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Kimberly A. Pickens, (Max) Zong-Ming Cheng and Stephen A. Kania

Poinsettia, Euphorbia pulcherrima, is an important holiday symbol and is the number one flowering potted plant in the United States. The technique of chromosome doubling has been utilized to increase size of flowers, stems, and leaves of many species, and has been used in poinsettia breeding to obtain new cultivars. Application of colchicine or oryzalin to in vitro tissues may be used to enlarge the inflorescences and brackets and reduce the height of `Winter Rose'™ poinsettias, reduce the likelihood of chimeric tetraploids, and provide a rapid means for producing many tetraploid plants. The purpose of this research was to evaluate the effect of colchicine and oryzalin on callus and adventitious shoot formation of `Winter Rose'™ poinsettia with in vitro grown leaf tissues and its potential for tetraploid induction. In vitro grown leaf midvein sections were placed on various media supplemented with either colchicine or oryzalin at various concentrations for 1–4 days. Colchicine was least damaging to leaf tissues at concentrations of 0.25 or 250.4 μm. A large amount of callus, as well as adventitious shoots, were produced. Regenerated shoots were found to be diploid, determined by flow cytometry. On media with oryzalin (28.9–144 μm), leaf tissues produced callus, but not adventitious shoots. Calluses produced on oryzalin-containing media were tested using the flow cytometer and were found to be diploid.

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Ying Li, Xiao-Li Hu, Robert N. Trigiano, Herbert Aldwinckle and Zong-Ming (Max) Cheng

Apple blotch caused by Alternaria alternata apple pathotype is a severe disease of apple (Malus ×domestica Borkh) occurring throughout the world, especially in eastern Asia. Phenotypic and genetic information about resistance/susceptibility of apple germplasm to this disease will be extremely valuable for selecting and developing new disease resistant cultivars. In this study, 110 apple cultivars obtained from the USDA apple germplasm in Geneva, NY, were evaluated for their resistance/susceptibility to apple blotch by field surveys, and inoculation of detached leaves with a suspension of germinated conidia of A. alternata apple pathotype. Disease incidence were different among the cultivars and categorized into resistant (R), moderately resistant (MR), or susceptible (S). Two molecular markers, S428, a random amplified polymorphic DNA (RAPD) marker associated with disease resistance, and a simple sequence repeat (SSR or microsatellite) marker CH05g07, linked to susceptibility were used to correlate the phenotypes expressed in field surveys and laboratory inoculations. The detection using either the S428 marker or the CH05g07 marker in 50 common breeding cultivars was consistent with R or S traits except for ‘Bisbee’ and ‘Priscilla’. These two cultivars were MR to apple blotch through phenotyping. However, SSR markers were detected, but RAPD markers were not and therefore were considered susceptible. Combined with the record of resistance to fire blight from Germplasm Resources Information Network (GRIN), ‘Dayton’, ‘Mildew Immune Seedling’, ‘Puregold’, and ‘Pumpkin Sweet’ were highly resistant to both diseases and considered as the best choices of parents for stacking resistance to multiple diseases in breeding program.

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Ying Chen, Xinlu Chen, Fei Hu, Hua Yang, Li Yue, Robert N. Trigiano and Zong-Ming (Max) Cheng

Agave species are economically important plants in tropical and subtropical desert ecosystems as ornamentals as well as potential bioenergy crops. However, their relatively long life cycles and the current lack of biotechnology tools hinder their breeding. In this study, an efficient system for micropropagation was developed for Agave americana L. by using basal stems as explants and grown on a modified Murashige and Skoog medium (MSI) or a 1/2 MSI medium supplemented with various concentrations of 6-benzylaminopurine (BA) for shoot proliferation. The highest number of shoots (18.5 shoots/explant) from basal stems was obtained on MSI supplemented with 13.32 μM BA. An efficient shoot regeneration system was also developed from leaf tissues. Combinations of auxin with cytokinin, basal media, and leaf regions were optimized for shoot induction. Adventitious shoot formation from leaf segments was induced and proliferated with combination ranging of 0.54 to 2.68 μM [α-naphthaleneacetic acid (NAA)] with 8.88 to 13.32 μM (BA), and the maximum frequency (≈69%) was obtained with 2.68 μM NAA plus 13.32 μM BA. MSI medium and the basal segment of leaf affected shoot induction. The highest rooting frequency and mean number of shoots occurred in 1/2 MSI containing with 4.92 μM indole-3-butyric acid (IBA) alone (90%, 3.4) or 1.48 μM IBA plus 1.61 μM NAA (92%, 5.2). Survival of in vitro plantlets after transfer and acclimatization to ex vitro conditions was 87%. This is the first complete protocol for micropropagation of A. americana.