Nematode culture and inoculum preparation Ditylenchus angustus was collected from infested plants of the rice cv. BR3 and A. besseyi from plants of cv. BR11, from a farmer’s field in the Gazipur district, Bangladesh. Infected stems or seeds were cut into small pieces and immersed in distilled water in petri-dishes for approx. 4 h to release nematodes into the water. Nematodes were then collected by sieving (20 μm mesh sieve) and identified under a compound microscope (Nikon AFX-IIA, Japan). Both nematodes were separately cultured on the fungus, hizoctonia solani following the techniques described by Latif and Mian (1995) and Latif et al. (1997). Effects of mixed inoculations of Aphelenchoides besseyi and Ditylenchus angustus on population dynamics and yield components in rain-fed pots Soil and plant material. A pot experiment was conducted in a net house at the Bangladesh Rice Research Institute (BRRI), Gazipur, during the rain-fed season in 2003, with rice cultivation soil [pH (H2O), 5.8; 0.9% organic matter, total C, 20.5 g kg-1; total N, 2.2 g kg-1). Clean and healthy matured seeds of rice cv. BR3 (germination rate >85%) were pre-germinated in a moist plastic tray (25 × 10 cm) in the dark at 28°C. Three-day-old sprouted seeds were planted at approx. 0.5 cm depth in each earthen pot (diam. 25 cm, height 30 cm) using sterilized forceps. The pots were then put in open space and left for 150 d in rain-fed conditions. Irrigation and weeding were performed as necessary, following the practices described by BRRI (2003). Two mL solution of Hyponex® fertilizer [containing (mg L-1): N (100), P (200), K (100), Mg (10), Mn (0.02), and B (0.1)] was added to each pot 20 d after planting. No pesticides were used during the experimental period. Inoculation of the rice seedlings Twenty days after sowing (DAS), the rice seedlings in each pot were inoculated at the base with nematodes at the rate of approx. 100 nematodes/ plant, as described by Rahman (1993) and Latif et al. (1997). The proportions of juveniles, males and females inoculated were 40, 25 and 35% for D. angustus and 36, 28 and 36% for A. besseyi. Treatments were ratios of A. bessey: D. angustus of 100:0, 0:100, 50:50, 75:25 or 25:75, and a non-inoculated control treatment was included. Initial penetration of nematodes into plants in the different treatments was confirmed by extraction of nematodes, as described by Rahman (1993) and Latif et al. (1997). Effects of mixed inoculation of Aphelenchoides besseyi and Ditylenchus angustus on population dynamics and yield components in a field trial An experiment was conducted in irrigated rice fields during 2003 to 2004, at BRRI, Gazipur. Well decomposed cowdung was applied to soil at 10 t ha-1. Ex perimental plots were fertilized with the recommended rates of N–P–K–S–Zn fertilizer (124–26–60–13–4 kg ha-1; BRRI, 2003). The procedure and method for inoculation of cv. BR3 seedlings with nematodes was as described for the pot experiment (above). Seedlings of BR3 were inoculated five treatments of A. bessey: D. angustus ratios of 100:0, 0:100, 50:50, 75:25 or 25:75, and an uninoculated control treatment was included. Based on chlorotic symptoms of ufra (symptom appeared at the bases of young leaves) and white-tip (symptom appeared at the tips of young leaves) at 20 d after inoculation, the infected seedlings were transplanted into 2 × 2 m plots at the rate of one seedling per hill. The distance between hills, and rows of hills, was 20 cm. Each plot was surrounded with a 15 to 20 cm high mud plastered boundary to prevent spread of nematodes from one plot to another. The crop was harvested from the central 1.5 × 1.5 m area of each plot. For the nematode population study, destructive samples with clear symptoms of ufra and white-tip atsix different rice growth stages were taken from outside of the 1.5 m × 1.5 m harvest plots. Nematode extraction and enumeration Infected rice stems of symptomatic samples were each opened with a sharp needle, cut into small pieces (approx. 0.5 cm) and immersed in water of a Petri dish for 3h. Similarly, for rice seeds, spikelets were cut into two pieces, lemmae and paleae were separated from endosperms, and immersed into water in a Petri dish for 4 h to release nematodes. Nematodes were collected by sieving (20 μm mesh sieve), and observed under a stereo microscope (Nikon AFXIIA, Japan) for enumeration. To avoid the enumeration of non plant parasitic nematodes, each sample was cross checked by standard compound microscope for confirmation of the two plant parasitic nematodes, based on their stylet shapes. Data recording and assessment of nematode populations and reproduction rate Data of temperature and relative humidity (RH) were recorded during the experimental period. Total duration of pot and field experiments was twelve months. In the field experiment, numbers of nematodes per hill were recorded, at six rice plant growth stages (tillering, 30 d after transplanting (DAT); booting, 75 DAT; flowering, 90 DAT; dough, 105 DAT; ripening, 120 DAT; harvesting, 135 DAT). The incidence of ufra and white-tip, numbers of rice panicles m-2, proportions of healthy panicles (%), 1000 grain weights (g), grain yields (t ha-1) and yield loss (%) were measured at harvest. Disease incidence (%) was measured according to number of infected tillers per hill while yield was measured from harvested crop from the central 1.5 × 1.5 m area of each 2 × 2 m plot, or on a per hill basis. The reproduction rates of the two nematode species were calculated according to the following equation: Rf = Pf / Pi, where, Rf is the reproduction factor or rate, Pf is the final nematode population, and Pi is the initial nematode population. Rf was determined at each rice plant growth stage for each treatment. In the pot experiment, treatments were arranged in a completely randomized design with 28 replica-tions. Each pot represented a replication. Three replications were destructively sampled at each of six rice growth stages. A total of 18 (three by six) replications were destructively sampled from 28 replications for population dynamics study, and the remaining 10 replications were used for the study of disease incidence and yield parameters. For the fi eld study, the experiment was laid out in a randomized complete block design with four replications. Six treatments along with non-inoculated (control) were followed both in pot and fi eld experiments (see above). All data were statistically analyzed using CropStats software. Statistical analyses were performed by analysis of variance (ANOVA) followed by Fisher’s least square diff erence (LSD) test. Mean separation was based on LSDs at P≤0.05 (Fisher, 1960).