The investigation of the rice white tip nematode Aphelenchoides besseyi infestations was carried out on rice seeds. One hundred and eleven samples of rice seeds were collected from Ayeyarwaddy, Bago, Shan State, Mandalay and Nay Pyi Taw regions, Myanmar, in which various local varieties (rainfed-lowland, irrigated-lowland, quality, upland, drought tolerance, submergence, salt tolerance, aerobic and hybrid rice) were grown. Nematodes were extracted from 100 discoloured rice seeds with three replications. Aphelenchoides besseyi was detected in rice seed samples from all collected regions, in which 53 out of 111 rice seed samples were infested with A. besseyi. The maximum population was observed in upland, quality and rainfed-lowland rice varieties, ranging from 193-459 indiv. (100 rice seeds)(-1). Four rainfed-lowland, one irrigated-lowland, five quality and five upland rice varieties were infested with the economic damage level of > 30 indiv. (100 rice seed)(-1). The densities of A. besseyi in relation to rice varieties are discussed.

The rice root-knot nematode, Meloidogyne graminicola, and the rice root nematode, Hirschmanniella oryzae, are soilborne pests causing damage to rice, and the pigeon pea cyst nematode, Heterodera cajani, is a pest to beans and sesame. Real-time PCR primers were designed for quantification. Relationships between the threshold cycle (Ct: y) values and number (no.) of nematodes inoculated (log(2)(no. (10 g soil)(-1)) : x) were: M. graminicola: y = -0.86x + 35.00; H. oryzae: y = -1.15x + 32.14; and H. cajani: y = -1.11x + 32.23. Meloidogyne graminicola and H. oryzae were detected in 25 and 38 out of 50 soils, collected from different fields in the lowland and central area of Myanmar, and their densities ranged from 1.0 to 4779 and from 0.4 to 787 (20 g soil)(-1), respectively, while H. cajani was detected only in two fields (3 and 268 (20 g soil)(-1)). The DNA-based method enables rapid and reliable quantification of the nematodes in soil.

Abstract A preliminary survey using 20 conventionally farmed fields in which fumigants have been applied every year showed that the root-lesion nematode Pratylenchus penetrans was distributed both in the upper (0–30 cm) and lower (30–60 cm) soil layers. In six of the 20 fields, P. penetrans was detected in the lower layers exclusively, suggesting that the most appropriate depth to sample soil is 0–60 cm to estimate the relationship between the density of P. penetrans and its damage to radish. There was a highly significant correlation (r = 0.923) between the density of P. penetrans in the 0–60 cm depth and the number of spots on a radish. No damage to radish was observed in soils with <2.5 individuals of P. penetrans per 20 g soil before cultivation. However, in cases in which the density of P. penetrans was 3.4–6.2 individuals per 20 g soil, the number of spots on a radish showed more variation (0–131.5 per radish) and there was no significant correlation between them. The nematode community structure of soils with 3.4–8 individuals of P. penetrans per 20 g soil, evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis, was significantly different (anova, PC2, P < 0.05) between soils with low (0–42) and high (more than 80) damage levels, suggesting that radish damage might be predicted on the basis of the prevailing soil nematode community structure.