Microbial pathogens and plant parasitic nematodes in pastures with declining vigour

Abstract

Two years after establishment, areas of low vigour (LV) were noticed within a white clover (Trifolium repens)/ryegrass (Lolium perenne) pasture. These areas became progressively larger, and, two years later, the pasture had low vigour, comprising only 3% white clover. Clover tissue nitrogen and phosphorus levels were greater in high vigour (HV) than in LV herbage. There were no differences (P > 0.05) in "total" bacteria, fluorescent pseudomonads, or proportions of deleterious bacteria in LV and HV white clover roots (mean logio CFUs for total count and fluorescent pseudomonads were 9.4 and 8.8, respectively, and the proportions of deleterious bacteria encountered in these groups were 6.9% and 17.5%). There was a 9-fold difference (P < 0.01) in the white clover dry matter between LV areas and HV areas in February, increasing to 25-fold (P< 0.01) in March. The total dry matter yield differences, which included grasses and clover, were 2.7-and 2-fold (P < 0.01) for the two months. More fungi were isolated (P < 0.05) from LV white clover roots than from HV roots (164 and 104 isolates, respectively). This was mostly due to greater numbers (P < 0.01) of Codinaea fertilis in LV roots (111 cf. 41 in HV). In ryegrass roots, there were also greater numbers (P < 0.01 ) of total fungi in LV roots (97 cf. 50 total A00024 isolates in HV), mostly due to higher populations of Fusarium oxysporum in LV roots (29 isolates cf. 5 in HV). There was no difference (P > 0.05) in the Soil Pathogenicity Index between LV and HV soil. The plant parasitic nematode populations in 250 ml of soil in LV and HV areas were 42.7 and 9.7 for Heterodera and 28.1 and 3.9 for Meloidogyne, respectively.

Cost of root disease on white clover growth in New Zealand dairy pastures

“…These include nematodes, fungi, and Oomycetes (Falloon 1985;Skipp and Christensen 1989;Waipara et al 1996;Watson and Mercer 2000;Sarathchandra et al 2000), which vary from highly host-specific through to broad-range generalists. In most cases, however, root diseases are often caused by a suite (disease complex) of pathogens (Skipp and Watson 1996).…”

“…In New Zealand, the bulk of research efforts were conducted in the mid 1980's through to the early 2000's (Falloon 1985;Skipp and Christensen 1989;Waipara et al 1996;Watson and Mercer 2000;Sarathchandra et al 2000), with relatively little work conducted for the past 15 years. This is at odds with the trend for increased value of pasture production on a per hectare basis.…”

Trichodermaspecies for biocontrol of soil-borne plant pathogens of pasture species

“…In New Zealand, soil-borne pathogens commonly-associated with diseases of grass and forage legume seedlings include Rhizoctonia solani (Kuhn), Pythium ultimum (Trow) (Skipp & Watson, 1996) and Sclerotinia trifoliorum Eriks (Skipp & Hampton, 1996). R. solani and P. ultimum can reduce establishment of grasses and legumes (Skipp & Christensen 1989a,b;Waipara et al,1996;Sarathchandra et al, 2000). In perennial ryegrass (Lolium perenne L.) these pathogens usually infect the seed or seedling prior to emergence (preemergence damping off -Falloon, 1985).…”

Best-practice pasture renewal for forage production and sustainability: description of a farmer-led study and initial findings

“…The individual genera of plant feeding nematodes listed in Table 3 are in order of their potential to damage pasture plants so that the high population levels of root knot (range 0-5459 × 10 3 /m 2 ) and cyst nematodes (0-509 × 10 3 /m 2 ) observed in some paddocks is likely to be of concern. As is the case for grass grub, these nematodes can increase rapidly in the first 2 to 3 years after establishment of new pasture (Sarathchandra et al 2000), even after cropping has been used to remove plant hosts as Watson et al (2000) found at a Bay of Plenty site. Some of the variables measured were significantly (P<0.05, n=24) correlated with each other.…”