Evaluation the Reaction of some Soybean Cultivars to Root-Knot Nematode, Meloidogyne javanica

Using nematode-resistant cultivars is the most economical and environmentally friendly management strategy for the management of the pathogens like nematodes known for causing great yield losses. Root knot nematode (Meloidogyne javanica) is distributed in all soybeans - producing regions of the world and can result in yield losses in almost all soybean-growing areas. The most important species in Iran is M. javanica, which has the widest host ranges of any of the root-knot nematodes. Control of M. javanica is accomplished through the use of pesticides, crop rotation and resistant cultivars. Resistance to nematodes is usually defined as a plant’s ability to inhibit nematode reproduction. Soybean, Glycine max (L.) Merrill, which had economic and nutritional significance, is currently the most important oil - seed crop cultivated in the world. The relationship between crop yield response and initial nematode densities is an important property of a crop resistance. The purpose of the current study was to determine damage functions of M. javanica for some soybean cultivars.
The experiments were conducted under greenhouse conditions and temperature maintained at 25±3°C. Pots (2500 grams) were fumigated with methyl bromide to eliminate existing biotic factors prior to planting and then were filled with a sterile soil composed of sand 60%, clay 14%, silt 26%, at pH 7. For evaluating the reaction of some soybean cultivars to the target nematode, infected roots collected from Isfahan province, identified using morphological methods, perineal pattern of adult females as well as molecular markers, amplification of 670 bp band of extracted DNA from egg and larvae using single egg mass culture. Then the nematode mass was cultured around the roots of 2-4 leaf stage tomato cultivar Ps using completely randomized design with five replications. Soybean plants inoculated with 8000 eggs of M. javanica per 2.5 kg of soil. After 80 days, the growth and physiologic factors of host plant such as root length, root fresh and dried weight, shoot length, shoot fresh and dried weight, pod number in plant, seed per pod, 100- seed weight, chlorophyll concentration, leaf area index (LAI) and leaf area ratio (LAR) as well as gall index, egg mass and reproductive factors of nematode was measured.
The purpose of this study was to determine damage function of M. javanica for some resistant and susceptible soybean cultivars. Similar to M. javanica, the other nematode species was identified using morphological as well as molecular markers as. In greenhouse condition, results showed that the root weight of the infected soybean cultivars increased in comparison to that of healthy roots and the reason is the hormonal imbalance and the gall formation in the roots by the target nematode. The shoot length and shoot fresh weight in infected plants decreased due to the absorption of nutrients and internodes distance reduction. Seed per pod is dependent characteristics on the genotype, and largely is independent of environmental factors and specific environmental stresses may affect grain formation period. The number of seeds per pod was completely genetic trait, indicating significant differences among cultivars, but the cultivars were not affected by nematode infection. The JK cultivar has the most final population of nematodes and Sahar cultivar has the least one. The JK cultivar was sensitive to 2.65 gall index and Williams and Elit cultivars were tolerant and showed less gall index and Sahar, L- 17, 033 along with DPX were recognized as resistant soybean cultivar, among which Sahar cultivar with 0 reproductive factor and 0.6 gall index was most resistant one. The use of resistant soybean cultivars is the most efficient and control methods for root- knot nematode.
The different soybean cultivars have varying degrees of sensitivity, tolerance and resistance to root-knot nematode infection. The present research indicates that using breeding methods as well as biotechnological techniques, tolerant and resistant cultivars can be produced and the farmers can choose the resistant ones to reduce application of hazardous chemicals. On the other hand it is necessary that by a thorough examination of nematode resistant genes in soybean plants and their incorporation in the sensitive plant, the nematode damage would get reduced. The use of resistant soybean cultivars is the most efficient and adequate control measure.