Characterization of Chromosome Constitution in Three Wheat-Thinopyrum intermedium Amphiploids Revealed Frequent Rearrangement of Alien and Wheat Chromosomes

Background: Thinopyrum intermedium (2n=6x=42) is an important wild perennial Triticeae species exhibiting many potentially favorable traits for wheat improvement. Wheat-Th. intermedium partial amphiploids serve as a bridge to transfer desirable genes from Th. intermedium into common wheat. Results: Three octoploid Trititrigia accessions (TE261-1, TE266-1, and TE346-1) with good resistances to stripe rust, powdery mildew and aphids were selected from hybrid progenies between Th. intermedium and the common wheat variety ‘Yannong 15’ (YN15). Genomic in situ hybridization (GISH), fluorescence in situ hybridization (FISH) and multicolor GISH (McGISH) analyses demonstrated that the three octoploid Trititrigia possess 42 wheat chromosomes and 14 Th. intermedium chromosomes. The 14 alien (Th. intermedium) chromosomes belong to a mixed genome consisting of J-, JS- and St-genome chromosomes rather than a single J, JS or St genome. Different types of chromosomal structural variation were also detected in the 1A, 6A, 6B, 2D and 7D chromosomes via FISH, McGISH and molecular marker analysis. The identity of the alien chromosomes and the variationes in the wheat chromosomes in the three Trititrigia octoploids were also different. Conclusions: The wheat-Th. intermedium partial amphiploids possess 14 alien chromosomes which belong to a mixed genome consisting of J-, JS- and St- chromosomes, and 42 wheat chromosomes with different structural variations. These accessions could be used as genetic resources in wheat breeding for the transfer of pest resistance genes from Th. intermedium to common wheat.

FURTHER EVIDENCE OF RESISTANCE IN BERBERIS VULGARIS TO RACE 15B OF PUCCINIA GRAMINIS f. sp. TRITICI

Plants of common barberry (Berberis vulgaris L.) were inoculated to determine their reaction to race 15B of wheat stem rust (Puccinia graminis Pers. f. sp. tritici Erikss. & Henn.). Only resistant-type infections occurred on plants inoculated with two pure cultures of race 15B-4 (Can.). Strong circumstantial evidence for the resistance of common barberry to race 15B was obtained from inoculations with sporidia from teliospores produced in the field. Sporidia from teliospores collected from the emmer wheat variety Vernal, which is selective for race 15B, produced only infections of a resistant type, and those from the common wheat variety Lee, also selective for 15B, caused both resistant and susceptible types of infections. Transfer of aeciospores to wheat from the susceptible type demonstrated that 15B was not present. Sporidia from teliospores on the varieties Reliance and Mentana, which are not selective for this race, caused infections of a susceptible type. Resistant-type and susceptible-type infections appeared when barberry leaves were infected with races 29 and 48A.

FREQUENCY OF MICRONUCLEI IN POLLEN QUARTETS OF COMMON WHEAT MONOSOMICS

The frequency with which 20 different monosomes of the common wheat variety, Chinese Spring, formed micronuclei in pollen quartets was determined. It was found that unless the study was made at an early developmental stage characterized by a distinct cell wall surrounding the quartets, the counts were unreliable, because some micronuclei were lost. The frequency of micronucleus formation was similar for anthers of a floret, florets of a spike, and plants of a monosome. Among the monosomes studied, there were three groups of three and four of two in which the total frequency of quartets with micronuclei, and the distribution of numbers of micronuclei per quartet, were strikingly similar. In the case of the groups of three, two monosomes were from the A and B genomes while one was from the D genome. This is interpreted as evidence of homoeology of chromosomes of a group and also that such chromosomes have undergone less change than those that do not form such series.