Root-knot nematodes (Meloidogyne spp.) are important polyphagous plant parasites worldwide. Intraspecific variation and the occurrence of physiological races have necessitated the development of taxonomic techniques enabling differentiation and classification of races related to major Meloidogyne spp. Accurate identification of their races and populations is essential for determining appropriate management approaches and benefits from further characterization and understanding of the variability within a single nematode species. Electrophoretle focusing of malic dehydrogenase, ?-glycerophosphate dehydrogenase and esterase for seven populations of Meloidogyne spp. by polyacrylamide gels was tested. These populations included 1, 2 and 4 populations of M. javanica and M. arenaria race I and II, respectively. Malic Dehydrogenase profiles obtained by polyacrylamide-gel electrophoresis indicated that differences between Moloidogyne arenaria and M, javainca were more pronounced than were differences between races or populations of M. arenaria. The enzyme patterns of the two species varied even though the nematodes were propagated on the same host plant (Rutgers tomato).Key words: Biochemical markers, Meloidogyne arenaria, M. javanica, root-knot nematode, molecular taxonomy.

Citrus fruit yield is considered a short-term response to the citrus nematode,Tylenchulus semipenetrans damage and therefore this study addressed parametersmeasuring overall appearance of the sampled trees. Soil and roots from 20 trees ineach of three mature: 'banzaheer' lemon, 'Baladi' mandarin, and 'Navel' orange andone immature: 'Navel' orange orchards, all grafted on sour orange rootstock, inEgypt were sampled for the citrus nematode, T semipenetrans. in February 2011 toinvestigate their correlations with tree parameters (tree height and vigor, canopydiameter, and trunk circumference) that reflect long-term nematode damage of thesampled trees. The correlation between pairs of these four parameters were alwayspositive and generally with high significant levels. Each of the four parameters wasnot significantly correlated with fruit yield of the mature trees but each of tree heightand vigor, and canopy diameter was correlated with fruit yield of the immature Navelorange. The relationships between pairs of these biotic parameters and Tsemipenetrans population density in fibrous roots and soil were not consistent.Eleven edaphic factors in mandarin and mature orange orchards were measuredand compared. Both soils were dominated by rough grainy particles of sand. Levelsof potassium, calcium, phosphorus, ammonium and nitrate as well as soil solutionpH, organic matter content and electric conductivity in the soil samples weresignificantly (P s 0.01) different between the mandarin and orange orchards. Toachieve better economic revenue of citriculture, local tackling of T. semipenetrans problem in newly reclaimed areas of Egypt was discussed.