Pataky Jerald K, Campaña M Andrea
Department of Crop Sciences, University of Illinois, Urbana 61801.
Plant Dis. 2007 Nov;91(11):1484-1488. doi: 10.1094/PDIS-91-11-1484.
The Rp1D gene confers a hypersensitive, chlorotic-fleck, resistant reaction to Puccinia sorghi, the casual agent of common rust of corn. About 40% of commercial sweet corn hybrids carry the Rp1D gene. Sine 1999, Rp1D-virulent (D-virulent) isolates of P. sorghi have occurred regularly in populations of P. sorghi in North America. Observations from sweet corn hybrid nurseries and other trials indicate that the frequency of D-virulent isolates affects severity of rust on Rp1D hybrids; however, the frequency of D-virulence at which the Rp1D gene is rendered completely ineffective is not known. The objective of this study was to assess whether common rust severity is reduced by the Rp1D gene in sweet corn hybrids infected by mixtures of D-virulent and Rp1D-avirulent (avirulent) P. sorghi. Forty pairs of Rp1D-resistant and susceptible (rp1d) versions of sweet corn hybrids from six different commercial breeding programs were evaluated in 2003 and 2004 in trials inoculated with one of five different ratios of avirulent:D-virulent inocula: 100:0, 90:10, 80:20, 60:40, or 0:100. When D-virulent P. sorghi was 100% of initial inoculum, common rust was equally severe on Rp1D and rp1d versions of the same hybrid. Thus, the Rp1D gene did not confer partial or residual resistance in these trials. When initial inocula consisted of 40% or less D-virulent P. sorghi, rust was significantly less severe on Rp1D versions than on rp1d versions of the same hybrids. Relationships between rust severity on Rp1D and rp1d versions of hybrids were explained by linear regressions in all trials. Slope coefficients (i.e., rust severity on Rp1D hybrids as a proportion of that on rp1d hybrids) were related to the percentage of D-virulent P. sorghi in the initial inoculum and were 0.21, 0.29, 0.51, 0.64, and 0.93 in 2003 and 0.25, 0.50, 0.67, 0.76, and 1.0 in 2004 for trials inoculated with 0, 10, 20, 40, and 100% D-virulent P. sorghi, respectively. Thus, the Rp1D gene may convey levels of control in proportion to the frequency of virulence in mixed populations of D-virulent and avirulent P. sorghi when the frequency of virulent isolates is less than 40%.
Rp1D基因赋予对玉米普通锈病病原菌高粱柄锈菌的过敏、褪绿斑点抗性反应。约40%的商业甜玉米杂交种携带Rp1D基因。自1999年以来，高粱柄锈菌的Rp1D毒性（D毒性）分离株在北美的高粱柄锈菌种群中定期出现。来自甜玉米杂交种苗圃和其他试验的观察表明，D毒性分离株的频率影响Rp1D杂交种上锈病的严重程度；然而，使Rp1D基因完全失效的D毒性频率尚不清楚。本研究的目的是评估在感染D毒性和Rp1D无毒（无毒）高粱柄锈菌混合物的甜玉米杂交种中，Rp1D基因是否能降低普通锈病的严重程度。2003年和2004年，对来自六个不同商业育种项目的40对Rp1D抗性和易感（rp1d）版本的甜玉米杂交种进行了评估，试验接种了五种不同比例的无毒：D毒性接种物之一：100:0、90:10、80:20、60:40或0:100。当D毒性高粱柄锈菌占初始接种物的100%时，同一杂交种的Rp1D和rp1d版本上的普通锈病严重程度相同。因此，在这些试验中，Rp1D基因没有赋予部分或残留抗性。当初始接种物由40%或更少的D毒性高粱柄锈菌组成时，同一杂交种的Rp1D版本上的锈病严重程度明显低于rp1d版本。在所有试验中，通过线性回归解释了杂交种的Rp1D和rp1d版本上锈病严重程度之间的关系。斜率系数（即Rp1D杂交种上锈病严重程度占rp1d杂交种上锈病严重程度的比例）与初始接种物中D毒性高粱柄锈菌的百分比相关，2003年接种0、10、20、40和100%D毒性高粱柄锈菌的试验中，斜率系数分别为0.21、0.29、0.51、0.64和0.93，2004年分别为0.25,、0.50、0.67、0.76和1.0。因此，当毒性分离株的频率小于40%时，Rp1D基因可能根据D毒性和无毒高粱柄锈菌混合种群中毒性的频率传递控制水平。
