Interactions between irrigated rice (Oryza sativa) growth, nitrogen amendments and infection by Hirschmanniella oryzae (Nematoda, Tylenchida)

Nitrogen amendments are often used to alleviate damage to rice plants caused by plant-parasitic nematodes. The population development of the endoparasitic nematode Hirschmanniella oryzae was followed on irrigated rice (Oryza sativa cv. indica IR-13240-108-2-2-3) cultivated in containers, each supplemented with one of three nitrogen amendments (N0 = 0, N1 = 80 and N2 = 160 kg ha−1) applied in the form of urea. The effects of nitrogen concentration on irrigated rice growth were determined with plants cultivated in soils either infested (I1) or uninfested (I0) with nematodes. Populations of H. oryzae continued to increase in both soil and roots throughout the crop cycle. Nitrogen was without effect on soil populations, but large root nematode population increases were observed with the N1 nitrogen amendment. Interactions were observed between nematodes and nitrogen on the rice yield components, depending on the level of nitrogen applied. The average single grain weight was the main affected yield component; N1 increased the weight of each grain, but this effect was largely reduced in the presence of H. oryzae. Even though nitrogen amendments were able to counterbalance the negative effects of H. oryzae, nitrogen applied at the N1 level was not considered a sustainable alternative because it increased nematode populations. Root nematode populations with nitrogen applied at the N2 level were similar to those observed with N0. However, at the N2 level, nitrogen induced spikelet sterility and the plant physiological disturbances caused by excessive in-soil nitrogen would prevent multiplication of H. oryzae root populations.