Tony Page

The 'ideotype concept' and its application to the selection of cultivars of trees providing agroforestry tree products

ABSTRACT The ideotype concept has been developed and modified for a number of different crops, including forest trees, over the last 35 years. In recent years it has been used in the domestication of agroforestry trees producing Agroforestry Tree Products (AFTPs), as an aid to the multiple-trait selection of superior trees for cultivar development. For example in west and central Africa, ‘fruit’ and ‘kernel’ ideotypes have been identified in lrvingia gabonensis (Bush Mango), based on quantitative characterisation of a number of fruit, nut and kernel traits. Subsequently, recognising the opportunity to develop different markets for the commercially important kernels, the ‘kernel ideotype’ has been subdivided into ‘oil’ and ‘food-thickening’ ideotypes, with options for further subdivision of the latter into ideotypes with either high viscosity or high drawability characteristics. Similar opportunities for the development of single-purpose cultivars from multi-purpose species have been identified in Sclerocarya birrea (Marula), indicating that with increasing information about the variability of AFTPs it is possible to develop a hierarchy of different ideotypes to meet different market opportunities. In S. birrea and Dacryodes edulis, future options exist to extend ideotypes with recognition of the variability in both nutritional and organoleptic qualities. In Australia, a very broad-based ideotype has been developed for the indigenous shrub Kunzea pomifera (Muntries) established on both morphological and physiological traits. Similar approaches are identified for timber trees (e.g. Triplochiton scleroxylon) and those like Santalum austrocaledonicum producing essential oils. It is concluded that ideotypes are a useful tool for visualising and conceptualising how to combine specific rare combinations of visible and invisible traits, aimed at the maximisation of Harvest Index, even when the traits are only weakly related.

Tree Domestication in Agroforestry: Progress in the Second Decade (2003–2012)

More than 420 research papers, involving more than 50 tree species, form the literature on agroforestry tree domestication since the 1992 conference that initiated the global programme. In the first decade, the global effort was strongly led by scientists working in humid West Africa; it was then expanded to the rest of Africa in the second decade, with additional growth in Latin America, Asia (mostly SE Asia) and Oceania. While the assessment of species potential and the development and dissemination of techniques for improved germplasm production were the principal activities in the first decade, the second decade was characterized by a growing research agenda that included characterization of genetic variation using morphological and molecular techniques, product commercialization, adoption and impact and protection of farmers’ rights. In parallel with this expanding research agenda, there was also an increasing use of laboratory techniques to quantify genetic variation of the chemical and physical composition of marketable products (e.g. essential oils, food-thickening agents, pharmaceutical and nutriceutical compounds, fuelwood). Looking to the third decade, suggestions are made for further development and expansion of both the science to underpin agroforestry tree domestication and applied research in support of development programmes to enhance the livelihoods of poor smallholder farmers worldwide.

Geographic and phenotypic variation in heartwood and essential-oil characters in natural populations of Santalum austrocaledonicum in Vanuatu

Phenotypic variation in heartwood and essential‐oil characters of Santalum austrocaledonicum was assessed across eleven populations on seven islands of Vanuatu. Trees differed significantly in their percentage heartwood cross‐sectional area and this varied independently of stem diameter. The concentrations of the four major essential‐oil constituents (α‐santalol, β‐santalol, (Z)‐β‐curcumen‐12‐ol, and cis‐nuciferol) of alcohol‐extracted heartwood exhibited at least tenfold and continuous tree‐to‐tree variation. Commercially important components α‐ and β‐santalol found in individual trees ranged from 0.8–47% and 0–24.1%, respectively, across all populations, and significant (P<0.05) differences for each were found between individual populations. The Erromango population was unique in that the mean concentrations of its monocyclic ((Z)‐β‐curcumen‐12‐ol and cis‐nuciferol) sesquiterpenes exceeded those of its bi‐ and tricyclic (α‐ and β‐santalol) sesquiterpenes. Heartwood colour varied between trees and spanned 65 colour categories, but no identifiable relationships were found between heartwood colour and α‐ and β‐santalol, although a weak relationship was evident between colour saturation and total oil concentration. These results indicate that the heartwood colour is not a reliable predictive trait for oil quality. The results of this study highlight the knowledge gaps in fundamental understanding of heartwood biology in Santalum genus. The intraspecific variation in heartwood cross‐sectional area, oil concentration, and oil quality traits is of considerable importance to the domestication of sandalwood and present opportunities for the development of highly superior S. austrocaledonicum cultivars that conform to the industrys International Standards used for S. album.

Sandalwood: basic biology, tissue culture, and genetic transformation

AbstractMain conclusionSustainable resource preservation ofSantalumspecies that yield commercially important forest products is needed. This review provides an understanding of their basic biology, propagation, hemi-parasitic nature, reproductive biology, and biotechnology. Many species of the genus Santalum (Santalaceae) have been exploited unremittingly for centuries, resulting in the extinction of one and the threatened status of three other species. This reduction in biodiversity of sandalwood has resulted from the commercial exploitation of its oil-rich fragrant heartwood. In a bid to conserve the remaining germplasm, biotechnology provides a feasible, and effective, means of propagating members of this genus. This review provides a detailed understanding of the biological mechanisms underlying the success or failure of traditional propagation, including a synopsis of the process of hemi-parasitism in S. album, and of the suitability of host plants to sustain the growth of seedlings and plants under forestry production. For the mass production of economically important metabolites, and to improve uniformity of essential oils, the use of clonal material of similar genetic background for cultivation is important. This review summarizes traditional methods of sandalwood production with complementary and more advanced in vitro technologies to provide a basis for researchers, conservationists and industry to implement sustainable programs of research and development for this revered genus.

Variation in Growth Traits and Wood Density in Whitewood (Endospermum medullosum): a Major Timber Species in Vanuatu

SUMMARY A breeding program aimed at increasing economic value of whitewood plantations in Vanuatu and conserving declining genetic resources will take direction from the results of this study. Genetic parameters for stem diameter breast height over bark (DBHOB), straightness and branching were estimated in an 11.4-year-old whitewood breeding population on Espiritu Santo Island. Wood density variation in one subpopulation was also studied. Trees with the fastest growth and best form were from Espiritu Santo. Growth and form trait heritability estimates ( = 0.10–0.16) were low to moderate, with moderate phenotypic variation (CVP = 17–36%). DBHOB at 11.4-years and 4-years were very closely genetically correlated (rA = 1.00 ± 0.17). Mean unextracted wood basic density at breast height was 330 (SD±21) kg/m3, or similar to mature-tree densities. Economic gain in growth traits can be expected from a recurrent selection and breeding program given the heritable genetic variation indicated in this study. Conserving genetic diversity in this species is a high priority.

Onset and duration of stigma receptivity in Kunzea pomifera (Myrtaceae)

The onset and duration of stigma receptivity in K. pomifera was evaluated by observing stigma peroxidase activity, pollen-tube growth and seed set, following controlled pollination of flowers of different ages. Peroxidase activity was negligible from 1 day before to 4 days after anthesis, increasing to a peak of 65% at Day 13. The percentage of pistils bearing germinated pollen and ovaries exhibiting pollen-tube entry increased when pollen was applied to the stigma from the day before anthesis, to a maximum at Days 6 and 7 after anthesis, respectively, followed by a decline by Day 9. Under greenhouse conditions the optimum pollination period, measured as the level of set seed after pollination, ranged from 2 to 11 days after anthesis. The knowledge of this aspect of the species reproductive biology is of considerable value in controlled pollinations for its improvement as a new crop.

Breeding behaviour of Kunzea pomifera (Myrtaceae): self-incompatibility, intraspecific and interspecific cross-compatibility

To examine breeding system characteristics of the endemic Australian prostrate shrub Kunzea pomifera, artificial hybridisations were undertaken using thirteen different genotypes of K. pomifera, to elucidate: (1) self-incompatibility, (2) intraspecific cross-compatibility in the species and (3) interspecific cross-compatibility with each of K. ambigua and K. ericoides. K. pomifera exhibited very low self-compatibility, with the barrier to self-fertilisation being prevention of pollen-tube growth in the style or ovary. Following intraspecific pollination amongst a number of different genotypes of K. pomifera, 38.4% of pollinated flowers developed fruit; arrest of compatible pollen-tubes in the style, preventing fertilisation, contributes to the low fruit set in this species. Interspecific compatibility was examined between K. pomifera (pistillate parent) and K. ambigua (staminate parent) where seed set per pollinated flower (4.47) was not significantly different from intraspecific crosses (4.66). In crosses between K. pomifera (pistillate parent) and K. ericoides as staminate plant, 0.037% of pollinated flowers produced fruit, with 0.0075 seeds per pollinated flower. Reproductive barriers between these two species were evident in the style of K. pomifera, where the growing tips of the K. ericoides pollen-tubes swelled and ceased to grow.

Production of sandalwood (Santalum austrocaledonicum) for improved smallholder incomes in Vanuatu

ABSTRACT Vanuatu is a Pacific Island nation with a wealth of forest resources that provide benefits to local communities on both subsistence and commercial levels. Sandalwood (Santalum austrocaledonicum) is sought for its fragrant heartwood oils and is harvested primarily from wild stands and sold to local exporters. It is the most lucrative of all forest products in Vanuatu and has been exploited commercially since the 1820s. Recent assessments of wild populations reveal that resources are now limited and, with current harvesting practices, are expected to decline further. However, considerable smallholder interest in establishing sandalwood plantings is being sustained by the current high international values for sandalwood products. Over the past 20 years the Vanuatu sandalwood price index has increased at an annual rate of 10% compared with 2.7% for the Vanuatu consumer price index (CPI). The rate of sandalwood planting in Vanuatu between 2000 and 2006 (14,250 trees p.a.) was significantly greater than for the previous 7 years 1993–1999 (478 trees p.a.). This study reveals that smallholder sustainable sandalwood production is economically feasible. A sandalwood agroforest harvested for heartwood has a Net Present Value (NPV) that is approximately 13.5 times swidden cropping, 1.5 times that of a pure stand of planted sandalwood harvested for heartwood and 280 times that of a sandalwood planting harvested for sapwood. The sandalwood agroforest returns the equivalent income to that of a Vanuatu Government employee with a technical college diploma, which is much greater than many smallholders can expect to earn from other activities. The low numbers of mature sandalwood accessible for seed collection and recent high demand for seed however, have led to considerable shortages of planting material to meet smallholder planting goals. This has resulted in significant price increases for sandalwood seed in all areas of Vanuatu. Recent research and development work has secured a genetic resource with improved heartwood oil quality. Thus the Vanuatu sandalwood industry will greatly benefit from deployment of selected genotypes to (a) increase supply of sandalwood seed available for agroforestry and (b) improve the heartwood oil quality of planted trees.

Basic Density, Diameter and Radial Variation of Vanuatu Whitewood (Endospermum medullosum): Potential for Breeding in a Low Density, Tropical Hardwood

SUMMARY Vanuatu whitewood (Endospermum medullosum L.S. Smith) is an economically important timber species for Vanuatu. Inter- and intraprovenance genetic parameters for stem diameter at breast height, basic density and radial variation in density, were estimated for two provenances selected from a 12.4-year-old open-pollinated seed orchard on Espiritu Santo Island, Vanuatu. Kole provenance exhibited the highest mean basic density, greatest mean diameter and greatest radial variation in density across the stem. Mean basic density at breast height was 345±2 kg/m3. Growth rings were not visually discernable and colour was homogenous across all samples. For radial variation determination, each pith-bark core was sectioned into four equi-length subcores (A–D). Subcore density increased consistently and significantly from pith to bark, with mean basic density of 308±3, 327±3, 343±3 and 359±3 kg/m3 for cores A–D respectively. The narrow-sense heritability estimate () was low (0.26±0.2) for diameter, with a moderate coefficient of additive genetic variation (CVA= 17.61%). Estimated for density was moderate (0.49±0.24), with a low coefficient of additive genetic variation (CVA= 5.39%). Though the precision of these estimates is modest, reflective of the small sample size, indications are that the heritable genetic variation in both growth and quality traits will result in economic gain from a recurrent selection and breeding program.

Reproductive biology of three commercially valuable Santalum species: development of flowers and inflorescences, breeding systems, and interspecific crossability

Santalum (sandalwood) spp. are hemi-parasitic trees, the heartwood of which produces valuable aromatic oil. There appears to be a significant commercial opportunity for establishment of a planted sandalwood resource. However, lack of basic biological knowledge is one constraint on such development. The study reported here addresses one such constraint. Controlled pollination using 13 genotypes of Santalumlanceolatum was undertaken to elucidate (i) self-incompatibility (ii) intraspecific cross-compatibility in the species, and (iii) interspecific cross-compatibility with S. album and S. austrocaledonicum. S. lanceolatum may be considered to have a facultative allogamous (incomplete outbreeding) breeding system. This study found variation between genotypes in the level of putative self-incompatibility: some (20%) were found to set seed following self-pollination, while the remaining 80% had no seed development with such pollinations. However, a significantly greater proportion of genotypes developed seed following intraspecific cross-pollination (62%) compared with self-pollination (20%). While total geographic isolation and significant morphological divergence exists between S. lanceolatum with each of S. album and S. austrocaledonicum this study found no indication of reproductive barrier(s) between them, indicating potential for use of interspecific hybridization in genetic improvement, but also suggesting the potential of undesirable gene flow between native and introduced species.