Fj. Correavictoria et Rs. Zeigler, PATHOGENIC VARIABILITY IN PYRICULARIA-GRISEA AT A RICE BLAST HOT-SPOTBREEDING SITE IN EASTERN COLOMBIA, Plant disease, 77(10), 1993, pp. 1029-1035
Forty-five international races of Pyricularia grisea, representing all
nine race groups, were identified in a ''hot spot' breeding site (San
ta Rosa) in Colombia, with the largest number included in the IA group
. The international race system did not fully describe the virulence s
pectrum of the isolates, since several races could be further differen
tiated into different pathotypes when local commercial cultivars were
used as differentials. Compatibility was present in the pathogen popul
ation for at least 13 known resistance genes and resistance sources te
sted. Frequency of virulent phenotypes on the 42 cultivars tested rang
ed from 0.0 to 0.86, with no cultivar susceptible to all isolates. The
lowest compatibility frequencies were associated with combinations of
resistance genes. It was unusual to recover isolates compatible with
cultivars K-8, Peta, Ceysvoni, IR-42, Fujisaka 5, Fukunishiki, Zenith,
and NP-125. No isolates were recovered that were compatible with the
newly released cultivars Oryzica Llanos 4 and 5 developed at this site
, and very few infected CICA 9. Analysis of the compatibility frequenc
y of isolates recovered from commercial rice cultivars revealed a mark
ed specialization for cultivar origin. Some cultivars were infected ma
inly by isolates recovered from the same cultivar. Virulence factors w
ere accumulated in the most virulent isolates, but no isolate was viru
lent to all rice cultivars. Regardless, matching virulence for all res
istance genes is already present in the pathogen population, indicatin
g that new combinations of resistance factors and/or new resistance ge
nes are needed. Rare compatibility with particular cultivars suggests
that combinations of certain virulence genes may be associated with po
or fitness. Differences in the distribution of virulence genes of P. g
risea among and within cultivars support the feasibility of gene deplo
yment strategies.