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

Botes, Willem Cornelus (2001-04)

Thesis (MScAgric.)--University of Stellenbosch, 2001.

Thesis

ENGLISH ABSTRACT: In cross pollinated crops, recurrent selection is used to increase the frequency of desirable alleles by breaking up existing linkage blocks and forming new gene combinations. Despite promising results from numerous feasibility studies, recurrent selection is seldom routinely used in wheat. A major obstacle has been the inability to readily achieve random interbreeding of large numbers of selected plants. In China the Taigu genetic male sterility gene, Ms2, has however been used to establish a recurrent selection programme in which field grown 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 seeds of an alloplasmie common wheat with Triticum tauschii cytoplasm (Maan et al., 1984) and is located at 3 map units from the centromere on chromosome arm SAS (Maan et al., 1987). In a study done during 1999 at Welgevallen to determine the frequency of natural intererossing under field conditions, Ms3 showed incomplete penetrance and only about two thirds of the seed set on male sterile plants could be attributed to intercrossing. Ms3 has stable expression in 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 et al., 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, found in cross 9SK3 of a routine breeding programme, showed that a single locus was not the cause of the male sterility. Chromosome abnormalities and gene imbalances were probably to blame. The male sterility probably relates to a T.urartu addition chromosome in the pedigree of cross 9SK3. To facilitate the production of large numbers of hybrid progeny, a simple hydroponic system was developed in which male sterile tillers cut at the flowering stage can be pollinated and 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 pollen shedding male tillers. It was found that cut tillers could be maintained in the hydroponic system as long as certain precautions were met: (a) The tillers must be handled with care so as not to damage the flag leaf which must be maintained for as long as period possible. (b) The tillers have a nutrient requirement 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 the nutrient 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 the recurrent selection programme in 1998, a total of 1881 plants were tested for seedling resistance and 597 plants were selected for use as parents and source material for 1999. In total 158 male sterile and 188 male fertile ears were used in the hydroponic pollination and a 63.47% 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 in 1998. These, together with 44 selections from a pedigree programme, formed the male component for 1999. In total 9564 plants were tested for seedling resistance during 1999. A total of 3230 resistant seedling were selected and planted. Again male fertile plants from the previous season were field planted and selected. The selected plants were subjected to mixograph testing. A total of 448 male sterile and 1020 male fertile ears were used for hydroponic pollination. Approximately 12000 seeds were harvested, the seed set being around 75%. The 157 F2:96K109 field selected plants (1999) and 64 selections from a pedigree programme formed the male component for 2000. Seedling resistance testing during 2000 included a total of 6465 plants and 2832 were selected and planted. The hydroponic system was improved during 2000 with new, larger capacity containers being used which improved cross pollination. In total 878 male sterile tillers and 1016 male fertile tillers were cut 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 selected during 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 to determine the variation for resistance within the populations. Both populations showed high level 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 recurrent selection. Integration with an excisting pedigree selection programme is viable and requires little additional input. Some of the these results have already been published (Addendum D).

AFRIKAANSE OPSOMMING: Herhalende seleksie word by kruisbestuiwers aangewend om die frekwensie voordelige allele te verhoog deur die opbreek van bestaande koppelingsblokke en vorming van nuwe geen-kombinasies. Hoewel uitstekende resultate m.b.V.herhalende seleksie reeds by koring verkry is, is die roetine aanwending egter beperk weens die gebrek aan effektiewe kruisbestuiwing van groot getalle plante. In China is "Taigu" genetiese manlike steriliteit, Ms2, egter met sukses aangewend vir die vestiging van 'n herhalende seleksieprogram vir landverboude koring. Die manlik-vrugbare plante word vir die bestuiwing van geselekteerde manlik-steriele plante aangewend (Huang et al., 1988). Nog 'n dominante manlike steriliteitsgeen, Ms3, is ontdek na EMS behandeling van sade afkomstig vanaf 'n alloplasmiese gewone koring met 'n Triticum tauschii sitoplasma (Maan et al., 1984) en is gesetelop chromosoom 5AS, 3 kaarteenhede vanaf die sentromeer (Maan et al., 1987). 'n Ondersoek na die frekwensie natuurlike kruisbestuiwing onder landtoestande (Welgevallen, 1999) het getoon dat onvolledige penetrasie van Ms3 lei tot ongeveer 5% selfbestuiwing en dat slegs twee-derdes van die saadset aan kruisbestuiwing toegeskryf kon word. Ms3 word wel stabiel uitgedruk onder normale glashuistemperature tydens blom nl. 16 - 25°C, maar onder warmer landtoestande, 21 - 35°C, is uitdrukking onstabiel met laer penetrasie van die geen (Maan et al., 1984). Die benutbaarheid van Ms3 onder landtoestande was dus onbevredigend. Die ondersoek na die oorsprong en ligging van 'n onbekende, manlike steriliteitsgeen (95K3) wat ontdek is in 'n roetine teelprogram het daarop gedui dat 'n enkellokus waarskynlik me ter sprake is nie, maar eerder chromosoom-abnormaliteite en geenwanbalanse. Die manlike steriliteit kan verband hou met 'n T urartu addisie chromosoom in die stamboom van hierdie bron. Ten einde kruisbestuiwing van 'n groot aantal plante te bewerkstellig, is 'n eenvoudige bestuiwersisteem ontwikkel gegrond op waterkultuurkweking van afgeknipte manlik-steriele (Ms3ms3), are. Manlik-steriele en manlik-vrugbare are is tydens blom geknip. Die manliksteriele are se blommetjies is oopgeknip en toegelaat om deur die manlik-vrugbare are bestuif te word. Die bestuifde manlik-steriele are (Ms3ms3) is hierna vir ongeveer 8 weke gelaat vir saadvorming. Afgeknipte are kan baie suksesvol in voedingsmedium onderhou word mits sekere eenvoudige voorsorgmaatreëls getref word, naamlik: (a) Die are moet met sorg hanteer word en die vlagblaar moet so lank as moontlik behou word. Are moet weekliks teruggeknip word ten einde verstopping en agteruitgang van vaatweefsel teen te werk. Die oorspronklik- afgeknipte halm is dus belangrik. (b) Die are toon 'n definitiewe voedingsbehoefte en 'n 20% voedingsoplossing was die beste van die oplossings wat getoets is. Die voedingsoplossing moet verkieslik weekliks vervang word wanneer are teruggeknip word. Op die tydstip behoort die houers met 'n steriliseringsmiddel gewas te word vir die verwydering van enige moontlike swamgroei aan die houers se wande. (c) Jik was die beter steriliseringsmiddel en het teen 0.05% toediening goeie swaminhibering bewerkstellig. (d) Hormone is nie in die roetinetoepassing gebruik nie aangesien die voordeel hiervan nie die ekstra insette regverdig nie. Verskillende strategieë is aangewend vir die seleksie van manlike en vroulike plante. Met die aanvang van die herhalende seleksieprogram in 1998 is 'n totaal van 1881 plante getoets vir roesweerstand en 597 geselekteer as bronmateriaal vir 1999. In totaal is 158 manliksteriele en 188 manlik-vrugbare are gebruik in die bestuiwersisteem vir die verkryging van die 1999 vroulike komponent. 'n Totaal van 3410 sade is verkry met 'n 63.47% saadset. Tesame met 157 F2:96KI09 landgeselekteerde plante is 44 seleksies vanuit 'n stamboom seleksieprogram gebruik as manlike komponent in 1999. Gedurende 1999 is 9564 plante getoets vir roesweerstand en 3230 geselekteer en geplant. Weereens het landseleksie plaasgevind. Die 157 seleksies is onderwerp aan miksograaf-toetsing. Vierhonderd agt- en - veertig manlik-steriele en 1020 manlik-vrugbare are is gebruik in die bestuiwersisteem. Ongeveer 12138 sade is geoes, teen 'n 75% saadset. Gedurende 2000 is die sade asook 64 seleksies uit 'n stamboom seleksieprogram aangewend as die manlike komponent. Roestoetsing is weereens in 2000 uitgevoer en 6465 plante is geïnokuleer waaruit 2832 plante geselekteer en geplant is. Die bestuiwersisteem is aangepas vir die hantering van groter aantalle are tydens 2000 en in totaal is 878 manlik-steriele are en 'n 1016 manlik-vrugbare are gebruik vir kruisbestuiwing. Die saadset is verhoog na 81.7% en 25380 sade is verkry. Om die hoeveelheid variasie binne die populasie te bepaal, is miksograaftoetsing op die 1999 F2-populasie uitgevoer. Die data het aangetoon dat groot hoeveelhede genetiese variasie beskikbaar is binne die populasie. Roestoetsing van die 1999- en 2000-bestuiwerpopulasies is ook uitgevoer om 'n indikasie te verkry van die verspreiding van weerstand teen blaar- en starnroes. Die blaamoes het 'n relatief lae vlak van weerstand getoon (± 50%) terwyl die stamroesweerstand baie hoë vlakke gehandhaaf het. Ms3 kan dus gebruik word om in kombinasie met waterkultuurkweking van gesnyde halms, 'n herhalende seleksieprogram van stapel te stuur. Integrasie met 'n bestaande stamboom seleksieprogram is ook moontlik en sal relatief min addisionele insette vereis. 'n Gedeelte van die werk is reeds gepubliseer en word hierbyaangeheg as Aanhangsel D.

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