O'------"~_..L..._'--_----""':::::......a.. __'

Figure 1. The reaction of wheat cultivars to L. nodorum(a) Results obtained after the

original inoculation

D. B. LethamBiological and Chemical Research Institute,

Rydalmere, N.S.w. 2116

Powdery scab, of potato caused by the fungusSpongospora subterranea (Wallr.) Lagerheim, was firstreported in New South Wales in 1927 from "two localitieson the Northern Tablelands" (1). A subsequent publication(2) did not give any further information on the distributionof this disease in New South Wales. Records in the BiologyBranch report that the disease occurred in 1927 on twoproperties at Ebor and one at Guyra. The location of one ofthe areas at Ebor is recorded, but the location of the othertwo sites is not. Powdery scab was also reported in 1933 atKatoomba and Rose Bay, but again the actual locationwhere the disease occurred is not given. Apparently nospecimens of the disease from any of these areas werekept.

TECHNICAL NOTESDistribution of Spongospora subterranea inNew South Wales

Fusarium Wilt of SpinachD. S. Trimboli

Yates Seeds Ltd., Milperra N.S.W. 2214

(1) Booth, C., (1971) - The Genus Fusarium. 1st Edition. TheEastern Press Ltd. London 130-134.

(2) Hungerford, C. W. (1923) - A Fusarium wilt of Spinach.Phytopathology 13: 205-209.

In December 1976, diseased spinach seedlings(Spinacia oleracea MilL) were received from a Melbournemarket garden. The disease symptoms were similar tothose described by Hungerford (2) for Fusarium wilt ofspinach. The seedlings were six weeks old.

The symptoms consisted of leaf chlorosis and inwardrolling, necrosis of the fibrous root system, tap root andcrown. A longitudonal section of the tap root and crownrevealed vascular browning typical of a vascular wilt syn­drome. Fusarium oxysporum (1, 3) was isolated from in­fected crowns.

The pathogenicity of single spore isolates of F ox­ysporum was assessed with three week old "EnglishHybrid" spinach seedlings using the root-dip inoculationtechnique at 30°C incubation. The inoculated seedlingsdeveloped the same symptoms as shown by the originaldiseased seedlings and the fungus was reisolated.

It was concluded that the fungus was F. oxysporum f.sp, spinaciae (Sherb) Synder & Hansen (1, 4) and that thisis the first record of the disease in Australia.

A culture has been lodged at the Biology Branch Her­barium, New South Wales, Department of Agriculture(DAR 28280).

REFERENCES

NEW DISEASES

(4) Walker J. C. (1952) - Diseases of Vegetable Crops. tst Edi­tion. McGraw-Hili Book Company. New York 403-404.

(3) Toussoun, T. A. & Nelson, P.E. (1976) - A pictorial Guide tothe Identification of Fusarium Species. 2nd Edition.University Park. Pennsylvania State University Press: 13­29.

36

T,,,!

12

(b) Results obtained after the seventhsuccessive passage

o

50

100-

100

REFERENCE(1) Harrower K. M. (1977) - Specialization of Leptosphaeria

nodorum to alternative graminaceous hosts. Trans­actions of the British Mycological Society 68: 101-103.

50

Time after inoculation (days)

seventh successive passage through Summit on a rangeof cultivars. Some show significant changes which wouldtend to rearrange their relative ranking in terms of sus­ceptibility. It is especially obvious in the more susceptiblecultivars that a decrease in the incubation period occursafter successive passages through that cultivar. It isshown in Table 1 that some of these reductions in theincubation period are significant, similarly a decrease inthe latent period of the isolate on both Summit and on Pin­nacle is also significant.

The relevance of these results is especially importantwhen considering the theory of multilines. It is well knownthat in large areas sown under one particular cultivar thatalthough that cultivar may originally have been classed ashaving a low level of susceptibility, that dramatic epidemicsof glume blotch often arise in those areas. The resultspresented here show that this is probably due to rapidsuccessive passages of the pathogen through a large andabundant host population which is basically isogenic.However, in areas which are sown with a range of cultivarsthe situation could arise whereby the pathogen coulddevelop a higher level of virulence towards the moresusceptible wheat cultivars growing near-by than hashitherto been thought possible. Clearly, in multilines wherethe population of wheat hosts is heterogenic this situationcould result in some degree of equalising the difference inthe apparent susceptibilities of different cultivars used inthe multiline to L. nodorum.

In other than the non-susceptible cultivar, i.e. Fleched'Or, these results thus suggest that virulence to a partlyresistant host, i.e. Teal, is decreased after successive pas­sages through a more susceptible cultivar. But, virulenceto a susceptible host is increased by successive pas­sages through it.

44