SUMMARY
A new selective medium containing pentachloronitrobenzene and 2‐aminobutane (the PAB medium) was developed for soil‐dilution plate enumeration of fungal propagules of Fusarium solani var. coeruleum and F. sulphureum from field soil. Growth of ‘weed‐fungi’ was less on the PAB medium than on the previously developed F. solani var. coeruleum isolation medium (the PM70 medium) and significantly more propagules of F. solani var. coeruleum were detected.
Propagule counts (x) of F. solani var. coeruleum and F. sulphureum from the PAB medium, after log10 (x/10 + 1) transformation, were linearly related to the angular transformation of measurements of soil infectivity from the tuber bait method using the susceptible cv. Catriona. Slopes from disease‐inoculum regressions for F. solani var. coeruleum and F. sulphureum in November and May were similar and this suggests that the mode of pathogenic action of F. solani var. coeruleum and F. sulphureum was similar. Recently harvested tubers, inoculated in November, however, were more resistant to infection by both pathogens than stored tubers inoculated in May. Storage of air dry soil at 4°C for 6 months reduced the population of F. sulphureum but not the population of F. solani var. coeruleum.
Whereas the PAB medium is recommended primarily for use in the isolation of F. solani var. coeruleum and F. sulphureum from field soil, the PM70 medium appears to be more suitable for recovery of these pathogens and others, including Phoma exigua var. foveata from diseased tuber tissue.
In pure swards at sites in 4 regions of New Zealand, Roa and S170 tal1 fescue (Fesluca arundinacea Schreb.) established slower than Ariki rye grass (Lolium x hybridum Hausskn). Ariki rye grass was generally superior to tall fescue at sites where soil moisture levels were maintained throughout the year (because of even rainfal1 or heavier soils), whereas tall fescue was more productive in areas prone to long periods of moisture stress (summer drought andlor light soils) particularly over the summer-autumn period. Roa tall fescue was better than S170 under frequent cutting but similar under infrequent cutting. Herbage of Roa tall fescue had a higher acceptability to sheep than S170.
Three pasture types were compared under 2 sheep management systems over 3 years. A basic temperate species mixture of ryegrass (Lolium x hybridum Hausskn. 'Grasslands Ariki') and white clover ( Trifolium repens L. 'Grasslands Huia') (pasture R) was compared with the same mixture plus either paspalum (Paspalum dilatatum Poir.) or kikuyu grass (Pennisetum clandestinum Hochst.) (pastilles P and K respectively). Subtreatments consisted of a ewe/lamb system stocked at 19.8 ewes/ha, and a put-and-take hogget system in which numbers were adjusted to match feed supply on a 20-day cycle. There were no significant differences in sheep production between R and P pastures in the ewe system (ewe and lamb live weights, greasy fleece weights) but there was a 7% advantage to P under the hogget system (intake of metabolisable energy/ha). Under the stocking rates used, paspalum content fell to low levels. Live weights of ewes on K pastures fell further in spring than those on other pastures but they recovered faster after lactation. Greasy fleece weights were also lower at spring shearing and on an annual basis but there were no differences at autumn shearing. Lamb production (live weight/ha) did not differ significantly among pastures during the 21 weeks lambs remained on the trial. Under the hogget system, estimated animal metabolisable energy intake of K pasture was 10%less than that on R with K yield being lower in spring and higher in autumn.
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