DIGESTIBILITY-RELATED HISTOLOGICAL ATTRIBUTES IN Bouteloua curtipendula (MICHX.) TORR. OF MEXICO

Abstract

Sideoats grama (Bouteloua curtipendula (Michx.) Torr.) is a C₄ forage species of great genetic diversity, adapted to arid and semi-arid regions of Northern Mexico and Southern U.S.A. In this study the histological attributes associated with digestibility and lignification were evaluated in 30 genotypes of B. curtipendula of Mexico to know their forage potential. A completely randomized design was used to sample mature green leaves at 65 d of regrowth from a live collection. Leaf tissue was fixed and processed for paraffin transversal sections (15 μm) and stained with safranin-O and fast green FCF. Lignified tissue was detected with phloroglucinol and HCl. The histological attributes measured in the cross sectional area were: highly digestible tissues, TAD (mesophyll, bulliform cells and phloem); partially digestible tissues, TPD (epidermis, vascular bundle sheath and the non-lignified extension of the vascular bundle sheath), and not digestible tissues, T non-D (xylem and the lignified extension of the vascular bundle sheath) in principal (NP) and secondary ribs (NS). Data were analyzed with Principal Component Analysis (ACP) and then the genotypes were grouped by histological attribute, using the hierarchical clustering method based on Euclidean distances; the group means were compared with Tukey’s test (P ≤ 0.05). Three principal components (CP) explained more than 90 % of the anatomical variability, and NS showed 21 % more area of TAD than NP. The mesophyll (28 %), the bulliform cell (23 %) and the bundle sheath (20 %) occupied more than the 70 % of the total leaf area. On average, the leaf of B. curtipendula is composed by 58 % of TAD, 33 % TPD and 9 % of T non-D. The group with higher values of TAD and TPD included genotypes G55, G17, G18, G16, G48 and G64, but G16 genotype showed the best forage attributes (56.8 % of TAD and 5.3 % of lignified tissue).