Jonathan P. Cornelius

Genetic diversity in Mesoamerican populations of mahogany ( Swietenia macrophylla ), assessed using RAPDs

Swietenia macrophylla King, a timber species native to tropical America, is threatened by selective logging and deforestation. To quantify genetic diversity within the species and monitor the impact of selective logging, populations were sampled across Mesoamerica, from Mexico to Panama, and analysed for RAPD DNA variation. Ten decamer primers generated 102 polymorphic RAPD bands and pairwise distances were calculated between populations according to Nei, then used to construct a radial neighbour-joining dendrogram and examine intra- and interpopulation variance coefficients, by analysis of molecular variation (AMOVA). Populations from Mexico clustered closely together in the dendrogram and were distinct from the rest of the populations. Those from Belize also clustered closely together. Populations from Panama, Guatemala, Costa Rica, Nicaragua and Honduras, however, did not cluster closely by country but were more widely scattered throughout the dendrogram. This result was also reflected by an autocorrelation analysis of genetic and geographical distance. Genetic diversity estimates indicated that 80% of detected variation was maintained within populations and regression analysis demonstrated that logging significantly decreased population diversity (P = 0.034). This study represents one of the most wide-ranging surveys of molecular variation within a tropical tree species to date. It offers practical information for the future conservation of mahogany and highlights some factors that may have influenced the partitioning of genetic diversity in this species across Mesoamerica.

Genetic variation in Costa Rican populations of the tropical timber species Cedrela odorata L., assessed using RAPDs

Cedrela odorata L. (Spanish cedar), an economically important timber species native to the American tropics, is the focus of increasing conservation concern due to high rates of deforestation within its native range. To assess the extent of the genetic diversity within and between populations of this species, samples were obtained from 10 widely dispersed populations within Costa Rica and analysed for random amplified polymorphic DNA (RAPD) variation. Fourteen 10‐mer primers were used to generate 97 polymorphic RAPD bands. Presence/absence data for all bands were subjected to a pairwise genetic distance analysis, according to Jaccards coefficient, then neighbour‐joining cluster analysis was performed on these distances, as was an analysis of molecular variance (AMOVA), to assess levels of differentiation between populations and regions, and Shannons Diversity Index was used to quantify levels of diversity within and between populations. Results indicated highly significant genetic differentiation (P < 0.004, AMOVA) between populations originating from the North Pacific and Atlantic/South Pacific regions of Costa Rica, with 35.3% of the total variation attributable to a difference between these areas. Little differentiation was recorded between populations from within the same region (P= 0.757, AMOVA), and 65.1% of the total variance was attributable to variation within populations. Estimated values for within‐population diversity, calculated as Hpop/Hsp by means of Shannons Diversity Index, were found to vary greatly between primers, but the overall within‐population component of genetic diversity was 0.45. Possible reasons for the high degree of intraspecific genetic variation within this species are discussed and the implications of these results for the conservation and use of its genetic resources are described.

What is the relevance of smallholders’ agroforestry systems for conserving tropical tree species and genetic diversity in circa situm, in situ and ex situ settings? A review

Smallholders’ agroforests may be valuable for conserving tropical trees through three main mechanisms. First, trees planted and/or retained by farmers in agricultural landscapes where wild stands were once found may be circa situm reservoirs of biodiversity. Second, farmland trees may support conservation in situ by providing an alternative source of product to reduce extraction from forest, and by acting as ‘corridors’ or ‘stepping stones’ that connect fragmented wild stands. Third, the additional value that planting assigns to trees may result in greater interest in including them in seed collections, field trials and field ‘genebanks’ that support ex situ conservation. Here, we critically review the evidence for these mechanisms, and highlight areas for research and for intervention so that agroforestry practices can better support conservation in each setting, with an emphasis on often neglected genetic-level considerations. Based on current global challenges to diversity, conservation will need to rely increasingly on a smallholder-farm circa situm approach, but concerns on long-term effectiveness need to be properly quantified and addressed. Connectivity between widely dispersed, low density trees in agricultural landscapes is an important factor determining the success of the circa situm approach, while improving farmers’ access to a diversity of tree germplasm that they are interested in planting is required. The circumstances in which agroforestry plantings can support in situ conservation need to be better defined, and research on the stability of active tree seed collections (how long are species and populations retained in them?) as ex situ reservoirs of biodiversity is needed.

Genetic variation in host susceptibility to attack by the mahogany shoot borer, Hypsipyla grandella (Zeller)

1 Attack by shoot borers (Hypsipyla grandella Zeller) is the main factor limiting the cultivation of Cedrela odorata and Swietenia macrophylla, two economically important members of the mahogany family. No viable methods of pest control are currently available. To assess for genetic variation in susceptibility to pest attack, a combined progeny/provenance test of C. odorata and a provenance test of S. macrophylla were established separately at CATIE, Turrialba, Costa Rica, and assessed intensively over an 84‐week period.

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.

The effectiveness of plus-tree selection for yield

Abstract In response to recent suggestions in the literature that plus-tree selection for yield in forest trees might in general be ineffective, the empirical information contained in 24 published reports was examined. It was found that progeny of plus-trees selected for yield traits tend to be faster growing than their controls. It is argued that this observed tendency is likely to be due at least in part to a response to selection. The reported values indicate that genetic gains of up to 15% in height and diameter growth, and up to 35% in volume per unit area, can readily be achieved through plus-tree selection. This is consistent with theoretical expectations. However, it should be emphasised that the amount of gain from any particular plus-tree selection system depends on the values of the parameters that determine the response to selection (selection intensity, genetic variance, heritability). In unfavourable situations, gain could be close to zero.

The trade-off between genetic gain and conservation in a participatory improvement programme: the case of peach palm (Bactris gasipaes Kunth)

ABSTRACT Finding an equilibrium between genetic resources conservation and genetic improvement can be difficult. The problem is explored in this paper, partly through a case study of a participatory improvement programme of peach palm (Bactris gasipaes Kunth, Palmae), implemented in the Peruvian Amazon by the World Agroforestry Centre (ICRAF) and the Peruvian National Institute for Agricultural Research and Extension (INIEA). Peach palm, which was originally domesticated by Amerindians, produces a range of useful substance and marketable products, but today the fruit and heart-of-palm are the principal products. The characteristics of the clients (subsistence smallholders and agro-industrial plantation companies) for these crops and those of the ICRAF-INIEA project are described, and the impact on genetic diversity of future management options is explored. This is followed by a wider discussion of the relationships between genetic gain and maintenance of genetic diversity for improvement, and their implications. The ICRAF-INIEA programme was designed to emphasize genetic conservation and timely germplasm delivery rather than genetic gain. The analysis presented here suggests that, with careful management, genetic diversity can be effectively conserved through 20 generations of improvement. Nevertheless, there is a fundamental conflict between genetic gain and genetic conservation. Consequently, no improvement programme can conserve all of the genetic diversity of a landrace or species and genetic resource management strategies must be developed to resolve these conflicts through explicit and informed decisions. Some such strategies, corresponding to different levels of emphasis on gain versus diversity, are presented.

Genetic variation in a Hypsipyla-attacked clonal trial of Cedrela odorata under two pruning regimes

Cedrela odorata is in many ways well suited to plantation silviculture. However, this potential has not been realized, largely due to the attack of the mahogany shoot borer, Hypsipyla grandella, which destroys growing shoots, retards growth and causes forking. The present paper reports on genetic variation in a shoot borer attacked clonal trial. We found significant provenance and clonal variation in several measures of final tree quality, all related to both form and growth. The results indicate the potential of genetic selection as an element of integrated management of mahogany shoot borers.

Is local best? Examining the evidence for local adaptation in trees and its scale

BackgroundAlthough the importance of using local provenance planting stock for woodland production, habitat conservation and restoration remains contentious, the concept is easy to understand, attractive and easy to ‘sell’. With limited information about the extent and scale of adaptive variation in native trees, discussion about suitable seed sources often emphasises “local” in a very narrow sense or within political boundaries, rather than being based on sound evidence of the scale over which adaptation occurs. Concerns exist over the actual scale (magnitude and spatial scale) of adaptation in trees and the relative dangers of incorrect seed source or restricted seed collection, leading to the establishment of trees with restricted genetic diversity and limited adaptive potential. Tree provenance and progeny field trials in many parts of the world have shown the existence of genotype by environment interaction in many tree species, but have not necessarily looked at whether this is expressed as a home site advantage (i.e. whether provenance performance is unstable across sites, and there is better performance of a local seed source).Methods/designThis review will examine the evidence for local adaptation and its scale in a number of native tree species from different trial sites across the globe (e.g. tropical, Mediterranean, temperate). These trials have been measured and in some cases results published in a range of formats. The data have, however, usually been presented in the form of which provenances grow best at which sites. The review will examine existing data (published and unpublished) in the context of the scale of local adaptation, with the results being presented in two formats: (a) relating survival, performance of provenances (classified by seed zone/provenance region of origin) to seed zone/provenance region of the planting site; (b) plotting survival, performance provenances against the distance (Euclidean/ecological) between the provenance and the trial site.

Tree Seed and Seedling Supply Systems: A Review of the Asia, Africa and Latin America Models

The paper reviews tree seed and seedling supply systems in sub-Saharan Africa, Asia and Latin America. Across these regions, the review found that some of the germplasm supply systems do not efficiently meet farmers’ demands and environmental expectations in terms of productivity, species and genetic diversity. In some countries, germplasm used is mostly sourced from undocumented sources and often untested. Germplasm quality control systems are only found in a few countries. Appreciation of the value of tree germplasm of high genetic quality is low. Non-government organisations (NGOs) in many African countries play a prominent role in the supply of germplasm which is usually given to farmers without charge. The practice of giving farmers free germplasm by NGOs in many African countries and also government participation in germplasm supply in some Asian countries has been blamed for crowding out private entrepreneurs, although this is not substantiated by any evidence to suggest that the smallholder farmers are willing and able to pay for the germplasm. In some Latin American countries, private companies, government and NGOs provide farmers tree germplasm in a partnership in which farmers provide land and labour in return. Overall, tree germplasm markets are large in Asia, due in part to large afforestation programs, intermediate in Latin America and small in Africa where smallholder farmers constitute the market. In countries where germplasm quality control is practiced, it is either through a legal framework or voluntary. A few countries in Africa, Asia and Latin America have developed protocols for certification of tree seeds based on the OECD. Some germplasm suppliers use branding as a way of differentiating their germplasm as having superior quality. To enhance the use of high quality germplasm, there is a need to demonstrate the value of using such germplasm and raise awareness of germplasm quality among the farmers and policy-makers.