Section 13 — Plant Genetics and Breeding 



many plants were found not possessing the 

 euploid chromosome number. While in diploids 

 loss of a chromosome seems to be lethal many 

 polyploid plants with off-numbers will survive. 

 But gain or loss of one or more chromosomes or 

 even the presence of a fragment apparently 

 disturbs plant development thus making these 

 plants unsuitable to grow as commercial crop 

 plants. 



In autotetraploid barley (4.v =•- 28) euploid 

 plants produced progenies with 38-57 per cent 

 euploid plants only. Among poor seeds aneu- 

 ploids were much more frequent than among 

 well-developed ones. Aneuploid plants showed 

 great variation in morphological appearance 

 ranging from very poor to almost normal growth. 

 Fertility of aneuploids was much more reduced 

 than fertility of euploids. 



In populations of autotetraploid sugarbeets 

 (4.v = 36) aneuploidy occurred in about 42-44 

 per cent of all plants investigated. Growth of 

 leaves and roots varied from very poor to almost 

 normal. Weight of aneuploid roots seldom 

 reached that of euploid ones. 



In some strains of wheat-rye hybrids 

 (6x = 42) aneuploids were present but in lesser 

 number. 



The occurrence of aneuploidy in autotetrap- 

 loids of homozygous and heterozygous plants as 

 well as in newly established amphipolyploids 

 enlightens the fact that production and/or 

 survival of off-number gametes and zygotes 

 must be primarily conditioned by induction of 

 polyploidy. Their presence necessarily leads to 

 reduce fertility in polyploids. In addition the 

 number of aneuploids in a plant progeny ap- 

 parently is depending upon the genotype used 

 and upon environmental conditions. 



fertility can be related to the frequency differen- 

 ces of aneuploids. In 1962 aneuploid plants had 

 a reduction in fertility of appr. 18 per cent, as 

 compared to euploids. The fertility of the euploid 

 plants of the most thoroughly examined tetra- 

 ploid population had a fertility which was only 

 3.3 per cent below that of the corresponding 

 diploid population. 



Meiosis has been studied in euploid plants 

 belonging to populations which differ in fer- 

 tility and frequency of aneuploids. In this con- 

 nection the types of diakinese configurations, 

 frequencies of bivalents and multivalent chro- 

 mosome associations, co-orientation of chromo- 

 somes at first metaphase and chromosome dis- 

 tribution at first anaphase have been studied. 

 The mechanism leading to differences in the 

 frequency of aneuploids will be discussed. 



13.17. Different Fertility of Mitotic and Meiotic 

 produced 4x-Forms in Primula malacoides 

 Franch. Kurt Skiebe (Quedlinburg/Ffarz., 

 Germany). 



The fertility of Primula malacoides was stu- 

 died, both generated by colchicine induction 

 and 2 x x hybridization. Plants within the 

 types were crossed exclusively. Comparison is 

 made from Ci to Cs. The fertility of the meiotic 

 produced 4x forms exceeds significantly the 

 mitotic originated ones. Therefore in future 4x 

 forms from unreduced gametes only should be 

 used in polyploid breeding. 



13.16. The Relation between Fertility and Cyto- 

 logical Properties in Autotetraploid Rye. 



Knut Aastveit (Vollebekk, Norway). 



Twelve years ago six autotetraploid popula- 

 tions of winter rye were produced by colchicin 

 treatment. The original tetraploid populations 

 have since been kept isolated. At the same time 

 new populations have been established by inter- 

 crossing and selection. In 1960, 1961 and 1962 a 

 number of populations were compared in respect 

 to fertility (seed set). Highly significant differen- 

 ces were found in several cases. It is concluded 

 that the fertility of autotetraploid rye is a heritable 

 character, which can be influenced by selection. 



Populations differing significantly in fertility 

 are now under cytological investigation. As far 

 as our results go, the population differences in 



13.18. Study of Pollen and Pollination in Rela- 

 tion to Partial Sterility of Autotetraploid 

 Rice. J. Bouharmont (Louvain, Belgium). 



In autotetraploid rice, there is no correlation 

 between the rate of meiotic irregularity and the 

 level of sterility, but a number of factors take 

 part in the reduction of seed setting. An 

 important one is the relatively lower quantity of 

 good pollen shed on the stigmata. We have to 

 consider the quantity and the quality of the pol- 

 len produced in the anthers, the abundance of 

 pollination and the pollen germination. 



After chromosome doubling, the number of 

 stainable pollen grains per spikelet is reduced by 

 about 30 per cent: the number of PMC's is 

 lowered (18 per cent) and some microspores 

 fail during their maturation (12 per cent). The 

 diploid pollen grains are larger than the haploid 

 ones (20 per cent) and their size is more variable: 



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