Section 13 — Plant Genetics and Breeding 



13.71. Sex Variability of Grape Vine Hybrid Off- 

 springs. M. Neagu (Bucharest, Rumania). 



The development of characteristics and fea- 

 tures with interspecific vine hybrids was studied in 

 the experiment plot for genetics and selection of 

 the Genetics Chair, Agricultural College, Bucha- 

 rest. 



Sexual offsprings were used, obtained by cros- 

 sing the native with foreign varieties belonging 

 to different geographical and ecological groups 

 {Proles pontica and Proles occidentalis). Mother 

 varieties such as Negru moale, Cabernet Sauvi- 

 gnon, Pinot gris, Italian Riesling, St. Emilion, 

 Gordan and Aligote have normal hermaphro- 

 dite flowers. 



Sex differentiation of the offsprings studied so 

 far proved to be a developmental phenomenon, 

 subject to the heredity of genitors historically 

 formed during ontogenesis and phylogenesis on 

 the one hand, and to the environmental factors 

 on the other hand. The percentage of individuals 

 with hermaphrodite flowers and that of individ- 

 uals with female flowers deviates from the clas- 

 sical ratio 1:1. 



Each hybrid combination shows different 

 segregation ratios between individuals with her- 

 maphrodite flowers and individuals with func- 

 tional female flowers. Thus, the percentage of 

 individuals with hermaphrodite flowers is lower 

 (38.9 per cent) with the hybrid combination 

 Braghina ■ St. Emilion, while the same per- 

 centage is higher (63.6 per cent) with Braghina 

 and Pinot gris. 



Likewise, the mother variety influences these 

 ratios in different ways. The hermaphrodite per- 

 centage ranges between 53.5-53.7 when Negru 

 virtos is mother variety, while with the Braghina 

 combinations the percentage is highly superior, 

 ranging between 55.9 and 63.6. 



The combination Braghina x Aligote pro- 

 duced an individual with male flowers as well. 



The optimum growth conditions enables the 

 blossoming of a big number of plants during 

 the third and even during the second year after 

 seeding. That is very important both for the 

 grape vine selection and for rational selection of 

 genitors, in order to obtain a high percentage 

 of plants with normal hermaphrodite flowers. 



13.72. The Effect of Ceitain Chromosome II Genes 

 on Fruit Size in the Tomato. L. Butler (Oakville, 

 Canada). 



Chromosome 2 of the tomato contains the 

 loci of 26 known genes. It also has regions which 

 control fruit size. Two Fa's which were segregat- 

 ; ng for tall/dwarf, smooth/peach, round/pear, 



simple/compound inflorescence, green/suflava, 

 and green/diluta were grown. Individual fruit 

 weights, measurements, and locule numbers 

 were recorded for each plant. The mean fruit 

 weight per plant varied from 18 g to 196 g. 

 The order of the genes on the chromosome is 

 d,p sufdil o s. Analysis of these data showed that 

 peach and diluta had no effect on fruit size. 

 Dwarf, pear and compound reduced fruit size 

 by 7.0,18.5, and 7.7 g respectively. Suflava, 

 in spite of its reduced chlorophyll, increased 

 fruit size by 11.1 g. The decrease brought about 

 by dwarf and compound is not the result of 

 pleiotropy . The effect of the pear locus on fruit size 

 mediated by two factors: locule number and 

 fruit shape. All pear-shaped fruits have 2-4 lo- 

 cules as a result of either the dominant pleiotropic 

 effect of this locus, or of a closely-linked domi- 

 nant gene. In these crosses there is a linear re- 

 lationship between locule number and weight; 

 each locule adds 6.5 g to the weight of an indi- 

 vidual fruit. Pear shape also reduces weight be- 

 cause the same number of cells in the locule wall, 

 if arranged in a pear shape instead of a sphere, 

 decrease weight from 100 g to 80 g. The effect of 

 suflava is probably pleiotropic because diluta 

 and suflava are both mutants of Condine Red. 



13.73. Leaf-Shape Differences in the Tomato. 



J. A. Jenkins (Berkeley, U.S.A.). 



Four recessive (dwarf, potato, entire, trifoliate) 

 and three dominant (Lanceolate, Mouse ear, 

 Curl) genes in the tomato modify leaf shape. 

 None of these genes has a noticeable effect either 

 on the initiation of leaf primordia or on the 

 structure of epidermal or mesophyll layers. They 

 do, however, markedly alter the length-width 

 relationships of mature leaves. Moreover, in 

 comparison with the normal, which has odd- 

 pinnately compound leaves with large terminal 

 segments and three or more pairs of laterals, 

 each of the mutant phenotypes has fewer lateral 

 leaflets and frequently a more entire margin. 

 Most, if not all, of these genes have pleiotropic 

 effects. Among the progeny of hybrids produced 

 by crossing the mutant lines with each other, 

 two hybrid combinations (potato-entire and 

 potato-trifoliate) were similar to heterozygous 

 lanceolate in having entire leaves with an almost 

 complete absence of lateral leaflets. Thus, similar 

 phenotypes may be produced by different gene 

 combinations. Studies of morphological, anatom- 

 ical and biochemical differences between lines 

 that differ by single genes and by combinations 

 of these genes are in progress. 



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