A Diploid–Tetraploid Cytochimera of Dashu Tea Selected from a Natural Bud Mutant

Polyploids play significant roles in tea production due to their strong tolerance to adverse environmental conditions and their high levels of certain chemical components. Tetraploid can be used to produce more polyploid tea plants, but there have been only a handful of tetraploids found in tea plants. In spite of the extremely low probabilities, bud mutant selection is an effective way to obtain polyploid tree crops. In the present study, a Dashu tea, cytochimera, derived from a bud mutation was identified by using flow cytometry and chromosome observation. The morphology and photosynthetic characteristics of leaves were investigated briefly. Some chemical components were determined. Finally, the pollen viability and ploidy of progeny were detected. The results show that tetraploid cells account for 71.48 ± 3.88%–72.19 ± 2.80% of the leaf tissue in this cytochimera. Compared with the original diploid, the cytochimera exhibited broader, longer, and thicker leaves. Its net photosynthetic rate (high to 41.77 ± 0.38 μmol CO₂‧m⁻²‧s⁻¹) was higher than that of the original diploid (peak value 28.00 ± 2.29 μmol CO₂‧m⁻²‧s⁻¹) for most of the day when measured in September. Notably, the total content of 19 free amino acids in the tender spring shoots of cytochimera was 22.96 ± 0.58 mg/g, approximately twice of that of the diploid materials analyzed. The contents of 10 free amino acids, including theanine, were significantly higher than those in diploids, with some free amino acid contents reaching up to seven times those observed in diploids. In addition, the cytochimera produced larger pollen grains than the original diploid, although the in vitro germination rate was lower (14.63 ± 1.11%). Three open-pollinated progenies of cytochimera were identified as triploids. To sum up, cytochimera has larger and thicker leaves, a higher photosynthetic rate, and higher content of total free amino acids and some free amino acids, especially theanine, than the original diploid. Moreover, cytochimera has a certain level of fertility and can produce triploids. These findings suggest the potential for selecting polyploid tea plants from bud mutants and for developing new tea germplasms with enhanced amino acid contents.