Nematode pathological data were normalized before analysis by transforming them into log (X + (min(X) /2)). Data were analyzed using analysis of variance (ANOVA) in SAS version 9.3, with means compared using Fisher’s protected least significant difference (LSD) test at p = 0.05. The Pearson correlation coefficient was used to assess the correlation between the measured parameters. The relationship between initial nematode population density (Pi) and plant yield (estimated by fresh and dry shoot weight and total fruit weight) was analyzed through regression analysis, fitting the data to the Seinhorst model using SPSS software version 15 and statGraph. In all assessments, the goodness of fit was estimated using the coefficient of determination, R2. The tolerance limit was quantified via Seinhorst’s equation: y = m + (1-m) × 0.95(Pi/T−1) for Pi > T, and y = 1 for Pi < T (Seinhorst, 1965, 1970, 1986). In this model, y represents the relative yield defined as the ratio between plant growth in an initial population density of the nematode (Pi) and the value obtained in the control plant; m is the minimum yield value (y at a very high initial nematode population density); Pi is the initial nematode population density; and T is the tolerance limit.

Results

Relationship between the initial population density and the pathological parameters

All initial population densities (Pi) of M. javanica harmed plant growth parameters in both cucumber cultivars, IRQS-22 and WGR-225 (Tables 1 and 2). The values of the investigated traits decreased as the initial nematode inoculum increased in both studied cultivars. Pathological parameters, including the number of galls, egg mass per root system, final nematode population (Pf), and reproduction factor (RF), were investigated at 120 days after inoculation as well (Tables 1 and 2). Statistical analysis revealed that the amount of nematode inoculum had a significant impact on various infection parameters, such as the number of root galls, egg masses, eggs, and nematode stages in the roots. Additionally, it affected the nematode population density in the soil, as well as the final nematode population density and the nematode reproduction factor. The lowest infection parameter values were recorded in the first level of infestation, with 2 J2s g^-1 soil. Subsequently, the values of the infection parameters began to increase, with the highest values observed at a level of 16 J2s g^-1 soil. Correspondingly, the severity of root galling of cucumber roots increased with the increase in the initial nematode population. The data trend revealed similarities between the two cultivars studied. The reproduction factor of M. javanica was inversely related to the initial population densities. The nematode had a higher maximum reproduction factor of 23.03 on the IRQS22 cultivar compared to 12.55 on the WGR225 cultivar showing the susceptibility of both cultivars to M. javanica. The highest RF occurred when there was an initial population density of two J2s g^-1 soil in both of the studied cultivars.

Table 1 Analysis of variance of effects of density (J2s g^-1 dry weight soil) of Meloidogyne javanica on the growth and yield of cucumber cultivars WGR225 and IRQS22 and the nematode pathological parameters.

*, ** and ns indicate significant difference p < 0.05, significant difference p < 0.01 and non-significant, respectively.

Table 2 Effects of initial population density (J2s g-1 dry weight soil) of Meloidogyne javanica on the growth and yield of cucumber cultivars WGR225 and IRQS22 and the nematode pathological parameters.

Means within a column followed by the same letter are not significantly different (LSD test, p ≤ 0.05).

Correlation coefficients between nematode pathological parameters and cucumber growth traits for WGR-225 and IRQS-22 are presented in Tables 3 and 4, respectively. The number of galls and egg masses was inversely related to stem height, number and weight of fruits at harvest, shoot fresh weight, shoot dry weight, and root fresh weight. However, fruit weight was not significantly correlated with nematode pathological parameters. No statistical correlation was observed between growth parameters and reproduction factor. Indeed, we found that the number and weight of fruits at harvest strongly correlate with shoot fresh and dry weight. As expected, Root fresh weight showed no significant correlation with other growth parameters. Based on this analysis, we focused further on the shoot fresh and dry weight for modeling.

Modeling the effect of nematode population densities on cucumber yield

Linear regression models failed to describe the relationship between shoot fresh weight and Pi accurately. However, the second-degree polynomial regression equations successfully depicted the relationship between shoot fresh weight and nematode initial density (Fig. 1). The Seinhorst model was also appropriately defined to represent the connection between the initial population density of nematodes and the fresh weight of the shoots. The IRQS22 cultivar showed better results with this model (Fig. 2).

The shoot dry weight was correlated to the nematode initial population using polynomial regression analysis up to order 3 (Fig. 3). The Seinhorst model similarly provided a robust fit for shoot dry weight in both cultivars (Fig. 4).

The Seinhorst model determined tolerance limits (T) of 5.708 and 1.808 J2s g-1 soil for the WGR225 and IRQS22 cultivars, respectively, for shoot fresh weight. Tolerance limits for the shoot dry weight of WGR225 and IRQS22 cultivars were established as 2.107 and 3.081 J2s g^-1 soil, respectively. Based on this equation, the WGR225 and IRQS22 cultivars had minimum shoot fresh weights (m) of 0.546 and 0.652, respectively, compared to unaffected plants. The minimum relative values (m) for shoot dry weight of the WGR225 and IRQS22 cultivars were 0.677 and 0.592, respectively.

Table 3 Pearson correlation coefficients of different traits of cucumber cultivar “WGR225” grown in soil inoculated with different densities (0. 2, 4, 8 and 16 J2s g^-1 dry weight soil) of Meloidogyne javanica.

* and ** indicate significant difference p < 0.05 and significant difference p < 0.01, respectively.

Table 4 Pearson Correlation coefficients of different traits of cucumber cultivar “IRQS22” grown in soil inoculated with different densities (0. 2, 4, 8 and 16 J2s g^-1 dry weight soil) of Meloidogyne javanica.

* and ** indicate significant difference p < 0.05 and significant difference p < 0.01, respectively.

Figure 1 Simple and second-degree polynomial linear regression equations for estimating aerial fresh weight (gr) of cucumber cultivars (WGR225 and IRQS22 ( via density (J2s g^-1 dry weight soil) of Meloidogyne javanica.

Figure 2 A) Seinhorst damage function model y = m + (1-m) 0.95 ^(Pi/T−1), where y is relative aerial fresh weight, m is the minimum relative aerial fresh weight, Pi is Meloidogyne javanica initial population density per 100 cm³ soil and T is the tolerance limit of cucumber cultivars (WGR225 and IRQS22(. B) Scatter plot of actual data against predicted values of relative aerial fresh weight of cucumber using Seinhorst damage function models y = 0.546 + (1-0.546) 0.95 ^(Pi/5.708-1) and y = 0.652 + (1-0.652) 0.95 ^(Pi/1.808-1) for WGR225 and IRQS22, respectively. The solid line shows a fitted simple regression line on scatter points.

Figure 3 Simple and second-degree polynomial linear regression equations for estimating aerial dry weight (gr) of cucumber cultivars (WGR225 and IRQS22 ( via density (J2s g^-1 dry weight soil) of Meloidogyne javanica.

Figure 4 A) Seinhorst damage function model y = m + (1-m) 0.95 ^(Pi/T−1), where y is relative aerial dry weight, m is the minimum relative aerial dry weight, Pi is Meloidogyne javanica initial population density per 100 cm³ soil and T is the tolerance limit of cucumber cultivars (WGR225 and IRQS22(. B) Scatter plot of actual data against predicted values of the relative aerial dry weight of cucumber using Seinhorst damage function models y = 0.677 + (1-0.677) 0.95 ^(Pi/2.107-1) and y = 0.592 + (1-0.592) 0.95 ^(Pi/3.081-1) for WGR225 and IRQS22, respectively. The solid line shows a fitted simple regression line on scatter points.

Figure 5 A) Seinhorst damage function model y = m + (1-m) 0.95 ^(Pi/T−1), where y is relative total weight of fruits, m is the minimum relative aerial fresh weight, Pi is Meloidogyne javanica initial population density per 100 cm³ soil and T is the tolerance limit of cucumber cultivars (WGR225 and IRQS22(. B) Scatter plot of observed data against predicted values of the relative total weight of fruits of cucumber using Seinhorst damage function models y = 0.401 + (1-0.401) 0.95 ^(Pi/2.180-1) and y = 0.697 + (1-0.697) 0.95 ^(Pi/3.049-1) for WGR225 and IRQS22, respectively. The solid line shows a fitted simple regression line on scatter points.

Since the tolerance limits for shoot fresh and dry weight showed contrasting results for the two studied cultivars. Therefore, the Sinnhorst equation was also established for the total weight of fruits (Fig. 5). For the total weight of fruits, the tolerance limits were determined as 2.180 and 3.049 J2s g-1 soil for the WGR225 and IRQS22 cultivars.

Discussion

Understanding the applicable principles and assessing damage functions under specific conditions for various crops are essential prerequisites for determining nematode damage threshold values and identifying potential management approaches (Ravichandra, 2014a). The present study was conducted to investigate the relationship between the population densities of M. javanica and the crop yields of the cucumber cultivars WGR225 and IRQS22.

The obtained data indicated that the initial population densities of the nematode had negative impacts on yield and plant growth characteristics of both cultivars. This study found that the extent of yield and shoot growth decreased with an increase in the inoculum level of M. javanica in both cucumber cultivars under investigation. A similar correlation was observed between the initial population density of Meloidogyne spp. and their host plants (Seinhorst, 1965, 1970; Al-Sabie and Ami, 1989; Schomaker and Been, 2006; Russo et al., 2007; Greco and Di Vito, 2009; Hussain et al., 2011; Charegani et al., 2012; Gharabadiyan et al., 2013; Moosavi, 2014; Wesemael et al., 2014; Kankam and Adomako, 2014; Nadeem et al., 2023).

The data we gathered showed that as the inoculum levels of the nematode increased, the severity of root gall occurrence and egg mass also increased. However, we observed a negative correlation between the initial population densities of M. javanica and the reproduction factor. In line with our results, numerous prior studies repeatedly reported that, unlike other nematode population indices, the reproduction rate is inversely related to the initial inoculum levels of the nematode (Charegani et al., 2012; Maleita et al., 2012; Moosavi, 2014, 2015; Ami and Shingaly, 2020; Nadeem et al., 2023). The decrease in nematode reproduction factor as inoculum levels increase is due to the competition of root-knot nematodes for space, food, and penetration (Ibrahim, 2002; El-Sharif et al., 2007; Joymatidevi, 2009; Hussain et al., 2011; Kumar et al., 2011; Charegani et al., 2012). This competition reduces the efficiency of females in egg production (Sumita, 2014) and results in an increase in the number of males in the root (David and Triantaphyllou, 1967).

In assessing plant tolerance, selecting appropriate growth parameters is crucial (Willig et al., 2023). The strong correlation between fruit number, fruit weight, and shoot fresh and dry weight justified focusing on shoot biomass for modeling. The present data showed a clear inverse correlation between the number of galls and the yield, suggesting that the root damage caused by RKN will likely be highly detrimental to the plants. However, no correlation was observed between root weight and other plant growth parameters. As a result, we decided to focus our modeling efforts on the fresh and dry weight of shoots as a key factor.

The analysis showed that the polynomial regression equations outperformed the linear regression in explaining the relationship between yield (shoot fresh and dry weight) and initial nematode density in the cucumber cultivars under study. The most suitable damage function equation for each parameter was determined using the coefficient of determination. The data were also suitably fitted to the Seinhorst model.

The Seinhorst equation models the nematode density–plant yield relationship as an inverted sigmoid curve, where the decrease in yield at a certain time point is a derivative function of the damage. The yield stays consistent until it reaches a specific nematode density, known as the tolerance limit, after which it decreases rapidly, eventually reaching the lowest yield level at the highest nematode density. The tolerance limit is the first measurable inhibition of plant growth caused by pathogen infection (Seinhorst, 1986). The Seinhorst model facilitates the comparison of tolerance limits for a specific pathogen across different crop varieties. The tolerance limit and the steepness of the reduction in yield over increasing nematode densities are agronomically important features (Pagan and Garcia-Arenal, 2020). In this study, based on the Seinhorst model, the tolerance limits were determined as 5.708 and 1.808 J2s g-1 soil for the WGR225 and IRQS22 cultivars, respectively, in terms of shoot fresh weight. For the shoot dry weight, tolerance limits for the WGR225 and IRQS22 cultivars were determined as 2.107 and 3.081 J2s g^-1 soil, respectively.

In comparison to the control plants, the WGR225 and IRQS22 cultivars demonstrated minimum shoot fresh weights (m) of 0.546 and 0.652, respectively. The minimum values (m) for shoot dry weight of the WGR225 and IRQS22 cultivars were 0.677 and 0.592, respectively. Previous research has documented the tolerance limit for Meloidogyne spp. at 0.65 J2 g^-1 soil for finger millet grain yield, 2.2 eggs and J2 g^-1 soil for African paddy rice (Oryza glaberrima), 0.18 eggs and J2 g^-1 soil for upland rainfed Asian rice, 0.50 eggs and J2 g^-1 soil for pepper, 0.19 eggs and J2 g^-1 soil for cantaloupe, 0.0002 J2 g^-1 soil for zucchini, 0.12 J2 g^-1 soil for cucumber, 0.5 egg and J2s g^-1 soil for bell pepper, and 0.74 eggs and juveniles cm^-3 soil for bell pepper cultivar Yolo Wonder (Di Vito et al., 1996; Giné et al., 2014; López-Gómez et al., 2015; Moosavi, 2015; Waweru et al., 2023). Contrasts in tolerance limits and minimum yields of different studies can be due to variations in plant species and cultivar, nematode species and population, soil type, the way of utilizing the inoculum, and environmental conditions (Hussey and Janssen, 2002; Greco and Di Vito, 2009; Ravichandra, 2014b; Mekete et al., 2003; Moosavi, 2015). The tolerance limits for shoot fresh and dry weight showed contrasting results for the two studied cultivars. Therefore, the Sinnhorst equation was also established for the total weight of fruits. For the total weight of fruits, the tolerance limits were determined as 2.180 and 3.049 J2s g^-1 soil for the WGR225 and IRQS22 cultivars. The main difference between the dry weight and fresh weight of a plant shoot lies in their water content. Dry weight reflects only the organic and inorganic matter, providing a precise measurement of biomass that is stable and less affected by external conditions. Dry weight is a more reliable measure for comparison of plant growth, biomass accumulation, or experimental treatments because it is not affected by fluctuating water content (Huang et al., 2019). The results of this study also showed close similarity in the tolerance limits for the shoot dry weight and the total weight of fruits.

Although IRQS-22 exhibited a higher reproductive factor (RF = 23.03) than WGR-225 (RF = 12.55), it demonstrated greater tolerance to M. javanica, as indicated by its higher tolerance index (T) for both shoot dry weight and total fruit weight. This finding highlights that tolerance and resistance are distinct traits that must be evaluated independently (Evans and Haydock, 1990; Teklu et al., 2022).

This research provides some key information on the resistance and tolerance levels of two cucumber cultivars (WGR225 and IRQS22). This information enhances our capacity to predict the extent of damage and yield reduction in the two cucumber cultivars as a function of initial M. javanica population density under greenhouse conditions, providing a practical foundation for designing targeted nematode management strategies.

Acknowledgements

We would like to thank Eng. Farhad saeidi Naeini for his support in providing the source of nematode. We are also grateful to Iranian Research Institute of Plant Protection for providing the techniqual supports.

Statement of Conflicting Interests

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References

Al-Hazmi, A. S., Al-Yahya, F. A. and Abdul-Razig, A. T. 1999. Damage and reproduction potential of Heterodera avenae on wheat under outdoor conditions. Journal of Nematology, 31(4S): 662-666.

AL-Sabie, R. F., Ami, S.N. 1989. The effect of inoculum levels of root-knot nematode Meloidogyne javanica on okra plant. Mesopotamia Journal of Agriculture, 21(3), 331-341. (In Arabic)

Ami, S. N. and Shingaly, S. G. A. 2020. Pathogenicity of root–knot nematode Meloidogyne javanica on cucumber plants at different inoculum levels under greenhouse conditions. Journal of Life Sciences Research, 1(2): 76-81.

Anwar, S. A. and McKenry, M. V. 2012. Incidence and population density of plant-parasitic nematodes infecting vegetable crops and associated yield losses in Punjab, Pakistan. Pakistan Journal of Zoology, 44(2): 327-333.

Carneiro, R. G., Mazzafera, P., Ferraz, L. C. C. B., Muraoka, T. and Trivelin, P. C. O. 2002. Uptake and translocation of nitrogen, phosphorus and calcium in soybean infected with Meloidogyne incognita and M. javanica. Fitopatologia Brasileira, 27: 141-150.

Charegani, H., Majzoob, S., Hamzehzarghani, H. and Karegar-Bide, A. 2012. Effect of various initial population densities of two species of Meloidogyne on growth of tomato and cucumber in greenhouse. Nematologia Mediterranea, 40: 129-134.

Chen, B., Sikandar, A., Ahmad, S., Luo, M. and Wu, H. 2022. Meloidogyne graminicola’s effect on growth performance of rice under low population density. Agronomy, 12: 587.

David, R. G. and Triantaphyllau, A. C. 1967. Influence of the environment on development and sex differentiation of root-knot nematode 1-Effect of infection age of the host plant and Soil temperature. Nematologica, 13: 102-110.

Di Vito, M., Vovlas, N., Lamberti, F., Zaccheo, G. and Catalano, F. 1996. Pathogenicity of Meloidogyne javanica on asian and african rice. Nematologia mediterranea, 24: 95-99.

Ehwaeti, M. E., Elliott, M. J., McNicol, J. M., Phillips, M. S. and Trudgill, D. L. 2000. Modeling nematode population growth and damage. Plant Protection, 19: 739-745.

Eisenback, J. D. and Triantaphyllou, H. H. 1991. Root-knot nematodes: Meloidogyne species and races. In: Nickle, W. R. (Ed.), Manual of Agricultural Nematology. New York: Marcel Dekker. pp. 191-274.

El-Sharif, A. G., Refaei, A. R., El-Ntagar, M. E. and Salem, M. M. 2007. The role of eggs inoculum level of Meloidogyne incognita on their reproduction and host reaction. African journal of agricultural research, 2(4): 159-163.

Evans, K. and Haydock, P. P. J. 1990. A review of tolerance by potato plants of cyst nematode attack, with consideration of what factors may confer tolerance and methods of assaying and improving it in crops. Annals of Applied Biology, 117: 703-740.

Gamalero, E. and Glick, B. R. 2020. The use of plant growth-promoting bacteria to prevent nematode damage to plants. Biology, 9: 381.

Gharabadiyan, F., Jamali, S. and Komeili, H. R. 2013. Determining of root-knot nematode (Meloidogyne javanica) damage function for tomato cultivars. The Journal of Agricultural Science, 58: 147-157.

Giné, A., López-Gómez, M., Vela, M. D., Ornat, C., Talavera, M., Verdejo-Lucas, S. and Sorribas, F. J. 2014. Thermal requirements and population dynamics of root-knot nematodes on cucumber and yield losses under protected cultivation. Plant Pathology, 63: 1446-1453.

Greco, N. and Di Vito, M. 2009. Population dynamics and damage levels. In: Perry, R. N., Moens, M. and Starr, J. L. (Eds.) Root-Knot Nematodes. Wallingford: CABI. pp. 246-274.

Gullino, M. L., Albajes, R. and Nicot, P. C. 2019. Integrated Pest and Disease Management in Greenhouse Crops. Springer Int Publishing.

Haji-Hassani, A., Tanha-Maafi, Z., Nicol, J. and Rezaii, S. 2010. Effect of the cereal cyst nematode, Heterodera filipjevi, on wheat in microplot trials. Nematology, 12(3): 357-363.

Heve, W. K., Been, T. H., Schomaker, C. H. and Teklu, M. G. 2015. Damage thresholds and population dynamics of Meloidogyne chitwoodi on carrot (Daucus carota) at different seed densities. Nematology, 17: 501-514.

Huang, W., Ratkowsky, D. A., Hui, C., Wang, P., Su, J. and Shi, P. 2019. Leaf fresh weight versus dry weight: which is better for describing the scaling relationship between leaf biomass and leaf area for broad-leaved plants? Forests, 10(3): 256.

Hussain, M. A., Mukhtar, T. and Kayani, M. Z. 2011. Assessment of the damage caused by Meloidogyne incognita on okra (Abelmoschus esculentus). Journal of Animal and Plant Sciences, 21: 857-861.

Hussey, R. S. and Barker, K. R. 1973. A comparison of methods of collecting inocula of Meloidogyne spp., including a new technique. The plant disease reporter, 57: 1025-1028.

Hussey, R. S. and Janssen, G. J. W. 2002. Root-knot nematodes: Meloidogyne species. In Starr, J. L. Cook, R. and Bridge, J. (Eds.) Plant Resistance to Parasitic Nematodes. Wallingford: CABI. pp 43-70.

Ibrahim, A. A. 2002. Effect of initial population densities of Meloidogyne javanica on tomato growth and nematode reproduction. Alexandria Journal of Agricultural Sciences, 47(2): 181-189.

Jamali, S., Pourjam, E. and Safai, N. 2012. Determining the relationship between population density of white tip nematode and rice yield. Journal of Agricultural Science and Technology, 14: 195-203.

Jepson, S. B. 1987. Identification of Root-Knot Nematodes (Meloidogyne species). Wallingford: CAB International.

Joymatidevi, L. 2009. Pathogenicity of root-knot nematode, M. incognita on two different indigenous plants of Manipur. Indian Journal of Nematology, 39(1): 122-125.

Kankam, F. and Adomako, J. 2014. Influence of inoculum levels of root knot nematodes (Meloidogyne spp.) on tomato (Solanum lycopersicum L.). Asian Journal of Agriculture and Food Sciences, 2(2): 171-178.

Karimipour Fard, H., Pourjam, E., Tanha Maafi, Z. and Safaie, N. 2018. Assessment of yield loss of wheat cultivars caused by Heterodera filipjevi under field conditions. Journal of Phytopathology, 166(5): 299-304.

Kumar, V., Singh, H. S. and Singh, R. V. 2011. Effect on pathogenic potential and population growth of M. incognita race-1 on Cowpea (Vigna ununguiculata L.). Annals of Plant Protection Sciences, 19(2): 428-432.

López-Gómez, M., Flor-Peregrín, E., Talavera, M., Sorribas, F. J. and Verdejo-Lucas, S. 2015. Population dynamics of Meloidogyne javanica and its relationship with the leaf chlorophyll content in zucchini. Crop protection, 70: 8-14.

Maleita, C. M. N., Curtis, R. H. C., Powers, S. J. and Isabel, M. D. O. 2012. Inoculum levels of Meloidogyne hispanica and M. javanica affect nematode reproduction, and growth of tomato genotypes. Phytopathologia Mediterranea, 51(3): 566-576.

Mekete, T., Mandefro, W. and Greco, N. 2003. Relationship between initial population densities of Meloidogyne javanica and damage to pepper and tomato in Ethiopia. Nematologia mediterranea, 31: 169-17.

Moosavi, M. R. 2014. Dynamics of damage to eggplant by Meloidogyne javanica. CIBTech Journal of Zoology, 3: 43-49.

Moosavi, M. R. 2015. Damage of the root-knot nematode Meloidogyne javanica to bell pepper, Capsicum annuum. Journal of Plant Diseases and Protection, 122: 244-249.

Nadeem, H., Khan, A., Gupta, R., Anees, A. and Ahmad, F. 2023. A Seinhorst model determined the host-parasite relationships of Meloidogyne javanica infecting Fenugreek cv. UM202. Journal of Nematology, 55.

Nicol, J. M., Turner, S. J., Coyne, D. L., den Nijs, L., Hockland, S., Tahna Maafi, Z. 2011. Current nematode threats to world agriculture. In J. Jones, G., Gheysen, and C. Fenoll, (Eds.) Genomics and Molecular Genetics of Plant-Nematode Interactions. Dordrecht: Springer Science Business Media. pp. 21-43.

Nicholson, A. J. 1933. The balance of animal populations. Journal of Animal Ecology, 2: 132.

Norshie, P. M., Been, T. H. and Schomaker, C. H. 2011. Estimation of partial resistance in potato genotypes against Meloidogyne chitwoodi. Nematology, 13: 477-489.

Paez, N., Arica, M. A. and Merodith, J. A. 1976. Individual and combined effect of Meloidogyne javanica on four tobacco Nicotiano tabacum cultivers in Venzeuela. Nematropica, 6(2): 68-76.

Pagán, I. and Garcia-Arenal, F. 2020. Tolerance of plants to pathogens: a unifying view. Annual Review of Phytopathology, 58: 77-96.

Phillips, M. S., Hackett, C. A. and Trudgill, D. L. 1991. The relationship between the initial and final population densities of the potato cyst nematode Globodera pallida for partially resistant potatoes. Journal of Applied Ecology, 28: 109-119.

Poudyal, D. S., Pokharel, R. R., Shrestha, S. M. and Khatri-Chetri, G. B. 2005. Effect of inoculum density of rice root knot nematode on growth of rice cv. Masuli and nematode development. Australasian Plant Pathology, 34: 181-185.

Ravichandra, N. G. 2014a. Horticulture and its role in the national economies. In: Ravichandra, N. G. (Ed.) Horticultural Nematology. New Delhi: Springer. pp. 1-3.

Ravichandra, N. G. 2014b. Nematode population threshold levels. In: Ravichandra, N. G. (Ed.) Horticultural Nematology. New Delhi: Springer. pp. 101-114.

Russo, G., Greco, N., d’Errico, F. P. and Brandonisio, A. 2007. Impact of the root-knot nematode, Meloidogyne incognita, on potato during two different growing seasons. Nematologia Mediterranea, 35: 29-34.

Sasanelli, N., Vovlas, N., Trisciuzzi, N., Cantalapiedra-Navarrete, C., Palomares-Rius, J. E. and Castillo, P. 2013. Pathogenicity and host-parasite relationships of Heterodera cruciferae in cabbage. Plant Disease, 97: 333-338.

Sasser, J. N., Carter, C. C., & Hartman, K. M. 1984. Standardization Of Host Suitability Studies and Reporting of Resistance to Root-Knot Nematodes. Cooperative Publication of The Department of Plant Pathology, North Carolina State University and the United States Agency for International Development, Raleigh, North Carolina, U.S.A., 7 pp.

Schomaker, C. H. and Been, T. H. 2006. Plant growth and population dynamics. In Perry, R. N. and Moens, M. (Eds.) Plant Nematology. Wallingford: CABI. Pp. 275-301.

Seinhorst, J. W. 1965. The relationship between nematode density and damage to plants. Nematologica, 11: 137-154.

Seinhorst, J. W. 1970. Dynamics of populations of plant parasitic nematodes. Annual review of phytopathology, 8: 131-156.

Seinhorst, J. W. 1986. Effects of nematode attack on the growth and yield of crop plants. In: Lamberti, F. and Taylor, C. E. (Eds.) Cyst Nematodes. New York and London: Plenum Press. pp. 191-209.

Sumita, K. 2014. Pathogenicity of root-knot nematode, Meloidogyne incognita in green gram. International Journal of Pure and Applied Bioscience, 2(6): 182-184.

Teklu, M. G., Schomaker, C. H., Been, T. H. and Molendijk, L. P. G. 2022. Tuber yield, quality and infestation levels of potato genotypes, resistant to the root-knot nematode, Meloidogyne chitwoodi. Potato Research, 66: 105-135.

Waweru, B. W, Pili, N. N., Wesemael, W. M. L., Wanjau, C., Teklu, M. G. and Gheysen, G. 2023. Population dynamics and damage threshold of Pratylenchus n. sp. and Meloidogyne javanica on finger millet. Nematology, 25: 1157-1168.

Wesemael, W. M. L., Taning, L. M., Viaene, N. and Moens, M. 2014. Life cycle and damage of the root-knot nematode Meloidogyne minor on potato, Solanum tuberosum. Nematology, 16: 185-192.

Whitehead, A. G. and Hemming, J. R. 1965. A comparison of some quantitative methods of extracting small vermiform nematodes from soil. Annals of Applied Biology, 44: 25-38.

Willig, J., Sonneveld, D., van Steenbrugge, J. J. M., Deurhof, L., van Schaik, C. C., Teklu, M. G., Goverse, A., Lozano-Torres, J. L., Smant, G. and Sterken, M. G. 2023. From root to shoot: quantifying nematode tolerance in Arabidopsis thaliana by high-throughput phenotyping of plant development. Journal of Experimental Botany, 74(18): 5487-5499.

Zijlstra, C., Donkers-Venne, D. T. H. M. and Fargette, M. 2000. Identification of Meloidogyne incognita, M. javanica and M. arenaria using sequence characterized amplified region (SCAR) based PCR assays. Nematology, 2(8): 847-853.