Document Type : Research Article
Department of Plant Protection, Faculty of Agriculture, Ferdowsi University of Mashhad
Introduction: The root-knot nematodes of the genus Meloidogyne are highly adapted, obligate plant parasites, consisting of nearly one hundred valid species, and are considered the most economically important group of plant-parasitic nematodes. The control of root- knot nematodes has been sought by the use of nematicides, resistant varieties, crop protection and organic amendments. Because of toxicity of nematicides for environment, human health and wild life, application of them are restricted. Identification of genes responsible for resistance to root-knot nematode and their mode of actions have attracted a lot of attentions to develop resistant cultivars. Resistance in the plant species is often due to the presence of specific genes. In resistant cultivars, resistance genes can prevent or suppress one or more stages of nematode infection cycle. In fact, in response to nematode infection, resistance genes can prevent or suppress one or more stages of nematode infection process. In the most incompatible interactions, depending on the mechanism of resistance, the root galls are reduced or eliminated at the sites of infection. Assessment of resistance to the root-knot nematodes in different tomato cultivars is helpful for selection of suitable cultivars with satisfying plant growth and nematode tolerance traits for suitable management of the root-knot nematode. Thus, in the present study we evaluate the response of some tomato cultivars for resistance to root-knot nematodes, Meloidogyne javanica, in greenhouse conditions.
Materials and Methods: In this study, the nematode population was obtained from roots of tomatoes collected at a glasshouse in Tirtash–Mazandaran, Iran.The root-knot nematode were purified and multiplied on tomato cv. Early Urbana plants. Then the nematode species were identified based on morphological and molecular methods. The seeds of ALYSTE F-1, ARYZA F-1, Rutgers, Early Urbana, Dutch Mobil and Hungarian Mobil tomato cultivars were spawned in equal proportions of cocopit, perlite and vermiculite and irrigated for 3 weeks. Then, the seedlings were transferred to the pots containing mixture of sterile soil, sand and vermiculite (1:1:1) with 9 cm diameter. After 2 weeks, the seedlings were inoculated with 3000 second stage juveniles (J2s) of M. javanica. The pots were kept for 70 days at 24-33°C and 50% relative humidity. Resistance evaluation was based on plant growth and nematode reproduction indices. Growth indices were fresh and dry weight of root and aerial part, root length, plant height and total fresh and dry weight and nematode reproductive indices were number of galls and egg masses/g root and total root, eggs/egg mass, eggs/root, J2s /soil, final nematode population and reproduction factor (RF) were measured and recorded. The experiment was carried out in a completely randomized design with 5 replicates in the both of inoculated and non-inoculated with nematode. Data were analyzed in Minitab version 17. The means were compared by using Fisher,s LSD. Also to determine the resistance level, resistance index (RI) and reproduction factor (RF) were calculated. The RI is depended to frequency of the gall and egg mass index in the root. To determine Gall Index (GI) and Egg mass Index (EI), 0= no galls or egg masses, 1= 1 to 2, 2= 3 to 10, 3= 11 to 30, 4= 31 to 100 and 5= more than 100 were considered, in the following for RI, 0-0.9= immune, 1-1.9= highly resistant, 2-2.0= resistant, 3-3.9= moderately resistant, 4-4.9= intermediate, 5-5.9= moderately susceptible, 6-6.9= susceptible and more than 7= highly susceptible. The reproductive factor (RF) of the root-knot nematode in the different genotypes was obtained by dividing the final and initial population densities of the nematode (RF = Pf/Pi).Thus, RF≤1, GI≤2 = resistant; RF≤1, GI>2= moderately resistant; RF>1, GI≤2= tolerant and RF>1, GI>2 susceptible.
Results and Discussion: This study results showed that ALYSTE F-1, had the lowest number of gall, egg mass, second stage juveniles and consequently the lowest nematode population and was recognized as moderately resistant cultivar. In terms of the growth indices, ALYSTE F-1 also had the highest growth characteristics and contained a significant difference with other cultivars. Totally, Rutgers, ARYZA F-1, Dutch Mobil, Hungarian Mobil and Early Urbana varieties were introduced as highly susceptible cultivars based on RF and GI. However, Dutch Mobil, Hungarian Mobil and Early Urbana had the highest nematode population and reproduction factor (RF). In terms of the growth traits, the results showed that Rutgers, as a highly susceptible cultivar, was more impressible than other cultivars followed by Dutch Mobil. The cluster analysis based on the sum of the plant growth and nematode reproductive traits showed that ALYSTE F-1 cultivar was distinct from the other cultivars. Thus, the cluster analysis confirmed the results of comparison of the average of the plant growth and nematode reproductive traits.
Conclusion: Based on the results of this study, ALYSTE F-1 was identified as a moderately resistant cultivar to the root- knot nematode, M. javanica. and the others were highly sensitive to the nematode.