m 2 Altura m Ocupación /per Iluminación W/ W/m VEEI 2 ·100lu
III.3.1. SISTEMA DE FACHADA TRASVENTILADA EN EL BLOQUE DE OFICINAS
that for
P. nanus
suggesting that the cause of the increased abundance ofP. nanus
beneath AR37+ did not act in a similar manner on other nematodes. Dry matter production and root mass data suggest that greater comparative root production by AR37+ was at least partly responsible for the greater abundance of
P. nanus
beneath this treatment. It is suggested that AR37+ dry matter production was effected byP. nanus
feeding but the extent to whjch this occurred could not be determined. Depth distributions of
P. nanus, Pratylenchus
and non-plant parasitic nematodes are given and discussed in terms of root distribution and possible deleterious effects of root herbivory. Keywords:Paratylenchus nanus, Lolium perenne, Neotyphodium
endophyte,Pratylenchus
Paratylenchus
spp., in common with some other ectoparasitic nematodes, feed on root hairs (Linfordet al.,
1 949; Rhoades & Linford, 1 96 1 ) and root epidermal cells (Wood, 1973). Root hairs are involved in the uptake of water and nutrients (Drew & Nye, 1969). A lack of visible pathological changes to cells that have been fed on byParatylenchus
spp. (Linfordet al.,
1 949; So]ov'eva, 1 975) has meant they are often considered weak plant pathogens. There are, however, many instances of root feeding by these nematodes having a deleterious effect on plant growth. Some of these effects may be solely due to the large numbers ofParatylenchus
sp. encountered in soil (Chapters 4 and 5) or the additional action of secondary pathogens entering plant roots via nematodefeeding wounds (Cole et al., 1 973; Inagaki et al., 1 973; Gubina, 1 975; Hirano, 1975; Savkina, 1 993).
Examples of pathogenic effects of Paratylenchus spp. include the observations of Shesteperov ( 1 978) who found that infestation of red clover (Trifolium pratense) by P. projectus caused a reduction in shoot weight, shoot height and an increased susceptibility to powdery mildew. Yields of birdsfoot trefoil (Lotus corniculatus), in addition to red clover were reduced after infestation by P. projectus (Townshend & Potter, 1982). Reduction of seedling establishment of lucerne (Medicago sativa), white clover, red clover and birdsfoot trefoil was also observed for P. projectus infestations (Townshend & Potter, 1982). Sunflower (Helianthus annuus) yields in the U.S. were significantly reduced by large numbers of P. projectus (Smolik, 1 987). P. bukowinensis has been found to be pathogenic to plant species of the Umbellifera (Brzeski, 1975; Brzeski & Radzikowska, 1980). Paratylenchus spp. have been implicated as causing yield reductions to some ryegrass cultivars (Yeates & Barker, 1 986) and ryegrassl white clover pastures (Yeates, 1985; Watson et al., 1 994) in New Zealand.
The results from Chapter 6 indicated that P. nanus may have a deleterious effect on seedlings of the perennial ryegrass (Lolium perenne) INeotyphodium sp. endophyte association designated AR37+. This paper reports the results of field sampling to determine the effect of P. nanus on mature perennial ryegrass plants grown in pure species plots, including AR37+. The seasonal and monthly population dynamics of P. nanus described in Chapters 4 and 5 provide data on the abundance of this nematode in a mixed pasture situation.
Materials and methods
SITE DESCRIPTION AND PLANT CHARACTERISTICS
Two sites, which form part of the National Endophyte Evaluation Trial, were sampled. They were established and maintained by a team lead by Dr J. P. J. Eerens (AgResearch, Ruakura Research Centre, Hamilton).
The two sites were located at: Tokanui Research Station (Waikato - lat. 38° 5.4' S 1 74° 19.3' E, ca 400 m from the site described in Chapters 4 and 5) with Otorohanga silt
loam soil (Typic Haploudand, wilting point 32%; field capacity 65%); and a private farm inland from Te Puke in the Bay of Plenty (Bay of Plenty - lat. 37° 53' S 176° 34' E) with Ohinepanea sandy soil (Typic Udivitrand, wilting point 10%; field capacity 25%). The Tokanui trial site was established in autumn 1 996 after maize (Zea mays) had been grown for the previous two years. In autumn 1996, an area 1 8 x 20 m was marked out and divided into 24 plots, each 3 x 5 m. Each plot was sown with a pure sward of one of seven Grasslands Nui perennial ryegrass INeotyphodium sp. endophyte combinations (herein referred to as treatments). The five treatments sampled in this study were: Grasslands Nui endophyte free (E-), Grasslands Nui infected with wild-type endophyte (E+), and Grasslands Nui artificially infected with one of three selected endophyte strains (ARl+, AR24+, and AR37+). Table 1 shows the known alkaloid profiles of each treatment (Popay & Wyatt, 1995; Ball et al., 1 997). It is likely that some of the selected endophyte strains produce as yet undiagnosed alkaloids (Pop ay & Wyatt, 1995). The site was grazed by sheep and beef cattle in common with the rest of the field until spring 1996 after which it was fenced and grazed separately.
The Bay of Plenty site was also established in autumn 1 996 as for the Tokanui site. The site was grazed in common with the rest of the field, by dairy cattle.
Table 1. Alkaloid profiles of Grasslands Nui perennial ryegrass plants infected with Neotyphodium sp. endophytes which were sown at Tokanui and Bay of Plenty sites (+, - denote presence and absence respectively).
Endophyte status E E+ ARl+ AR24+ AR37+ Perarnine + + +
NEMATODE AND HERBAGE SAMPLING
Lolitrem B Ergovaline
+ +
Nematode sampling of the Tokanui site was carried out on the 2 1 November 1 997, 1 1 February and 1 6 �arch 1 998. Fifteen perennial ryegrass plots were sampled to give the following treatment x replicate combinations: E- x 3, E+ x 3, AR37+ x 2, AR24+ x
4 and AR 1 + x 3. Three samples from grazed pasture adjacent to the ryegrass trial site were also taken on each date.
Twelve perennial ryegrass plots at the Bay of Plenty site were sampled on 2 April 1998 to give the following cultivar x replicate combinations: E- x 2, E+ x 2, AR37+ x 2, AR24+ x 3 and AR 1+ x 3.
Each sample consisted of three 2.5 cm diameter cores to 20 cm depth, divided into 0-1 0 and 10-20 cm depths. The pasture samples consisted of transects adjacent to three sides of the trial, along which three 2.5 cm diameter cores were taken, and were included for comparison between ryegrass plots and normal pasture which contained at least 40% white clover, along with ryegrass, Poa sp., and a small percentage of broadleaf weeds.
Nematodes were extracted from the three bulked cores using a variant of the tray method (Chapter 3), and counted in a Doncaster dish under a stereomicroscope at 80x magnification. All plant parasitic nematode genera were identified and counted separately, all other nematodes were counted collectively. Life stages of P. nanus were determined during counting.
Four soil moisture samples were taken at the time of nematode sampling: two from within the ryegrass plots and two from the outside plots. Samples consisted of three 2.5 cm diameter cores, divided as for nematode samples then dried in an oven at 90°C for 48 h. Soil moisture is expressed as percent dry soil.
At the �arch 1 998 sampling, root samples were taken from all ryegrass plots at Tokanui. Each sample consisted of three 5 cm diameter cores to 20 cm depth, divided into 0-10 and 10-20 cm depth. Roots were washed from cores, oven dried at 90°C and weighed.
Herbage was mown to 4 cm height to coincide with grazmg, and herbage dissections were taken prior to each mowing. Herbage mowing and dissection was carried out by a team lead by Dr 1. P. 1. Eerens and the data presented here is part of their data set.
All statistical analyses were as reported in Chapter 6. Results
The soil moisture data are presented in Table 2. At both sites, soil moisture content was greater in 1 0-20 than 0-10 cm depth on all sampling dates. Soil moisture was lower under pasture than under ryegrass.
Table 2.