ARBUSCULAR MYCORRHIZAL DEVELOPMENT IN 3 CRUCIFERS

To determine the developmental patterns of arbuscular mycorrhizae (AM) in three crucifers (Brassicaceae) of differing life histories, we ino culated seedlings of the annual Capsella bursa-pastoris, biennial Hesp eris matronalis, and the perennial Matthiola incana with Glomus intrar adices. The plants were grown either alone or in a matrix of living ro ots of the mycotrophic grass Sorghum sudanense. The percent root lengt h colonized was greatest in C. bursa-pastoris and least in H. matronal is. Colonization was greater in plants grown in the grass matrix than in plants grown alone, and colonization in grass matrix-grown plants c ontinued to in crease over the 90-day growth period, whereas colonizat ion leveled off or decreased near the end of the growth period in cruc ifers grown alone. No arbuscules were observed in crucifer roots at an y time, which suggests that AM in these crucifers is nonfunctional. Fu rthermore, the increase in colonization only in pots with both crucife rs and active mycotrophic roots suggests that AM development in crucif er roots is primarily the consequence of progressive root senescence i n the crucifer and continued inoculum spread from the mycotrophic plan t.