Varietal Susceptibility and Disease Resistance of Tomato Cultivars against Meloidogyne incognita in Greenhouse Condition

Tomato (Solanum lycopersicum L.) is a member of family Solanaceae. Tomato is a good source of vitamins (A, C and K), potassium and magnesium. It contains essential carotenoids such as lutein, lycopene and natural antioxidants.
       
Plant-parasitic nematodes caused significant losses in vegetable crops. They attack more than 3000 species of plants, including almost all cultivated plants and reduced world crop  production (Abad et al., 2003). The estimated yield loss in tomato crop by plant-parasitic nematodes is about 23% in India (Kumar et al., 2020). Root-knot nematodes (Meloidogyne spp.) are one of the most economically destructive genera of nematodes in horticultural and field crops, causing an estimated annual loss of US$ 100 billion globally (Oka et al., 2000).  They are sedentary endoparasites that affect the root system of plants (Mitkowski et al., 2003).
       
These nematodes are difficult to control due to their short life span, high population density and reproductive capacity (Sikora and Fernandez, 2005).
       
Various methods have been employed over the years to manage nematode infestation, including chemical, physical, organic amendments, biological control and cultural land management practices (Tariq et al., 2020). However, chemical nematicide usage is a common, effective and widespread practice to manage nematodes and minimize yield loss (Arita et al., 2020; Ji et al., 2020). Nematicides use to check the development and reproduction of nematodes highly toxic to the environment. These chemicals enhance biodegradation and environmental pollution for a long time and have a negative impact on flora and fauna (Mahmood et al., 2016). Because of the restrictions on chemical pesticide use and their adverse effects on the environment, as well as on human and animal health, therefore, alternative strategies for nematode management are highly desirable (Ntalli et al., 2020). Nematode infestation levels could be minimized in the soil by using resistant cultivars with crop rotation (Ansari et al., 2018). The use of resistant cultivars is an environmentally friendly, safe, most comfortable and economically feasible alternative strategy to manage root-knot nematodes (Sujatha et al., 2017). The cultivars which do not support disease development or resist the pathogens’ growth and provide high yield called resistant cultivars. Numerous cultivars of different vegetable crops viz., tomato, carrot, okra, cucumber and brinjal have been recorded as resistant to Meloidogyne spp. (Tariq et al., 2022; Ahmad et al., 2018). The resistant cultivar may suppress the harmful nematode density by 10-50% (Oostenbrink, 1966). The susceptibility of different vegetable cultivars against nematode has been reported by researchers (Montasser et al., 2019).
       
The present study was designed to evaluate the disease resistance in nine cultivars of tomato against Meloidogyne incognita in greenhouse conditions, which can be used for the sustainable management of nematodes.
 

Collection of tomato cultivar
 
Nine cultivars of tomato (Jyoti-4, Navuday, P-21, T9, Pusa-Rohini, Pusa-Sheetal, Pusa-Ruby, Tomato-Ped and Tomato-Round) were procured from Indian Institute of Agriculture Research (IARI), New Delhi and Chola seeds store Aligarh, Uttar Pradesh, India.
 
Collection and maintenance of nematode inoculum
 
Infected roots were collected from the eggplant field from village Panjipur, district Aligarh. Eggmasses were detached from the infected roots and collected in a petri dish having distilled water. Meloidogyne spp. was identified by perineal patterns in the laboratory (Eisenback1985). After identification, single eggmass was cultured and maintained on eggplant in the greenhouse of the Department of Botany, Aligarh Muslim University, Aligarh. Eggmasses were hand-picked using sterilized forceps from heavily infected roots of eggplant. The second stage juveniles (J2s) were obtained from hatched eggs by incubating hand-picked egg masses in sterile distilled water at 27±2°C. The hatched juveniles were collected after every 24 hours and distilled water was added. The concentration of freshly hatched second-stage juveniles was standardized.
 
Screening of tomato cultivars
 
Screening of tomato cultivars for resistance against M. incognita was performed in clay pots. Surface sterilized seeds (1.0% NaOCl for 15 min) of each tomato cultivar were sown in clay pots containing 1kg autoclaved sandy loam soil and manure in the ratio 3:1 for preparation of nursery. Two weeks old seedlings of each cultivar were transplanted singly into each pot of 15 cm diameter (1 kg mixture of soil). Only one healthy seedling of each cultivar was maintained in each pot, including the control. Experiment was conducted in the year August, 2019 at section of Plant Pathology and Nematology, Department of Botany, Aligarh Muslim University, Aligarh, India.
 
Inoculation technique
 
Each pot was inoculated with 1500 freshly hatched second-stage juveniles (J2s) of M. incognita by making 3-4 holes around the rhizosphere of plant. This experiment was carried out in a completely randomized design (CRD) with five replications of each cultivar. The uninoculated plants were used as control. The plants were given the required amount of water and proper care was taken during the experiment period.
 
Data collection and observations
 
Plants were uprooted after three months. The roots of each tomato cultivar were gently uprooted from the pots and washed carefully to avoid egg mass losses and observations were recorded. The following morphological parameters, such as shoot and root length, fresh and dry weight of shoot and root were recorded. Physiological parameters like chlorophyll and carotenoid content were also estimated. Pathological parameters viz., number of egg masses/root, number of eggs/eggmass, nematode population per 250 g of soil and the number of galls were also noted. The percent reductions in various parameters over the control were calculated by using the formula.
 

                               
Host rating status towards the nematode assessed by estimating the number of galls per root system.
       
Rating scale for the assessment of the level of resistance of plant cultivars against root-knot nematodes, based on the number of galls (Taylor and Sasser, 1978).
 
 
Statistical analysis
 
The experimental data were analyzed statistically by one-way analysis of variance (ANOVA) using SPSS-17 statistical software (SPSS Inc., Chicago, IL, USA). Mean values statistically compared differentiated by Duncan’s multiple range test at P<0.05.
 

The statistical comparison of means of different parameters and the presence of galls revealed that none of the cultivars was found immune or highly resistant against Meloidogyne incognita. The nematodes displayed variable effects on the reproduction and plant growth of different tomato cultivars. According to the rating scale of galls and reductions in growth parameters, cultivars Pusa-Ruby and Tomato-Ped were found highly susceptible. Five cultivars, namely Jyoti-4, Navuday, Pusa-Sheetal, P-21 and Tomato-Round were found susceptible, while cultivar Pusa-Rohini was found moderately susceptible. Only one cultivar viz., T9, was found moderately resistant. All cultivars showed a significant reduction in growth parameters over their respective controls.
       
In the roots of highly susceptible cultivars viz., Pusa-Ruby and Tomato-Ped, the highest number of eggmasses were recorded as (166) and (137), respectively. Susceptible cultivars, namely, Jyoti-4, Navuday, Pusa-Sheetal, P-21 and Tomato-Round, also showed a high number of eggmasses but less than highly susceptible cultivar. Among susceptible cultivars, the number of eggmasses noted in P-21, Jyoti-4 and Tomato-Round was (118), (84) and (73), respectively, while cultivars Navuday (31), Pusa-Sheetal (59) recorded the lesser number of eggmasses. The number of eggmasses found in moderately susceptible cultivar Pusa-Rohini was (23). The minimum number of eggmasses (16) was observed in moderately resistant cultivar T9. A significant variation was also recorded in the number of eggs/eggmasses among all tested cultivars. Cultivars Pusa-Ruby and Tomato-Ped indicated the maximum number of eggs/eggmasses (253) and (218) respectively. Susceptible cultivars showed variation in the number of egg/eggmasses as P-21 and Jyoti-4 showed (152) and (121), respectively, while cultivars Pusa-Sheetal, Navuday and Tomato-Round showed (74), (57) and (98), respectively. In cultivar, Pusa-Rohini 34 eggs/eggmasses were recorded whereas only (20) were found in cultivar T9.
       
All cultivars behaved differently regarding the formation of galls. The maximum number of galls was recorded in Cultivar Pusa-ruby. The second highly susceptible cultivar Tomato-Ped showed galls on the root. Among susceptible cultivars, P-21 and Jyoti-4 indicated higher number of galls in their group. The number of galls observed in other susceptible cultivars, namely, Tomato-Round, Pusa-Sheetal and Navuday. Among all cultivars, the minimum number of galls was found in moderately resistant cultivar T9. (Table 1b)


       
Variation in nematode populations was also observed in all tested cultivars. Cultivars Pusa-Ruby and Tomato-Ped showed the highest nematode population as (1649) and (1456), respectively. Among the susceptible cultivars, P-21 and Jyoti-4 showed higher nematode populations as (1302) and (1225), respectively, while Tomato-Round, Pusa-Sheetal and Navuday recorded as (942), (850) and (653), respectively. Nematode population observed in moderately susceptible cultivar Pusa-Rohini was (584). Least nematode population (268) was recorded in moderately resistant cultivar T9 (Table 1b).
       
All tested cultivars showed a significant reduction in total plant length (shoot and root) compared to their controls. Maximum percent reduction i.e., 54.29% in total plant length was observed in highly susceptible cultivar Pusa-Ruby, whereas another highly susceptible cultivar Tomato-Ped showed 49.72% reduction. Minimum reduction of 18.16% in total plant length was found in moderately resistant cultivars T9. Among susceptible cultivars, the reduction in total plant length observed in P-21 and Jyoti-4 was 42.12% and 38.97%, respectively. The other three susceptible cultivars, viz., Tomato-Round, Pusa-Sheetal and Navuday, showed reduction in total plant length as 34.57%, 31.13% and 30.38%, respectively. In comparison, the reduction in plant length observed in moderately susceptible cultivar Pusa-Rohini was 24.16% (Table 1a).


       
All of the nine cultivars showed significantly variable reductions in fresh and dry weight of plant. The cultivars Pusa-Ruby and Tomato-Ped showed maximum reduction in fresh weight of the plant as 54.41% and 50.01%, respectively. Susceptible cultivars P-21, Jyoti -4, Tomato-Round, Pusa-Sheetal and Navuday showed plant fresh weight reduction as 39.09%, 39.29%, 34.02%, 33.66% and 30.11%, respectively. The reduction in plant fresh weight observed in moderately susceptible cultivar Pusa-Rohini was 25.14%, while the minimum reduction in plant fresh weight 16.18% was found in moderately resistant cultivar T9. A similar trend was also observed in the reduction of dry weight of plant in all cultivars. Cultivars Pusa-Ruby and Tomato-Ped noted higher reduction in the dry weight of the plant as 52.13% and 48.50%, respectively. Among susceptible cultivars, a significant reduction in dry weight of the plant observe in P-21 and Jyoti-4 was 40.11% and 42.00%, respectively, whereas other susceptible cultivars Tomato-Round, Pusa-Sheetal and Navuday showed reduction in plant dry weight as 32.67%, 33.61% and 30.08%, respectively. The reduction inplant dry weight observed in cultivar Pusa-Rohini was 22.70%. Minimum reduction in plant dry weight 18.11% was found in moderately resistant cultivar T9 (Table 1a).
       
The nematode infestation also caused reduction in plant yield. Highly susceptible cultivar viz., Pusa-Ruby and Tomato-Ped showed maximum reduction in yield. Susceptible cultivars also represent significant yield reduction compared to their respective control. Susceptible cultivars, namely, P-21, Jyoti-4, Tomato-Round, Pusa-Sheetal and Navuday showed reduction in yield. Moderately susceptible cultivar Pusa-Rohini showed reduction in yield. T9 showed a minimum reduction in yield (Table 1b).
       
There was a significant reduction in chlorophyll and carotenoid content due to nematode infestation in all tested cultivars. Cultivars Pusa-Ruby and Tomato-Ped showed maximum reduction in chlorophyll content as 51.43% and 49.33%, respectively. Susceptible cultivars P-21 Jyoti-4, Tomato-Round, Pusa-Sheetal and Navuday showed reduction in chlorophyll content as 40.00%, 37.88%, 34.98%, 32.90% and 27.40%, respectively. Cultivars Pusa-Rohini and T9 also showed reduction in chlorophyll content as 23.71% and 19.98%, respectively. Another biochemical parameter i.e., carotenoid content was also recorded in all tested cultivars. Reduction in carotenoid content observed in all tested cultivars is presented in Table 1b. The reduction in carotenoid content recorded in cultivars Pusa-Ruby and Tomato-Ped was 54.38% and 48.53%, respectively. Susceptible cultivars P-21, Jyoti-4, Tomato-Round, Pusa-Sheetal and Navuday showed reduction in carotenoid content as 39.50%, 39.90%, 35.12%, 30.29% and 27.19%, respectively. Moderately susceptible cultivar Pusa-Rohini showed 22.14%, while moderately resistant cultivar T9 showed 18.03%reduction in carotenoid content (Table 1b).
       
Positive and significant relationships were observed between number of root gall and the percent reductions in total plant length (R2 = 0.97), total fresh weight (R2 = 0.97), total dry of plant (R2 = 0.98), chlorophyll (R2 = 0.99), yield (R2 = 0.98) and carotenoids content (R2 = 0.99) represented by Fig 1.


       
The use of resistant cultivar is considered as an important strategy to manage nematode disease in the plants. In the present study, nine tomato cultivars’ response was assessed based on root galls and reduction in plant growth characters. M. incognita caused significant damage in all the tested cultivars. According to Taylor and Sasser scale (1978), none of the cultivars was found immune or highly resistant against M. incognita. However, one cultivar was found moderately resistant. The present findings showed significant variations in the number of galls, eggmasses, eggs and nematode populations of M. incognita in all tested cultivars. The number of galls, eggmass, eggs and nematode population was significantly higher in highly susceptible and susceptible tomato cultivars than moderately resistant. While minimum was observed in moderately resistant cultivars. Resistance and susceptibility of plants against parasitic nematodes also depend on the nematode’s ability to reproduce (Cook and Evans, 1987). The high number of root galls and increased population density observed in susceptible cultivars might be due to the higher invasion of nematodes preferred by susceptible cultivar. On the other hand, moderately resistant cultivar permitted few juveniles to enter in the root. Resistant host stops or slows down the invasion and growth of nematode juveniles (Williamson et al., 1996). Sasser (1954) also., reported that resistant cultivars showlow nematode invasion rate than susceptible cultivars.
       
In the present study, the growth of tomato cultivars was negatively correlated with the number of galls. Maximum reduction in plant growth parameters was observed in highly susceptible cultivars. Susceptible cultivar showed a moderate level reduction in pant growth while moderately resistant cultivar indicated minimum reduction. Many researchers have also reported reductions in plant height and weight, yellowing of leaves as a result of root-knot nematodes infection (Azam et al., 2011). Infective second-stage juveniles enter the host roots by the epidermis and move through the root cortex to establish a feeding site, called giant cells in the vascular tissues. This feeding site provides adequate nutrition for the growth and reproduction of nematodes (Abad et al., 2010). These giant cells receive more nutrients, so the decreased amount of nutrients translocate to the normal cells causes reduced fruit growth (Escobar et al., 2015). Reduction in shoot lengths, root length and fresh weight of plant was likely a result of nematode feeding on giant cells (Siddiqui et al., 2014). The formation of galls and eggmasses in the root system ceases the absorption and translocation of water and minerals in the plant, due to which plant growth is reduced. Similarly, all tested cultivars showed reduction in plant yield due to nematode infestation. Similar results were also observed by other workers that resistant cultivars yield comparatively better than susceptible cultivars (Ansari et al., 2018). In addition to plant growth reduction, some biochemical changes were also found in all cultivar of tomato. The reductions in chlorophyll and carotenoid content were observed, which was also supported by Melakeberhan et al., (1986). These reductions in chlorophyll and carotenoid contents are the results of nutrient deficiency in the plant.
 
 

This study demonstrates that the cultivation of resistant or moderately resistant cultivars could minimize nematode infestation and minimize yield losses. The use of resistant cultivars is an efficient and environmentally acceptable approach to manage root-knot nematode. Resistant cultivars are the low-cost strategy because there is no extra cost to spend as nematicide or pesticide. Furthermore, resistant cultivars can be used in breeding programs for developing new resistant cultivars against the nematode. Further study is necessary to search out nematode-resistant cultivars of tomatoes.
 

None.