I. RESEARCH NOTES

New cases of male - sterility and new restorer source in T. aestivum

E. OEHLER and M. INGOLD

Federal Agricultural Research Stations, Lausanne, Switzerland

During our studies in view of improving the resistance to disease in cultivated wheat, we have carried out, among others, two groups of crosses. One consists of a line of Triticum timopheevi ZHUK. crossed with four cultivars of T. aestivum HOST (Probus, Mont - Calme 245, Heine VII and Derenburger Silber) and the other, of an hexaploid line, obtained from a cross Aegilops ventricosa x T. timopheevi 2 (creator: SIMONET) crossed with the cultivars Probus, Heine VII and Cappelle. In each case T. aestivum was the pollinator.

F₁ plants are morphologically intermediate between parents, and their fertility is very low, as WIENHUES (1951) and SIMONET (1957) reported. We can ascertain the same thing for the majority (75 to 95%) of the F'₂ plants and for a large proportion (75%) of the F'₃ to F'₅ plants. The stamens remain indehiscent due to irregularities at the meiosis; Only a small number of ovules is able to develop. After one backcross with T. aestivum, we obtain one to two seeds per ear; with two to three successive backcrosses we got five to ten seeds per ear.

In this material, we could isolate from the F'₂ self-fertile plants, the stamens of which being partly or completely dehiscent and producing respectively 5 to 17 and 17 to 22 seeds per ear. We have thus obtained stable and fertile lines of the T. aestivum type.

The progeny of some F'₂ plants showed a different behaviour pattern. After 5 to 7 consecutive backcrosses, the stamens remained indehiscent. There are:

3 plants	T. timopheevi x Heine VII
1 plant	T. timopheevi x Derenburger Silber
1 plant	Aegtr. vent. Tim 2 x Heine VII
1 plant	Aegtr. vent. Tim 2 x Cappelle

In this material hand-pollinated with T. aestivum, the average fertility reaches 55% (18 seeds per ear) and can even arrive at 100% for certain ears. The same fertility is obtaind, when such plants flower freely side by side with T. aestivum plants, which are acting as pollinators. This case of stamens' indehiscence is thus different from that caused by cytological instability. It is a case of male-sterility comparable to those described by the American authors ( WILSON, Ross, SCHMIDT ) obtained from crosses T. timopheevi x Bison.

These different male-sterile forms were crossed with a series of T. aestivum from our own collection.

All F₁ issued of these crosses are male-sterile. On the contrary, crosses carried out with the French cultivar Frimepi* have all given completely fertile F₁ as well with the male-sterile obtained from Timopheevi as with those issued of Aegtr. vent- Tim 2.

While examining 20 F₂ progenies, we noticed a segregation between fertile and sterile plants. The proportion seems to be three fertile for one sterile, but these figures have still to be confirmed. Primepi can thus be considered as a restorer cultivar.

Crosses from male-sterile with self-fertile types obtained from the same material (timopheevi x aestivum) also give fertile plants. However, the F₁ is not homogenous. One finds fertile plants, other are sterile, and at last for a certain number only a part of the stamens are dehiscent. The F₁ behaviour can be partially determined by the fact that the self-fertile types used in the crosses are heterozygous for the restorer genes. The presence in F₁ of plants with partially dehiscent stamens indicates a more complex inheritance than the one of the Primepi restorer.

Table 1. Cultivars and strains of T. aestivum giving no restoration of male-fertility

Table 2. Fertility of F₁ (male-sterile x Primepi)