Pathogenicity and control of Meloidogyne spp . on some spinach , Swiss chard , and table beet plant cultivars

The pathogenicity of the root-knot nematodes Meloidogyne arenaria, M. incognita and M. javanica on spinach cvs. ‘Balady’, ‘Barkly’, ‘Orient’, ‘Pacific’ and ‘Solanicy’, Swiss chard cvs. ‘Balady’ and ‘Ford Hook’, and table beet cvs. ‘Asgro Wonder’, ‘Balady’, ‘Detroit Dark’ and ‘Detroit Spainal’ was determined in several greenhouse tests. The results show that the tested chenopodiaceous plant cultivars were either susceptible or highly susceptible to the tested root-knot nematode species except spinach cv. ‘Pacific’ and table beet cv. ‘Asgro Wonder’ which exhibited moderately susceptible reaction to M. arenaria and M. javanica. In a separate control experiment, the pathogenicity of M. incognita on spinach cv. ‘Balady’ was studied in a greenhouse experiment. Soil treatments with dried plant materials of Monterey cypress, Brazil peppertree, lime and China tree induced great reductions (81.4-91.8%) in the numbers of root galls and egg masses of M. incognita on infected spinach plants. On the other hand, treatments with plant materials of blue gum tree, California pepper tree, lantana and pomegranate gave 49.8-69.3% reduction of root galls and egg masses of M. incognita on infected spinach plants.

Spinach, Swiss chard, and table beet are cool season vegetable crops that are widely grown in northern Egypt with some pest and disease problems (Ibrahim et al., 2021). Little information is available on the pathogenicity of the root-knot nematodes (Meloidogyne spp.) on spinach and other similar vegetable crops (Castillo and Jimenez-Diaz, 2003;Manachini et al., 2002;Premachandra and Gowen, 2015;Ibrahim et al., 2021). Therefore, the objectives of the present research were to study the pathogenicity of M. arenaria, M. incognita and M. javanica on some spinach, Swiss chard and table beet cultivars and the control of M. incognita on spinach cv. 'Balady' under greenhouse conditions.

Materials and Methods
Inocula of the root-knot nematodes M. arenaria originally isolated from peanut and M. incognita and M. javanica originally isolated from spinach plants were obtained from infected roots of tomato (Solanum lycopersicom L.) cultivar 'Rutgers' grown in the greenhouse. Eggs of these nematode species were extracted from infected tomato roots with sodium hypochloride (NaClO) solution (Hussey and Barker, 1973).
The reactions of five spinach ('Balady', 'Barkly', 'Orient', 'Pacific', 'Salonicy'), two Swiss chard ('Balady', 'Ford Hook') and four table beet ('Asgro Wonder', 'Balady', 'Detroit Dark Red', 'Detroit Spainal') cultivars to M. arenaria, M. incognita and M. javanica were determined in several greenhouse tests. Seeds of the tested plant cultivars were sown in 15 cm diameter clay pots filled with a mixture of equal volumes of steam sterilized sand and clay soil. After emergence, seedlings were thinned to one seedling/pot. Two weeks after emergence, soil of treated pots was infested by creating holes near the plant roots and then adding an initial population (Pi) of 4000 eggs/pot of M. arenaria, M. incognita or M. javanica. Non-treated pots served as control. All treatments were replicated five times. Pots were arranged in a randomized complete block design in a greenhouse maintained at 20-26 o C. The experiments were conducted in 2020 and 2021.
Sixty days after inoculation, experiments were terminated, and roots were washed free of soil. Roots infected with root-knot nematodes were immersed in an aqueous solution of phloxine B (0.15 g/L water) for 15 minutes to stain the nematode egg masses. Plants were rated on a 0-5 scale according to the numbers of egg masses (Taylor and Sasser, 1978). Plants with 0-2 egg masses/plant were considered resistant; 3-10 egg masses /plant, moderately resistant; 11-30 egg masses/plant, moderately susceptible; 31-100 egg masses/plant, susceptible; and ˃100 egg masses/plant highly susceptible (Taylor and Sasser, 1978;Ibrahim et al., 2019).
Soil amendments with dried plant materials were examined in the greenhouse for their effects on the reproduction of M. incognita on spinach cv. 'Balady'. These included dried leaves of Monterey cypress (Cupressus macrocarpa Hartw.), blue gum (Eucalyptus globules Labill.), Brazil peppertree (Schinus terebinthifolia Raddi), California peppertree (Schinus molle L.), China tree (Melia azedarach L.), lantana (Lantana nana L.), and peels of both lime fruits (Citrus aurantifolia (Christm.) Swingle) and pomegranate fruits (Punica granatum L.). The tested plant materials were obtained from the Agricultural Experiment Station of Alexandria University, Abees, Alexandria, Egypt, oven dried at 60 o C for 48 hrs, and ground into a fine powder by an electric grinder.
Seeds of spinach cv. 'Balady' were sown in 15 cm diameter clay pots filled with a mixture of equal portions of autoclave sterilized sand and clay soil. After emergence, seedlings were thinned to one seedling/pot and ten days later the tested plant materials were incorporated into the upper part of the soil of treated pots at the rate of 30 g/pot. Two weeks after emergence, the soil was inoculated with the tested nematode at the rate of 5000 eggs/pot. Treatments were replicated five times. Pots were arranged in a randomized complete block design in a greenhouse at 20-26 o C. The experiment was conducted in 2020 and repeated in 2021.
The experiment was terminated 60 days after soil inoculation. Roots were washed free of soil. The numbers of M. incognita galls and egg masses were determined along with the dry weights of the shoots and roots. Data of the dry weights of the shoots and roots of the tested spinach plants were analyzed with analysis of variance (ANOVA) and means separated with least significant differences tests (LSD, SAS Institute, 1997).

Results
Results obtained from experiments of 2020 were almost like those in 2021 (Tables 1-3). The reactions of the tested spinach cultivars to infection by M. arenaria, M. incognita and M. javanica are presented in Table   1.  The effects of soil amendments on reproduction of M. incognita on spinach cv. 'Balady' are presented in Table 3. The applied soil treatments suppressed nematode infection and greatly reduced the numbers of M. incognita galls and egg masses on infected spinach roots compared to the control. The highest reductions (81.4-91.2%) of nematode egg masses were recorded with treatments of Brazil peppertree (S. terebinthifolia), China tree (M. azedarach), lime (C. aurantifolia) and Monterey cypress (C. macrocarpa) plant materials. Treatments with California peppertree (S. molle), and pomegranate (P. granatum) plant materials gave 64.1 -69.3% reduction in nematode egg masses. On the other hand, treatments with lantana (L. nana) and gum tree (E. globules) leaves resulted in only 48.7 -58.8% reduction in M. incognita egg masses. Treatments with the tested plant materials caused significant increases in shoot and root dry weights of treated spinach plants compared to the control (Table 3).

Discussion
This research demonstrated that most of the tested chenopodiaceous plant cultivars were susceptible and good hosts for M. arenaria, M. incognita and M. javanica as these nematode species infected and reproduced successfully on the tested plant cultivars. The results support earlier studies (Ibrahim et al., 2013;2019) indicating that M. arenaria, M. incognita and M. javanica can infect and reproduce on some cabbage, cauliflower, cotton, flax and turnip cultivars. Also, Ibrahim et al. (2019) showed that some species and cultivars of banana, bitter almond, palm trees and peach were susceptible and good hosts for M. incognita and M. javanica. A recent study by Ibrahim et al. (2021) showed that some spinach, Swiss chard, and table beet cultivars were susceptible to the cyst nematode Hererodera schachtii. The tested root-knot nematode species significantly decreased shoot and root dry weights of the susceptible and highly susceptible spinach, Swiss chard, and table beet cultivars. Similar results were obtained by Ibrahim et al. (2013Ibrahim et al. ( , 2019 who found that infection with M. arenaria, M. incognita and M. javanica reduced growth of some cabbage, cauliflower, cotton, flax and turnip cultivars. It is evident that infections with M. incognita or M. javanica induced more root galls and egg masses and growth damage on infected spinach, Swiss chard and table beet plant cultivars as compared with M. arenaria infection. Previous studies in Egypt (Ibrahim et al., 2010(Ibrahim et al., , 2013(Ibrahim et al., , 2019 showed that M. arenaria is of low occurrence and less pathogenic compared to M. incognita and M. javanica.
The results showed that soil treatments with dried plant materials of lime, Monterey cypress, China tree and Brazil peppertree greatly reduced the numbers of galls and egg masses of M. incognita on infected spinach plants. In similar study, Tasi (2008) reported that peels of some citrus fruits were effective against M. incognita. Also, Ibrahim et al. (2013) indicated that soil treatments with dried plant materials of castor bean, goosefoot and lantana greatly reduced infection of M. incognita on infected cabbage plants. Moreover, the present results are in agreement with those of other authors who described the effective use of organic soil amendments to control root-knot and cyst nematodes (Saifullah et al., 1990;Radwan et al., 2004;Ibrahim et al., 2013Ibrahim et al., , 2014.

Conclusions
It is concluded from the study of determining the host status of certain spinach, Swiss chard, and table beet cultivars to M. arenaria, M. incognita and M. javanica that resistance to these nematode species is of significance and can be useful to incorporate in breeding programs during planning control measures for rootknot nematodes. More research is needed for the development of resistant or tolerant cultivars of these vegetable crops to root-knot nematodes.