Section 13 — Plant Genetics and Breeding 



can be stated, however, that in general, those 

 analogs showing toxicity to insects also are 

 toxic to barley, although there are exceptions 

 to this rule. 



13.57. Outlines of the Cacao Selection and Breeding 

 Programme in San Thome. J. C. Ascenso 

 (Lisbon, Portugal). 



The cacao breeding programme in San Thome 

 includes single plant selection in the local popu- 

 lation, introduction of hybrid seed and selected 

 parents and hybridization work utilizing clones 

 selected locally and abroad. 



13.58. (D.), Evolutionary Maize Breeding. Alexander 

 Grobman (La Molina, Lima, Peru). 



Recent information has become available on 

 evolutionary rates of improvement of maize 

 grain yield components, through studies of 

 archaeological and living maize ears in Peru 

 stratified over a period of nearly 2500 years. 

 It has been possible to establish differences in 

 evolutionary rates of change of quantitative 

 ear characters between "tripsacoid" and "non- 

 tripsacoid" maize races. The former have a 

 steeper rate of improvement of ear length, 

 which becomes evident after the introduction 

 of "tripsacoid" maize germplasm in certain 

 geographic areas. 



Modern breeding evidence points also to the 

 yield enhancing effect of the introduction of 

 tripsacoid germplasm into intervarietal hybrids 

 of maize studied in the highland region of Peru. 



Phylogenetic relationships have been estab- 

 lished on the other hand between more than 

 200 races of maize in Latin America, based on 

 morphological, genetical, cytological, and other 

 kinds of characters. Tentative degrees of teosinte 

 and Tripsacum introgression into these races 

 have been estimated. 



On the basis of all this evidence, breeding 

 schemes may be divided in different areas of 

 Latin America to better utilize heterosis in 

 intervarietal and interracial hybridization as a 

 first step in the improvement of yield of grain 

 of maize. 



13.59. Parthenogenesis in Polyploid Populations. 



O. J. Eigsti (Chicago, U.S.A.). 



Polyhaploid individuals appear in popula- 

 tions supposedly all polyploid. Parthenogenesis 



accounts for the origin of polyhaploids. These 

 variants cause the entire population to produce 

 more and more seed each generation. The 

 discovery of a parthenogen was made from self 

 pollination of a supposedly tetraploid Citrullus 

 vulgaris. Subsequent observations confirmed 

 continuing origin of polyhaploids during each 

 generation and the data support the conclusion 

 that a frequency of 1 seed per thousand tetra- 

 ploid carry polyhaploid embryos. Such indi- 

 viduals are not easily recognized in field popula- 

 tions. Pollen from polyhaploids produces di- 

 ploid hybrids instead of triploid hybrid seed in a 

 field where such seed production is the goal. The 

 practical problem created must be recognized 

 and compensation made to eliminate the ulti- 

 mate and unfavorable influence upon the pro- 

 duction of seedless watermelon fruit. Similar 

 origins of polyhaploids among populations of 

 Polygonatum commutatum, a naturally occurring 

 polyploid species, causes confusion taxonomical- 

 ly within the glabrous forms that make up the 

 P. biflorum complex. Propagators of tetraploid 

 cultures and studies dealing with evolution 

 among polyploid species must recognize the 

 role played by parthenogenesis. More and more 

 cases are being discovered since this discovery 

 was made. 



13.60. Cytoplasmic Replacement through Andro- 

 genesis in Maize. Sherret S. Chase (Sycamore, 

 U.S.A.). 



In maize, as in many other species, cytoplasm 

 is transmitted by the female gamete only. 



Following a suggestion of the author, the 

 Nebraska inbred line N6 has been converted 

 (Goodsell, S. F. Crop Sci. 1, 227-228, 1961) to 

 the "Texas-sterile" cytoplasmic phase by utilizing 

 the rare androgenetic individuals (paternal 

 monoploids) resulting from crossing N6 as male 

 to a diploid "Texas-sterile" cytoplasm stock. 



The present report is concerned with the at- 

 tempt to increase the effective rate of androgen- 

 esis by utilizing a specially synthesized "Texas- 

 sterile" tetraploid, Emerson-brown, marker 

 strain as the cytoplasmic donor. Initial results 

 indicate that crosses of inbreds to this strain do 

 yield higher frequencies of androgenetic indi- 

 viduals and, even more interesting, that an ap- 

 preciable portion of the androgenetic individ- 

 uals are diploid. 



Cytoplasmic transfer through androgenesis 

 has the advantage over the customary back- 

 crossing technique of leaving the chromosomal 

 system intact. 



229 



