Seed Coat Anatomy and the Scarification of Cicer Milkvetch Seed1

Abstract

The impermeable seed coat of cicer milkvetch (Astragalus cicer L.) restricts water imbibition and results in poor seed germination and subsequent stand establishment. Our objectives were to study the seed coat anatomy, areas of initial water imbibition, scarification effects on the seed coat, and the relationships between seed characters and percentage hardseed. Seed from 10 polycross progenies with a wide range of hardseededness (12 to 77% after scarification) were used. Scanning electron microscopy showed the following: the cuticle had a distinct faveolate pattern at the strophiole at magnifications of ✕ 125 and higher; the malpighian cells became longer and thinner as they neared the strophiole in comparison to the rest of the seed coat; the osteosclereids were shorter and wider at the seed tip in comparison to other sites on the seed coat; and the osteosclereids were not present at the hilum or the strophiole. In general, the seed coat anatomy was similar to that of small‐seeded legume species belonging to the subfamily Papilionoideae. The strophiole and seed tip accounted for 98% of the area of imbibition following mechanical scarification. The effect of mechanical scarification on the seed coat varied from no effect to small scrapes and indentations, large cracks, and complete removal. The strophiole accounted for 75% of the area of imbibition following H2SO4 (18.0 m0l H2SO4 L‐1) scarification. The effect of H2SO4 to the seed coat occurred in a distinctive pattern at the strophiole. The cuticle and exterior portions of the malpighian cells were dissolved, forming a circular cavity that had a large groove at its base. Percentage hardseed following mechanical scarification was correlated (P = 0.05) with seed length, width, volume, and weight (r = −0.91, −0.66, −0.88, and −0.82, respectively). Density was the only seed character that was significantly correlated (r = 0.70) with percentage hardseed following H2SO4 scarification. None of the seed characters were significantly correlated with natural permeability. Although the progenies did not differ for seed coat anatomy, it appears that selection can be made for increased permeability following mechanical scarification. Of the seed characters measured, weight would be the easiest to use when selecting for increased permeability.