II.3. Concentric leaf spot in barley.
H. Ahokas. Department of Genetics, University of Helsinki, P. Rautatiekatu 13, SF-00100 Helsinki 10, Finland.
The concentric leaf spot (CLS) disorder was first observed in the F3 generation from the cross Bozujor (= Nishiki-hen, AHOR 2378) x HA 21 (a mutant from Pirkka) in 1971.
The spots vary in size and form. Typically, they consist of brown, necrotic circles concentric to each other. The circles, as well as the brownish inter-circles are approximately of the same width or strength in a spot, or in the spots on a leaf blade. In the focus of a spot, one can usually see a brown centre. The areas of a blade with CLSs lose their green and turn brownish. Sometimes the circles are not very distinct, with only the brownish areas pronounced, or the brownish blotches are so dark that one cannot easily distinguish the brown circles. The disorder can spread from a small focal point to affect most of a blade. Some spots are shown in Figure 1. The diagnostic trait can be found in any leaf from the first one to the flag leaf, with one or more leaves affected. In some plants the sheath and even the awns can show this characteristic.
Figure 1. Concentric leaf spots on leaves from different plants.
No pathogen could be found at the spots when sectioned and observed under the light microscope at 400x and lOOOx magn, but all the cells at the circles looked vacuolized and necrotic.
Two small F2 populations were scored for the disorder in 1972 (Table 1). The first one was inspected only once, the second at least twice a week during the season. The fairly small estimates for the X2 suggest that the ability to show this phenotype is based on the homozygosity of recessive, complementary alleles in two unlinked loci. I propose that these hypothetic alleles be called cls 1 and cls 2.
Table 1. Distribution of normal and CLS plants in two F2 populations.
In addition to those mentioned, CLS has also been observed in the F3 generation from the cross CI 5029 x Pirkka. As Bozujor and CI 5029 are evidently of the Oriental barley type, cls 1 and cls 2 could have a peculiar geographic distribution.
The focal point in the spots suggests that the spot might actually be caused by an external inductor. The circles themselves could be a hypersensitive reaction of a certain genotype against, e.g., the toxines from the bite or sting of an insect, or the germination or toxines of the cell of an unvirulent micro-organism. These and the possible presence of a virus or a mycoplasma-like biopathogen will be studied further. Sterile cultures from the embryos in glass bottles have already been started.
CLS of barley resembles, in its rough features, the Chiltex spot and Manhattan leaf spot no. 1. of Sorghum (Webster 1965, Casady and Paulsen 1971). Several inherited leaf disorders in barley, evidently of other types, were recently studied, and previous studies were referred to by Jensen (1971).
References:
Casady, A. J. and A. Q. Paulsen. 1971. J. Hered. 62:193-196.
Jensen, J. 1971. Barley Genetics II:213-219.
Webster, O. J. 1965. Crop Sci. 5:207-210.
