Manandhar H K, Jorgensen H J Lyngs, Smedegaard-Petersen V, Mathur S B
Plant Pathology Division, Nepal Agricultural Research Council, P.O. Box 1126, Khumaltar, Lalitpur, Nepal.
Plant Pathology Section, Department of Plant Biology, The Royal Veterinary and Agricultural University, Thorvaldsensvej 40, DK-1871, Frederiksberg C, Copenhagen, Denmark.
Plant Dis. 1998 Oct;82(10):1093-1099. doi: 10.1094/PDIS.1998.82.10.1093.
Seedborne infection of rice by Pyricularia oryzae and its transmission to seedlings were studied quantitatively with naturally infected seeds of three rice cultivars collected from three locations in Nepal. A linear relationship on a logistic scale was found between panicle symptoms and seed infection, i.e., the more symptoms the higher seed infection. However, healthy-looking panicles and branches of panicles could also yield infected seeds. Postharvest measures such as winnowing and sun-drying significantly reduced seed infection by P. oryzae and filled grains had a lower degree of infection than unfilled grains. Sporulation of P. oryzae was most often confined to the embryonal end of germinating seeds. In contrast, most of the nongerminating seeds had sporulation all over the seed surface. Transmission of P. oryzae from seeds to seedlings, studied under various seeding conditions, showed that the transmission rate was always low. Thus, a seed sample with 21% seed infection resulted in less than 4% seedlings with blast lesions. Seed transmission was found for light covering of the seeds with soil or for moist seeding without covering. Transmission was rarely found when seeds were completely covered, and never in seedlings raised under water seeding conditions. Lower infection frequency was observed in seedlings raised in unsterilized soil than in seedlings raised in sterilized soil. Also, percent recovery of P. oryzae from infected seeds was higher in sterilized soil than in unsterilized soil and declined with time. Seedlings grown under low temperature (15 to 20°C) conditions did not develop blast lesions but when the same plants were transferred to high temperature (25 to 30°C) conditions, blast lesions were detected. This confirmed the latent infection in seedlings by P. oryzae grown under low temperature conditions.
利用从尼泊尔三个地点收集的三个水稻品种的自然感染种子，对稻瘟病菌引起的水稻种传感染及其向幼苗的传播进行了定量研究。在逻辑尺度上，发现穗部症状与种子感染之间存在线性关系，即症状越多，种子感染率越高。然而，外观健康的穗部和穗分支也可能产生感染的种子。扬谷和晒干等收获后措施显著降低了稻瘟病菌对种子的感染，饱满谷粒的感染程度低于未饱满谷粒。稻瘟病菌的孢子形成最常局限于发芽种子的胚端。相比之下，大多数未发芽的种子在种子表面都有孢子形成。在各种播种条件下研究了稻瘟病菌从种子到幼苗的传播，结果表明传播率一直很低。因此，种子感染率为21%的种子样本导致出现稻瘟病病斑的幼苗不到4%。发现当种子用土壤轻度覆盖或进行无覆盖的湿播时会发生种子传播。当种子完全被覆盖时，很少发现传播，在水播条件下培育的幼苗中从未发现传播。在未灭菌土壤中培育的幼苗比在灭菌土壤中培育的幼苗感染频率更低。此外，从感染种子中回收稻瘟病菌的百分比在灭菌土壤中高于未灭菌土壤，且随时间下降。在低温（15至20°C）条件下生长的幼苗没有出现稻瘟病病斑，但当将同一植株转移到高温（25至30°C）条件下时，检测到了稻瘟病病斑。这证实了在低温条件下生长的稻瘟病菌对幼苗的潜伏感染。
