Spore abundance and morphological root modifications of arbuscular mycorrhizal fungi-infected black pepper (<em>Piper nigrum</em> L) plants in reddish brown latesolic soil of Matale in Sri Lanka

Abstract

Arbuscular Mycorrhizae (AM) is a symbiotic association between fungi and roots of higher plants, which enhances plant growth and production. Black pepper (Piper nigrum L: Family Piperaceae), the second most valuable spice crop in Sri Lanka, is also identified as a host crop of mycorrhizae. However, existing indigenous AM species, their spore abundance and root colonization is not yet well studied or documented. Therefore, the present study was conducted to collect data on AM spore density and morphological features of modified roots due to infection of existing AM species in black pepper fields. Rhizosphere soils of randomly selected, 20 well-grown black pepper plants in RBL soils of Matale in Sri Lanka were evaluated for pH, moisture and major nutrients while AM spore abundance and AM colonization in stained roots were examined microscopically. The soil pH (4.7-5.9), total N (0.18-0.23 %), and organic C (1.57-1.75%) levels in study sites were preferable for biological activities while variability was observed in available P (4.4-29 ppm), exchangeable K (188-788 ppm) and volumetric moisture (9.8-24%). The AM spore (size >50 µm) density in examined soils were high and ranged from 1600-9000 spores kg-1 soil. Both live (slight yellowish to dark brown in colour) and dead (black) spores were present and globular or spherical in shape without any special hyphal attachments. About 95% of examined roots were infected with AM with modifications such as arbuscules or vesicles or both. Networks of non-septate, extra-radical hyphae and branched intra-radical hyphae could be seen. Arbuscules observed were in different maturity and highly branched. Both inter or intracellular vesicles found were oval or ellipsoid in shape. Thus, most of the mature black pepper plants in RBL soils of Matale were found infected with indigenous vesicular arbuscular mycorrhizae (VAM) and morphological features of their spores, hyphae, arbuscules and vesicles were similar to fungi of order Glomerales, which consisted with Glomus spp