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Yan Ma and Junyu Chen

From 1986 through 1993 wild rose species were investigated throughout China to catalog and to characterize the rose germplasm resources in mainland China. Many of the 94 rose species and 144 rose varieties in China have not been extensively utilized. The basic features of Chinese rose species are as follows. (1) There are many valuable and rare Rosa species in China. These species are sources of many unique and outstanding characters such as intense fragrance, white and yellow flower color, recurrent flowering and resistance to stress. More than 80% of the rose species in China are native to only China. (2) Although most Rosa species are still in the wild state, a few species cultivated from very early time have many forms available. (3) The number of rose species gradually increases from Northeast to Southwest China. The distribution centers of Rosa species in China are Sichuan and Yunnan Provinces. Chinese rose species can be introduced and used directly in gardens, or in breeding programs to develop new roses.

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Yan Ma, David H. Byrne and Jing Chen

A high priority in rose (Rosa spp.) breeding research is the transfer of disease resistance, especially to black spot (Diplocarpon rosae Lib.), from wild diploid Rosa species to modern rose cultivars. To this end, amphidiploids (2n = 4x = 28) were induced with colchicine from five interspecific diploid (2n = 2x = 14) hybrids involving the black spot resistant diploid species R. wichuraiana Crép, R. roxburghii Thratt., R. banksiae Ait., R. rugosa rubra Hort., and R. setigera Michaux. Two application procedures (agitation of excised nodes in colchicine solution or tissue culture of shoots on medium with colchicine), five colchicine concentrations (0.0, 1.25, 2.50, 3.76, and 5.01 mmol), and five durations (2, 3, 5, 8, and 10 d) were used. After colchicine treatment, the materials were cultured in vitro and the surviving explants were examined for the “gigas” characteristics typical of doubled diploids. Chromosome counts of morphologically suspect genotypes confirmed 15 amphidiploids among 1109 plants that survived colchicine treatment. Although the effect of colchicine treatment varied some among interspecific hybrids, 2.50 mmol for 48 h of node agitation or 1.25 mmol for at least 5 d of shoot culture were optimal.

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Yan-Ling Zheng and Huan-Cheng Ma

Mumian (Bombax ceiba) is a deciduous tree that can grow in the dry-hot valley of southwestern China. However, natural regeneration of mumian is significantly inhibited by some factors such as high temperature that can accelerate seed deterioration. The objective of this study was to identify the change of seedling growth component(s) in response to seed aging at 45 °C either at low relative humidity (15%) or at high relative humidity (100%) for 0, 1, 2, 3, and 4 days. Germination assay results at 30 °C in darkness showed an interaction between relative humidity and aging duration. At high temperature and low relative humidity seedling growth, weight of used seed reserve and fraction of seed reserve depletion significantly decreased with increasing of aging duration. But the conversion efficiency of mobilized reserve to seedling tissues did not change significantly. In contrast, at high temperature and high relative humidity, seedling growth and conversion efficiency of seed reserve utilization decreased significantly, but weight of used seed reserve and fraction of seed reserve depletion did not change significantly until seeds were dead. It was concluded that there existed a different pattern of seed reserve utilization for seeds aged at low and high relative humidity, and humidification of seeds at 45 °C for 1 day is a possible way to increase germination of mumian.

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Yan Ma, David H. Byrne and Jing Chen

An objective of our rose breeding research is to transfer resistance to blackspot and other diseases from wild diploid species to modern rose cultivars. Interspecific hybrids among blackspot-resistant diploid species were chosen for chromosome doubling to produce fertile amphidiploids that could be hybridized to the tetraploid commercial germplasm. Five such F1 interspecific hybrids were treated with colchicine. The study included two different application procedures (shake in colchicine solution or colchicine in media), four colchicine concentrations (0.05%, 0.1%, 0.15%, and 0.20%), and five treatment periods (1, 3, 5, 8, and 10 days). After colchicine treatment, all the materials were cultured in vitro. One thousand-thirty-seven surviving explants were selected for typical “gigas” characteristics of doubled diploids. Chromosome counts on shoot tips of these selected genotypes confirmed 15 amphidiploids. The best colchicine treatment varied among the interspecific hybrids. Higher colchicine concentrations or duration reduced growth rating, rooting, and percent survival. The recognition of amphiploids and ploidy chimeras from young seedlings will also be discussed.

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Yan Ma, David H. Byrne and Katrina G. Porter

Several colchicine-induced amphidiploids of blackspot-resistant, wild diploid rose species were produced for interbreeding with tetraploid garden roses. Shoot-tip chromosome counts confirmed that 86-7 (Rosa wichuraiana Crep. × R. rugosa rubra Hort.) and 86-3 (R. laevigata Michx. × R. banksiae Aiton) are amphidiploids (2n = 4x = 28), and that 84-1000 (R. roxburghii Tratt. × R. laevigata Michx.) is a mixoploid with diploid (2n = 2x = 14) and hypotetraploid (2n = 4x-1 = 27) sectors. The measured volume of pollen grains and guard cells was higher in the tetraploids. Pollen stainability was higher in amphidiploids 86-3 and 86-7 than in mixoploid 84-1000. The amphidiploid 86-7 has greater pollen fertility as determined by crossing with a range of commercial tetraploid roses than 86-3 and 84-1000, but is less fertile than its parental diploid species. Leaflets of the amphidiploids are larger and more crinkled along the midrib than in their diploid parents. These three amphidiploids provide new additions to tetraploid rose germplasm.

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Yan Ma, Charles F. Crane and David H. Byrne

The tetraploid (2n = 4x = 28) rose 86-7 (Rosa wichuraiana × R. rugosa rubra) and its hybrids with the thornless tetraploid rose cultivar Basye's Blueberry (2n = 28) were analyzed for meiotic configuration frequencies and meiotic abnormalities. Genomic relationships in these hybrids were interpreted with the aid of a model of meiotic chromosome association in tetraploids. The closest-fitting model solutions indicated a 2:2 (AABB) pattern of genomic relationships, with 65% to 90% of all association between most closely related genomes. Some of the optimal solutions were transitional to a “ring4” pattern, in which one of the possible pairing arrangements is suppressed. The same configuration frequencies could also reflect a “4:0” pattern of equally similar genomes with fractionally more than two independent pairing and chiasma-forming domains per chromosome. Observed meiotic abnormalities included chromosome stickiness and asynchronous chromosome contraction within cells. Pollen stainability varied independently of meiotic irregularity or multivalent frequency. The observed configuration frequencies are consistent with partially tetrasomic inheritance that retains considerable heterozygosity, but allows individual contributions from parental genomes to become homozygous.

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Xiaobo Zhang, Derong Su, Luyi Ma and Yan Zhao

Buffalograss [Buchloe dactyloides (Nutt.) Engelm.] is a warm-season grass for low-maintenance lawns. The objective of our study was to assess the genetic variation in 10 accessions of buffalograss obtained from the Chinese Academy of Agricultural Sciences by random amplified polymorphic DNA (RAPD) markers. Fourteen of the 60 primers screened generated 72 highly repeatable polymorphic bands. A dendrogram constructed on the basis of the unweighted pair group method arithmetic average clustering algorithm revealed that nine of 10 accessions formed two distinct clusters. Genetic similarity coefficients calculated from the RAPD data ranged from 0.30 to 0.89 with the lowest value of 0.30 measured between No. 4 and No. 7 from Japan and the United States, respectively. The highest value of 0.89 was measured between No. 6 and No. 8 from the United States and Mexico, respectively. The cophenetic correlation coefficient (r) was 0.92, indicative of a very good fit between the data matrix and the resulting cluster analysis. Principal coordinate analysis (PCO) clearly grouped nine accessions on the two axes with a single accession from the United States that did not cluster with others. The PCO clustering pattern corresponded well with the dendrogram. No. 7 from the United States did not cluster with any other accessions either in the dendrogram or on the basis of the PCO.

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Yan Ma, David H. Byrne, Jing Chen and Amanda Byrne

Several rose species (Rosa rugosa, R. wichuraiana, R. setigera, R. laevigata, R. banksiae, R. roxburghii, R. odorata and hybrids) were employed to establish the appropriate nutrient media for shoot multiplication and root initiation of cultured shoots and to describe a procedure for the successful transfer to soil of plants obtained in vitro. Cultured shoot tips and lateral buds from different genotypes proliferated multiple shoots on a basal medium (MS salt, vitamins, glycine, sucrose and agar) supplemented with 0mg/l to 6mg/l 6-benzylamino purine (BA) and 0mg/l to 0.5 mg/l naphthalene acetic acid (NAA). Most rose species cultured in a modified MS medium supplemented with 2mg/l BA showed good growth and shoot proliferation. The buds nearest the apex exhibited the slowest rate of bud development. Root development was enhanced and shoot development inhibited by lowering the concentration of MS salts to quarter- and half-strength. With difficult-to-root species, rooting was improved by supplementing the media with auxin or giving them 3-7days of dark treatment.

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Yan Ma, David H. Byrne and David M. Stelly

Mitotic chromosome numbers and measurements were determined from enzymatically digested shoot tips for 14 species of Rosa, subgenus Hulthemia, Platyrhodon, and Rosa (the latter represented by sections Pimpinellifoliae, Cinnamoneae, Synstylae, Banksianae, Laevigatae, and Bracteatae). All were 2n = 14 or 2n = 28, as expected from previously published chromosome counts in Rosa. Arm lengths of chromosome pairs measured from digitized images were analyzed for similarity using a least-squares algorithm. On this basis, tetraploid species were compared to their diploid relatives. This study demonstrates the value of karyotypic data in combination with morphological and ecological information for examining the evolution of Rosa.

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Yan-xin Duan, Ying Xu, Ran Wang and Chun-hui Ma

‘Akizuki’ (Pyrus pyrifolia Nakai) is a dominant Asian pear cultivar with gradually increasing cultivation area in Shandong province. However, this cultivar is found susceptible to cork spot disorder in recent years. In this study, we explored the physiological-biochemical mechanism of cork spot disorder in pear fruit, and investigated the effectiveness of spraying calcium (Ca), boron (B) solution or prohexadione calcium (P-Ca) on cork spot incidence. Cork spotted fruit had the characteristics of significantly larger fruit size with shorter fruit pedicels. Compared with normal fruit, cork spotted fruit had lower content of total soluble solids, soluble and reducing sugar, and vitamin C. In addition, cork spotted fruit accumulated much higher levels of N and Mg, and lower levels of K and P. However, Ca deficiency was not observed in cork spotted fruit, on the contrary, we determined high concentrations of Ca and free Ca2+ in disordered fruit. At the same time, the ratios of K/Ca, Mg/Ca, and (K+Mg)/Ca were significantly lower in cork spotted fruit as compared with normal fruit. Among all treatments, spraying with 3500 times dilution of P-Ca at 15-day intervals from 30 to 90 days after full bloom showed promise for reducing cork spot incidence in ‘Akizuki’ pear without affecting fruit quality attributes. This research herein reveals the physiological-biochemical characteristic of cork spot disorder, and implicates P-Ca as a potential tool to reduce cork spot incidence in Asian pear cultivar Akizuki.