Section 13 — Plant Genetics and Breeding 



families without chlorophyll mutants. In the case 

 of ethylene imine no correlation was found, 

 perhaps on account of the low number of proge- 

 nies tested (78). 



13.25. A Contribution to the Effect of Acute Gamma- 

 Radiation of Jonathan Apple Scions. P. D. 



Misic (Cacak, Yugoslavia). 



In order to improve Jonathan apple, besides 

 the method of hybridization, acute gamma-radia- 

 tion of dormant scions has been used. The 

 applied doses of gamma-rays, ranging from 

 1500 rep (1 hr 7 min) to 10,000 rep (7 hr 20 

 min), showed the different effects on scion sur- 

 vival, length of growth and changes of leaves and 

 shoots. 



There was no visible suppressing effect of the 

 lowest gamma dose (1500 rep) on scion survival. 

 The doses increasing from 3000 rep to the highest 

 one (10,000 rep), however, showed clear suppres- 

 sing effects (3000 and 4500 rep) or full lethal ones 

 (6000 and 10,000 rep). 



Total new growth per scion showed no statis- 

 tically significant difference between control and 

 1500 rep, but the reductions in growth were 

 significant among 1500, 3000 and 4500 rep 

 respectively. 



The induced changes such as disturbance of 

 ortostichy and appearance of rosette, pinnately- 

 serrate leaves, adventive shoots and bifurcation 

 of leaf veins became more frequent when the 

 dose increased. On the other hand, the per- 

 centages of induced dichotomy per total number 

 of shoots, leaf chlorosis and bifurcation of leaf 

 petiols were less frequent when the dose 

 increased. The doses of 1500 and 3000 rep, 

 however, produced rather high and approximate- 

 ly the same rates of induced dichotomy shoot 

 growth (19.5 and 19.4 per cent respectively) 

 per cm of total growth. 



To summarize: the lower acute gamma-radi- 

 ation doses applied (1500 rep in 1 hr 7 min and 

 3000 rep in 1 hr 13 min) showed more numerous 

 primary effects. 



13.26. Formation Process in Avena sativa provoked by 

 the Influence of Ionizing Radiation. G. M. Zak- 



harova and I. E. Gloushchenko (Moscow, 

 U.S.S.R.). 



It is known that under the influence of different 



factors which affect negatively the development 

 of plants (low temperatures, high doses of 

 ionizing radiation, some chemical compounds) 

 there occur plants in the oat, progeny (Avena 

 sativa) with characters of wild oats (Avena 

 fatua). The results obtained by us while studying 

 the formation process in oats show the same 

 phenomenon. 



The experimental work has been carried out 

 with two oat varieties: Pobeda (Victory) and 

 Dippe. They had white grains and awnless 

 spikes (or spikes with delicate awns). The dry 

 seeds of these varieties have been irradiated by 

 X-rays, the doses being 8000-13,000 r. Plants 

 obtained out of non-irradiated seeds have been 

 used as a control. 



Cytological and field investigations have 

 shown that the chosen doses of X-rays affect 

 negatively the development of cultured oats. 

 By the further studies of irradiated forms of prog- 

 eny it has been established that the variety Dippe 

 in X3 had 4.3 per cent of plants with wild oat 

 characters and 1.4 per cent of plants with the 

 characters of both oats and wild oats; in x 4 5.5 per 

 cent of plants with the characters of wild oats and 

 0.3 per cent of plants with oats and wild oats 

 characters. 



The Pobeda in X3 had 9.4 per cent of plants 

 with wild oat characters and 0.2 per cent of 

 plants with the characters of oats and wild 

 oats; in X4 32.7 per cent of plants with wild 

 oat characters and 0.6 per cent with oats and 

 wild oats characters. 



The newly-formed wild oat forms as a rule 

 are dwarfish and completely or partially sterile. 

 It should be noted that the plants with wild oat 

 characters had white spikes (maternal type). 

 It is important that the modified forms have 

 appeared only in X3 and in the progeny of the 

 plants which in Xi and X2 had coarse curved 

 awns. No wild oat forms have been noticed in 

 the control nor in the irradiated plant 

 progeny which had spikes with awns, no awns 

 or coarse awns. 



At present it has been established that ionizing 

 radiation disturbs physiological and biochemical 

 processes and this no doubt changes different 

 biological properties of the organism. To all 

 appearance x-rays in the dose of 8000-13,000 r 

 provoke such important changes in the metabo- 

 lism that awnless oat plants or plants with 

 delicate awns give forms with coarse curved 

 awns. The latter have labile heredity, a fact 

 demonstrated by the presence in the progeny of 

 such plants of great diversity. As a result of the 

 disturbance of physiological harmony there 

 appear in the progeny of irradiated oat plants 

 new specific forms with the characters of wild 

 oats. 



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