Twenty-Five Years of Male-Sterile Facilitated Recurrent Selection in Barley

Using a phenotypic marker-assisted system developed by Falk and Kasha (1982), a Male-Sterile Facilitated Recurrent Selection (MSFRS) program was initiated at the Agriculture and Agri-Food Canada research facility in Brandon, Manitoba, in 1980. The purpose was to develop germplasm that would accumulate additive genetic effects for beneficial traits, including (horizontal) disease resistance and improved grain and biomass yield. After 25 cycles of recurrent selection, involving multiple genotypes from global sources, 4 populations have been developed demonstrating improved levels of disease resistance, to multiple pathogens that are prevalent in the Northern Great Plains, when compared to conventionally bred genotypes. As well, one six-row forage cultivar has been developed, with high biomass production and grazing tolerance, as well as several elite lines showing promise as future forage cultivars. Several hulless lines have also been produced showing markedly reduced levels of deoxynivalenol (DON) mycotoxin, incited by the pathogen Fusarium graminearum. The MSFRS program is a low-cost approach to long-term germplasm enhancement that can be applied to direct development of forage barley as well as parental lines demonstrating multiple disease resistance in a single background.

Introduction

In the late 1960’s, a number of researchers around the world began to investigate the possibility of introgressing numerous traits in barley using naturally occurring genic male sterility from several sources. Under certain conditions, barley could be made to out-cross in the field in a manner similar to that of rye (Secale cereale L.). Hockett and Eslick (1970) observed that enough out-crossing could take place, in barley, to provide for a useful tool in developing Composite Cross populations for use in germplasm improvement and, possibly, direct cultivar development. This approach would be advantageous over conventional crossing by virtue of being able to generate potentially large quantities of hybrid seed, under the right conditions, without much labour input and allow for relatively rapid production of multi-way crosses. In North America, multi-way crosses, for agronomically useful traits, were successfully produced, in the form of Male-Sterile-Derived Composite Cross populations (Ahokas and Hockett, 1981). To ensure that hybrid seed could be easily identified, the male-sterility genes were linked to visual genetic markers, including orange lemma and shrunken endosperm characters (Falk and Kasha, 1982). These developments allowed for practical recurrent selection breeding in the field.

Materials and Methods

In 1980, hybrid seed was obtained from Dr. E.F. Hockett, Montana State University that was produced from a long-standing (20 yr) composite cross population (CC XXXIII) containing the msg6 male sterile gene. At the same time, elite germplasm containing the male-sterile msg6, and the linked genes for orange lemma (o) and shrunken endosperm (sex), were obtained from Dr. D.E. Falk, Guelph University. Controlled crosses were made in the greenhouse in 1980 and 1981 involving male-sterile and male fertile plants between both the CC XXXIII and marker populations. Marker-tagged male sterile progeny, from this initial cross, were then crossed to 102 elite barley lines varying widely in genetic background and agronomic performance. Each set of crosses was maintained separately, in isolation from other barley, in the field and allowed to hybridize freely over 3 successive seasons, from 1982 to 1984. This initial work was conducted by Dr. R.B. Irvine, who preceded the author as breeder at the Brandon Research Centre.

From 1985 to 1990, elite lines were introduced to each successful field population with the aim of increasing the level of hybrid seed production in the field and reducing the incident of ergot (Claviceps purpurea). Initial hybrid seed set was <1% and incidence of ergot exceeded 10% of all male sterile spikes. By 1990, hybrid seed set was > 5%, on average, and ergot infection was approximately 1% of male sterile spikes. Of the original 102 populations, only four populations were selected that could consistently produce a relatively high level of hybrid seed and acceptably low levels of ergot infection, in an agronomically acceptable background.

Commencing in 1991, cultivars and elite lines were used as recurrent male parents in a MSFRS program using each of the four marker-assisted male sterile populations. After 4 cycles of recurrent selection, male fertile offspring were then placed in head row selection nurseries and selected on phenotype and then evaluated as lines in replicated field trials. During recurrent selection, offspring were subjected natural field pathogens which exerted moderate selection pressure for resistance to multiple pathogens in an environment favouring the development of multiple pathogens. The local environment also favoured selection against lodging in most years.

Results and Discussion

It was noted, since early in the production of lines from the MSFRS populations, that the material tended to be late, seed production tended to be sub-standard, but an abundance in biomass. This lent itself to development of forage type barley for use mainly in silage. Our program also produced forage lines from conventional crosses, in parallel. We then evaluated performance of MSFRS forage lines against conventionally bred lines to determine what advantages, if any, the MSFRS approach would have over the (more labour-intensive) conventional ear-to-row pedigree method.

We first examined level of disease resistance of at least 500 lines from each of the two breeding methods, for resistance to a number of diseases. Table 1 compares the standard (Std) population vs. the Male-Sterile Derived (MSD) population for general leaf diseases in the field (LeafDis), Net Blotch (Nblot) and Spot Blotch (Sblot) in disease nurseries, Fusarium Head Blight (FHB), and the associated mycotoxin deoxynivalenol (DON), in the FHB nursery, Common Root Rot (CRR) in a field nursery, as well as two races of Net Blotch (Net857 and Net858), one race of Scald (Scld1493), and QCCJ Stem Rust (Stemrst), from laboratory inoculation.

Table 1.


Results show that, except for Scald, the MSD population consistently had lower disease incidence scores than Std populations selected in the same environments. In the case of FHB, several hulless selections demonstrated very low DON levels that may be released as cultivars in the near future (data not shown), based on their DON levels and overall agronomic performance. Thus, breeding for disease resistance using MSFRS can be advantageous over conventional approaches for some major diseases in barley.

The second advantage for MSFRS is in the development of high biomass forage barley. Figure 1 compares yield gain, vs. the check variety Virden, of conventional vs. MSFRS barley lines over 14 years of testing. By 2004, conventionally bred forage lines produced a yield advantage, over Virden, of approx. 8%, whereas the MSFRS lines averaged a 25% yield gain. This dramatic improvement in yield is off-set by susceptibility to lodging that is generally severe. However, each population has produced a few lines with good to excellent resistance to lodging. One of these lines, tested as FB006, is slated to be released as a cultivar in 2005. FB006 has an average 12.5% yield advantage over Virden with improved forage quality. Several other selections show equal or greater promise.


Figure 1. Comparison of mean annual yield gain - conventional vs MSFRS - in 6R barley (Bdn).

In conclusion, MSFRS is a very useful breeding tool for long-term germplasm development where multiple disease resistance is desired and direct production of high-yielding forage cultivars is a goal of the breeding effort.

References

Ahokas, H., and Hockett, E.F. (1981). Performance tests of cytoplasmic male-sterile barley at two different latitudes. Crop Sci. 21(4): 607-611.
Falk, D.E. and K.J. Kasha. (1982). Registration of a shrunken endosperm, male-sterile germplasm to facilitate hybridization in barley.
Hockett, E.F. and Eslick, R.F. (1970). Natural outcrossing on genetic male sterile barley. Crop Sci. 10(2): 152-154.

Mario C. Therrien
AAFC Brandon Research Centre, Box 1000A, RR#3, Brandon, MB Canada R7A 5Y3

Presented at the 18th North American Barley Researchers Workshop, July 17-20, 2005