Early development of vesicular-arbuscular mycorrhizas in autumn-sown cereals

Abstract

Fractional infection of roots of winter cereals (wheat, barley and rye) by vesicular-arbuscular mycorrhizal fungi was monitored in three fields in south-east England over three successive seasons. In most cases there was a peak in fractional infection (up to 60% root length infected) in the period from November to December. This extensive development of mycorrhizas during this period has not previously been noted in winter cereals, and has importance as a determinant of the growth response of annual crops. Differences in experimental technique may have led to this phenomenon being overlooked in earlier work. Fractional infection levels then either dropped sharply or continued to rise gradually until late spring in the three seasons studied. In all cases, a second peak in arbuscular development was noted just prior to ear formation, followed by a post-anthesis decline. These fluctuations in fractional infection have been compared with similar trends recorded for dry weight increases of roots over a winter cereal season, and may be influenced by date of sowing. The winter decrease in fractional infection by VAM noted in two out of the three seasons was apparently due to a relative reduction in the coarse endophytic component of the mycorrhizal association. In contrast, infection due to fine endophytes was more stable and persisted as the major proportion of the association throughout the winter and post-anthesis declines in fractional infection.