Section 13 — Plant Genetics and Breeding 



thick culms, dark green color, dense spikes and 

 short awns, described as semibrachytic or 

 "uzu", possess a recessive gene that has a pleio- 

 tropic effect on the plant, shortening stature, 

 rachis internodes, and awns. One strain, C.I. 

 7439 from Korea, when compared with Mo. 

 B-475 at different fertility levels was less pro- 

 ductive, the higher grain yield of B-475 re- 

 sulting from more tillers and larger seeds. C.I. 

 7439 set more seeds per spike and had a straw/ 

 grain ratio of 1.46 vs. 1.88 for Mo. B-475. 



When C.I. 7439 was crossed with Mo. B-475, 

 the Fi was tall and had lax spikes and long awns 

 like B-475. The F2 segregated into three phenoty- 

 pic classes — tall, lax-spike, long-awns ; tall, dense- 

 spike long-awns ; short, dense-spike, short-awns— 

 with minor variations in height and spike density 

 within each class. Segregation was conditioned 

 by one major gene affecting spike density in 

 addition to the "uzu" gene. Effects of the spike 

 density and "uzu" genes on several plant 

 characters were measured by comparing sets 

 of partially isogenic lines derived from different 

 F2 plants. Plants with the recessive spike den- 

 sity gene had reduced plant height and seed size 

 in addition to the reduction in rachis internode 

 length. Plants with recessive "uzu" genes had 

 lower grain yields, reduced height, smaller 

 seed size, increased sterility, and later heading 

 date than "non-uzu" counterparts. In the "uzu" 

 types primary selection for high tiller capacity 

 and larger seed size will be needed to obtain 

 maximum yield. Superior winter hardiness was 

 observed in all three phenotypic classes. 



13.52. A Genetical Study of "Cold Test" Reaction in 

 Seed Corn. Shu Ting Chang (Hong Kong). 



The maize material involved in this investiga- 

 tion included inbred lines, single and double 

 hybrids, and open-pollinated progenies of 

 single hybrids, grown on the Wisconsin Univer- 

 sity farm at Madison in 1957 and 1958. Re- 

 presentative ears of each of these classes were 

 harvested at successive stages of maturity, the 

 moisture content of the kernels ranging from 

 60 to 18 per cent. In order to simulate preharvest 

 frosts as they might occur in the field conditions, 

 the ears were exposed to freezing treatments 

 of varying intensity and duration, under con- 

 trolled conditions in a specially equipped freezing 

 cabinet. 



The following conclusions can be drawn 

 from these studies: 



1. Significant differences between inbred lines 

 and between hybrids of which they are the 

 parents are shown to exist in respect to 



tolerance to freezing injury as well as to 

 pathogenic fungi attacking theerminating 

 seed. 



2. In general, hybrids are more tolerant to 

 frost injury effects on germination and to 

 attack by soil-borne seed-decaying patho- 

 gens than are their parental inbred lines. 



3. The ability of seed corn to resist damage 

 to germination by freezing treatments is 

 not necessarily correlated with inherent 

 resistance to attack by soil-borne seed- 

 decaying organisms. The tolerance of 

 hybrids to freezing injury was not as strong- 

 ly affected by the maternal parents as was 

 resistance to attack by soil-borne organisms 

 under "cold test" conditions. 



4. The effect of age on freezing seed viability 

 under "cold test" conditions is significantly 

 greater for inbred lines than for hybrids. 



1 3.53. Resistance to Low Temperatures in Connection 

 with the Stages of Organogenesis of the Ear 

 in Some Genotypes of Wheat. Misic Todor 

 (Novi Sad, Yugoslavia). 



The winter hardiness of six genotypes of wheat 

 in dependence on the stage of organogenesis 

 of the ear (21, 50, 58, 70, 91, 104 and 1 12 days 

 after emergence) has been examined in a field 

 test, conducted after the split plot method in 

 conditions with and without a snow cover, as 

 well as in a laboratory experiment. A regularity 

 was found to exist in the gradual increase in the 

 percentage of winter killing from the early 

 stages of organogenesis of the ear to the later 

 ones, which was particularly remarkable in 

 genotypes with low winter hardiness. The winter 

 killing resulted in a significant decrease in grain 

 and straw yields, 1000 kernel-weight and hecto- 

 liter weight of grain. This decrease is in accord 

 with the percentage of winter killing in depen- 

 dence on the stage of organogenesis of the ear 

 in a given genotype. 



13.54. Inheritance of Frost Resistance by Wheat. 



A. Popovic (Kragujevac, Yugoslavia). 



At the Plant Breeding Institute in Kragujevac 

 the frost resistance of 15 Fi, 7 F2 and 4 F3 

 hybrid combinations of wheat were studied. 

 The highest level of frost resistance was by hy- 

 brids which originated from steppe x steppe- 

 like varieties. The combination "Minhardi x 

 Bankuty 1201" had 100 per cent of survived 



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