Studies of Wild Plant Pathosystems

Studies of wild plant pathosystems are notable for their extreme rarity. Examples include:

  • Senecio vulgaris/Erysiphe fisheri (Harry & Clarke, 1986, Bevan, et al., 1993a,b).
  • Glycine canescens/Phakopsora pachyrhizi (Burdon & Speer, 1981, 1984; Burdon, 1987).
  • Linum marginale/Melampsora lini (Burdon & Jarosz, 1991, 1992).
  • Populus tricocarpa/Melampsora occidentalis (Hsiang & Van der Kamp, 1985).
  • Wild sunflower (Zimmer & Rehder, 1976).
  • Wild oats (Dinoor, 1977).
  • Wild barley (Wahl, et al, 1978).
  • Wild Trifolium (Burdon, 1980).
  • Wild oats (Burdon, et al, 1983).

There appear to be no studies whatever on the functioning of the gene-for-gene relationship in a wild pathosystem. Of necessity, the n/2 model (see 4.15) is based entirely on theoretical and mathematical considerations, and its validity has still to be demonstrated in a wild pathosystem.

There is now an acute need for studies of the autonomous controls of wild plant pathosystems. Apart from life cycle and taxonomic studies, it appears that the whole of plant pathology, the whole of crop entomology, and the whole of crop nematology, are based on studies of the crop pathosystem. One example of this total concentration on the crop pathosystem will suffice. It is generally believed that wheat stem rust (Puccinia graminis tritici) has attracted more scientific publications than any other plant disease, particularly with reference to disease resistance in the wheat host. This is an alternating rust (i.e., a heteroecious rust, see Chapter 8) and its winter host is wild barberry (Berberis spp.). But, although innumerable papers have been published about resistance to this rust in wheat, it appears that not one paper has been published concerning resistance to this rust in the wild barberry host. Perhaps it should be remarked also that most of these papers on resistance to stem rust deal with vertical resistance, and there are almost none dealing with horizontal resistance (see 6). This incredible bias is a remarkable example of suboptimisation.

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