Trichome Density Influences Drying Rate of Alfalfa Forage.

A.W. Lenssen, J.D. Banfield, and S.D. Cash
Departments of Entomology, Mathematics and Statistics, and Plant, Soil, and Environmental Sciences, Montana State University, Bozeman, MT 59717

Alfalfa (Medicago sativa L.) cultivars with erect glandular hairs have been developed and released for potato leafhopper [Empoasca fabae (Harris)] resistance. Trichomes decrease water loss in some plant species, but their influence on drying rate of harvested alfalfa forage is unknown. We conducted a study measuring water loss from field-grown, harvested forage of three erect, glandular-haired alfalfa germplasms, KS161, KS210, and KS224, eglandular 'Arc', and 'Kenland' red clover (Trifolium pratense L.). Harvests were taken once in 1995 and 1997, and four times in 1996. Plant height, phenological stage, upper and lower stem diameters, leaf:stem ratio, and apical stem densities of simple, procumbent glandular, and erect glandular trichomes were determined. Forage drying rate constants were calculated by a combination of parametric and nonparametric modeling techniques. The harvest x germplasm interaction was significant for all parameters measured. The density of erect glandular hairs on stems differed among entries in all 6 harvests, with mean values being similar to those reported by Danielson et al. (1989) for the three perennial Medicago species, prostrata, glandulosa, and glutinosa, that provided the original sources used to transfer the erect glandular hair trait into alfalfa. Despite populational differences in erect glandular hair densities, drying rate constants only differed among alfalfa entries in two of the six trials. Correlations between density of total trichomes (simple + procumbent glandular + erect glandular) and drying rate constants were negative and significant, indicating that increasing total trichome density may retard water loss from cut forage. Correlations of erect glandular hair density with drying rate constants were generally low and nonsignificant, except for one harvest. Erect glandular hairs, at the densities measured in this study, generally did not influence drying rates of alfalfa forage. However, density of total trichomes was significantly and negatively correlated with drying rate for each of the five entries, with correlation coefficients ranging from -0.45 to -0.67. Our results indicate that selection for decreased pubescence may increase water loss from harvested forage. Further research is necessary to determine if drying rate of alfalfa forage can be improved through selection for reduced density of trichomes.

References

Baker, E.L, M. Collins, and N.L. Taylor. 1993. Developmental patterns and hay drying effects of red clover stem trichomes. p.235-239. In Proc. Amer. Forage Grassl. Council. Des Moines, IA. 29-31 March 1993.

Danielson, S.D., R.F. Mumm, G.R. Manglitz, and E.L. Sorensen. 1989. Glandular hair densities in three perennial Medicago species. Euphytica 43:15-19.