First-division restitution in hybrids of Langdon durum disomic substitution lines with rye and Aegilops squarrosa

Durum wheat ‘Langdon’(LDN) caused a high frequency of first‐division restitution (FDR) and partial fertility in hybrids with rye, Secale cereale L., and Aegilops squarrosa L. In order to determine the genetic control of FDR, a complete set of 14 Langdon durum D‐genome disomic substitution lines (LDNDS) was crossed with ‘Gazelle’ rye and one accession (RL5286) of A. squarrosa. The microsporogenesis and fertility of the hybrids were studied. The results showed that most of the hybrids expressed a high frequency of FDR and partial fertility. However, the hybrids of 2D(2A), 4D(4A), 5D(5B) and 6D(6B) crossed with both rye and A. squarrosa, as well as 1D(1A) with A. squarrosa, had either little or no FDR and were completely sterile. These hybrids had different types of first meiotic divisions compared with LDN control hybrids. The hybrids with 2D(2A), 4D(4A) and 6D(6B) had a high frequency of random segregation of chromosomes at the first division. The hybrids with 5D(5B), as expected, showed high homoeologous pairing. The hybrid of 1D(1A) with A. squarrosa had a high frequency of equational division at first division. These results suggest that the reduced or absent FDR in such hybrids might be related to the substitution of chromosomes with an FDR gene and poor compensation ability of the D‐genome chromosomes for their homoeologous A‐ or B‐ genome chromosomes. Cytological analysis suggested that chromosome 4A in LDN most likely carries a gene for high frequency of FDR in hybrids. In addition, some monads were observed at the end of meiosis in the hybrids of 3D(3A) and 6D(6A) crossed with rye. They were formed from FDR cells that failed to divide at second division, suggesting that the LDN 3A and 6A chromosomes might carry genes for normal second division of FDR cells in the rye crosses.