VIEW ARTICLE
Research Rate of Lesion Expansion in Leaves as a Parameter of Resistance to
Xanthomonas campestris pv. oryzae in Rice. M. F. Koch, Department
of Plant Breeding, Agricultural University, P.O. Box 386, Wageningen,
Netherlands, and T. W. Mew, Department of Plant Pathology, International Rice
Research Institute, P.O. Box 933, Manila, Philippines. Plant Dis. 75:897-900.
Accepted for publication 4 March 1991. Copyright 1991 The American
Phytopathological Society. DOI: 10.1094/PD-75-0897. Lesions on five rice (Oryza sativa) cultivars clip inoculated with
three strains of Xanthomonas campestris pv. oryzae at two plant
ages appeared 4–5 days after inoculation and continued expanding until leaf
senescence. A quadratic model accounted for 99% of the variation in the measured
values. Mean lesion length and mean daily rate of lesion expansion were highly
correlated. Younger plants and susceptible cultivars had higher rates of
increase than older plants and moderately susceptible cultivars, respectively.
The rate of expansion decreased somewhat with time for strains PXO71 and PXO99
and increased or remained the same for strain PXO86. There were no major
differences among cultivars for the change in the rate of lesion expansion over
time. Because of this, there were no major changes in the relative levels of
resistance of the six cultivars over time. Therefore, multiple scorings are not
expected to give extra information about this factor. The observed differences
between strains for the change in the rate of lesion development over time may
indicate a characteristic of strains of X. c. oryzae worth further study. |