Relative Parasitic Fitness Of Four Major Prevalent Races Of Puccinia Striiformis F.sp.tritici

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is one of important wheat diseases in China.Due to the strong variability of Pst,single large-scale cultivation of resistant varieties has led to generate new physiological races and result in resistance lose of resistant varieties.A total of 13 commercial wheat varieties around China,which included Aikang 58,Xiangmai 25,Yangmai 20,Zhongmai 175,Liangxing 99,Zhoumai 18,Chuanmai 42,Jimai 22,Xiaoyan 22,Yangmai 16,Mianmai 37,Zhoumai 22,Neimai 836 and Mingxian 169 employed for control and 4 predominant races(or pathotypes)of Pst,namely CYR32,CYR33,G22-9,and G22-14 were employed for the test of relative parasitic fitness(RPF)by using a drop inoculation method.The RPF were measured including urediniospore germination rate,latent period,urediniospore pustule length,urediniospore pustule density,infection area,sporulation intensity,lesion expansion speed,and sporulation period.In addition,the RPFs of four races were tested under different temperature and light tolerance in a controlled envrionment.The results indicated that parameters of relative parasitic fitness of four Pst races(or pathotypes)on thirteen wheat varieties were significant difference(P = 0.00)on sporulation intensity,lesion expansion speed,urediniospore pustule length,sporulation period,urediniospore pustule density,and latent period.Urediniospore germination rates of four Pst races(or pathotypes)for test were significantly different(P = 0.00),whereas no correlation with different varieties was observed(P = 1.00).The infection area of the tested races on the different varieties were significantly different(P = 0.00),but no obvious manifestations among various races(P = 0.20).Principal component analysis(PCA)showed that sporulation intensity which represents sporulation capacity and scalability,latent period which indicats infection ability,and urediniospore germination rate which represents urediniospore vitality,were fully contributed to the RPF in the interaction of four races and thirteen wheat cultivars.Based on previours study,RPF could be calculated by the formula as following: RPF =(Sporulation intensity × Urediniospore germination rate)/ Latent period.Sporulation and infection of G22-9 on the 13 large-scale cultivated varieties were the strongest,and its RPF was higher than that of the predominant races of CYR32 and CYR33.Wheat seedlings showed cool damage symptom and no visible chlorosis or pustule were observed at 8? and 24? constantly.Relative parasitic fitness of G22-9 was the highest at 15? and 20? by comparision with CYR32,CYR33 and G22-14.For the RPF test under different light tolerance,the results showed RPF of CYR32 was highest under 500 Lux,and G22-9 was the second.In the experiment,sporulation intengsity was increased with the increasing of light tolerance.