Gebruik van genetiese manlike steriliteit in herhalende seleksie met koring (Triticum aestivum)

[摘要] ENGLISH ABSTRACT:In cross pollinated crops, recurrent selection is used to increase the frequency of desirablealleles by breaking up existing linkage blocks and forming new gene combinations. Despitepromising results from numerous feasibility studies, recurrent selection is seldom routinelyused in wheat. A major obstacle has been the inability to readily achieve randominterbreeding of large numbers of selected plants. In China the Taigu genetic male sterilitygene, Ms2, has however been used to establish a recurrent selection programme in which fieldgrown male sterile plants were pollinated by selected male fertile plants (Huang et al., 1988).Another dominant gene for male sterility, Ms3, was found after EMS treatment of the seedsof an alloplasmie common wheat with Triticum tauschii cytoplasm (Maan et al., 1984) and islocated at 3 map units from the centromere on chromosome arm SAS (Maan et al., 1987). Ina study done during 1999 at Welgevallen to determine the frequency of natural intererossingunder field conditions, Ms3 showed incomplete penetrance and only about two thirds of theseed set on male sterile plants could be attributed to intercrossing. Ms3 has stable expressionin plants grown within the normal range of greenhouse temperatures for wheat, 16 - 2SoC.Under warmer field conditions, 21 - 3SoC, its penetrance is, however, incomplete (Maan etal., 1984). The utility of Ms3 under field conditions is therefore unsatisfactory.An attempt to determine the location and origin of an unknown male sterility gene, foundin cross 9SK3 of a routine breeding programme, showed that a single locus was not the causeof the male sterility. Chromosome abnormalities and gene imbalances were probably toblame. The male sterility probably relates to a T.urartu addition chromosome in the pedigreeof cross 9SK3.To facilitate the production of large numbers of hybrid progeny, a simple hydroponicsystem was developed in which male sterile tillers cut at the flowering stage can be pollinatedand maintained for about 8 weeks, long enough to produce viable seeds. For pollination,florets on male tillers are cut open and placed in a container with a similar number of pollenshedding male tillers.It was found that cut tillers could be maintained in the hydroponic system as long as certainprecautions were met: (a) The tillers must be handled with care so as not to damage the flagleaf which must be maintained for as long as period possible. (b) The tillers have a nutrientrequirement and a 20% solution showed the best results of the nutrient solutions tested. (c)The sterilizing effect of Jik at O.OS%gave excellent fungal control en helped to sustain thenutrient solution. (d) Although the treatment of tillers with hormones improved seed quality,it was not justified by the additional inputs required.Different selection strategies were used for male and female plants. At the onset of therecurrent selection programme in 1998, a total of 1881 plants were tested for seedlingresistance and 597 plants were selected for use as parents and source material for 1999. Intotal 158 male sterile and 188 male fertile ears were used in the hydroponic pollination and a63.47% seed set was obtained, resulting in 3410 seeds, forming the 1999 female component.One hundred and fifty seven F2:96K109plants were selected from a field grown population in1998. These, together with 44 selections from a pedigree programme, formed the malecomponent for 1999. In total 9564 plants were tested for seedling resistance during 1999. Atotal of 3230 resistant seedling were selected and planted. Again male fertile plants from theprevious season were field planted and selected. The selected plants were subjected tomixograph testing. A total of 448 male sterile and 1020 male fertile ears were used forhydroponic pollination. Approximately 12000 seeds were harvested, the seed set beingaround 75%. The 157 F2:96K109 field selected plants (1999) and 64 selections from apedigree programme formed the male component for 2000. Seedling resistance testing during2000 included a total of 6465 plants and 2832 were selected and planted. The hydroponicsystem was improved during 2000 with new, larger capacity containers being used whichimproved cross pollination. In total 878 male sterile tillers and 1016 male fertile tillers werecut and intercrossed. In total 25380 seeds were harvested, the seed set being 81.7%.In an attempt to determine the amount of variation within the 157 F2-families selectedduring 1999, mixograph testing was performed. The data showed variation among families.Seedling resistance testing for leaf and stem rust was performed on the 1999 and 2000 FIs todetermine the variation for resistance within the populations. Both populations showed highlevel of stem rust resistance but lower levels of leaf rust resistance (± 50%).Ms3 can thus be used in combination with hydroponic tiller culture to facilitate recurrentselection. Integration with an excisting pedigree selection programme is viable and requireslittle additional input. Some of the these results have already been published (Addendum D).

[发布机构] Stellenbosch University