Section 13 — Plant Genetics and Breeding 



many generations before complete compatability 

 is achieved. Another addition of chromatin is a 

 duplication. Stern showed that duplication of 

 certain genes in Drosphila leads to the production 

 of a larger quantity of the substance normally 

 produced by that gene. Wallace and Vetukhiv 

 showed an advantage for heterozygous Drosphila 

 if there is a mechanism for maintaining hetero- 

 zygosity. Two alleles in a disease conditioning 

 allelomorphic series such as found by H. H. Flor 

 in flax and J. G. Moseman in barley may give 

 resistance to two or more races of a parasitic 

 organism. A priori reasoning leads one to 

 believe that a duplication of a specific locus offers 

 many possible means for improving a species. 

 In a self-pollinating organism, a true breeding 

 heterozygote might be possible. 



Detecting an irradiation-produced duplication 

 of a specific locus may be possible by genetic 

 techniques. The proposed method involves 

 irradiating crossed barley seeds and following the 

 pollen sterility of F1X1 and phenotypes of 

 F2X2 plants. The desired aberration, an unequal 

 reciprocal translocation between comparable 

 arms of homologous chromosomes should give 50 

 per cent pollen sterility. The progeny from such 

 plants can be studied for segregation. Alleles 

 showing partial dominance may express the 

 hybrid phenotype in the homozygous duplicated 

 condition. 



13.93. On Natural Periodical Change of Inbreeding 

 and Crossbreeding in Plants. J. P. Mirjuta 

 (Novosibirsk, U.S.S.R.). 



Many papers on selective fertilization have 

 appeared, in a number of which it is stated that 

 when applying a mixture of pollen from the 

 variety itself + other varieties of the same species, 

 the strain-population is mainly fertilized by its 

 own pollen, whilst deep inbred lines are to a 

 greater extent fertilized by pollen of the other 

 varieties. 



In our own experiments on corn and spinach, 

 we compared two pollen mixtures, viz. (1) 

 variety itself + other variety, and (2) plant 

 itself W + other variety. The strain-population 

 plants selected related pollen to a higher degree 

 from mixture (2) than from mixture (1). With 

 deep inbred lines the reverse is true. In addition 

 it was found for deep inbred lines that selection 

 for own line pollen is higher than selection for 

 own plant pollen but lower than selection for 

 initial variety pollen. 



This means that in not-inbred plants, pollen 

 selection is directed towards inbreeding (adap- 

 tation to natural inbreeding), whilst during the 



course of inbreeding a shift towards the opposite 

 takes place, because deep inbred plants select 

 unrelated pollen, that is they are directed 

 towards crossbreeding (adaptation to natural 

 crossbreeding). 



It should be noted that natural inbreeding is 

 widely spread even among such crosspollinators 

 as corn, spinach and hemp. Consequently, 

 deep inbred plants should be present in strain- 

 populations as the result of natural inbreeding. 

 We found that the corn variety contains 15 per 

 cent of plants at a level of inbreeding where 

 other variety pollen is favoured. 



1. Or brothers 



1 3.94. Some Biochemical and Physiological Properties 

 of Plant Reciprocal Hybrids. S. I. Issaev and 

 V. V. Vartapetyan (Moscow, U.S.S.R.). 



Numerous investigations on morphological, 

 physiological and biochemical properties of 

 reciprocal hybrids of woody plants (apple-tree) 

 as well as other plants (tomato) were carried on 

 since 1935 in I. V. Michurin Horticulture 

 Institute and since 1955 in Moscow State Uni- 

 versity, Chair of Genetics. 



The choice of the maternal plant often deter- 

 mines the difference in properties of the 

 hybrid generation derived from the same pair of 

 initial forms. 



Initial varieties influence more actively the 

 expression of properties of the hybrid generation, 

 when they are used in the initial pair as maternal 

 plant. 



Hence it was demonstrated, that crossing of 

 frostresistent (northern varieties) and frost- 

 sensitive (southern varieties) of apple-trees 

 produced more frost-resistant hybrid Fi, in the 

 case where the northern variety was used as 

 maternal plant. 



Content of sugar and vitamin C in fruits of 

 reciprocal tomato hybrids was higher in the case, 

 where the variety with high level of these sub- 

 stances was taken as maternal plant. The choice 

 of the maternal plant influenced also the degree of 

 heterosis. Heterosis of a certain property in- 

 creased, when the maternal plant of the pair 

 was characterized by the same property. 



Special experiments were carried out with 

 grafts and the reciprocal crosses on these. These 

 experiments showed that additional influence of 

 the maternal plant on the properties of the 

 progeny could be explained mainly by metabolic 

 action of plant plastic substances on the embryo, 

 which developed on this plant. 



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