A male sterile mutant in Triticum aestivum

A FOSSATI and M. INGOLD

Federal Agricultural Research Station, Nyon, Switzerland

Genic male sterility has been reported in T. durum by BOZZINI and in T. aestivum by PUGSLEY and KRUPNOV. In these three cases, the first male sterile plants were observed in F₃ or F₄ of intervarietal crosses.

Seeds of the winter variety Probus were irradiated in 1966 with X-rays at a dosis of 24 kR and planted in the nursery. One ear of each M₁ plant was bagged, each ear giving a M₂ progeny. Among the 300 M₂ progenies, one segregated eight fertile to four sterile plants. The sterile plants were morphologically quite similar to the fertile ones but the florets remained broadly open at flowering. The anthers were typically thin and slightly curved. A microscopical examination showed only empty pollen grains. The sterile M₂ plants were discovered rather late at flowering and were therefore left open pollinated by the surrounding plants.

From each M₂ plant, a M₃ progeny was sown. These M₃ progenies segregated as follows:



The small number of progenies from M₂ fertile plants does not allow to check the ratio of segregating to not segregating progenies. Within the segregating progenies, the observed ratios fit a theoretical 3 : 1.

The segregation within progenies from M₂ sterile plants does not fit the 3 : 1 ratio. This can be explained as follows:

Going from the hypothesis of a single recessive gene for male sterility, the four M₂ sterile plants could have been pollinated by three types of plants:

1. normal fertile plants of neighbouring progenies

2. fertile plants of the same progeny homozygous for the dominant allele, like plants No. 1 to 4

3. fertile plants of the same progeny heterozygous for this allele like plants No. 5 to 8.

The cases 1and 2 will give only fertile M₃ plants while the case 3 will segregate 1 : 1. The observed ratios have to be considered as a mixture of these three possibilities.