Molecular cytogenetic discrimination and reaction to wheat streak mosaic virus and the wheat curl mite in Zhong series of wheat -: Thinopyrum intermedium partial amphiploids

Thinopyrum intermedium (2n = 6x = 42, JJJ(s)J(s)SS) is potentially a useful source of resistance to wheat streak mosaic virus (WSMV) and its vector, the wheat curl mite (WCM). Five partial amphiploids, namely Zhong 1, Zhong 2, Zhong 3, Zhong 4, and Zhong 5, derived from Triticum aestivum x Thinopyrum intermedium crosses produced in China, were screened for WSMV and WCM resistance. Zhong I and Zhong 2 had high levels of resistance to WSMV and WCM. The other three partial amphiploids, Zhong 3, 4, and 5, were resistant to WSMV, but were susceptible to WCM. Genomic in situ hybridization (GISH) using a genomic DNA probe from Pseudoroegneria strigosa (SS, 2n = 14) demonstrated that two partial amphiploids, Zhong I and Zhong 2, have almost the identical 10 Th. intermedium chromosomes, including four J(s), four J, and two S genome chromosomes. Both of them carry two pairs of J and a pair of J(s) genome chromosomes and two different translocations that were not observed in the other three Zhong lines. The partial amphiploids Zhong 3, 4, and 5 have another type of basic genomic composition, which is similar to a reconstituted alien genome consisting of four S and four J(s) genome chromosomes of Th. intermedium (Zhong 5 has two J(s) chromosomes plus two. J(s)-W translocations) with six translocated chromosomes between S and F or J genomes. All three lines carry a specific S-S-J(s) translocated chromosome, which might confer resistance to barley yellow dwarf virus (BYDV-PAV). The present study identified a specific J(s)2 chromosome present in all five of the Zhong lines, confirming that a J(s) chromosome carries WSMV resistance. Resistance to WCM may be linked with J or J(s) chromosomes. The discovery of high levels of resistance to both WSMV and WCM in Zhong 1 and Zhong 2 offers a useful source of resistance to both the virus and its vector for wheat breeding programs.