The Amphiploids 317 



pretation for problems in Sola mini:*''' Certain species ol" potato carry 

 valuable economic traits, e.g., specific resistance to phytophora, and 

 these would be desirable to incor|)orate in the present jxilyploid 

 species, S. tuberosum. 



A study oi meiosis in hybrids between S. demissum and S. rybinii 

 as well as in haploid S. demissum shows pairing and suggests similar- 

 ities coujjled with these observations; the backcrossing of Fj S. demis- 

 sum X ^- tuberosum to .S'. tuberosum showed increased seed set with 

 each backcross.^*' One is led to recall the well-known elimination of 

 donor jjarent genotypes in certain interspecific backcrosses involving 

 Gossypium hirsutum and G. barbadense.^^^ These species have been 

 studied extensively, and recombintions on a gene-for-gene basis that 

 would permit transfer from one species to another runs into serious 

 difficulty after backcrossing. If a similar situation holds in Solanum, 

 then the program of amphiploidy and species h) bridization requires 

 further analysis."*^ 



Enough similarity exists between genomes of .S'. rybinii, S. tubero- 

 sum, and .S'. demissum to produce bivalents. By multiple crosses other 

 species like 5. antipoviczii can be crossed to S. tuberosum through the 

 amphiploid .S'. antipoviczii X S. chacoense}'"-' Another case, S. acaule 

 and .S. ballsii, can be introduced through appropriate amphiploids 

 crossed to S. tuberosum when the species in question cannot be crossed 

 alone. For practical work such an approach appears promising,ioT of 

 course, dependent upon chromosomal differentiation, which may in- 

 crease the difficulties considerably.^"'^' ^'^^- ^•^' ^^ 



Three amphiploids can be made within the genus Cucurbita.^^ 

 These are: C. maxima X C. pepo, C. maxima X C. mixta, and C. 

 maxima X C. moschata.^'^-^ The first is self-sterile; the second is 

 slightly self-fertile and segregates noticeably; the third is self-fertile 

 and cross-sterile with parental species. A relatively stable population 

 develops from the third ami:)hiploid with slight segregation. The 

 am])hiploid carried insect resistance to squash vine borer (Melittia 

 satyri)iiformis Hubner) , contributed by C. moschata, plus flavor and 

 fruit characteristics, contributed by C. tuaxiina. Diploid varieties, 

 Buttercup, Banana, Golden Hubbard, and Gregory, represent C 

 maxima; Butternut, Golden Cushaw, and Kentucky Field, C. mos- 

 chata. According to tests carried out at Cheyenne, Wyoming, Burling- 

 ton, Vermont, and Feeding Hills, Massachusetts, insect resistance was 

 stabilized. The fruits compared favorably with the comparable vari- 

 eties, in general, tliis particular combination may be regarded as a 

 "potential new species" with prospects of becoming \aluable eco- 

 nomically (cf. Chapter 13) .^-^ 



Theoretical problems must not be disregarded.^''' A \'ariaut like 

 C. pepo appeared sporadically in the first and later generations of the 

 Eastern material. Taxonomic similarity to C. pepo raises the ques- 



