IMPROVED PLANTING STOCK THROUGH SYNTHETIC VARIETIES S81 



Synthetic Varieties of Forage Crops 



There has been considerable diversity of opinion on the procedure 

 for, and the improvement possible through the development of synthetic 

 forage varieties. 



The Ranger variety was the first synthetic alfalfa variety registered 

 (1944) by the Committee on Varietal Standardization and Registration of 

 the American Society of Agronomy. According to Kehr (1959), the major 

 objectives in the breeding of this synthetic were to develop a winter- 

 hardy and, particularly, a bacterial wilt-resistant variety. The 

 original base populations from which the first selections were made were 

 from 3 varieties (Cossack, Turkistan, Ladak) from widely separated 

 provenances--Russia, Turkistan, and India. Five strains (synthetics that 

 had been developed by selfing, out-crossing with wilt-resistant lines, 

 and isolated increase) were blended in prescribed proportions for the 

 Syn-0 generation breeder seed. On this base population, the Syn-1, Syn-2 , 

 and Syn-3 were produced for foundation, registered, and certified seed, 

 respectively. As of 1959, more than 200 million pounds of certified seed 

 of this variety had been produced and planted since its release. Kehr 

 also noted that, "Taking into consideration the many factors which 

 influence wilt test results, it was concluded that the wilt reaction of 

 Ranger has been sufficiently constant so that field performance has not 

 been altered since the variety was released." 



Pearson and Elling (1960) concluded that varieties of alfalfa 

 superior in wilt resistance and common leafspot resistance can be produced 

 by combining clones of superior general combining ability for these 

 characteristics. Their experimental results indicated that synthetic 

 variety performance essentially agreed with the average performance of 

 all the crosses among the clones of which each synthetic was composed. 



Kehr et at. (1961a) found great variability in the forage yield per- 

 formance of four generations of individual alfalfa synthetics. Factors 

 which may contribute to performance as generations are advanced include 

 relationship of parental clones, method of producing the Syn-1 generation, 

 fertility and compatibility relationships, natural selection, genotype 

 and environmental interaction in both seed and forage production, age and 

 quality of seed, and sampling error. 



On the basis of their study of forage yields of the Syn-1 generation 

 of 4-clone synthetics produced by using the Syn-1, Syn-2, Syn-3, and Syn-4 

 generations of parental two-clone synthetics, Kehr, Lowe, and Graumann 

 (1961b) suggested commercial production of Syn-1 generation synthetics 

 until the necessary genotypes are available for commercial production of 

 true hybrid alfalfa by controlled crossing. Pearson and Elling (1961) 

 also suggested that the clonal crosses of highly selected alfalfa clones 

 would be more desirable than combinations of clones as synthetic varieties. 



Theurer and Elling (1963) evaluated the 10 single crosses, 26 possible 

 Syn-2 generation synthetics, and the S\ progenies of 5 alfalfa clones for 

 resistance to bacterial wilt. The best single cross was not significantly 

 more resistant than the better synthetic varieties. In a subsequent paper 

 (Theurer and Elling, 1964), they reported the forage yield performance of 

 the same single crosses and Syn-2 synthetics. Synthetics developed from a 

 larger number of clones tended to yield the most forage in Syn-2. One 

 or more single crosses surpassed the yield of the best synthetic each year, 

 but the differences were in no case significant. They noted that their 



