Development of vesicular-arbuscular mycorrhizae in crop plants

Vesicular-arbuscular mycorrhizae developed extensively in a wide range of crop plants grown in field plots and in controlled environment. At 25–28 days after sowing, generally few roots (0.6–19%) were colonized by the mycorrhizal fungus Endogone. The proportion of roots colonized subsequently increased rapidly to maximum levels ranging from 48 to 84%. A three-phase pattern of mycorrhizal development involving sequentially a lag phase, a phase of extensive development, and a phase of constancy in the proportion of mycorrhizal to non-mycorrhizal roots was found in bean (Phaseolus vulgaris L.) and soybean (Glycine max (L.) Merr.). A similar multiphase development of mycorrhizae was evident also in some other hosts. The relationship of the different phases of mycorrhizal development to physiological changes in the host is discussed.