High‐yield timothy (Phleum pratense L.) strains developed by ‘clone and strain synthesis’, a method for breeding perennial and self‐incompatible crops

Abstract

While breeding methods to exploit only general combining ability (GCA) have been widely adopted in perennial and self‐incompatible forage crops, maize breeders have had great success in improving maize yield by developing hybrid breeding, whereby not only GCA but also specific combining ability (SCA) can be effectively exploited. A number of trials to apply hybrid breeding to such crops have not been successful because of severe inbreeding depression and/or ineffectiveness in commercial seed production. The objective of this study was to evaluate the potential of ‘clone and strain synthesis’ (CSS), a method in which both GCA and SCA can be exploited effectively to breed perennial and self‐incompatible crops. CSS consists of two procedures: (i) harvest of syn‐1 seeds from two seed parental clones after mating of each clone with a pollen parental strain under separate, isolated conditions; and (ii) even mixing of the syn‐1 seeds to produce subsequent generations, as is done to develop conventional synthetic strains from a number of parental clones. Therefore, the yield of a strain developed by CSS depends partly on combining ability, including SCA, among the three parental materials. Fifteen timothy (Phleum pratense L.) strains were developed by CSS for verification. The productivity test results indicated that four strains in the syn‐2 had significantly higher yield levels than the commercial variety adopted as their pollen parent, suggesting the potential of CSS to breed high‐yield varieties for forage, biofuel, or other uses. Yield of the strains was applied to a diallel analysis to evaluate the relative importance of SCA toward GCA; the results suggested that SCA was important in determining yield level.

DNA Profiling of Seed Parents and a Topcross Tester and its Application for Yield Improvement in Timothy (Phleum pratense L.)

“…Taking the following two facts into consideration, the high yield in the topcross progeny of clone c‐01 is likely attributable to GCA rather than SCA. First, the yield in all CSS strains derived from crosses with c‐01 as seed parent was, without exception, remarkably higher than other strains with no involvement of c‐01 in the previous study of KAES (Tamaki et al, 2009). Second, c‐01 also showed the third highest combining ability in another polycross progenies trial having 41 entries at KAES (total DMY for 2 yr from 2001 was 123.0% of Aurora and 106.2% of the average of all progenies).…”

“…The distribution of the 51 clones was more widely dispersed than Aurora in a scatter plot of PCOA. Six clones (b‐15, c‐01, c‐02, c‐08, c‐17, and c‐23) whose topcross progenies showed high performance on yields and had been selected for demonstrating the potential of CSS (Tamaki et al, 2009) are marked in Fig. 2 Five of these clones, b‐15, c‐02, c‐08, c‐17, and c‐23, were located far from the 16 individuals of Aurora in the scatter plot by PCOA.…”

“…PCOA1 and PCOA2 are the first and second principle coordinates, respectively. Symbols •, ○, and ▵ denote clones (b‐15, c‐01, c‐02, c‐08, c‐17, and c‐23) used in Tamaki et al (2009), the other 45 clones, and 16 individuals of Aurora, respectively.…”

“…In addition, Fig. 1 and 2 clearly indicate that five out of the six clones (b‐15, c‐02, c‐08, c‐17, and c‐23), whose topcross progenies showed high yield performance and had been selected for demonstrating the potential of CSS (Tamaki et al, 2009), were distantly located from Aurora. Distant locations of these clones identified by SSR profiling also supported the potential for DNA profiling.…”

Evaluation of forage yield performance in advanced generations of a timothy “clone and strain synthesis” strain

“…Regarding CSS development, although high yield performance was found in Syn2 of timothy CSS strains (Tamaki et al . ), no report describes yield performances in their subsequent generations.…”