Tb. Adhikari et al., Virulence of Xanthomonas oryzae pv. oryzae on rice lines containing singleresistance genes and gene combinations, PLANT DIS, 83(1), 1999, pp. 46-50
Fifty isolates of Xanthomonas oryzae pv. oryzae were collected from differe
nt rice-producing districts of Nepal and evaluated for their virulence on t
hese 11 rice lines having from one to four resistance genes: IRBB4 (Xa4), I
RBB5 (M5), IRBB7 (Xa7), IRBB8 (xa8), IRBB10 (Xa10), IRBB14 (Xa14), and IRBB
21 (Xa21), two-gene combination AY4+5 (Xa4 and xa5), three-gene combination
s NH21-37-1-1 (Xa4,xa5, and xa13) and NH24-10-1-3 (Xa4, xa5, and Xa21), and
four-gene combination NH56-1-44-4 (Xa4, xa5, xa13, and Xa21). The ability
of an isolate to cause lesions with different lengths across the lines was
interpreted as virulence. Isolates that were consistently associated with h
igh or low virulence were statistically differentiated. Most isolates produ
ced large lesions on near-isogenic lines with single genes and small lesion
s on lines with different gene combinations. Based on infection responses o
n the two-, three-, and four-gene combinations, five virulence groups were
identified. Isolates in virulence group I were widely distributed. The line
x isolate interactions were generally not significant with gene combinatio
ns, indicating a low possibility of specificity. A line with a four-gene co
mbination, NH56, showed wider spectrum and higher level of resistance to X.
oryzae pv. oryzae than the other lines. The results of this study will fac
ilitate the deployment of effective resistance to X. oryzae pv. oryzae in N
epal.