SELECTION OF SPECIFIC STEM WEIGHT AND ASSOCIATION WITH AGRONOMIC AND QUALITY CHARACTERISTICS IN ALFALFA.

Abstract

The study of readily measurable agronomic traits which may estimate total dry matter production and the determination of their relationships with quality characteristics needs more emphasis in alfalfa breeding. The main objective of this study was the selection of specific stem weight (SSW) and its relationship to other agronomic and nutritive traits. A secondary study was on agronomic and nutritive traits and their relationship with one another. Means, standard deviations, analyses of variance, and correlations were obtained on 98 Mesa-Sirsa alfalfa clones for SSW, plant height, yield, leaf-stem ratio, stem acid detergent fiber (ADF), leaf ADF, stem acid detergent lignin (ADL), and leaf ADL. The means of SSW (70-47 mg/5 cm), plant height (58-48 cm), yield (52-23 g), leaf-stem ratio (2.1-1.0), stem ADF (45-42%), and stem ADL (10.1-9.1%) varied from one harvest to another depending on the temperature. Significant differences were observed among alfalfa clones on June 1980 for SSW, plant height, yield, leaf-stem ratio, stem ADF, stem ADL, and leaf ADL. Range values were as follows: SSW (92-53 mg/5 cm), plant height (70-41 cm), yield (82-22 g), leaf-stem ratio (1.6-0.6), stem ADF (50-36%) stem ADL (13-8%), leaf ADF (18-13%), and leaf ADL (5-3%). A low correlation was reported between stem ADF and SSW (0.34) and also was observed between stem ADF and leaf ADF (0.46). The SSW probably would be more effective in increasing total dry matter production in dense stands. The coarseness of the stem was not related with high fiber. High leaf ADF could be useful in selecting for leaf cells which are more resistant to rupture and would gradually release soluble protein in the rumen; thus, the incidence of bloat probably would be reduced. A low stem ADF would make the stem more digestible; therefore, intake of the stem fraction may be greater. With more coarse material in the rumen, salivary secretion might be stimulated. The SSW and stem ADF could be used to select individual genotypes which could increase growth and development and at the same time improve forage quality, since SSW and stem ADF are not related.