COMPARISON OF THE ANATOMY AND DEGRADABILITY OF STRAW FROM VARIETIES OF WHEAT AND BARLEY THAT DIFFER IN SUSCEPTIBILITY TO LODGING

The consequences of selection for shorter, stiffer-strawed varieties t hat are less susceptible to lodging on the degradability of forage and straw obtained from cereal crops were investigated with particular re ference to the characteristics of the basal internode where the mechan ical stress is likely to be greatest. Quantitative measurements of tis sue area, mean cell wall thickness, cell wall density and cell size we re made on two wheat cultivars, Riband (strong) and Norman (weak), and on two barley cultivars, Blenheim (strong) and Tyne (weak). The culti vars were selected for comparison on the basis of their straw strength in field trials. At growth stage (GS) 59 in wheat (ear emergence comp lete) the neutral detergent fibre (NDF) content of the basal internode of Riband (74.6%) was lower than Norman (86.0%), and the NDF degradab ility (NDFD) of Riband (34.7%) was slightly greater than Norman (32.0% ). No significant differences in lignin content were found between the wheat cultivars. In barley at the same growth stage, the NDF content of the basal internode of Blenheim (84.8%) was lower than Tyne (89.2%) , and the NDFD of Blenheim (30.2%) was greater than Tyne (23.7%) but n o significant differences in lignin content were associated with the d ifference in NDFD. At GS 32-37 (stem elongation) in barley the NDF con tent of the basal internode of Blenheim (81.5%) was also lower than Ty ne (86.3%), but the NDFD of Blenheim (71.7%) was much greater than Tyn e (42.8%). No significant differences in lignin content were associate d with this large difference in NDFD. The cultivars of wheat and barle y less susceptible to lodging showed lower NDF content and higher in v itro degradability in the basal internode than the more susceptible cu ltivars. No evidence of differences in the extent of cross-linking by ether-bound ferulic acid was found in wheat, but stems of Blenheim bar ley showed evidence of a greater degree of cross-linking than in Tyne. The anatomical features of Norman wheat were consistent with stem wea kness caused by thinner, smaller cells than the stronger Riband. Howev er, in contrast, the anatomy of Tyne barley indicated that the straw m ay be too stiff, resulting in failure due to root lodging or brackling while the thinner more cross-linked cell walls of Blenheim may allow the stem to bend under load. The relationship between the anatomical f eatures, chemical composition and in vitro degradability of the stems was investigated using stepwise multiple regression. Thickness of scle renchyma, thickness of epidermis and density of epidermis (area fracti on of cell wall) were selected by the method of 'backward elimination' from an initial regression model to predict NDFD using all the anatom ical features measured. Thickness of sclerenchyma was ranked first whe n the selected anatomical features were incorporated into a regression model with NDF and lignin content using the method of 'forward select ion'. Anatomical differences between varieties had an effect on degrad ability distinct from that due to the overall chemical composition. Th e results emphasise the contribution made by anatomical features to th e stem degradability and lodging characteristics of cereals.