Spread of endomycorrhizal colonization and effects on growth of apple seedlings



An experiment to determine the short-term characteristics of root colonization by two vesicular-arbuscular (VA) mycorrhizal fungi with apple (Malus × domestica Borkh.) was initiated concurrently with an experiment to determine longer-term effects of colonization by these fungi on the growth of apple seedlings. Short-term characteristics of colonization were determined by sequential harvesting of a cuvette system which also allowed monitoring of hyphal spread from inoculated ‘spreader’ plants, through a root-free soil region, to non-inoculated ‘receiver’ plants. Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe exceeded Glomus macrocarpum Tul. & Tul. in rate of initial colonization, amount of maximum colonization, and persistence of arbuscules and external hyphae. Colonization by either fungus reduced shoot fresh weight 11 days after inoculation but increased shoot and total fresh weight by day 38. Hyphae of G. mosseae had traversed through 2 and 3 cm of root-free soil to colonize non-inoculated ‘receiver’ roots by 29 days, and hyphae of G. macrocarpum by 38 days. G. mosseae colonized ‘receiver’ roots more intensely than did G. macrocarpum at 2 and 3 cm, and 3 and 4 cm distance, at subsequent harvests. The fungi were effective, singly and in combination, in increasing apple plant biomass, as compared to non-mycorrhizal controls. Relative height growth rate, and colonization at harvest, of G. macrocarpum-inoculated plants were less than those of G. mosseae-inoculated or G. mosseae + G. macrocarpum- inoculated plants, but greater than those of the non-mycorrhizal control trees.