Summary• Shoot branching is important for the establishment of plant architecture and productivity.• Here, characterization of rice (Oryza sativa) reduced culm number 1 (rcn1) mutants revealed that Rcn1 positively controls shoot branching by promoting the outgrowth of lateral shoots. Molecular studies revealed that Rcn1 encodes a novel member of ATP-binding cassette protein subfamily G (ABCG subfamily), also known as the white-brown complex (WBC) subfamily, and is designated OsABCG5.• Rcn1 is expressed in leaf primordia of main and axillary shoots, and in the vascular cells and leaf epidermis of older leaves. In addition, Rcn1 is expressed in the crown root primordia, endodermis, pericycle and stele in the root. No effect on Rcn1 expression in shoots or roots was seen when the roots were treated with auxins. Phenotypic analyses of rcn1 and tillering dwarf 3 (d3) double mutants at the seedling stage clarified that Rcn1 works independently of D3 in the branching inhibitor pathway.• Rcn1 is the first functionally defined plant ABCG protein gene that controls shoot branching and could thus be significant in future breeding for high-yielding rice.
Timothy (Phleum pratense L.) is the most important perennial forage grass grown in Hokkaido, Japan. Hence, the improvement of its nutritive value by breeding could be effective in enhancing animal productivity in the region. Effective improvement of the nutritive value of the grass requires a study on how the relative genotype ranking of the nutritive value changes in different environments. The objective of the present study was to investigate the magnitude of genotype × year interaction (G × Y) and genotype × location interaction (G × L) in the nutritive value of timothy. We grew 15 early‐maturing clones of timothy in Kunneppu in 2004 and 2005 to estimate G × Y and 11 early‐maturing clones in Kunneppu and Nakashibetsu in 2007 to estimate G × L, and analyzed the first crops by near‐infrared reflectance spectroscopy. The ratio of low‐digestible fiber content to organic cell wall content (Ob/OCW), Ob content and water‐soluble carbohydrate (WSC) content were significantly correlated between the 2 years and between the two locations, with non‐significant effects of G × Y and G × L. We conclude that the relative ranking of genotypes in different years and at different locations should be consistent for the traits and that selection for the traits in a single environment should be useful in effective improvement of the nutritive value of timothy.
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.
Assessment of genetic diversity based on DNA profiling contributes to the selection of superior parents for heterosis. The objective of this study was to investigate how closely the yields of timothy (Phleum pratense L.) topcross progenies are related to the genetic diversity between their seed parents and the pollen tester parent ‘Aurora’, and to predict their yield potentials from the index based on simple sequence repeat (SSR) marker polymorphisms. Genetic diversity among 67 genotypes, which consisted of 16 plants of timothy cultivar Aurora, the pollen parent for topcross testers, and 51 clones derived from breeding populations was evaluated based on 28 SSR markers carrying 408 alleles. Genetic distance (GD) was estimated for all possible pairs of genotypes and then the mean of the GD estimates between each clone and Aurora (GDA) was also assessed to find the relationship between GDA estimates and yields of topcross progenies derived from all crosses between each clone and Aurora. The GDA estimates of the clones ranged from 0.653 to 0.756, and a correlation coefficient between the GDA estimates and yields of their topcross progenies was 0.675 (p < 0.001). These results strongly suggest that GD would provide reliable information on the yields of the assumed topcross progeny lines and that it will help breeders to accelerate yield improvements for a practical breeding program of timothy.
Integration of reciprocal recurrent selection (RRS) with the formation and use of heterotic groups is a key strategy for yield improvement in timothy {Phleum pratense L.) breeding.
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