Disease incidence, growth, and physiological characterization of rice cultivars with different susceptibility to bakanae disease

Bakanae disease is a serious problem in many rice-producing countries because it causes significant yield loss. Disease incidence, seedling growth, and physiological traits, such as leaf chlorophyll content, endogenous gibberellin (GA), and abscisic acid (ABA) production, were investigated in two moderately tolerant cultivars (Milyang 313 and Saenuri) and one susceptible cultivar (Daebo) after seeds were inoculated with bakanae disease. We evaluated their susceptibility to the disease during two seeding times (April 30 and May 10, 2016) in a nursery bed. The results showed that, 30 days after seeding, the degree of bakanae disease incidence, seedling emergence, seedling elongation, dry weight per plant, leaf chlorophyll content, and endogenous GA production corresponded to the degree of varietal tolerance. Bakanae disease incidence was lower in the tolerant cultivars, Milyang 313 and Saenuri, thus, seedling emergence rate and leaf chlorophyll content were higher than in the susceptible cultivar, Daebo. Meanwhile, seedling elongation and dry weight per plant were greater in the susceptible cultivar 30 dayscultivar, Daebo. Meanwhile, seedling elongation and dry weight per plant were greater in the susceptible cultivar 30 days after seeding. Content of endogenous GA (GA3 GA1 GA8) markedly increased in all three cultivars and at the later seeding time. GA levels were markedly affected by degree of susceptibility, disease incidence, and seedling elongation. In contrast, GA20 did not show any consistent trend. The endogenous ABA level of the infected cultivars was markedly increased, compared with the control, but this hormone did not show any consistent tendency between the susceptible cultivar and the tolerant cultivars across seeding times. These results demonstrate that Milyang 313 and Saenuri are tolerant, whereas Daebo is susceptible to bakanae disease, thus, these tolerant cultivars should be utilized in breeding programs to produce more bakanae-disease-tolerant cultivars.