Survey on mycorrhizal fungi in apple orchards

Mycorrhizas are of great benefit for the production of apple, rendering nutritional benefits and promoting healthy tree growth, as was shown for potted trees.  To maximize field use however, interactions between natural populations of mycorrhizas, and that of land management practices and soil properties should be explored more, since very little information is available.

A two year survey on the nature and scope of naturally occurring mycorrhizas was carried out in 30 orchards, in various cultivation areas of the Western and Eastern Cape.  Four scion/rootstock combinations, i.e Cripp’s Pink/M7, Cripp’s Pink/M793, Golden Delicious/M7 and GoldenDelicious/M793, two farming practices, i.e. conventional and organic, as well as two main soil types, i.e. heavy textured and light textured soils, were selected.  Mycorrhizal status, in as far as the glomalin status is concerned, was found to be statistically similar for farming types and soil types.  Neither was there any significant effect on glomalin concentrations when different cultivars were planted. Nonetheless, rootstock M7 seems to promote more glomalin production than M793.  There was no consistency regarding glomalin concentrations associated with specific production areas.  Glomalin concentrations were consistently and positively correlated with % soil C over two consecutive spring seasons. Glomalin also correlated with P, K, NH₄ and N, but not consistently, and in spring only.  Root colonisation levels were similar with regard to glomalin concentrations. Mycorrhizal spore counts were highly variable throughout. In total 31 Glomus species and accessions were identified in 17 groups of orchard sites, each group representing similar soils and cultivars.  These results clearly indicate the presence and abundance of naturally occurring mycorrhizhal species in local apple orchards that are capable of colonising apple roots adequately.  If managed correctly, these natural populations could contribute to increase productivity in these areas. Being abundantly present suggests that these species could inall likelihood mask the effects of field inoculation with artificial strains.