Section 13 — Plant Genetics and Breeding 



13.87. Genetical Differences in the Sensitivity Against 

 2,4-D auxin-herbicide in Tissue Culture. Bela 

 Faludi (Budapest, Hungary). 



The effect of auxin-herbicide 2,4-D consists of 

 the induction of tumorous growth in the resting 

 meristematic cells in the stem of dicotyledonous 

 plants. In order to study the sensitivity against 

 the herbicide it is conducive to exclude the en- 

 vironmental non-genetical differences and the 

 morphological factors of uptake and transport as 

 well. For this purpose the tissue culture method 

 offers a good opportunity. The proof of varietal 

 differences apart from its theoretical signifi- 

 cance might form the basis of the selection de- 

 creasing the sensitivity of cultivated plants 

 against the herbicide. 



In tissue cultures of potato tubers (Solarium 

 tuberosum) we tested 12 varieties, and found 

 considerable differences in the extent and char- 

 acter of tumorous growth. 



We subjected five varieties of characteristic 

 behaviour to a detailed biometrical investiga- 

 tion to examine the extent of variance among the 

 varieties, among the individual plants within 

 the variety and to compare it with the variance 

 of the method applied. The investigated varieties 

 were the following in the order of their sensiti- 

 vity: Margit, Aquila, Ella, Delta, Gul Baba. The 

 extent of multiplication of the fresh weight of the 

 cultures amounted in two weeks time: 0.8; 

 1.0; 1.5; 1.6; 3.2. The variances in the F-value 

 were for varietal differences 1041, for intra- 

 varietal differences 70, and for differences be- 

 tween tissues of individual tubers 83 respectively. 

 On the basis of these data we may conclude 

 that differences among varieties are highly sig- 

 nificant concerning the exclusively genetically 

 determined resistance. The variance in the same 

 variety was not significant. These data indicate 

 that prospects for clone selection are not favour- 

 able. On the other hand the prospects of the 

 varietal selection are promising to obtain resist- 

 ant potato varieties against the 2,4- D herbicide. 



13.88. Some Vine Clones Resistant to Plasmopora. 



P. Coutinho (Lisboa, Portugal). 



The extent of damage caused by Plasmopora 

 viticola in most regions of Portugal is very im- 

 portant. 



This paper refers to attempts made since 1945 

 with regard to this subject. 



The adopted criterion of selection is described. 



At present we are studying 110 clones of F2 

 of interest on account of their resistance. 



There are another 18 clones already in an 



advanced stage (experimental field scale), 

 so far the most interesting being clone C.27, a 

 cross of "Jaen X Azal branco". 



Finally some of their productivity and quality 

 characteristics are mentioned. 



13.89. Mechanism of the Loss of Fusarium 

 Wilt Resistance in Hybrid Bananas. D. L. 



Richardson and D. J. Hutchison (La Lima, 

 Honduras). 



In the classical method of banana breeding a 

 Fusarium wilt susceptible triploid clone "Gros 

 Michel" is used as the female parent. The major- 

 ity of functional eggs produced by this clone are 

 triploid, resulting from a meiotic restitution of 

 the chromosome complement. Genes conferring 

 wilt resistance are introduced through the use 

 of wilt-resistant diploid male parents and the 

 resulting tetraploid hybrids are screened for 

 commercial usefulness. Many cases are now 

 recorded where resistant segregates have been 

 grown for years before giving rise to susceptible 

 sub-clones, but no satisfactory explanation of 

 this loss of resistance has been proposed. That 

 resistance genes are found in only a single dose 

 in these autotetraploids, presents a situation 

 where the somatic loss of chromosomal material 

 containing resistance genes could result in the 

 appearance of wilt susceptible sub-clones, 

 Cytological studies indicate that this explana- 

 tion is probably correct. 



13.90. Breeding of Tobacco for Resistance to Ordi- 

 nary Tobacco Mosaic (Marmur tabaci Holmes). 



Serapion J. Bayubay (Los Baflos, Philip- 

 pines.). 



Crosses between mosaic resistant varieties 

 Ambalema and Ky 52 (White Burley) and the 

 susceptible but otherwise desirable varieties 

 Marogui, Simmaba C, Vizcava and Romero 

 were made in the Central Expt. Station, Manila, 

 in March 1950. Including reciprocals, 16 cross 

 combinations were obtained. 



The F2 seeds and seeds of the parental plants 

 were planted in rows with the corresponding 

 parents planted beside each hybrid and were 

 inoculated with the mosaic disease by rubbing 

 mosaic infected leaves over the surface of each 

 of the three young top foliage of the plants. 

 Bagged F2 seeds from each line that had no mo- 

 saic were again planted in progeny rows the fol- 

 lowing season and F3 plants were evaluated for 

 their agronomic characters and degree of 



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