Of the 2 million ha of rice land affected by flood every year in Assam, India, 490,000 are planted to deepwater rice. During the long growing period from March to December, deepwater rice is exposed to attacks by different pests and diseases. Among them, infestation by rice stem nematode, Ditylenchus angustus, commonly called ufra disease, is considered a major problem, causing a 30-100% yield loss.
Several deepwater and semideepwater rice varieties were screened for resistance to ufra nematode during 1991-92 under field conditions at RARS. Among the entries tested, a few Rayada selections collected from Bangladesh, such as Rayada 16-06, Rayada 16-09, and Rayada B3, were resistant to ufra in Assam. These lines were further screened for ufra resistance and yielding ability in a replicated trial from 1993 to 1997 in diseased and disease-free areas. The diseased plot was selected from a naturally infested field and ufra disease pressure was further increased by adding inoculum at sowing, whereas earthen bunds around the field kept the control plot ufra-free. Table 1 presents the panicle infestation rate and grain yield per hectare of the lines over the years. Statistical analysis (3 RBD) followed after transformation of percentage infestation data.