6 research outputs found
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Mineral nutrition influences physiological responses of pear in vitro
Abnormal physiological responses of plant cultures such as shoot tip necrosis, callus, and hyperhydricity are some of the most difficult challenges in shoot micropropagation, and their causes are not well understood. Five Murashige and Skoog mineral salt factors, which influence the growth of pear shoot cultures, were tested in a five-dimensional surface response experimental design. Pyrus communis ‘Old Home × Farmingdale 87,’ ‘Horner 51,’ and ‘Winter Nelis’; Pyrus dimorphophylla; and Pyrus ussuriensis ‘Hang Pa Li’ shoot cultures were grown on 43 computer-designed treatments to represent the design space of all possible treatment combinations. Analysis of shoot response to these treatments identified the factors that both contributed to physiological disorders and remedied them. Undesirable callus formation was common for pear shoots cultured on standard medium and decreased on formulations with increased NH₄NO₃, Fe, and mesos (CaCl₂, KH₂PO₄, and MgSO₄) for most genotypes. Shoot tip necrosis varied with the genotype, but low mesos or low nitrogen concentrations contributed to the necrosis. Hyperhydricity was more prominent with low mesos or low NH₄NO₃. Hooked and upwardly curled new leaves were seen in most genotypes and resulted from use of low mesos in P. communis and low nitrogen for ‘Hang Pa Li’ and P. dimorphophylla. Fasciation and hypertrophy were seen infrequently and resulted from wide imbalances in several nutrients simultaneously. In general, standard concentrations of Murashige and Skoog iron and micros combined with high mesos and moderate nitrogen compounds produced normal shoots without physiological disorders.This is the publisher’s final pdf. The article is copyrighted by the Society for In Vitro Biology and published by Springer. It can be found at: http://link.springer.com/journal/11627Keywords: Mineral nutrition, Micropropagation, Pyrus, Nitrogen, Meso
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Mesos components (CaCl2, MgSO4, KH2PO4) are critical for improving pear micropropagation
Pear accessions and species show a broad response to tissue culture media due to the wide genetic diversity that exists in the available pear germplasm. An initial study of mineral nutrition using a systematic response surface approach with five Murashige and Skoog medium mineral stock solutions indicated that the mesos factor (CaClâ‚‚, MgSOâ‚„, and KHâ‚‚POâ‚„) affected most plant responses and genotypes, suggesting that additional studies were needed to further optimize these three mesos components for a wide range of genotypes. Short stature, leaf spots, edge necrosis, and red or yellow coloration were the main symptoms of poor nutrition in shoot cultures of 10 diverse pear genotypes from six species. A surface response experimental design was used to model the optimal factor and factor levels for responses that included overall quality, leaf character, shoot multiplication, and shoot height. The growth morphology, shoot length, and multiplication of these pear shoots could be manipulated by adjusting the mesos components. The highest quality for the majority of genotypes, including five P. communis cultivars, P. koehnei, P. dimorphophylla, and P. pyrifolia 'Sion Szu Mi', required higher concentrations (> 1.2x to 2.5x) of all the components than are present in Murashige and Skoog medium. 'Capital' (P. calleryana) required high CaClâ‚‚ and MgSOâ‚„ with low KHâ‚‚POâ‚„; for 'Hang Pa Li' (P. ussuriensis), low CaClâ‚‚ and moderate to low MgSOâ‚„ and KHâ‚‚POâ‚„ produced high-quality shoots. Suitable combinations of the meso nutrients produced both optimum shoot number and shoot length in addition to general good plant quality.Keywords: Phosphorous, Pyrus, Media optimization, Calcium, Magnesiu
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The feasibility of using diploid by tetraploid crosses to obtain triploid hops (Humulus lupulus L.)
The hop (Humulus lupulus L.) is a dioecious, diploid (2n=2x=20) species. Triploid
hops (2n=3x=30) are easily obtained from tetraploid by diploid crosses and are preferred
because of their natural seedlessness and increased vigor. The female inflorescence is used
for flavoring beer. Because brewers require product consistency, the brewing characteristics
of a new aroma-type hop must closely match the variety it is intended to replace while
showing improved adaptation and agronomic traits. Since triploid offspring should more
closely resemble the tetraploid parent from which they receive two-thirds of their genetic
material, breeders have traditionally selected known varieties to be the tetraploid parent with
the expectation this will increase the likelihood of obtaining progeny with similar brewing
chemistry. Tetraploid female parents are obtained through colchicine treatment of desirable
diploid varieties.
Naturally occurring tetraploid seedlings, sometimes found among the offspring of
tetraploid by diploid crosses, if suitable for breeding, could eliminate the tedious colchicine
treatment process now used to obtain tetraploids. Two such tetraploid males were obtained
from an Oregon cross in 1983. Since these two tetraploid males had attractive quality traits
similar to other males in the USDA germplasm collection with a proven history of producing
aroma-type progeny, they were thought to be suitable for use in a polyploid breeding program
for aroma hops.
The objective of this study was to determine the feasibility of using males as tetraploid
parents in diploid by tetraploid crosses to obtain triploid aroma hops. Tettnanger, a prized
German aroma hop, was used as the diploid female parent for these crosses.
Meiotic cells of the two tetraploid males showed some abnormalities at anaphase I and
the quartet stage; however, fertility, as determined from seed production and germination,
was adequate for breeding. Of 185 seedlings obtained, 57 were triploid females. The diploid
by tetraploid seedling population had a higher percentage of males than previously reported
for tetraploid by diploid crosses. One tetraploid male produced no triploid female offspring.
Seed content of the female triploid seedlings when subjected to a heavy pollen load averaged
2.4% compared to 20.1% for diploid seedlings from Tettnanger crosses. Triploid progeny
produced higher average yield than the Tettnanger parent.
The two tetraploid males and Tettnanger were very similar in chemical quality traits
comparable in male and female hops. Comparison among triploid and diploid progeny from
diploid by tetraploid crosses and diploid open-pollinated Tettnanger seedlings demonstrated
that the male parent influenced the a ratio, cohumulone content, and humulene to
caryophyllene ratio of the offspring. Many of the female triploid offspring genotypes showed
chemical quality traits similar to those of Tettnanger