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Howick, South Africa

Horsley T.N.,University of KwaZulu - Natal | Horsley T.N.,Shaw Research Center | Johnson S.D.,University of KwaZulu - Natal
Southern Forests | Year: 2010

A previous observation that self-pollen tubes traversed the style at a slower rate than cross-pollen tubes in Eucalyptus grandis and E. urophylla suggested the presence of cryptic self-incompatibility (CSI) in these species. The aim of the present study was, with the help of molecular markers, to examine the siring ability of self- and cross-pollen in a single clone of E. grandis, after both mixed- and single-donor pollinations, in order to confirm the presence of CSI. Single-donor cross-pollinations set a significantly higher number of seeds per flower pollinated compared to those performed with self-pollen, while there were no significant differences between the open control and single-donor self-pollinations. Molecular markers revealed that 100% of the progeny from mixed-donor pollinations were outcrossed, confirming the competitive advantage of cross-pollen. In addition, there was a significant change in the self:outcross seed ratio between single- and mixed-donor pollinations, suggesting that the observed deficit of selfed seeds in mixed-donor fruits could be the result of differential pollen tube growth. From the extremely low seed yields following single-donor self-pollinations, it is clear that an additional incompatibility mechanism is operating in E. grandis, and this is suggested to be late-acting self-incompatibility, acting before fertilisation. © NISC (Pty) Ltd.

Van Der Westhuizen A.,Shaw Research Center
Acta Horticulturae | Year: 2014

Meta-topolin (mT) is a relatively new cytokinin isolated from poplar leaves in 1975 and is closely related to 6-benzyladenine (BA). Research on the use of mT in tissue culture has been conducted on several species, including Hypericum, citrus rootstock, Aloe, banana (Musa acuminata), pineapple (Ananas comosus), and Barleria. 6-Benzyladenine (BA) is the most widely used cytokinin in the regeneration stage of the tissue culture of most plant species, because of its availability and price, but it has a few drawbacks which include causing the hyperhydricity (vitrification) of shoots and it can have a negative effect on rooting. In light of this a series of trials were initiated to determine the effect of mT on the regeneration, hyperhydricity, and rooting of Eucalyptus species. In the initial trial various concentrations of mT (ranging from 1.2 to 14.5 mg·L-1) were tested with the resulting shoot growth compact and stunted. In a follow-up trial, a mT concentration of 0.2 mg·L-1 was found to produce shoots that were less vitrified and that resulted in better in vitro rooting. Further trials on rooting of other eucalypt species are in progress to determine the benefits of mT. © 2014, International Society for Horticultural Science. All rights reserved.

Stanger T.K.,Sappi Forests Pty Ltd | Galloway G.M.,Shaw Research Center | Retief E.C.L.,Shaw Research Center
Southern Forests | Year: 2011

Hybrid clones with Eucalyptus grandis as one parent and, generally, E. urophylla as the other parent, are deployed commercially as monoclonal blocks by Sappi in the subtropical region of coastal Zululand, South Africa. In monoclonal blocks genotypes are grown in self-competition. Performance under this scenario may not necessarily correlate well with performance where genotypes are competing for resources with a number of genetically dissimilar genotypes. There is an uncertainty whether plot configuration or size influences clonal ranking and therefore selection of clones for commercialisation. Final results at age eight years of a trial testing eight selected Eucalyptus hybrid clones in single-tree, eight-tree line, and eight × eight tree square plots are reported in this paper. Ranking of the eight clones between the half rotation (44 months) and full rotation (94 months) measurement have remained stable in the single-tree and line plots, but there have been some changes in the square plots. At 94 months, clonal ranking between the single-tree and line plots was consistent (r p = 0.98) with only two clones changing ranks. When comparing the clonal ranking of the single-tree plots to the large square plots rank changes have been significant (r p = 0.65). The overall means for the three different plot types are very similar. The range of the clonal means for tree volume in the single-tree plots (0.4042 m 3) is more than five times the range for the square plots (0.0709 m 3). Gain predictions using data from the single-tree plots overestimated the realised gains measured in the square plots. The top-performing clone in the single-tree plots had a predicted gain of 74% over the trial mean, but only yielded 7% more in the square plots. Similarly, the worst-ranked clone in the single-tree plots did not perform as poorly as what was predicted (-59%) and produced only 13% less than the trial mean on the square plots. © 2011 Copyright Taylor and Francis Group, LLC.

Eksteen A.B.,University of KwaZulu - Natal | Eksteen A.B.,South African Sugarcane Research Institute | Grzeskowiak V.,Shaw Research Center | Jones N.B.,Shaw Research Center | Pammenter N.W.,University of KwaZulu - Natal
Southern Forests | Year: 2013

This study describes the stomatal response occurring during water stress and subsequent recovery of three Eucalyptus grandis clonal hybrids. The aim was to investigate the degree to which stomatal conductance (gs) and stomatal density differ between the clonal hybrids across seasons and in response to water stress. Plants from one E. grandis × E. camaldulensis (GC) and two E. grandis × E. urophylla (GU1 and GU2) clones were grown for 18 months in 80 l planting bags. Plants were subjected to three watering treatments: control (100% field capacity), chronic water stress (maintained at 15% of field capacity) and acute water stress (cyclic water stress, where water was withheld until leaf wilting point, and a subsequent period of recovery followed). Stomatal conductance was measured after 6, 12 and 18 months growth. At 12 months of age, the recovery of gs 1, 2 and 7 d after rewatering (following acute water stress) was further investigated. The GC hybrid showed consistently higher gs than the GU clones at each measurement period. Stomatal conductance was 24-66% higher during winter (after 12 months growth) than during summer. The recovery of stomatal conductance from acute water stress was more rapid in the GC clone than the GU clones. Chronic water stress was shown to decrease gs in GU clones by up to 70%, but not in the GC clone. Water stress did not affect stomatal density or size. Remarkably, stomata were absent from the adaxial leaf surface of clone GU1 leaves, but not from the leaves of the other E. urophylla hybrid cross (GU2). Total biomass of the GC clone was significantly greater at 9 months growth, but after 18 months growth the GU1 clone had attained greater biomass accumulation (although not significantly). Measurement of gs, transpiration, stomatal density and total biomass in the GU1 clone indicated stomatal sensitivity to water stress, a favourable trait during periods of drought. The differing growth strategies of the GU and GC clones could be partially explained by their differences in stomatal sensitivity in response to water stress. © 2013 Copyright NISC (Pty) Ltd.

Ford C.M.,Shaw Research Center | Ford C.M.,University of Pretoria | Jones N.B.,Shaw Research Center | Chirwa P.W.,University of Pretoria
Southern Forests | Year: 2014

In response to the Fusarium circinatum pine pathogen threat in southern Africa, research has been conducted on the development of F. circinatum-tolerant P. patula and P. patula hybrids. The objective of this study was to investigate the propagation potential of these taxa in two vegetative propagation systems, hydroponic sand beds and polythene bags with composted pine bark growing medium. Significant differences (p < 0.001) in mortality associated with F. circinatum were observed between the P. patula × P. tecunumanii (LE) hybrid (6%) and P. patula (19-23%). No significant differences in mortality associated with F. circinatum were observed within P. patula × P. tecunumanii (LE) families, which ranged from zero to 15%. Significant mortality differences (p < 0.001) were observed between P. patula families, which ranged from 8% to 44%. The number of rooted cuttings produced, per hedge established, over the four-year period was significantly better (p < 0.001) in the P. patula × P. tecunumanii (LE) hybrid (52) than in P. patula (29-33). Significant differences (p < 0.001) were also observed in the number of rooted cuttings produced per family, with P. patula × P. tecunumanii (LE) families ranging from 35 to 70 cuttings per hedge plant established and P. patula families between 20 and 42 cuttings. Over the four-year duration of the trial all taxa showed increased productivity in hedges grown in a hydroponic sand bed system, which received more consistent fertilisation and yielded an average of 55 rooted cuttings per hedge, over those grown in polythene bags with composted pine bark medium, which yielded 41 cuttings on average. This study demonstrated that the P. patula × P. tecunumanii (LE) hybrid is a feasible substitute for P. patula in both vegetative propagation systems, as it not only shows improved survival, through increased F. circinatum tolerance, but also improved productivity. © 2014 Copyright © NISC (Pty) Ltd.

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