The biology of the plant parasitic nematodes Paratylenchus nanus and Paratrichodorus minor in soil under pasture : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University

Abstract

The plant parasitic nematodes Paratylenchus nanus and Paratrichodorus minor were identified from soi ls under grazed pasture in the Waikato region of New Zealand. Host range testing showed that all hosts of P. nanus were grasses, while P. minor hosts included both grasses and clovers. Several variations to the Whitehead and Hemming tray extraction method were compared. The optimum variant was found to yield ca 75% of the total nematode fauna. Sampling of P. nanus populations from 0-10 cm and 10-20 cm soi l depth showed that the abundance of P. nanus peaked in summer. A Population Age Index, based on developmental stages, showed P. nanus population age increased from a minimum in spring to maximum in winter. Positive correlations occurred with soil temperature and negative correlations with soil moisture and rainfall. Accumulated temperature and rainfall (Activity Index) was correlated with P. nanus abundance. Evidence is presented for density-dependence in the P. nanus population at 0-10 cm depth. Multiple regression models were fitted and results are discussed in terms of population dynamics. Seedlings of five grasses were inoculated with one of three rates of P. nanus. There was a deleterious effect of the high rate of P. nanus inoculum on shoot dry matter only for Lolium perenne infected with a selected Neotyphodium sp. endophytic fungus (AR37+). Sampling of soil beneath grazed pasture determined the relationship of P. nanus populations with mature L. perenne plants. For all samplings, AR37+ supported a consistently greater abundance of P. nanus than other plants. Dry matter production and root mass data suggest that greater root production by AR37+ was partly responsible for the greater abundance of P. nanus beneath these plants. Implications for field sowing of AR37+ in the presence of P. nanus populations are discussed. Sampling in soil from a second grazed pasture which contained populations of both P. minor and P. nanus showed the P. minor population had no seasonal periodicity while P. nanus had distinct spring and summer peaks. P. minor abundance was correlated with rainfall and Activity Index. There was no evidence for competition occurring between these two nematodes at the population levels studied. This thesis is written as a senes of papers, which follow the format of the international journal Nematology (Koninklijke Brill NV, Leiden). Therefore, each chapter contains Summary, Keywords, Introduction, Materials and Methods, Results, Discussion and References. The General Introduction and General Discussion chapters are additional to this format.