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Cucurbit Genetics Cooperative Report 11:20-21 (article 10) 1988

Preinoculation peroxidase activity in cucumber leaves not associated with race 2 anthracnose resistance

Linde, D.C.

Department of Plant Pathology, University of Minnesota, St. Paul, MN 55108

Rhodes, B.B.

Clemson University Edisto Research and Education Center, Blackville, SC 29817

Anthracnose, caused by the fungus Colletotrichum lagenarium (Pass.) Ell. and Halst., is one of the major foliar diseases of cucumbers. An inexpensive screening aid for anthracnose resistance would be useful to plant breeders, since it would permit testing in the seedling stage instead of running field tests. Biochemical assays are potential screening aids.

Preinoculation levels of peroxidase activity in cucumber leaves were investigated for their possible association with race 2 anthracnose (2) resistance. Peroxidase activity has been implicated in disease resistance in plants (1). Three experiments were conducted.

Methods.
In experiment 1, the resistant line 'ARF79-95', the susceptible cultivar 'Model', the reciprocal F1 progeny, and the F2 population were gown in the field in a completely random design replicated in 4 locations. The youngest fully-expanded leaf was harvested at the 10-leaf stage. The plants were then inoculated with anthracnose race 2 (10,000 spores/ml) and rated for disease reaction for 5 weeks. The soluble, ionically-bound, and covalently-bound peroxidases were extracted from the leaf samples (5) and their activities determined with the guaiacol assay (4).

In experiment 2, soluble peroxidase activity of 7 different genotypes as well as individuals from reciprocal F2 populations of a cross between 'AR 79-95' and 'Model' were determined using the o-tolidene assay (3). Leaf samples were taken from plants in the 2-leaf stage.

In experiment 3, the isozymes of the soluble peroxidases extracted from the leaves in experiment 2 were separated using flatbed isoelectric focusing. A constant level of peroxidase activity was applied in each lane.

Results.
All 3 peroxidase fractions gave similar results for least squares means (Table 1) and the analysis of variance (Table 2) for soluble peroxidase activity of parents and progeny. Preinoculation levels of peroxidase activity varied with location and with location by genotype interaction.

Variations in genotype were primarily maternal. In the F2, there was no consistent relationship between peroxidase activity and disease rating from location to location. Likewise, the use of the substrate o-tolidene in experiments 2 and 3 did not reveal any relationship between soluble peroxidase activity or activity of individual isozymes and disease ratings of parents or progeny.

In conclusion, preinoculation levels of peroxidase activity, as assayed with 2 nonspecific substrates, showed no relationship to race 2 anthracnose resistance and were not useful as a screening aid.

Table 1. Least squares means of locations and genotypes for soluble peroxidase activity (AU/g fresh weight leaf)z.

Location number
Least squares mean
Genotype
Least squares mean
1
59.8 a
Model
58.1 a
2
58.2 a
Model x AR79-95
56.1 a
3
38.4 b
AR79-95 x Model
49.6 b
4
57.3 a
AR79-95
49.9 b
z Means within each column separated by LSD at 5%.

Table 2. analysis of variance of soluble peroxidase activity (AU/g fresh weight leaf) for the parents and reciprocal F1 progeny of the cross 'Model' x 'AR79-95.

Source of variation
df
Sums of squares
F ratio
Location (L)
3
2330
21.8**
Genotype (G)
3
417
3.9*
L x G
9
3700
11.5**
Error
15
534
 
Total
30
6982
CV (%)
11
 
*, **Indicates significance at the 5 and 1% levels, respectively.

Literature Cited

  1. Fric, F. 1976. Oxidative enzymes. In: R. Heitfuss and P.H. Williams (eds.). Physiological Plant Pathology, an Encyclopedia of Plant Physiology: New Series, Vol. 4. Springer-Verlag. New York. p. 617-651.
  2. Jenkins, S.F., Jr., N.N. Winstead and C.L. McCombs. 1964. Pathogenic comparisons of three new and four previously described races of Glomerella cingulata var. orbiculare. Plant Dis. Rptr. 48: 619-622.
  3. Loy, J.B. 1972. A comparison of stem peroxidase in bush and vine forms of squash (Cucurbita maxima Duch. and C. pepo L.). J. Esp. Bot. 23 (75): 450-457.
  4. Maehly, A.C. and B. Chance. 1954. The assay of catalases and peroxidases. In: D. Glick (ed.) Methods of Biochemical Analysis. Vol. !. Interscience. New York. p. 357-423.
  5. Van den Berg, M. and J.J.W. Wijsman. 1981. Genetics of the peroxidase isoenzymes in petunia. Theor Appl. Genet. 60 (2): 71-76.
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