Pollen Parent Research Articles

Development of chromosome segment substitution lines derived from indica rice donor cultivars DV85 and ARC10313 in the genetic background of japonica cultivar Taichung 65

We have developed two sets of chromosome segment substitution lines (CSSLs) of cultivated rice (Oryza sativa) carrying donor segments from indica cultivars DV85 and ARC10313. The lines in each set contain chromosomal segments that cover most of the donor genome in a uniform genetic background (ssp. japonica cv. Taichung 65). The starting materials were several recombinant inbred lines derived from the crosses Taichung 65 × DV85 and Taichung 65 × ARC10313. The CSSLs were generated by repeated backcrossing to Taichung 65 (pollen parent), with marker-assisted selection applied at several marker loci. The CSSLs of DV85 (TD-CSSLs) comprise 45 lines that cover 76.6% of the DV85 genome, and the CSSLs of ARC10313 (TA-CSSLs) comprise 44 lines that cover 74.4% of the ARC10313 genome. We investigated the genetic control of days-to-heading in both sets of CSSLs and demonstrated the genetic contribution of several chromosome regions. These CSSLs provide a valuable tool for rice germplasm enhancement, and we expect them to reveal the genetic basis of traits specific to the donor cultivars.

Introgression lines of rice (Oryza sativa L.) carrying a donor genome from the wild species, O. glumaepatula Steud. and O. meridionalis Ng

To broaden the available rice genetic resources, we developed two populations of introgression lines of cultivated rice (Oryza sativa) carrying donor segments from the wild species Oryza glumaepatula and Oryza meridionalis. These lines contain overlapped introgressed donor segments that covered most parts of the genome of the two donors in the same of O. sativa genetic background (ssp. japonica, cv. Taichung 65). The introgression lines were developed through repeated backcrossing with Taichung 65 as a pollen parent and marker assisted selection. O. glumaepatula introgression lines consist of two sets of the lines (with O. glumaepatula and Taichung 65 cytoplasm, respectively): these comprise a total of 69 lines that cover 79.5 to 89.2% of the Oryza glumaepatula genome. The O. meridionalis introgression lines also consist of two sets of the lines (with O. meridionalis and Taichung 65 cytoplasm, respectively): these comprise a total of 78 lines covering the 81.5 to 98.0% of the Oryza meridionalis genome. These introgression lines significantly broaden rice genetic resources, and will facilitate analyses of the genetics of traits specific to the donor species.

Relationship between Nuclear Genome Construction and the Plastome-genome Incompatibility of Progenies from Intra- and Inter-ploid Cross of Evergreen Azaleas × Rhododendron japonicum f. flavum

In intersubgeneric crosses of diploid evergreen azaleas (EV) × diploid Rhododendron japonicum f. flavum (JP), many progenies become albino as a result of plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP. To clarify the mechanism of the incompatibility, inter- and intra-ploid crosses of diploid (2x) EV × diploid (2x) JP, tetraploid (4x) EV × tetraploid (4x) JP, 2x EV × 4x JP, and 4x EV × 2x JP were conducted. Seeds were obtained in all crosses, although the number of progenies per capsule was relatively low in crosses with 4x JP as a pollen parent. Plastome-genome incompatibility between a plastid genome from EV and a nuclear genome from JP was observed in progenies from 2x EV × 2x JP, 4x EV × 4x JP, and 2x EV × 4x JP, but not in 4x EV × 2x JP. This result indicates that plastome-genome incompatibility was broken by relative increase of the genome from EV in the nuclear genome of progenies.

Relationship Analysis of Soybean Cultivars Breeded by Intracultivar Selection or Pollen Tube Pathway and Parents by Simple Sequence Repeat Markers

Relationship Analysis of Soybean Cultivars Breeded by Intracultivar Selection or Pollen Tube Pathway and Parents by Simple Sequence Repeat Markers

Development of the Male-sterile Line of Eggplant Utilizing the Cytoplasm of Solanum aethiopicum L. Aculeatum Group

In order to develop a new male-sterile line of eggplant (Solanum melongena L.), the F1 rootstock ‘Assist’ (Solanum aethiopicum Aculeatum L. Group × S. melongena ‘DMP’) was continuously backcrossed to S. melongena ‘Uttara’ using ‘Uttara’ as a recurrent pollen parent up to BC4 generation. All examined F1 ‘Assist’ produced pollen grains while BC1 plants segregated into male fertile and sterile plants. The male-sterile plant did not produce any pollen grains. BC2, BC3, and BC4 progenies obtained from male fertile backcross progenies were segregated into male fertile and sterile plants and each segregation ratio fitted 3 : 1. BC3 and BC4 progenies obtained from male-sterile backcross progenies were fixed to male-sterility without segregation. Selfed progenies of the male fertile BC2 progeny were segregated into male fertile and sterile plants and the segregation ratio fitted 15 : 1. Therefore, the pollen non-formation characteristic is assumed to be a form of cytoplasmic male-sterility (CMS), induced by incompatibility between the cytoplasm of S. aethiopicum Aculeatum Group and the nucleus of S. melongena. Further, these segregation results indicated that two independent dominant fertility restorer (Rf) genes control the fertility restoration of this CMS. High values of fruit set, number of seeds per fruit, and the seed germination rate found in BC4 progenies indicate that the cytoplasm of S. aethiopicum Aculeatum Group has no notable negative effect on seed fertility of S. melongena. A new male-sterile line of eggplant could be developed by utilizing the cytoplasm of S. aethiopicum Aculeatum Group.

Inheritance of hairiness and pod shattering, heritability and correlation studies in crosses between cultivated cowpea (Vigna unguiculata (L.) Walp.) and its wild (var. pubescens) relative

Crosses were made between five cultivated cowpea varieties and a wild relative var. pubescens (as pollen parent) to study the inheritance of hairiness, pod shattering, as well as heritability and correlations among yield and yield related traits. F1 plants exhibited dominance for both hairiness and pod shattering traits. Segregation in F2 populations approximated 3:1 and 13:3 for hairy and non-hairy stem and 13:3 for hairy and non-hairy pod. The ratio of 13:3 and 15:1 ratios were observed among the F2 populations for shattering and non-shattering pods. Broadsense heritability estimates showed that days to pod maturity averaged 77.93%, 100 seed weight 68.45%, seeds pod−1 69.76% and number of branches plant−1 had 62.54% (all high). Days to first flowering and pod length were moderate (57.31 and 54.29%, respectively). Number of pods plant−1 had low heritability estimates with an average of 39.0%. Correlations among number of pods plant−1, seeds pod−1, seeds plant−1 and seed yield plant−1 (0.485–0.568) were significantly positive. Correlations between seed pod−1 and seed plant−1 with number of pods plant−1 were 0.909 and 0.996, respectively. High broadsense heritability averaged 77.93% for days to pod maturity, 68.45% for 100 seed weight, 69.76% for seeds pod−1 and 62.54% for number of branches plant−1. Days to flowering and pod length plant−1 had moderate estimates of 57.31 and 54.29%, respectively, while pods plant−1 was low (39.90%). Potential utilization of the hairiness trait and the implication of pod shattering in cowpea improvement were discussed. Positive correlations among these yield components, as well as high to moderate broadsense heritability estimates of the yield related traits can be utilized for direct and indirect selection to improve grain yield in cowpea.

On gene dispersal studies in complex landscapes: a reply to the comment on García et al. (2005, 2007)

On gene dispersal studies in complex landscapes: a reply to the comment on García <i>et al.</i> (2005, 2007)

Genetic analysis on oil content in rapeseed (Brassica napus L.)

High oil content is one of the most important characteristics of rapeseed (Brassica napus L.) breeding. In order to understand the genetic basis of seed oil content, a series of reciprocal crosses between rapeseed parents with high oil content (53110, 61616 and 6F313), medium-oil content (Zhongshuang 9) and low oil content (51070 and 93275) were conducted. It was found that the oil content of F1 hybrid seeds in rapeseed was mainly controlled by the maternal genotype. The maternal effect value of oil content was estimated to be 0.86. The pollen parent had a xenia effect on oil content, estimated to be 0.14 which changed the mean value by 1.86 percent. The inheritance of oil content was studied in a set of 8 × 8 diallel crosses of different varieties. The results indicated that the inheritance of oil content could be explained by an additive-dominant-epistasis model. Although the dominant and additive effects played major roles and accounted for more than 70% of the total variance, there was also a small epistatic effect. The broad and narrow sense heritability of oil content was 83.88 and 36.94%, respectively. Based on the oil content differences between the reciprocal crosses in the same offspring generation (F1 and F2) in rapeseed, it could be concluded that there were significant cytoplasmic effects on oil content. In this study, two lines with significantly cytoplasmic effects, either positive or negative, were selected.

Hybridization of two diploid Vaccinium section Cyanococcus species with diploid Vaccinium arboreum in section Batodendron

Several characteristics from sparkleberry (V. arboreum) would be useful if transferred to highbush blueberry cultivars, but to date all direct crosses have failed. The purpose of this research was to see whether crosses of diploid V. darrowii and diploid V. fuscatum (both section Cyanococcus) with diploid V. arboreum (section Batodendron) could be made and to assess the possibility of transferring traits from V. arboreum into cultivated blueberries of section Cyanococcus. Many crosses were successful and easy to make. Crosses were more productive when V. arboreum was the pollen parent, but some hybrids were also obtained with V. arboreum as seed parent. Pollen stainability of F1 (V. darrowii × V. arboreum) hybrids was low, ranging from 0.9 to 23.7%. Numerous meiotic abnormalities were found in the F1 hybrids. These led to a high percentage of incomplete and unstained tetrads and probably to the production of unreduced gametes.

Broadening the genetic base of crop brassicas by production of new intergeneric hybrid

Wide hybridization between crop brassicas and their wild relatives is an important approach towards increasing the genetic variability, which can be utilised for brassica breeding programs. A new intergeneric hybrid between Erucastrum cardaminoides and Brassica oleracea var. alboglabra was produced using embryo rescue techniques. The F1 hybrid was intermediate between the male and female parent for most of the morphological characters. Cytological studies of pollen mother cells of the hybrid revealed a preponderance of univalents at metaphase I. The number of bivalents in the digenomic hybrid was lower than expected. However, the presence of trivalent and quadrivalent in cells indicated some homoeology between the two genomes and hence the possibility of introgression of genes into the cultivar. The first backcross progeny was obtained using B. oleracea var. alboglabra as the pollen parent. Further, it is being used for developing new alloplasmic lines. The intergeneric hybrid was also used as bridge species to transfer wild (E. cardaminoides) cytoplasm to B. napus and B. carinata. The new intergeneric hybrid and bridge cross hybrids produced in the present investigation have contributed towards increasing the genic and cytoplasmic variability and thus broadening the genetic base of crop brassicas.

Occurrence of Unreduced Female Gametes Leads to Sexual Polyploidization in Lantana

Lantana camara, a member of the verbena family, is a popular ornamental yet highly invasive plant. It can escape from cultivation through seed dispersal and can contaminate native lantana species (Lantana depressa) through cross-pollination. Ploidy manipulation is being used as a genetic approach to produce sterile, noninvasive lantana cultivars. Polyploids have been observed in lantana (Lantana), but little information is available about the mechanisms for lantana polyploidization and the possible effects of natural polyploidization on the sterility (or fertility) of lantana triploids. In this study, we analyzed the ploidy level of more than 1500 lantana progeny from self, open, and/or controlled pollinations of 10 commercial cultivars and seven breeding lines. Our results confirmed the occurrence of unreduced gametes, specifically, unreduced female gametes (UFGs), in lantana. The frequency of UFG formation varied among commercial cultivars, and cultivars/breeding lines could be categorized into two groups: UFG producers and nonproducers. Tetraploid cultivars Gold, Pink Caprice, and Radiation fall into the UFG-producing group, while diploid cultivars Cream, Denholm White and Lola and tetraploid cultivars Carlos, Dallas Red and Irene belong to the nonproducer group. The frequency of UFG formation observed in nine UFG producers was 5.5% to 100%, varying with cultivar, growing condition, and/or pollination scheme. Progeny of the cross between ‘Carlos’ (seed parent) and ‘Gold’ (pollen parent) also showed the ability to produce UFGs, indicating that the trait (UFG formation) could be transmitted from ‘Gold’ to its progeny and is likely to be controlled by nuclear gene(s). Lantana triploids with or without the UFG-forming ability in its genetic background showed a significant difference in seed set: the former produced abundant seed when pollinated, while the latter produced little or no seed. The results stress the need to avoid using lantana with UFG-forming ability as parents in crosses designed to produce sterile triploids for invasiveness control. Additionally, the results from this study suggest multiple pathways for emergence and evolution of polyploids in cultivated and naturalized lantana populations.

Parentage Analysis of Freedom Rootstock

The rootstock Freedom is the offspring of two open-pollinated parents (1613-59 and Dog Ridge 5), sources of root-knot nematode resistance. As phylloxera has increased in importance in vineyards, the risk of <i>Vitis vinifera</i>-derived phylloxera susceptibility from the unknown pollen donors is a concern. To clarify the pedigree of Freedom, genetic profiles of 31 potential progenitors were analyzed with 30 microsatellite markers. We confirm the reported parent (1613-59) and grandparent (1613C) of Freedom and identify 3306C (<i>V. riparia</i> x <i>V. rupestris</i>) as the pollen parent of 1613-59. We were unable to identify the pollen parent of Dog Ridge 5.

No evidence of apomixis in matroclinal progeny from experimental crosses in the genus Fragaria (strawberry) based on RAPDs

Crossing experiments in Fragaria have frequently resulted in some matroclinal progeny. These have been attributed to either accidental selfing and/or pollen contamination, or apomixis. In this study 202 carefully controlled intra and interspecific crosses in Fragaria were made. No progeny were produced from 164 interploid crosses made between diploids, hexaploids and octoploids but 38 intraploid crosses resulted in 904 F1 plants, of which 42 (4.6%) were found to be morphologically matroclinal. All matroclinal progeny subsequently studied by RAPDs were found to be hybrids and not apomicts. The absence of apomixis among matroclinal progeny in this study casts doubt on previous reports of apomixis in Fragaria. Our results showed that the complete morphological similarity of progeny to the seed parent, even in recessive characteristics, cannot therefore be taken as evidence of apomixis, and may rather indicate the heterozygosity of the pollen parent, emphasising the need to use DNA markers for confirmation of apomixis.

Ethidium Bromide-induced Mutations from Inflorescence Cultures of Indiangrass

Immature inflorescences of a Sorghastrum nutans (L.) Nash selection were cultured on CCm medium with 5 mg·L−1 2,4-dichlorophenoxyacetic acid and 1 mg·L−1 N6-benzyladenine (BA) for 5 weeks. Callused inflorescence cultures were placed on CCm medium with 1 mg·L−1 BA (CCmB1) and 0 or 250 mg·L−1 ethidium bromide (EtBr) for 24 h. Cultures were transferred to CCmB1 without EtBr for shoot regeneration and then to CCm without plant growth regulators for rooting. Rooted shoots were transferred to soil under greenhouse conditions and then to the field. Fifteen putative M1 mutants with atypical phenotypes were detected among 71 EtBr-treated regenerants. Two self-incompatible putative M1 mutants were progeny-tested by using a wild-type Indiangrass seedling as the pollen parent. M1 selection ISU06-35 was a dwarf mutant whose M2 testcross progeny segregated 1:1 tall:dwarf seedlings. M1 selection ISU06-56 was a red-flowered mutant whose M2 testcross progeny segregated 1:1 green-flowered:red-flowered seedlings. These results are consistent with both M1 mutants being dominant nuclear mutations.

Studies on quantitative trait loci related to activity of lactate dehydrogenase in common carp (&lt;I&gt;Cyprinus carpio&lt;/I&gt;)

The reciprocal intergeneric hybrids between common wheat and Roegneria kamoji were successfully obtained by means of embryo culture. Morphology, chromosome pairing behavior at meiosis, fertility, and resistance to scab of the hybrid F1 and BC1 were studied. The results showed that the morphology of the reciprocal intergeneric hybrids F1 between R. kamoji and T. aestivum cv. Chinese Spring were intermediate type between the two parental species. The chromosome configuration at metaphase I (MI) of pollen mother cell (PMC) in reciprocal F1 was 40.33I + 0.78II + 0.03III and 40.40I + 0.79II, respectively. All of the F1 plants showed complete male sterility, and the seeds of BC1 were obtained by backcrossing with Chinese Spring pollen. The somatic chromosome numbers in BC1 plants of (R. kamoji x Chinese Spring) F1 x Chinese Spring ranged from 55 to 63. Many univalents were observed at MI of PMC, which resulted in the sterility of BC1 plants. Similarly, the chromosome numbers in BC1 plants of (Chinese Spring xR. kamoji) F1 x Chinese Spring also ranged from 55 to 63; however, many bivalents at MI of PMC and fertile pollen were observed resulting in partial fruitfulness in some BC1 plants by self-crossing. A plant (2n=63) with 42 wheat chromosomes and 21 R. kamoji chromosomes was obtained from R. kamoji x Chinese Spring cross, which had a chromosome configuration at MI of 26.40I + 18.30II. Because many univalents existed, this plant showed complete male sterility, and BC1 plants were obtained by back-crossing with Chinese Spring as the pollen parent. The chromosome numbers of BC1 ranged from 40 to 59, which contained less alien chromosomes. Although the morphology of the spike in BC1 plants was similar to that of Chinese Spring, these BC1 plants were still sterile. All F1 and most of the BC1 plants showed high resistance to Fusarium graminearum, which indicated that the resistance to scab from R. kmoji can be transferred into wheat.Microsatellite markers were used to make marker regression analysis on activity of lactate dehydrogenase based on double pseudo-testcross strategy using Windows Map Manager2.0 software. The parents that came from the cross between progenies of Hebao-cold tolerance red carp and Barbless carp and F2 progenies were used as segregating populations. For maker regression, a total of 12 markers associated with activity of lactate dehydrogenase were significant at P<0.05 and HLJE222 was significant at P<0.01. The variance explained by these loci, ranged from 4.00% to 10.00%. Locus HLJE222 was closely linked to the gene related to activity of lactate dehydrogenase of common carp. For further identification, EST-SSR markers were used to screen the protein and nucleotide database using bioinformatics tools in order to find the homologies. High sequence similarities of HLJE222 marker were observed with the nucleotide sequence of DAZ associated protein 1mRNA of zebrafish(94%), and protein sequence of DAZ associated protein 1(97%). DAZ protein is one of the short chain dehydrogenases, which is an important enzyme in the process of glucose metabolism in the organisms. This family contains a wide variety of dehydrogenases. This indicates that locus HLJE222 was closely linked to the gene associated with activity of lactate dehydrogenase of common carp.

A study of scab resistance in 16 apple progenies using parents with partial scab resistance

A study was conducted to examine the inheritance of partial resistance to apple scab [Venturia inaequalis (Cke.) Wint.] using as parents a set of apple (Malus × domestica Borkh.) cultivars that show a range of field resistance to the disease, but are not known to carry any major-gene resistance. Akane, Alkmene, Antonovka, Carola, Chehalis, Goldgelbe, Katja and Summerred were used as pollen parents, and Spartan and an unnamed selection of Splendour × Gala parentage were used as seed parents in a factorial 2 × 8 mating design. One hundred seedlings of each family were planted in a randomized complete block design at a site with heavy annual natural scab infections. Each seedling was rated for infection severity for 3 consecutive years using a six-point categorical scale. A χ2 procedure was used to estimate the contribution of each parent to field resistance (analogous to general combining ability, GCA) and the contribution of the particular male-female combination (analogous to specific combining ability, SCA). Infection severity tended to increase over the 3 yr of the study. Antonovka and Chehalis had the highest analogous GCA for resistance (defined here as absence of sporulating lesions). Specific combining ability was present in 2 of 3 yr, but was small in magnitude relative to GCA. The field resistance of a given parent tended to be a poor predictor of its breeding value. However, 13 of the 16 families had at least 30% of seedlings with a potentially useful degree of partial resistance (low severity of infection). The results are discussed in the context of breeding apples with durable scab resistance.Key words: Fruit breeding, Malus, partial resistance, Venturia inaequalis

Male Reproductive Success at Three Early Life Stages in the Tropical TreePlatypodium elegans

We conducted a paternity analysis within a population of the Neotropical tree Platypodium elegans using microsatellite markers to determine rates of gene flow and to investigate whether postpollination selection affects male reproductive success. Paternity was assigned for three early life stages (aborted fruit, mature seeds, and seedlings) of five adult trees. The rate of pollen immigration into the population was high (>40%). Significant heterogeneity in pollen allele frequencies was discovered among families but subsequently declined across life stages. Comparisons of parentage among the three life stages showed no significant differences in the number of progeny resulting from immigrant pollen, and, similarly, the average distance between mating pairs did not differ over time. Only self‐fertilized seeds exhibited a significant decline across life stages, indicating inbreeding depression due to self‐pollination. Estimates of total and effective numbers of pollen donors were high, and we did not detect a selective advantage among paternal trees. High initial levels of pollen heterogeneity and the lack of evidence for selection among outcrossed seeds of pollen parents suggest that differences in male fitness at early life stages other than self‐fertilization are due to initial pollination success rather than the differential survival of progeny among fathers.

Morphological and molecular analyses of Rosa damascena × R. bourboniana interspecific hybrids

Rosa damascena Mill is the most important scented rose species cultivated for rose oil production. Rosa bourboniana L. (Edward rose), a related species, is popular on account of its longer blooming period and ease of propagation. With an aim to combine the oil quality of R. damascena and recurrent flowering habit of R. bourboniana, two cultivars (Jwala and Himroz) of R. damascena were crossed with R. bourboniana. The F1 hybrids obtained were evaluated using morphological, random amplified polymorphic DNA (RAPD) and microsatellite (SSR) markers. Twenty-two selected RAPD and three SSR primer pairs were utilized for hybrid identification. According to presence or absence of bands RAPD and SSR markers were classified into seven types of markers. The bands specific for the pollen parent and occurring in the hybrids were good markers to confirm the hybridity. The non-parental bands expressing uniquely in hybrids were effective in distinguishing the hybrids from each other. Cluster analysis, based on Jaccard's similarity coefficient using unweighted pair group method based on arithmetic mean (UPGMA), reliably discriminated the hybrids into two main clusters. These results indicate the practical usefulness of RAPD and SSR markers in hybrid identification in scented roses. The approach is advantageous for its rapidity and simplicity, for identification of hybrids at the juvenile stage. One of the studied morphological traits – prickle density, can also complement in the identification of interspecific hybrids between R. damscena (♀) and R. bourboniana (♂).

Selection of Highly Informative Microsatellite Markers to Identify Pollen Donors in ‘Hass’ Avocado Orchards

‘Hass’ is the most popular avocado (Persea americana Mill.) cultivar in the world. It has been characterized as a crop requiring cross-pollination. However, the potential extent of self-pollination and the most effective pollen donors (best cross-pollinizing cultivars) have not been determined. In this study, 56 markers were screened against ‘Hass’ and nine commonly used pollinizing cultivars grown in southern California: ‘Bacon,’ ‘Ettinger,’ ‘Fuerte,’ ‘Harvest,’ ‘Lamb Hass,’ ‘Marvel,’ ‘Nobel,’ ‘Sir Prize,’ and ‘Zutano.’ Seventeen microsatellite, i.e., simple sequence repeat (SSR) markers, were found to be very promising for paternity analysis. Four highly informative SSR markers were selected to accurately and unequivocally identify pollen parents of ‘Hass’ fruit from an orchard interplanted with these pollinizing cultivars. From 2003 to 2006, 7,984 ‘Hass’ fruit were analyzed for their paternity. Overall, the pollen parents of 99.55% of the analyzed fruit could be unequivocally identified with a single multiplex polymerase chain reaction (PCR). Only 36 fruits (<0.45%) required a second PCR reaction to reach unequivocal identification of the pollen parents.

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

AbstractWhile 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.