Stalk lodging (the structural failure of plant stems prior to harvest) remains a major constraint to global cereal crop production, reducing yields, impairing grain quality, and increasing harvest losses. Since cellulose microfibrils are the primary load-bearing components in plant cell walls, the microfibril angle is widely considered a critical determinant of stalk mechanical properties. X-ray diffraction is a common technique for microfibril angle measurement, yet its applicability to cereal crops has not been fully validated. This study assessed the utility of X-ray diffraction based microfibril angle measurements for maize (Zea mays) and sorghum (Sorghum bicolor) stalks using the T-parameter method. Rind tissue samples from multiple maize and sorghum genotypes were analyzed using two diffractometers with copper (Cu) and molybdenum (Mo) X-ray sources. Corresponding internodes were also evaluated for rind penetration resistance, material bending stiffness, and bending strength to test whether measured microfibril angles reflected biologically meaningful variation. Across all genotypes and internodes, including preliminary observations from phenotypic extremes in select groups, microfibril angle values were highly uniform, with maize averaging 24.6° (Cu) and 29.1° (Mo) and sorghum averaging 24.3° (Cu) and 29.4° (Mo). microfibril angles exhibited extremely low variability (coefficient of variation < 3.3%), in stark contrast to the much higher variability observed in mechanical properties (CV = 20.5–47.1%). Systematic differences of ~20% between Cu- and Mo-based measurements were consistent across sample groups. Correlations between microfibril angle and mechanical properties were weak or absent; only Cu-derived microfibril angle showed a marginal relationship with bending stiffness, while Mo-derived microfibril angle showed no significant correlations. Pooled analyses further confirmed that microfibril angle remained nearly constant despite a wide range of mechanical property values. Collectively, these findings demonstrate that X-ray diffraction based microfibril angle measurements using the T-parameter method have limited applicability to cereal stalk tissues, as the method failed to capture biologically relevant variation. The uniformity of measured angles, lack of correlation with mechanical properties, and dependence on X-ray source raise concerns about the suitability of this method for maize and sorghum. These results highlight the need for refined or alternative microfibril angle measurement techniques to better understand the role of cellulose microfibril orientation in stalk lodging resistance.
Oduntan et al. (Sat,) studied this question.