| Plant cell walls may be involved in pre-existing defense and in active response to pathogen infection. Cell wall concentration can be measured approximately by neutral detergent fiber (NDF). Three consecutive cycles (C-1, C-2, C-3) from uniparental mass selection in smooth bromegrass (Bromus inermis Leyss.) for NDF, one cycle (C+1) from biparental mass selection for high NDF, and the base population of the selection were evaluated in the field at high and low disease potentials at three locations for two years and three harvests each year. All the five populations above, the third cycle (V-3) from biparental mass selection for low NDF from the same base population, and two other populations were compared in the greenhouse in two experiments with and without inoculation by Cochliobolus sativus Drechsl. ex Dastur, a fungus causing leaf blight. The field experiment showed that selection for low NDF, accompanied by slight selection pressure for disease resistance, resulted in a reduction of NDF and a change in NDF composition without an increase in disease susceptibility or a loss in dry matter yield. On average, NDF was reduced 3.5 g/kg dry matter per cycle (P < 0.001) by selection for low NDF, and increased 11.1 g/kg in one cycle (P < 0.001) by selection for high NDF. However, in the greenhouse, only population V-3 had lower NDF than the base population without inoculation. For inoculated plants, only population C-2 had lower NDF ( P < 0.05) than the base population. Populations with small differences in NDF concentration and composition at the time the plants were inoculated did not differ in reaction to C. sativus. Inoculation or high proportion of foliage diseased was often associated with high NDF, high acid detergent lignin (ADL) and high lignin on a cell-wall basis (CW-lignin) in both the field and the greenhouse. While the differences in NDF, ADL or CW-lignin among selection cycles were similar at different disease potentials in the field, population differences in ADL or CW-lignin were dependent on whether plants were inoculated with C. sativus in one greenhouse experiment. |
