Section 13 — Plant Genetics and Breeding 



or hypoxanthine (2), and cystine methionine or 

 thiosulfate (1 out of 2) proved to be of decreased 

 pathogenicity. 



In the latter organism, restoration of patho- 

 genicity by supplementing infected tissue with 

 the nutrient required was observed in one of 

 adenineless strains and a close correlation be- 

 tween the nutritional characters and the loss of 

 pathogenicity was confirmed, though trials with 

 the other adenineless and the two phenylalanine- 

 less mutants have been unsuccessful, suggesting 

 other mutations for decreased pathogenicity 

 operating in these strains. 



Experiments are under way to induce rever- 

 tants with respect to the nutritional deficiency 

 and observe whether they restore the pathogeni- 

 city. 



13.101. Initial and Adaptive Tolerance of Ustilago 

 scitaminea and U. maydis on Various Concen- 

 trations of Sodium Arsenate. Elisa Hirsch- 

 horn (Llavallol, Argentina). 



102 monosporidial cultures of U. scitaminea 

 and 70 of U. maydis, from different origins, 

 were tested in various concentrations of sodium 

 arsenate, in order to determine the limits of ini- 

 tial tolerance and the limits of adaptability to 

 increased concentrations. 



U. scintaminea. The initial tolerance ranged 

 from 1.1 to 3.5 mg/ml. The following results 

 are obtained for initial tolerance and adaptive 

 tolerance (number of strains between brackets). 

 1.1-H.l (15, no adaptation); up to 2.2->3.0-4.8 

 (62); up to 1.75-M-8 (16); up to 3.5^7.0-8.0 

 (9). Adaptation was transitory, as found after 

 4-7 retransfers on arsenate-free medium. Te- 

 trad analysis showed for initial tolerance (toler- 

 ance: no tolerance) : 4 and 2 : 2. The 

 acquired tolerance, however, was not transmitted 

 sexually. 



U. maydis. Initial tolerance ranged from 

 4.0 to 10.0 mg/ml. All 70 strains first adopted 

 to 20.0 and then 59 strains to 50.0 and 11 strains 

 to 65.0. Transitory adaptation was found in 60 

 strains, though only after 20-25 retransfers on 

 arsenate-free medium. However, 6 strains which 

 adapted to 65.0, did not loose adaptation during 

 4 years. 



Tetrad analysis showed for initial tolerance 

 (tolerance: no tolerance) 4 : 0, 2 : 2, 3 : 1 and 

 1:3. Sexual transmission of acquired tolerance 

 was found in 2 strains (adapted to 20.0 mg/ml), 

 with tetrads (tolerance: no tolerance) : 4, 

 2 : 2, 3 : 1 and 1 : 3. The nature of adaptability 

 is considered. 



13.102. (D.) Changing of Tomato Heredity under the 

 Influence of Light and Low Temperatures. 

 L. Rastunkova and R. Glavinich (Moscow, 

 U.S.S.R.). 



Under the simultaneous influence of light and 

 low temperatures we have succeeded in changing 

 the heredity of the late Moscow region tomato 

 variety No. 7, created by R. Glavinich by means 

 of vegetative hybridization, as well as of the 

 middle variety The Best. The two varieties 

 have round red tasty fruit, but in Moscow condi- 

 tions often give many green fruit. The tempera- 

 tures of the experiment have been + 2 and — 5 and 

 the day length 10 hours. The germinated seeds 

 have been kept in low temperature conditions 

 for the time from 6 to 10 days. 



The influence of light and low temperatures 

 on the tomato plants of these varieties decreased 

 the vegetative period of the experimental plants 

 as compared to the control plants as well as to 

 the plants of the standard variety Gruntovoj 

 Gribovskij. Beside that, the experimental plants 

 had different fruit size to compare with the control 

 ones. The experimental fruits have become smaller 

 but more numerous. Some of the experimental 

 plants had changed colour of the fruit, as well as 

 their form. They were elongated and of crimson 

 colour. 



All these acquired characters have been in- 

 herited by the second and the third generations 

 and some of the plants of No. 7 and The Best 

 varieties can be used as good seed material. 



13.103. Ionizing Radiation in the Evaluation of the 

 Genetica! Constitution of Some Characteristics 

 in Plants. A. Tavcar (Zagreb, Yugoslavia). 



1. From genus hybrid (Triticum aestivum x 

 Secale cereale) > Triticum aestivum a homozy- 

 gous Tr. aestivum (2« = 42 chromosomes with 

 hairless upper internodium of the stem was se- 

 lected. In R2 gen. from seed irradiated with 5000 

 to 7500 r of gamma-rays, some speltoids with 

 hairy upper internodium, similar to the male par- 

 ent Secale cereale, have developed. During 8 

 generations of nonirradiated seed only Tr. 

 aestivum of hairless upper stem were observed. 



2. In (Vicia Faba maior x V. F. minor) 

 homozygous V. F. maior and V. F. minor plants 

 were selected. Some of their seeds were irradiated 

 with gamma-rays. From their V. F. maior seed 

 also some V. F. minor and from their V. F. minor 

 some V. F. maior mutants were selected. From 

 seeds of the parents used for hybridization after 

 irradiation no changes from V. F. maior to 

 V. F. minor or vice versa were observed. 



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