Production and cytogenetics of hybrids of Triticum aestivum x Leymus innovatus

Genetic control of compatibility in crosses between wheat and its wild or cultivated relatives

In the recent years, the agricultural world has been progressing towards integrated crop protection, in the context of sustainable and reasoned agriculture to improve food security and quality, and to preserve the environment through reduced uses of water, pesticides, fungicides or fertilisers. For this purpose, one possible issue is to cross-elite varieties widely used in fields for crop productions with exotic or wild genetic resources in order to introduce new diversity for genes or alleles of agronomical interest to accelerate the development of new improved cultivars. However, crossing ability (or crossability) often depends on genetic background of the recipient varieties or of the donor, which hampers a larger use of wild resources in breeding programmes of many crops. In this review, we tried to provide a comprehensive summary of genetic factors controlling crossing ability between Triticeae species with a special focus on the crossability between wheat (Triticum aestivum L.) and rye (Secale cereale), which lead to the creation of Triticale (x Triticosecale Wittm.). We also discussed potential applications of newly identified genes or markers associated with crossability for accelerating wheat and Triticale improvement by application of modern genomics technologies in breeding programmes.

Chromosomal Behavior during Meiosis in the Progeny of Triticum timopheevii × Hexaploid Wild Oat

The meiotic behavior of pollen mother cells (PMCs) of the F2 and F3 progeny from Triticum timopheevii × hexaploid wild oat was investigated by cytological analysis and sequential C-banding-genomic in situ hybridization (GISH) in the present study. A cytological analysis showed that the chromosome numbers of the F2 and F3 progeny ranged from 28 to 41. A large number of univalents, lagging chromosomes, chromosome bridges and micronuclei were found at the metaphase I, anaphase I, anaphase II and tetrad stages in the F2 and F3 progeny. The averages of univalents were 3.50 and 2.73 per cell, and those of lagging chromosomes were 3.37 and 1.87 in the F2 and F3 progeny, respectively. The PMC meiotic indices of the F2 and F3 progeny were 12.22 and 20.34, respectively, indicating considerable genetic instability. A sequential C-banding-GISH analysis revealed that some chromosomes and fragments from the hexaploid wild oat were detected at metaphase I and anaphase I in the progeny, showing that the progeny were of true intergeneric hybrid origin. The alien chromosomes 6A, 7A, 3C and 2D were lost during transmission from F2 to F3. In addition, partial T. timopheevii chromosomes appeared in the form of univalents or lagging chromosomes, which might result from large genome differences between the parents, and the wild oat chromosome introgression interfered with the wheat homologues' normally pairing.

Genome composition, stability and fertility of hexaploid alloploids between Triticum turgidum var. carthlicum and Leymus racemosus

Hexaploid alloploids between the tetraploid wheat Triticum carthlicum and the perennial tetraploid Leymus racemosus were analysed for chromosome composition and cytogenetic stability. GISH analysis showed different lines to have from 11 to 16 Leymus chromosomes. The alloploids showed a relatively high frequency of univalents in meiotic metaphase and of aneuploid plants and hence they are not stable. The seedset is lower than in wheat, but high enough to secure a safe propagation and preservation. The alloploids are discussed in relation to widening the genetic variation of breadwheat and wheat breeding.

The cytogenetics of a Triticum turgidum x Psathyrostachys juncea hybrid and its backcross derivatives

Psathyrostachys juncea (2n = 2x = 14, NN), a source of barley yellow dwarf (BYDV) virus resistance with tolerance to drought and salinity, has been successfully hybridized in its autotetraploid form (2n = 4x = 28, NNNN) as the pollen parent to durum wheat (Triticum turgidum L.). The 2n = 4x = 28 (ABNN) F1 hybrid has a mean meiotic metaphase-I configuration of 20.29 univalents + 0.29 ring bivalents + 3.36 rod bivalents + 0.14 trivalents. Spike length, internode length, glume awn length and lemma awn length, as well as the general spike morphology of the F1 hybrid, are intermediate with those of the two parents. Pollinating the ABNN F1 hybrid has given backcross (BC)-I derivatives of an amphiploid (AABBNN) that expresses limited self-fertility. BC-2 derivatives have been obtained from these plants. Direct transfers of useful genes from Ps. juncea to wheat would require substantial genetic manipulation strategies. Both conventional and novel methodologies, which may complement each other, and so facilitate reaching an agricultural objective end point, are addressed.

Cytogenetical studies on the genus Oryza. XIV. Intergeneric hybridizations between tetraploid Oryza species and diploid Leersia species

Intergeneric hybrids involving Oryza punctata (2n = 48, BBCC) with Leersia tisseranti (2n = 24), O. punctata with L. perrieri (2n = 24), O. latifolia (2n = 48, CCDD) with L. tisseranti and O. latifolia with L. perrieri were produced at frequencies varying from 0.11% to 0.23% of the pollinated spikelets. Plant morphologies of the hybrids strongly resembled the tetraploid Oryza species. Five hybrids obtained from the four cross-combinations had the expected chromosome number of 2n = 36 (trihaploid) in the somatic cells. The average meiotic chromosome pairings per cell were 0.23II + 35.58I + 0.14(1)/2I (dividing univalent) for O. punctata x L. tisseranti; 0.11II + 35.51I + 0.22(1)/2I for O. punctata x L. perrieri; 0.17II + 35.63I + 0.11(1)/2I for O. latifolia x L. tisseranti; and 0.25II + 35.49I + 0.15(1)/2I for O. latifolia x L. perrieri. From these results, it seems that most of the bivalents observed at MI with a low frequency had originated from the autosyndetic association of the chromosomes of O. punctata or O. latifolia. The results described above suggest that there is no genomic relationship between the parental species in each cross combination.

A novel intergeneric hybrid in the Triticeae: Triticum aestivum x Psathyrost achys juncea

Two hybrid embryos of intergeneric origin between Triticum aestivum cv Fukuho (2n=6x=42, AABBDD) and Psathyrostachys juncea (2n=2x=14, NN) were successfully rescued. One hybrid plant had the expected chromosome number of 28 (ABDN), whereas the second plant had 35 chromosomes. The average meiotic chromosome pairing in the 35-chromosome hybrid was 21.87 univalents + 6.38 bivalents + 0.11 trivalents + 0.009 quadrivalents, which indicates that two copies of the N genome were present. Chromosome pairing in the 28-chromosome hybrid was low (1.35 bivalents), and pointed out the lack of homology between the wheat genomes and the P. juncea genome. These new hybrids showed some necrosis and chlorosis, which caused severe floral abortion in the plant that had 35 chromosomes. These problems became gradually less severe after 18 months.