Section 13 — Plant Genetics and Breeding 



noted capability for land improvement can also 

 be correlated, under the climatical conditions 

 of our country, with the objectives of timber 

 production in this case. 



The existence of many black locust cultivares 

 may be possibly an evident increase of the 

 aesthetical task of this species in the crowded 

 centres, due to the great variation of their habitus, 

 to the colour of the flowers and the different 

 time of the blossom. At the same time, it appears 

 possible to choose and propagate as aesthetical 

 forms in cultivation, only these cultivares which 

 correspond with the other specified objectives. 

 So we have: Robinia Decaisneana and the hy- 

 bridogenous populations R. pseudacacia R. 

 neomexicana and R. pseudacacia R. viscosa. 



When we analyze the objectives of breed- 

 ing for each species of trees, we can see 

 that it is generally possible to correlate the 

 majority of the four objectives above, in order 

 to obtain more efficiency in the tree improve- 

 ment work. 



13.32. Some Important Characteristics of Autote- 

 traploids of Tree Species induced by Colchicine 

 Treatment. Sin-Kyu Hyun and Chung-Suk 

 Kim (Suwon, Korea). 



With a view to produce new germ plasm to be 

 used in tree breeding as well as to obtain triploid 

 forms which would result in vigorous growth 

 through hybridizing diploid with tetraploid, 

 induction of polyploidy has been conducted by 

 means of colchicine treatment for twenty-four 

 tree species. 



In total 9300 colchiploids were produced as 

 the result of treating seed or apical growing 

 point with colchicine and those are now 4-7 

 years old. 



The optimum colchicine dosage as evaluated 

 by the frequency of stable tetraploids was not 

 related to the optimum colchicine dosage as 

 evaluated by the frequency of abnormal seed- 

 lings. Apparently, the physiological condition 

 related to the development of tetraploid tissue 

 was of greater significance than the colchicine 

 dosage. 



Some important characteristics of induced 

 autotetraploids so far observed are as follows: 



1. In all induced tetraploids, the increased 

 stomata-size as well as the decreased stomata- 

 frequency which were observed at their seedling 

 age are maintaining up to the date (age of 7). 



2. The frequency of gigas pollen was much 

 higher in An plants than in the corresponding 

 In plants. 



3. The frequency of deformed pollen as well 

 as the pollen sterility were higher in An plants 

 than in the corresponding 2/; plants. 



4. In both Hisbiscus syriacus and Robinia 

 pseudoacacia the elongation of pollen-tube was 

 slower in An plants than in the corresponding 

 In plants as observed on artificial media 

 (with Robinia) as well as in the styles (with 

 Hisbiscus). 



5. The corolla of An plant was apparently 

 larger in Robinia pseudoacacia (Gigas type) 

 than in the corresponding 2n plants, but it 

 was not so with Hibiscus syriacus. 



6. The induced tetraploids of Robinia pseudo- 

 acacia were classified into four types as follows 

 according to the forms expressed by the grown 

 plants. 



(a) Gigas type 



(b) Spinless and pendulous type 



(c) Brush type 



(d) Dwarf type 



In the wild population of In Robinia pseu- 

 doacacia too, the similar four types of plant 

 form are recognizable. 



In order to elucidate the relations between the 

 forms occurring in the wild population of Ro- 

 binia pseudoacacia and the forms acquired by 

 chromosome doubling by colchicine treatment, 

 karyotypic analysis of those plants are now 

 progressing. 



13.33. Notes on Some Needle Characteristics of 

 Soft Pine Species and Hybrids. Howard B. 

 Kriebel (Wooster, U.S.A.). 



Needle characteristics of 6 species and 8 hy- 

 brids of soft pines were studied. Many of the 

 needles were replicated samples from trees 

 analyzed independently by other workers. 

 Other samples were taken from arboreta in 

 Ohio and Illinois, and from hybrids of controlled 

 pollinations made in Ohio. 



Needle characters studied included length, 

 relative cross-sectional area, margin, position 

 and number of rows of stomata, position of 

 resin canals, and number of resin canals. 



Needle cross-sectional area was intermediate 

 in hybrids P. monticola V griffithii and P. flexilis 

 griffithii, but not in other hybrids. The P. mon- 

 ticola x peuce hybrid was intermediate between 

 the two parent species in number of needle 

 serrulations on the inner edge. Needles of P. 

 flexilis James had from 2 to 4 rows of dorsal 

 stomata (in previous studies P. flexilis was re- 

 ported to have 2 rows). 



The following species and hybrids were found 



220 



