Harvesting genetics for productive plantations : creating new germplasm

Tree breeding has had significant impacts on the success of the South Africa forest industry. Examples are cited for tree growth rate, where for instance, a mean genetic improvement of 39% has been measured in F2 E.grandis over unimproved controls over various sites. The mean improvement of F1 over P0 was recorded as 15% in the genetic gains trials, which compares with the realised reduction of rotation length by 10-15% in sawtimber crops. In E.grandis sawtimber, the impact of wood splitting has been reduced by approximately 29%. Similarly, substantial progress has been made in stem form, and species selection against pest and diseases. Selection of species with suitable properties for pulp yield is currently gaining momentum, with the increasing use of E.smithii, and the initiation of Project Pulp. Tree breeding will have to harness increasingly sophisticated technologies to make advances in the traits which have already undergone some improvement, such as tree growth. This is due to the gradual fixing of the genes which are easily captured, leaving the more challenging inheritance for advanced breeding techniques. There is a constant change in the market needs from trees (and tree breeders), as technologies change, markets change, and the environment changes. Tree breeding will continue to be a critical tool in maintaining a healthy forestry industry. Southern African Forestry Journal No.195 2002: 83-8

Consideration of wood quality traits in the prediction of <I>Eucalyptus grandis</I> sawtimber recovery and veneer value recovery in South Africa.

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Broad- and narrow-sense heritabilities in a South African cloned open-pollinated Eucalyptus grandis breeding population

Genetic variances and heritabilities of a 66-month old cloned Eucalyptus grandis breeding population of families, derived from open-pollinated selections, were estimated. The genetic variance for the growth traits was largely additive genetic variance, whereas the proportion of non-additive genetic variance was notably higher for stem form and disease tolerance. A notably larger proportion of non-additive variance was observed for the growth traits and stem form among the F2 families. This is probably due to the reduction in additive variance through selection for general combining ability for these traits in the previous generations. No selection for disease took place in earlier generations and the proportion of non-additive genetic variance for this trait remains approximately the same for families of different generations.Southern Hemisphere Forestry Journal 2007, 69(2): 81–9

A comparison of deterministically predicted genetic gains with those realised in a South African Eucalyptus grandis breeding program

Tree breeders attempt to predict the genetic gains that are likely to be achieved through selection and breeding of new generations, using stochastic or deterministic modelling. There are many factors  that may cause a discrepancy between the predicted and realised genetic gains. Often the predictions for genetic gains are based on single trait selection, whereas in reality the breeding tends to be multitrait in nature. The violation of Hardy-Weinberg conditions, assumptions regarding outcrossing and relatedness, assumptions regarding the effect of the interaction between the  environment and the genotype, and numerous possible errors in the process of breeding, all could  result in unexpected discrepancies between the realised and predicted genetic gains. A series of genetic gains trials containing representatives of three generations of Eucalyptus grandis selections  were compared with the view to verifying the effectiveness of the E. grandis breeding program. Genetic gains of the F3 (third generation of pedigreed progeny) over the F2 generation (second generation of pedigreed progeny) were 15% for tree growth (volume). A comparison between F2 and P0 revealed an improvement of between 20% and 33% for growth. This exercise highlighted complexities of modelling the predicted genetic gains of assimilated genetic breeding trials. The predictions of genetic gains did deviate (in both directions) from those realised, although these deviations may be explained as functions of imperfect modelling. On average, however, the predicted genetic gains for tree volume over three  generations was 13% between generations,  whereas the average realised genetic gain in the genetic gains trial was 14%. It is therefore assumed that the E. grandis breeding population is indeed performing as expected, following classical tree breeding assumptions. Southern Forests 2009, 71(2): 141–14

A comparison of collinearity mitigation techniques used in predicting BLUP breeding values and genetic gains over generations

Collinearity potentially has a negative impact on the prediction of genetic gains in tree breeding programs. This study investigated the reliability and impact of best linear unbiased prediction (BLUP) using various collinearity mitigation techniques and of two computational numerical precisions on the genetic gains in breeding populations. Multiple-trait, multiple-trial BLUP selection scenarios were run on Eucalyptus grandis (F1, F2 and F3) and Pinus patula (F1 and F2) data, comparing predicted breeding values of parents (forward prediction) with those realised in progeny (backward prediction of parents). Numeric precision had an impact on intergenerational correlations of BLUPs of some scenarios, indicating that it may not always be optimal to use higher precision when there is collinearity in the data. The relative difference in genetic gains between techniques varied by up to 0.38 standard deviation units in the less-stable pine population. This highlights the potentially large impact that instability can have on the efficiency of a breeding programme. BLUP performed close to expected in the relatively stable (less collinear) population (eucalypt F1), and performed poorly in the other two populations. In the unstable pine data, some of the techniques resulted in improved intergenerational correlations coming in line with expected performance. This study indicates that BLUP can perform as expected and also confirms the potential problem of instability and consequences thereof. BLUP users should examine the nature of the population of predicted values and should these be outside expectation, various mitigation techniques should be explored.http://www.tandfonline.com/loi/tsfs20nf201

An investigation of assumptions made in estimating genetic parameters and predicting genetic gain in a Eucalyptus nitens breeding programme in South Africa

It is important to have an understanding of the population genetics and validity of the pertinent underlying assumptions of a species in order to design an effective breeding strategy. In a South African breeding population of Eucalyptus nitens, various scenarios investigating a range of assumptions were developed and used to predict genetic gain in the F2. These were compared with realised gains achieved in a series of genetic gain trials. In the two scenarios using firstly, actual flowering for family (provenance) and, secondly, estimated flowering after 30 % roguing of poor families, a coefficient of relationship of 0.33 resulted in predictions closest to realised gain, on average. The statistical information suggested that outcrossing in the seed orchards was[80 %. Indications were that the effects were additive, and that very little or no heterosis had occurred, due to the still significant provenance effects and the lack of provenance rank changes in the F2. The custom of assuming a degree of inbreeding (and using a coefficient of relationship of 0.33) and of including provenance effects in the models, on average resulted in genetic gain predictions which were very similar to the realised genetic gains in this population of E. nitens.Masonite Ltd., Mondi Ltd, NCT Forestry Co-Operative Ltd., PG Bison, TWK Ltd. and York Timbers Ltd.http://link.springer.com/journal/110562016-01-31hb201