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Glandular Trichomes on Medicago Species¹

Glandular hairs have been implicated in resistance of Medicago species to the alfalfa weevil [Hypera postica (Gyllenhal)]. Using light and scanning electron microscopy, we studied the morphology of glands on annuals (diploid M. disciformis DC, tetraploid M. scutellata (L) Mill.) and perennials (diploid M. prostrata Jacq., tetraploids M. sativa L. subsp, sativa and praefalcata) as the itial phase of an investigation to determine the role of glands in resistance.

Erect and procumbent multicellular types with capitatestalked morphology are present. The stalk of erect trichomes is composed of four to six cells including an enlarged basal cell arising from the epidermis. Gland heads contain numerous ceils arranged in distinct tiers. The basal tier contains four cells that constitute about one-third of the head. Two additional tiers, which together contain 8 to 16 cells, form the remainder of the gland head.

The procumbent trichomes are generally composed of a basal cell embedded in the epidermis, a single stalk cell, and a gland head of four cells in two tiers. The gland curves sharply at the stalk and basal cells, so that much of the axis parallels the adjacent epidermis. The direction of bending is highly stabilized toward the terminal on stems and toward the distal ends of stipules, petioles, leaflets, peduncles, and sepals. Diploid and tetraploid annuals (M. disciformis DC, M. scutellata Mill.) and diploid perennial (M. prostrata Jacq.) contain erect andprocumbent glands. M. sativa L. subsp, sativa (tetraploids, ‘Buffalo’ ‘DuPuits’, ‘Lahontan’, and ‘San Pedro’, and diploid CADL 15) have only procumbent glands. In M. sativa subsp. praefalcata (Sinskaya) C. R. Gunn, erect glands are generally confined to floral structures, with only precumbent glands on vegetative parts. We found a few plants with erect glands on vegetative parts.

Key Words: Morphology • Scanning electron microscopy • Upright and procumbent glandular hairs • Medicago disciformis • M. scutellata • M. prostrata • M. sativa

² Research associate, Div. of Biology and research agronomist, AR, SEA, USDA, Kansas State Univ., Manhattan.

Received for publication November 20, 1978.

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