Morphology and fungal growth in elongated rice seedlings infected with Gibberella fujikuroi, and control of the disease in a flooded nursery.

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  • イネばか苗病による徒長苗の形態とばか苗病菌の分布およびプール育苗による発病抑制
  • イネ バカナエビョウ ニ ヨル トチョウ ナエ ノ ケイタイ ト バカナエ ビョウキン ノ ブンプ オヨビ プール イクビョウ ニ ヨル ハツビョウ ヨクセイ

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We studied the morphology of rice seedlings with typical elongation symptomatic of bakanae disease, the distribution of the fungus in the seedlings, and cultural methods to control the disease in nursery boxes. We used naturally infected seeds that either possessed husks (“ordinary seeds”) or had the husks removed (“processed seeds”). Ordinary seeds germinated to produce elongated seedlings with significant elongation of the first to the third leaf sheaths and the second to third leaf blades. In the elongated seedlings from ordinary seeds at the transplanting stage, mycelia were observed within vessels and the parenchymatous tissues adjacent to the vascular bundles in the bases of the culms and in vessels farther up the culms, but were limited to the region less than 2 cm above the bases of the culms. Then the elongated seedlings from both types of seeds were transplanted to pots. More than 30% of the hills from the ordinary seeds recovered and became healthy, but more than 50% had died by 63 days after transplanting. Recovery depended on the growth of tillers free of pathogen mycelia, because the diseased main culms died soon after transplanting. More than 80% of the hills from processed seeds recovered. Because of these results, we speculated that many of the elongated seedlings from the processed seeds were not infected, but had elongated as a result of diffusion of gibberellin from diseased rice seedlings in the environs. We then grew seedlings in a flooded nursery (pool nursery) to suppress development of the disease. In nursery boxes where the water level was kept above the surface of the soil until the seedlings reached the transplanting stage, the incidence of elongated seedlings was reduced. The suppressive effect may be due to reduced mycelial growth in the culum under flooding conditions.<br>

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