Showing papers in "Biology and Environment-proceedings of The Royal Irish Academy in 1999"

Glomus claroideum, an arbuscular mycorrhizal fungus new to Ireland, and its distribution in an Irish tree nursery

Abstract: The arbuscular mycorrhizal (AM) populations in fumigated soil and AM colonisation of ash and sycamore were investigated in the main bare-root nursery in Ireland Only one AM spore type was found in the soil This was identified as Glomus claroideutm (Walker and Vestburg 1998) and a single-spore culture has been lodged as BEG 62 In a sand/pot study using the single-spore culture as inoculum, both ash and sycamore showed no growth response to inoculation Ash seedlings had 25% AM infection, which was characterised by abundant arbuscules, hyphae and occasional hyphal coils, but no AM infection occurred in sycamore In the nursery, chlamydospores of G claroldeum increased in the soil between June-December, but there was a greater AM infectivity estimate based on the 'niost probable number' test compared with AM spore counts Ash seedlings had an AM colonisation ranging 10-35%, whereas sycamore was sparsely mycorrhizal ( < 2%) There was positive correlation between spore numbers of G claroideum and AM colonisation of ash growing in one part of the nursery converted from agricultural land but not in another, which had been n1efs3rrA Monsanto, USA) In spring (April-May) of the following year, the seed-beds were rotavated lightly, raked, and seed of ash and sycamore were sown at 25g m-2 and 30g m-2 respectively At the cleared forest site, seed of ash and sycamore was sown during May 1992 There were 26 and 14 rows of ash and sycamore respec tively, and each row was 175 m in length At every sixth and third row of ash and sycamore respec tively (five rows in total), two seedlings were lhfted at about 1Om, 85m and 160m along the row, providing a total of 30 seedlings per tree species On the converted agricultural land, seed of ash and sycamore were sown during April 1993, and two seedlings were sampled at 50m and 10Gm along six rows at five row intervals, giving a total of 24 seedlings sampled per treatment Soil ( 0 SOGml volume from 0-15cm surface) was also collected for AM spore analyses at each site sampled SPORE EXTRACTION AND QUANTIFICATION Each soil sample (50g fresh mass) was sieved according to the sieving and decanting procedure of Gerdemann and Nicolson (1963) The slevings were centrifuged at 1300g for 3mmn The pellet was resuspended in 45% sucrose and centrifuged again at 1300g for 1mmn The supernatant was poured onto a 30pm sieve, washed thoroughly with delonised water and examined mucroscopically in a Petri dish containing a 5mm square grid for spore counting PREPARATION OF POT CULTURES One set of trap cultures was prepared by planting ash seed in a mixture of nursery soil and 198 autoclaved (under steam pressure at 121 ?C for 15run), medium-grade sand (2.1 v/v) in auto claved 10cm diameter pots. A control consisted of ash seed planted into autoclaved nursery soil and sand (2 1) to check for possible contamination Another set of trap cultures was produced using one-year old ash taken from the nursery. Adhering soil was washed from the root systems using tap water and autoclaved deionised water and these seedllngs were planted in autoclaved sand in pots All the pots were left for four months in the glasshouse and were watered regularly with delonised water. The conditions of the glasshouse were thermostatically controlled (17-25?C) and supplemented with mercury vapour lamps with an extended photoperiod of 16h (130-60,tmol m-2 s 1) Spores were extracted from the soil/sand of the trap cultures by wet sieving through 38pm mesh Only one spore type was identified, and it was used to prepare single-spore cultures One spore was placed on the root systems of four-week old seedlings of either ash or plaintain (Plantago lanceolata L.), planted into autoclaved sand contain ing lOnml Miracle-Gro solution (25% full strength, an all-purpose plant food, ICI Garden Products, Surrey, UK) and enclosed in sternle sun transparent bags (44cm x 20.5cm with 24mm2 0 024m filter disc, Sigma, Germany) and grown in the glasshouse GROWTH AND INOCULATION OF PLANTS IN POTS Spores (10 per seedling and taken from single spore cultures) were placed on the root systems of four-week old seedlings of ash and sycamore and then propagated under glasshouse conditions in the same way as the single-spore cultures Con trol, uninoculated seedlings were also grown under the same conditions. The plants were harvested after a 24-week propagation, and growth measure ments for ash and sycamore were made The sand was wet-sieved and spore production was deter muned ARBUSCULAR MYCORRHIZAL INOCULUM POTENTIAL OF NURSERY SOIL An estimation of mycorrhizal infective propagules in the nursery soil was carried out using the 'most probable number' (MPN) method (Porter 1979). Seedlings of plaintain were grown in a ten-fold dilution (10?10-) senes of nursery soil mixed with autoclaved soil in Hyco-container trays in a 5 x 5 (dilution by block) random block design. The seedlings were grown under This content downloaded from 207.46.13.76 on Wed, 24 Aug 2016 04:14:59 UTC All use subject to http://about.jstor.org/terms GLOMUS CLAROIDEUM NEW TO IRELAND glasshouse conditions for eight weeks For each dilution, the percentage mycorrhizal infection per root length was estimated on five seedlings per block (a total of 25 seedlings), using the method of Glovannetti and Mosse (1980). An estimate of AM propagules was determined using the MPN table in Alexander (1982) MYCORRHIZAL ASSESSMENT AND MEASUREMENT OF PLANT GROWTH Washed root systems were fixed overnight, cleared in 10% KOH and stained by autoclaving in 0.03% Chlorazol Black E in lactoglycerol (Brundrett et al 1984) The stained root sys tems were dissected into 1cm segments and 50 were selected randomly and mounted in 50% glycerol Length of total AM infection of each seedling was estimated within each segment (Ocampo et al 1980) Total root length of seedlings was estimated by the line intersect method (Tennant 1975) and shoot length was measured Dry mass of root and shoot was determined after oven drying at 80?C for 48h