RACE-SPECIFIC RESISTANCE TO XANTHOMONAS-ORYZAE PV ORYZAE CONFERRED BY BACTERIAL-BLIGHT RESISTANCE GENE XA-10 IN RICE (ORYZA-SATIVA) INVOLVES ACCUMULATION OF A LIGNIN-LIKE SUBSTANCE IN HOST TISSUES

When seedling leaves of rice (Oryza sativa L.) cultivars carrying the Xa-10 gene for bacterial blight resistance were infiltrated with suspensions of cells from races 2 or 5 of Xanthomonas oryzae pv. oryzae, a rapid, race-specific incompatible reaction occurred: the leaf tissue became dark greenishbrown, and the rate of bacterial multiplication decreased compared to compatible interactions. By 48-72 h after inoculation, the affected area was dark brown. Lignin-like phenolic compounds accumulated throughout the incoulation site in the incompatible combination, beginning by 18-24 h after inoculation and reaching a maximum by 72 h. With the Xa-4 resistance gene, incompatible reactions involved localized water soaking, inhibition of lesion development, and deposition of a lignin-like polymer around the perimeter of the infiltration site. Compatible interactions between cultivars with either Xa-4 and race 2 or Xa-10 and race 1 were similar: both displayed a uniformly water-soaked, yellow-green, spreading lesion by 24-48 h after inoculation. Lignin-like substances were detected by 96-120 h following inoculation and were limited to the perimeter of the infiltration site. Infiltration of cultivars containing the Xa-10 gene with water or UV-killed bacteria elicited no responses. The phenotypes conferred by resistance genes Xa-4 and Xa-10 were distinguished rapidly by histological reactions. © 1991 Academic Press Limited.