Introduction

The use of male sterility to facilitate recurrent selection (Male Sterile Facilitated Recurrent Selection "MSFRS") is a wheat breeding technique considered a source of male sterility, composite crosses and recurrent selection (^{Villaseñor et al., 2002a}). It is rarely used in autogamous species because naturally there is no male sterile germplasm allowing recombination and breeding with the same efficiency achieved in allogamous ones (^{Sorrells and Fritz, 1982}; ^{Bockelman and Sharp, 1986}). In order to obtain male sterile recombinant sources, wheat breeders have isolated mutants induced by recurrent irradiation or spontaneous mutations, which are mostly linked to deleterious effects, thus hardly ever fixed in the source populations (^{Ramage, 1979}), despite this limitation, several male sterile genotypes have been reported for population breeding, such as: Pugsley (^{Suneson, 1962}), Probus (^{Fossati e Ingold, 1970}), Cornerstone (^{Driscoll, 1977}), Taigu 1 (^{Liu et al., 1986}) and the LZ (^{Zhou et al., 2008}), among others, some of which have been mapped to locate the male sterility gene(s) (^{Daryl et al., 2002}).

There are few wheat MSFRS studies in Mexico, ^{Villaseñor et al. (2000b)} reported that controlling both parents improved grain yield (4.7% cycle), increased variability and proved to be more effective and practical than the traditional technique; ^{Solis et al. (2002)} evaluated MSFRS genetic gain for stripe rust resistance, after seven cycles of selection for yield, finding that resistance improvement was low because it was not the selection criterion, however, in advanced selection cycles, high yield and resistant genotypes were detected due to the high level of recombination.

^{Villaseñor et al. (2002a)} indicated that population breeding success depends largely on the sterility source, these authors used a chromosomal deficiency that segregated into different levels of male sterility, which limited 100% fertile inbred lines generation, consistent with ^{Thompson and Shantz (1978)} and ^{Driscoll (1977)}, thus, the ideal germplasm for MSFRS should be controlled by genetic effects, stable and not linked to deleterious effects (^{Ramage, 1979}); and controlled by a single dominant gene, enabling selection techniques for line generation (^{Villaseñor et al., 2002a}). Accordingly, this research aimed to describe the generation, isolation, segregation and phenotypic stability of a dominant male sterile gene in wheat (Triticum aestivum L.) called "Oly".

Materials and methods

Results

Plant spikes covered in greenhouse behaved as follows: spring-summer 2001, 57 fertile and 47 sterile; spring-summer 2002, 92 fertile and 106 sterile, and spring-summer 2003, 152 fertile and 141 sterile. Spikes were either 100% sterile or 100% fertile. Moreover, sterile plants progeny always segregated 1:1 for sterile: fertile and fertile plants progeny always segregated 100% fertile, proving that sterility is controlled by a single dominant gene.

The χ_i ² test is presented in Table 1 for fertile and sterile segregation, remarkably, the evaluation was performed in 31 rainfed contrasting conditions, if the National Test (ERTHT) average yield is considered an indicator (^{Villaseñor and Espitia, 2000a}), ranging from 1 715 kg ha^-1 (Terrenate 2011) to 8 087 kg ha^-1 (Juchitepec 2011), the altitude was also variable among sites, from 2 240 m (Chapingo) to 2 890 m (Juchitepec). In each planting, 153-968 spikes were covered from the same number of plants, and in the 31 sites, expected χ² exceeded experimental χ_i ², supporting 1:1 segregation (fertile: sterile). Spikes (plants) were always 100% fertile or sterile.

Table 1 Male sterile gene "Oly" segregation in various locations and tests from 2009 to 2012. 

*=kg ha^-1 de la media del experimento ERTHT; **= Ji- cuadrada calculada; *** = Ji- cuadrada de tablas. al 0.05 de probabilidad.

Table 2 shows the comparison between the 8 varieties and their reconversion to male sterility, where similarity among varieties was 80% to 100%, i.e. at worst, 8 out of10 descriptors showed similar reconversion. The deleterious effects are common in mutant wheat (^{Ramage, 1979}; ^{Zhou et al., 2008}) and with poor phenotypic expression, in our study, phenotypic description and over 7 000 plants evaluation indicate that the isolated dominant male sterile mutant, called "Oly" is not linked to deleterious effects, enabling its manipulation to create populations and practice MSFRS.

Table 2 Similarity among eight varieties and their fertile F₁ after fourth backcross based on 10 UPOV descriptors, Roque, Guanajuato. Fall- winter, 2011-2012.