An in vitro shoot regeneration technique combined with colchicine application has been employed to produce hexaploid plants from leaf segments of the triploid cherry rootstock'Gisela 6'(Prunus ceransus ×P.canescens).Leaf segments were treated firstly with colchicine(0-200 mg·L-1) in the liquid modified WPM medium supplemented with auxin(IBA 0.5 mg·L-1) and cytokinin(BA 5.0 mg·L-1) for five days and then transferred on the same regeneration solid medium with no colchicine for 56 days.In this case,putative hexaploid shoots were only regenerated from the leaf explants in the treatment of 50 mg·L-1 colchicine after 8 weeks on the regeneration medium.Flow cytometry was used for ploidy determination.The hexaploid plants were distinguishable from the triploid on morphological characters.All plants were successfully transplanted into field and topworked on the sweet cherry trees to evaluate its agronomic traits.
This study was conducted to investigate the effect of four different NH4+:NO3- ratios (200:0, 100:100, 50:150, and 0:200 mgL-1) in nutrient solution on growth, the nitrogen concentration of various organs, and in vivo nitrate reductase activity (NRA) in pear (Pyrus pyrifolia cv. Niitaka) seedlings in sand culture. Nutrient solutions used in this experiment were adjusted to pH 6.5 and trickle-irrigated 3 times a day, having nitrogen concentration of 200 mgL-1. Tree height and dry weight of seedlings were restricted when NO3- was the sole nitrogen source in the nutrient solution but there was no significant difference among other NH4+:NO3- ratios. The concentrations of nitrate-N in leaves and stems were increased with increasing the NO3- ratio in the nutrient solution, but that of root was not affected. The concentrations of total and reduced nitrogen in leaves and stems increased with increasing the ratios of NH4+ in nutrient solution, but those in roots were insignificantly changed. In vivo +NO3- NRA of all organs was not related to the NH4+:NO3- ratios, whereas the in vivo -NO3- NRA of all organs increased with increasing the ratio of NO3- in all the organs except roots where it decreased. The nitrate reduction occurred in various organs of pear seedlings. Growth and NRA were higher in ammonium or nitrate alone than combined application. Results showed that recommendable NH4+:NO3- ratio for the nutrient solution in pear is 50:150 mgL-1.
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