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Digestion of Stem Tissues in Panicum Species¹

Previous research on C₄, C₃, and intermediate species in the Panicum genus has shown variations in leaf blade anatomy and in digestibility. However, the stems have not been examined for such characteristics. The objective of this research was to determine cross-sectional tissue percentages and histological reactions of tissues for lignin in upper and lower internodes of seven Panicum species differing in photosynthetic pathways and the reaction of tissues to rumen microbial degradation using microscopic techniques. The proportion of dry weight in stem averaged 31% for the seven species, ranging from 23 to 40%. About half (48 ± 10%) of the stem cross-sectional area was parenchymand, in general, large differences in tissue types between upper and lower internodes did not occur. The epidermis, sclerenchyma ring, and vascular bundle (except phloem) contained lignin in most all species and were not degraded in stems of any species during 48 h incubation with rumen microorganisms. The parenchyma showed a variable reaction for lignin, with the lower internodes giving a positive reaction with chlorine sulfite in all but P. antidotale. Two species, P. maximum and P. virgatum, showed positive lignin reactions in the parenchyma with acid phloroglucinol. The parenchyma in lower internodes tended to be less digestible than that in upper ones and was significantly less digestible (P < 0.05) after 48 h digestion in P maximum, P. virgatum, and P. milioides. Variations occurred in the degree of degradation among species. No distinctive characteristics for stems in these species were related to photosynthetic type.

Key Words: Plant anatomy • Light Microscopy • Scanning Electron Microscopy • Digestibility

² Microbiologist, Richard B. Russell Agric. Res. Ctr., USDA-ARS, Athens, GA, 30613.

³ Professor, Agronomy Dep., Univ. of Georgia, Athens, GA 30602.

Received for publication October 28, 1983.