Root–shoot allometry of tropical forest trees determined in a large-scale aeroponic system

Background and Aims

This study is a first step in a multi-stage project aimed at determining allometric relationships among the tropical tree organs, and carbon fluxes between the various tree parts and their environment. Information on canopy–root interrelationships is needed to improve understanding of above- and below-ground processes and for modelling of the regional and global carbon cycle. Allometric relationships between the sizes of different plant parts will be determined.

Methods

Two tropical forest species were used in this study: Ceiba pentandra (kapok), a fast-growing tree native to South and Central America and to Western Africa, and Khaya anthotheca (African mahogany), a slower-growing tree native to Central and Eastern Africa. Growth and allometric parameters of 12-month-old saplings grown in a large-scale aeroponic system and in 50-L soil containers were compared. The main advantage of growing plants in aeroponics is that their root systems are fully accessible throughout the plant life, and can be fully recovered for harvesting.

Key Results

The expected differences in shoot and root size between the fast-growing C. pentandra and the slower-growing K. anthotheca were evident in both growth systems. Roots were recovered from the aeroponically grown saplings only, and their distribution among various diameter classes followed the patterns expected from the literature. Stem, branch and leaf allometric parameters were similar for saplings of each species grown in the two systems.

Conclusions

The aeroponic tree growth system can be utilized for determining the basic allometric relationships between root and shoot components of these trees, and hence can be used to study carbon allocation and fluxes of whole above- and below-ground tree parts.     

Production and rooting behaviour of <Emphasis Type="Italic">rol</Emphasis>B-transgenic plants of grape rootstock ‘Richter 110’ (<Emphasis Type="Italic">Vitis berlandieri × V. rupestris</Emphasis>)

Genetic improvement of grape rootstocks is aimed at protection against grape phylloxera and other soil-borne pests and diseases, good rooting and graft compatibility as well as adaptability to a wide range of soil and climatic conditions. Apart from the long evaluation period required, breeding is complicated by the high heterozygosity in grapes. As an alternative to traditional crossing, gene transfer permits addition of single traits, largely without affecting the genetic background of existing valuable cultivars. Here we report on the production and rooting behaviour of transgenic grape rootstock ‘Richter 110’ carrying the Agrobacterium rhizogenes rolB gene, which is known to promote rooting. Transformation was achieved by co-cultivation of somatic embryogenic callus with Agrobacterium tumefaciens LBA4404 harbouring plasmid pHrB. The T-DNA of pHrB contains the hpt gene, conferring hygromycin resistance, and the rolB gene under control of its own promoter. PCR using transgene-specific primers verified the presence of hpt in all 36 hygromycin resistant clones selected, while only 24 clones also possessed the rolB gene. Rooting behaviour was examined in vitro, using tip, node and internode explants, and in aeroponic culture in the greenhouse, using single-node cuttings. Compared to internodes of non-transgenic ‘Richter 110’, those of rolB-transgenic clones in general showed significantly higher rooting ability and, in contrast to the former, were able to root profusely even in the absence of auxin. Cuttings of three rolB-transgenic clones in aeroponic culture produced almost twice as many primary roots as those of the non-transgenic control.     

Evaluation of aeroponics for clonal propagation of Caralluma edulis,Leptadenia reticulata and Tylophora indica – three threatened medicinal Asclepiads

The present study explores the potential of aeroponic system for clonal propagation of Caralluma edulis (Paimpa) a rare, threatened and endemic edible species, Leptadenia reticulata (Jeewanti), a threatened liana used as promoter of health and Tylophora indica (Burm.f.) Merill, a valuable medicinal climber. Experiments were conducted to asses the effect of exogenous auxin (naphthalene acetic acid, indole-3-butyric acid, indole-3-acetic acid) and auxin concentrations (0.0, 0.5, 1, 2, 3, 4 or 5gl⁻¹) on various root morphological traits of cuttings in the aeroponic chamber. Amongst all the auxins tested, significant effects on the length, number and percentage of rooting was observed in IBA treated nodal cuttings. Cent per cent of the stem cuttings of C. edulis rooted if pre-treated with 2.0 gl⁻¹ of IBA for 5 min while 97.7 % of the stem cuttings of L. reticulata and 93.33 % of stem cuttings of Tylophora indica rooted with pre-treatment of 3.0 gl⁻¹ of IBA for 5 min. Presence of at least two leaves on the nodal cuttings of L. reticulata and T. indica was found to be a prerequisite for root induction. In all the species, the number of adventitious roots per cutting and the percentage of cuttings rooted aeroponically were significantly higher than the soil grown stem cuttings. Shoot growth measured in terms of shoot length was significantly higher in cuttings rooted aeroponically as compared to the cuttings rooted under soil conditions. All the plants sprouted and rooted aeroponically survived on transfer to soil. This is the first report of clonal propagation in an aeroponic system for these plants. This study suggests aeroponics as an economic method for rapid root induction and clonal propagation of these three endangered and medicinally important plants which require focused efforts on conservation and sustainable utilization.