Section 13— Plant Genetics and Breeding 



13.74. A Novel Type of Gamete Elimination in 

 Tomatoes. Charles M. Rick (Davis, U.S.A.). 



Unusual segregations are encountered for genes 

 on chromosome 4 in certain mating combi- 

 nations, always involving var. Gondine Red 

 (GoR) as one parent and Pearson (Psn) or related 

 vars. as the other. Although normal recessive 

 F2 ratios are obtained in other combinations, 

 the proportion of mutants is 51 per cent for afl, 

 70 per cent for wi, and 77-81 per cent for wA 

 when entering the cross on the Psn chromosome 

 and 12 per cent for di, 10 per cent for e, and 

 0.6 per cent for ful when on the GoR chromo- 

 some. All Fi's have normal phenotype and are 

 cytologically normal in all respects. In a distorted 

 h'4 F2, all of 96 + segregants proved to be 

 heterozygous and 96 per cent of the F3 families 

 segregated in the same abnormal fashion. The 

 cause of the disturbance can be transmitted 

 equally well from either sex. The CoR factor is 

 inherited in the fashion of a single gene as 

 ascertained from 1 normal : 1 disturbed F2 

 segregations from the cross C0R/+ X wA (Psn). 

 CoR/Psn hybrids show considerable abortion 

 of pollen and ovules, although the extent to 

 which abortion is associated with disturbed 

 segregation is still not clear. The data discount 

 dominance reversal, cytoplasmic influence, and 

 zygotic elimination as causes of the disturbance, 

 render unlikely paramutation or other mutation- 

 al phenomena, and suggest gamete elimination 

 affecting both sexes. Although no model is 

 entirely compatible with all observations, the 

 best fit is provided by a gamete killer of comple- 

 mentary determination and with nearly complete 

 expression. Map distances from a killer with 

 100 per cent penetrance would be 9-12 for wA, 

 16 for ul, 29 for afl, 1 for fid, 32 for e, and 35 for 

 di. These spatial relations are in the right order 

 and roughly approximate map distances known 

 for fid, e and di. 



Research partly supported by grant GM 06209 

 of the U.S. Public Health Service. 



13.75. Spontaneous Origin of a Balanced Lethal 

 Condition in a Synthetic Oenothera Hybrid. 



H. T. Stinson (Ithaca, U.S.A.). 



The Fi hybrid between the complex heter- 

 ozygous circle of 14 angustissima strain of 

 Oenothera parviflora and the 7 paired Douthat 

 4b race of O. argillicola forms a circle of 14 

 chromosomes at meiosis. The hybrid has a half 

 lethal system; the a parviflora (cup) complex is 



transmitted through the egg only, whereas the 

 argillicola complex (a), being lethal-free, can be 

 transmitted by pollen and egg. Consequently, 

 the circle of 14 apa hybrid should yield equal 

 numbers of apa and aa plants on selfing. This 

 expected behavior has been observed in numer- 

 ous F 2 families, although an excess of apa segre- 

 gates is sometimes seen. In one pedigree history 

 in which apa individuals were continually 

 selfed, aa segregates failed to appear in the F3 

 through F 2 generations. Also, no aa segregates 

 appeared in progenies from the crosses F3, F4, 

 F5 apa $$ X argillicola get- The reciprocal 

 crosses (argillicola $$ X ocpa^), however, yiel- 

 ded only aa segregates. The a complex of the true 

 breeding apa hybrid is thus apparently no longer 

 transmitted through the egg. Substitution crosses 

 confirm that the aberrant behavior of the apa 

 hybrid resides in the a complex. In F 7 , the last 

 generation grown to date, seven aa segregates 

 were present among 806 offspring. Recipiocal 

 crosses revealed these aa segregates to be male 

 fertile but female sterile. This unexpected result 

 suggests that the failure of the a complex to be 

 transmitted through the egg is due to an egg 

 lethal (incompletely penetrant) rather than to 

 megaspore competition. 



13.76. Multiple Effect of Fertilization in Floral 

 Plants. I. M. Polyakov (U.S.S.R.). 



The widespread conception of fertilization 

 considers this process only as syngamy (double 

 fertilization in floral plants). Gamete combi- 

 nation is considered to be of random character 

 (with some exceptions). 



Physiological and biochemical aspect of 

 fertilization is regarded as one that has no 

 direct effect on formation and modification of 

 hereditary disposition of the progeny. According 

 to this conception fertilization is nothing but a 

 "bridge" that helps the germinal plasma to pass 

 from one progeny to another. 



There is a considerable number of facts now 

 showing that physiology of fertilization has a 

 direct effect on heredity, variability and vitability 

 of progeny. The main facts are connected with 

 finding the effect of polyfatherhood. This effect is 

 expressed both in general stimulating and some- 

 times specific modifying action on behalf of that 

 part of the pollen, which physiologically "par- 

 ticipates" in the process without participating in 

 double fertilization (in some cases the pollen 

 may belong to other species). This fact also 

 manifests itself in changing the character and 

 range of offspring variability when pollination 

 changing conditions are changed (especially 



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