Abstract
Production of fully fertile F₁ hybrids using the Triticum
timopheevii (Zhuk.) Zhuk. cytoplasmic male-sterility system in common
wheat (I. aestivum L.) is difficult to achieve. Examination of
individual fertility restoring (Rf) genes in T. timopheevii cytoplasm
may provide the information needed to breed more suitable R-lines and
A-lines. Individual chromosomes of R113 were studied by developing
chromosome substitution lines for each of the 21 chromosomes of R113
from crosses to Chris monosomics. R113 chromosome substitution lines
(R-sub lines) were developed by selfing monosomic F1 plants. The 381
Fy R-sub lines were crossed to two A-lines, mst-Chris and mst-Era. A
total of 335 and 327 Fi progenies were evaluated for mst-Chris and
mst-Era crosses, respectively. The F₁ progenies having chromosomes
1A, 3A, and 6B of R113 produced a high level of fertility
(seed/spikelet) in bagged spikes and few or no male sterile plants.
Two Rf genes, probably Rf6 located on 3A and Rf1 on 1A of R113, had
weaker restoring effects than Rf4 on 6B. R-sub lines of chromosomes
2A and 6A produced more male sterile Fi plants and appeared to have
dominant fertility restoration inhibitor genes. R-sub lines of
chromosome 5D produced no male sterile F₁ plants in mst-Era crosses
suggesting that mst-Era has a fertility restoring factor on 5D which
is not present in mst-Chris. Male sterile F₁ plants were backcrossed
to their respective R-sub lines to develop a new set of A-lines.
Eight R-sub lines produced TCF1, BC₁F1, and BC2F1 progenies that were
male sterile in I. timopheevii cytoplasm. Eighteen male sterile
(timopheevii) R-sub lines were crossed to four single gene R-lines,
L11, L13, L19, and L22, to evaluate fertility restoration. Crosses of
single Rf gene R-lines to mst-Era produced more fertile progeny than
mst-Chris crosses. R-line L11 and L22 produced lowest and highest F1
fertility, respectively. R-sub lines 6A-07 and 7D-12 produced nearly
male sterile plants in I. timopheevii cytoplasm and high fertility in
crosses to single gene R-lines. Thus, partial or complete elimination
of the dominant inhibitors may be necessary to produce A-lines that
can be easily restored.