Section 13 — Plant Genetics and Breeding 



different stages in the breeding system. Under 

 field conditions only 10-20 per cent of the total 

 flowers produced on a plant ultimately set pods, 

 and under controlled self-pollination this pod set 

 may be as low as 2-3 per cent. 



In some genotypes, damage to the papillae of 

 the stigma during pollination by insects or 

 mechanical means is necessary for pollen 

 germination and pollen tube development. In 

 such genotypes, foreign pollen appears to have 

 a developmental advantage over pollen from the 

 same plant. Unsatisfactory pollen tube devel- 

 opment causes the flower to absciss. 



When pollen tube growth is normal, the young 

 ovary develops until it reaches 20-22 mm in 

 length, but if fertilization is not effective, the 

 young ovary falls off at this stage. 



After self-pollination of some genotypes, up 

 to 80 per cent of the pods initially developed may 

 reach a length of 40 mm. Pod development then 

 stops and the ovules within these pods de- 

 generate. Occasionally a single ovule develops 

 normally, in which case, degeneration of the 

 other ovules occurs at a much later stage. 



Embryological studies show that this ovule 

 degeneration in Broad Bean resembles thesoma- 

 toplastic sterility in Medicago sativa as described 

 by Brink and Cooper. 



13.23. Effectiveness and Specificity of Ionizing 

 Radiations and Some Chemical Substances in 

 Inducing Mutations in Winter Wheat. 

 V.V. Khvostova, V. S. Mojaieva and N. S. 

 Aigaes (Moscow, U.S.S.R.). 



1. A comparison was made of the mutagenic 

 effect of gamma-rays in dosages of 10, 15 and 

 20 kr and of fast neutrons with energy 1-2 

 MeV in dosages of 350 rad (210 rad for neutrons 

 and 140 for gamma) and of 750 rad (425 rad for 

 neutrons and 286 for gamma) and ethylene imine 

 in concentrations of 0.01-0.04 per cent treating 

 air-dry seeds (at room temperature) of winter 

 wheat Triticum-Agropyrum hybrid- 186. 



2. Taking into account the largest number of 

 progenies segregating mutants in M 2 , the most 

 effective mutagene proved to be ethylene imine in 

 concentrations of 0.01 : 50.8 percent of progenies 

 segregated mutants; on the second place stood 

 fast neutrons in dosages of 740 rad, producing 

 36.5 per cent of progenies with mutants, on 

 the third place were gamma-rays in dosages of 

 10 kr: 6.2 per cent of progenies. 



3. The spectrum of the mutations, appearing 

 under the action of neutrons, gamma-rays and 

 ethylene imine proved to be different. The nar- 

 rowest spectrum was produced by the neutrons: 



a total number of 208 mutants showed 80 per 

 cent of erectoids, squareheads and speltoids. and 

 only 20 per cent other changes. Among 81 

 mutants, which appeared after gamma-ray 

 treatment, the number of other types of mutants 

 amounted to 33 per cent. After treatment with 

 ethylene imine there were found 100 mutants, 34 

 per cent belonging to the above mentioned three 

 types, 66 per cent various other forms. 



Thus, ethylene imine appeared to be the most 

 effective mutagene, producing at the same time 

 the most broad mutation spectrum. 



4. Under the action of these mutagenes, 

 valuable agricultural forms are produced: 

 resistant to lodging, to fungal diseases, and 

 highly productive. 



13.24. Mutation Research in Canary Grass. 



D. E. Bremer-Reinders (Wageningen, The 

 Netherlands). 



In studying the influence of chemical mutagens 

 and X-rays on the frequency and spectrum of 

 mutations in Phalaris canadensis (2w = 12) 

 comparable doses (seedling percentage surviving 

 treatment) were chosen. 



Irradiation with 15,000 r decreased the num- 

 ber of seeds per spike in the Mi -generation to 

 about 50 per cent of the control. A corres- 

 ponding dose of ethylene imine decreased the 

 Mi-fertility to about 36 per cent of the control, 

 while the corresponding E.M.S. treatment 

 decreased the fertility of Mi to about 15 per 

 cent of the control. 



Of 406 progenies tested after irradiation 

 (15,000 r) on an average 20 per cent contained 

 chlorophyll mutations. With ethylene imine this 

 was nearly 27 per cent in 78 progenies, while with 

 E.M.S. this amounted to nearly 30 per cent in 

 325 progenies. Related to the number of seed- 

 lings the percentage of chlorophyll mutants was 

 nearly 3 per cent with 15,000 r and 2.6 per cent 

 with ethylene imine, while it amounted to 7 per 

 cent with E.M.S. 



The spectrum of chlorophyll mutants, after 

 chemical treatment, had more common chloro- 

 phyll aberrants, while in the case of irradiation 

 with 15,000 r more of the rarer mutant chloro- 

 phyll types and other morphological seedling 

 mutants occurred. 



With 15,000 r and with E.M.S. there was a 

 correlation between the occurrence of chloro- 

 phyll mutants and major morphological mutant 

 types. In both cases (406 and 325 progenies 

 respectively) the chance that morphological 

 mutants will appear is more than twice as great 

 in M 2 -families with chlorophyll mutants than in 



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