Root-invading fungi of milk vetch on the Loess Plateau, China

Root-invading fungi of milk vetch (Astragalus adsurgens) at different growth stages grown in three ages of sown pasture soil were studied in Huanxian county, Gansu province, China. Pathogenicity was tested by seed and soil inoculation. A total of 44 fungi were isolated from milk vetch roots, 32 from the roots of field plants and 37 from the roots of potted seedlings. The total percentage of root segments yielding fungal colonies increased with age of plants; they were 70.5%, 82.3% and 97.8% in 1-, 3-, and 5-year-old plant roots, respectively, differences that were significant (P < 0.05). The frequency of isolation from roots of plants at re-greening, branching, flowering and yellowing growth stages were 62.0%, 95.3%, 93.0% and 83.7%, respectively. The total percentage of root segments yielding fungal colonies from 3-, 6- and 12-week-old potted seedlings were 21.8%, 44.7% and 32.0%, respectively, differences that were also significant (P < 0.05). Seedlings were easily infected and symptoms of damping-off disease were common in seedlings younger than 3-week-old. Of the 44 fungi isolated and tested for pathogenicity by seed inoculation, 19 decreased seed germination rate, 12 decreased seedling shoot length, and 22 decreased seedling root length. Fusarium solani, F. oxysporum, F. chlamydosporum, F. avenaceum and Gliocladium roseum were strongly pathogenic to milk vetch. In soil inoculation tests, these same fungi (except for F. chlamydosporum) decreased seedling root dry matter production significantly (P < 0.05), but seed germination and seedling survival were not affected by any of these fungi.