Effects of in vitro subculture on the physiological characteristics of adventitious root formation in microshoots of Castanea mollissima cv.'yanshanhong'

Microshoots of Castanea mollissima cv.＇yanshanhong＇ in vitro acquired an enhanced rooting capability with increasing numbers of subculture.In this study,we investigated the effect of successive subculture on adventitious root formation in vitro by the determination of the endogenous hormone level and the enzyme activity.The levels of indoleacetic acid（IAA）,abscisic acid（ABA）,cytokinins（CTK） and gibberellic acid（GA3） were determined by high performance liquid chromatography（HPLC）,and the activities of indoleacetic acid oxidase（IAAO）,peroxidase oxidase（POD）,and polyphenol oxidase（PPO） were measured by ultraviolet-spectrophotometer assay after the induction of rooting at 2nd,4th,6th and 8th subculture.The relationships between physiological characteristics and subculture numbers or rooting rate were as follows：The levels of endogenous IAA in microshoots gradually increased,and endogenous levels of ABA,CTK and GA3 in microshoots decreased slightly after serial subcultures.The level of IAA was highly correlated with subculture numbers and rooting rates.The ratios of IAA/ABA and IAA/CTK both acutely raised with increasing rooting rate during successive subcultures and had high correlations with rooting rate.The activity of IAAO and POD are significantly negatively related with subculture numbers,and the activity of PPO increased after subcultures.

Factors involved in the success of Castanea henryi stem cuttings in different cutting mediums and cutting selection periods

Chinquapin(Castanea henryi) is a dual-purpose tree species in China valued for as a source of timber and starch.We investigated the effect of four cutting mediums(pure vermiculite;peat:river sand at 3:1 v/v;peat:krasnozem at 1:1 v/v;and pure krasnozem) and three stem cutting periods(March,May,and July) on rooting performance of C.henryi cuttings.Different cutting periods and cutting mediums greatly influenced the rooting rate of C.henryi,ranging from 3.35 to 77.31%.Principal component analysis indicated that the best combination of cutting period and cutting medium was semi-hardwood cuttings(May cuttings)+krasnozem.Histological evidence indicated that adventitious root initials were present by week 5-6,and that the site of root primordia initiation was observed in the vascular cambium.Stem anatomical structures observed at different periods indicated that a xylem/radius ratio of29.90-37.42% and a fractured phloem fiber ring are indicative of rooting success.The relational model between rooting index and medium properties indicated that nutrient content and porosity significantly influenced callus production.However,pH strongly affected C.henryi root formation,with the Pearson correlation coefficients for May and July cuttings of-0.856 and-0.947,respectively.Our protocol is helpful to achieve mass clone propagation of improved C.henryi genotypes,thus overcoming a common hurdle in chinquapin breeding programs.