Individual Narrow-sense Heritability Research Articles

Genetic variability and <i>ex situ</i> conservation strategies for the neotropical tree <i>Parkia platycephala</i> Benth.

Parkia platycephala, known commonly as faveira, is a native species that occurs widely throughout Brazil and has high nutritional value and ecological potential. The objective of this study was to estimate the genetic variability in a P. platycephala provenance and progeny test. The test was established using a randomized block design, with 45 progenies from three provenances. The evaluated quantitative traits included height (HEI), diameter at ground level (DGL), and diameter below the first bifurcation (DFB). The data were submitted to Restricted Maximum Likelihood/Best Linear Unbiased Prediction (REML/BLUP) analysis, from which estimates of genetic parameters, genetic correlations, BLUPs, genetic gains, and effective population size were obtained. Estimates of individual narrow sense heritability (h2a) and within progeny heritability (h2w) ranged from low to moderate (0.01 a 0.39), with the highest values observed for DGL (0.32 and 0.39, respectively). The coefficient of individual variation (CVgi(%)) and between progeny genetic variation (CVgp(%)) indicate the existence of genetic variability between and within provenances. The FST vaues demonstrate low to moderate genetic differentiation among the three populations, and genetic correlations between traits were all positive and significant. The results obtained show that there is genetic variability between the studied provenances and progenies. This ensures not only the ex situ conservation of the species, but it can also be exploited in breeding programs.

Updating knowledge in estimating the genetics parameters: Multi-trait and Multi-Environment Bayesian analysis in rice

Among the multi-trait models selected to study several traits and environments jointly, the Bayesian framework has been a preferred tool when constructing a more complex and biologically realistic model. In most cases, non-informative prior distributions are adopted in studies using the Bayesian approach. However, the Bayesian approach presents more accurate estimates when informative prior distributions are used. The present study was developed to evaluate the efficiency and applicability of multi-trait multi-environment (MTME) models within a Bayesian framework utilizing a strategy for eliciting informative prior distribution using previous data on rice. The study involved data pertaining to rice (Oryza sativa L.) genotypes in three environments and five crop seasons (2010/2011 until 2014/2015) for the following traits: grain yield (GY), flowering in days (FLOR) and plant height (PH). Variance components, genetic and non-genetic parameters were estimated using the Bayesian method. In general, the informative prior distribution in Bayesian MTME models provided higher estimates of individual narrow-sense heritability and variance components, as well as minor lengths for the highest probability density interval (HPD), compared to their respective non-informative prior distribution analyses. More informative prior distributions make it possible to detect genetic correlations between traits, which cannot be achieved with non-informative prior distributions. Therefore, this mechanism presented to update knowledge for an elicitation of an informative prior distribution can be efficiently applied in rice breeding programs.

Effects of previous land use on genotype-by-environment interactions in two loblolly pine progeny tests

Loblolly pine (Pinus taeda L.) is widely used for forestry in southern Brazil, with most seeds coming from clonal seed orchards. This study investigated the effects of previous land use on the adaptability, stability, and productivity of loblolly pine progenies in southern Brazil, aiming to produce a second-generation clonal seed orchard (CSO). Two progeny tests were installed in southern Brazil. In FARA, 52 open-pollinated loblolly pine progenies were tested, and in TUNAS, 65 open-pollinated loblolly pine progenies were tested, 35 of which were common to both tests. FARA is a rotation area previously used for annual agronomic crops (oats, corn, soy, beans), whereas, TUNAS is a recycled loblolly pine plantation forest. The diameter at breast height (dbh) and stem height were measured at six years of age, and the wood volume was calculated. Genetic parameters were estimated using REML/BLUP method in SELEGEN software. The adaptability, stability, and productivity of the progenies were estimated by the relative performance harmonic mean of the breeding values method (MHPRVG). The breeding values for volume were used to estimate genetic gains through selection. The heritability values were slightly higher in FARA compared to those in TUNAS. Most of the individual narrow-sense heritability values were between 0.10 and 0.20 for growth traits. And most of the family-mean heritability values were above 0.50. In FARA, the selection strategy resulted in up to 26.37% genetic gain, while for TUNAS, it reached about 20%. GE effects are significant for volume. Because of the significant GE effects it is necessary to consider previous land use in the selection of genotypes for the formation of loblolly pine CSOs in the tested region. Considering the MHPRVG ranking, the maximum genetic gain estimated is 13.20%. The choice of more stable genotypes can circumvent the challenges imposed by crop rotation in the tested areas.

Growth and Wood Quality Traits in aDipteryx alataVog. (Fabaceae) Progeny and Provenance Test

AbstractDipteryx alata Vog. presents an excellent economic potential because of its multiple uses. However, it is currently threatened as a result of the degradation of the biome in which it occurs, the Brazilian Cerrado. Therefore, our goal was to provide subsidies for future breeding and ex situ conservation programs of D. alata. We evaluated genetic variation in growth, stem form, and wood quality traits in a progeny and provenance test planted in a random complete block design. The traits were measured in 37-year-old trees. Significant effect for provenance was obtained for all evaluated traits except bifurcation, but progeny effect was significant only for acoustic wave velocity (AWV). The estimates of individual narrow sense heritability were of low magnitude for all traits except AWV (0.24 ± 0.09). Eleven groups were formed based on Mahalanobis genetic distance with 83.1% of progenies allocated to one group. Dipteryx alata has genetic variability between progenies and provenances that can be explored to obtain genetic gain, especially for AWV. We also recommend the use of multi-trait selection index to obtain gains for both growth and wood quality traits. Controlled pollination between individuals from different progeny groups would increase variability in next generation breeding.

Parâmetros genéticos e seleção inicial de procedências e progênies de taxibranco (<i>Tachigali vulgaris</i>) em Roraima

Este trabalho teve como objetivos estimar parâmetros genéticos de procedências e progênies de polinização livre de taxi-branco e selecionar genótipos superiores quanto ao crescimento inicial em campo. O experimento foi instalado em 2015, no Campo experimental Serra da Prata, pertencente à Embrapa Roraima e localizado no Município de Mucajaí - RR. O delineamento experimental utilizado foi em blocos ao acaso, com 28 progênies provenientes de três procedências e 20 repetições, sendo cada parcela experimental constituída por uma planta. Foram avaliados aos 6, 12 e 18 meses após o plantio, a porcentagem de sobrevivência, a altura da planta (ALT) e o diâmetro do caule a 10 cm do solo (DC) ou o diâmetro à altura do peito (DAP). As análises genético-estatísticas foram realizadas por meio do procedimento REML/BLUP, com análise de deviance, obtenção das estimativas dos parâmetros genéticos e predição dos valores genéticos nas diferentes idades. A sobrevivência geral variou de 50,68% a 62,10% aos 18 e aos 6 meses, respectivamente. As únicas diferenças significativas observadas foram entre progênies, para ALT e DC, aos seis meses. Com exceção do DAP avaliado aos 18 meses, as demais estimativas de herdabilidade em nível individual no sentido restrito foram moderadas, sendo estas inferiores às estimativas da herdabilidade da média de progênies. Os ganhos com a seleção de progênies e indivíduos foram de baixos a moderados e variaram entre as idades avaliadas, sendo decrescentes com o aumento da idade das plantas.

Inheritance of resin yield and main resin components in Pinus elliottii Engelm. at three locations in southern China

Resin terpenes are used as raw material by an array of industrial sectors. Slash pine (Pinus elliottii Engelm.) is a multi-purpose tree, best known as a resin-tapping tree species for commercial production of resin. Breeding program of slash pine aimed to improve resin yield (RY) has been implemented for the past decade. The objective of this study was to examine the genetic variation for RY and main resin components in three progeny trials including 32 families planted in Ganzhou, Jian, Jingdezhen in southern China. In total, 22 components, including 5 monoterpenes and 17 diterpenes, were detected in the resin flow of slash pine in the present study. Individual narrow-sense heritability was moderate for RY (h^i2 = 0.19–0.32) and moderate to high for monoterpene components (h^i2 = 0.17–0.62) at different sites. A significant site effect for most of the studied properties was observed with the joint analysis of all trials. The estimates of type-B genetic correlations showed that the genotype-by-environment (G × E) interaction had a relatively strong influence on RY and most of the resin chemical components. The genetic correlations (rg) between RY and β-pinene were positive and strong at all three sites (rg = 0.76–0.86). In breeding program of slash pine, one feasible strategy would be to improve RY through selection for high β-pinene. The main components of diterpenes showed moderate to strong and negative correlations with α-pinene, and those with β-pinene were weak and nonsignificant.

Genotypic variation in the basic density, dynamic modulus of elasticity and tracheid traits of Pinus elliottii in three progeny trials in southern China

Abstract A firm understanding of the genetic relationships among wood properties is a prerequisite for breeding for higher wood quality in Pinus elliottii families. To examine and deal with such relationships, increment cores were sampled at breast height from 1260 trees in 42 open-pollinated families in three 27-year-old Slash pine progeny trials in southern China, and genetic variation, genotype-by-environment (G × E) interaction, genetic correlation and correlated response were investigated. The basic density (BD), dynamic modulus of elasticity (MOED) and tracheid traits were found to be under moderate to strong genetic control for the three locations combined, with individual narrow-sense and family mean heritability ranging from 0.28 to 0.44 and 0.52 to 0.69, respectively. Type B genetic correlation estimates indicated that the G × E interaction had a small-level influence on wood properties. Strong genetic correlations (rg) were found between BD and MOED at the three sites (rg = 0.46–0.85), and BD or MOED showed moderate to strong correlations with most tracheid traits at specific localities. In tree breeding programs, one possible strategy would be to improve pulpwood quality and the strength of structural wood through selection for different wood quality traits.

Identification of contrasting tropical popcorn inbreds for studying aluminum toxicity tolerance inheritance

Genetic improvement of crops is an essential approach to overcome the aluminum (Al) toxicity in acidic soils. The objectives of this study were to identify contrasting popcorn inbred lines with respect to Al tolerance and investigate its genetic control. Using a complete randomized block design, three sequential experiments were performed that assessed 18, 10, and 2 inbred lines growing in the presence and absence of Al. The inbreds were assessed for relative root growth (RRG), hematoxylin staining, Al content, and external root morphology. Then, the two most contrasting inbreds were crossed and jointly assessed with four derived generations in a fourth trial in a complete randomized block design. The plants were assessed for relative and net root length. The inbred 11–60 had the least RRG (0.02 and 0.06), the greatest accumulation of Al (1660.3 μg/g), and strong blue staining of the root tips with intense epidermal degradation. The inbred 11–133 had the most RRG (0.15–0.37) and the least hematoxylin staining, Al accumulation (926.4 μg/g), and root inhibition in the root tips, associated with no damages on root apices. Dominance effect contributed negatively with all Al-tolerance indexes, although in general, the average degree of dominance indicated partial dominance. The dominance × dominance effects contributed to increasing relative root length, whereas additive × additive effects increased net lateral root length. The individual narrow-sense heritabilities were high, ranging from 49.0 to 66.0%. Based in the results, recurrent selection based on progeny and hybrid breeding are recommended for developing Al-tolerant populations.

Non-destructive wood density assessment of Scots pine (Pinus sylvestris L.) using Resistograph and Pilodyn.

We tested two methods for non-destructive assessment of wood density of Scots pine standing trees: one based on penetration depth of a steel pin (Pilodyn) and the other on micro-drilling resistance (Resistograph). As a benchmark we used wood density data from x-ray analysis (SilviScan). We assessed in total 622 trees of 175 full-sib families growing in a single progeny test. Pilodyn was applied with bark (PIL) and without bark (PILB). Raw Resistograph drilling profiles (RES) were adjusted (RESTB) in order to eliminate increasing trend caused by needle friction. Individual narrow-sense heritability of benchmark SilviScan density (DEN; 0.46) was most closely approached by that of adjusted RESTB (0.43). Heritabilities were lower for unadjusted RES (0.35) as well as for PIL and PILB (both 0.32). Additive genetic correlations of the benchmark DEN with RES, RESTB, PIL and PILB were 0.89, 0.96, 0.59 and 0.71, respectively. Our results suggest that Resistograph is a more reliable tool than Pilodyn for wood density assessment of Scots pine; however, we highly recommend adjusting Resistograph drilling profiles prior to further analyses.

Genetic parameters of growth and stem forking for black spruce progeny tested in New Brunswick, Canada

We investigated genetic parameters for juvenile to mature growth and stem forking in black spruce [Picea mariana (Mill.) B.S.P.] in order to obtain reliable estimates for supporting eastern Canadian tree breeding strategies. The study was based on data collected from two series of progeny tests of black spruce in New Brunswick (NB) including 285 open-pollinated families and more than 57,000 individual trees. Height (HT), diameter at breast height (DBH), and stem forking (SF) were periodically measured between ages 5 and 35 years. Results showed that tree volume (V), HT and DBH were highly genetically controlled, with average individual narrow-sense heritability ( $$h_{i}^{2}$$ ) estimates of 0.29, 0.29 and 0.21, and family mean heritability ( $$h_{F}^{2}$$ ) estimates of 0.82, 0.85 and 0.77, respectively. SF had low $$h_{i}^{2}$$ (= 0.06 on average) but had moderate $$h_{F}^{2}$$ (= 0.56), indicating family selection might effectively reduce SF. Both $$h_{i}^{2}$$ and $$h_{F}^{2}$$ increased with age and then stabilized or declined, being the highest around ages 15–20 years for all traits. The type-B genetic correlation ( $$r_{B}$$ ) estimates were moderate to high for all the traits, suggesting negligible genotype × environment interactions. Strong age–age genetic correlation estimates were found for growth traits, implying the potential for practicing early selection. Age–age genetic correlation estimates were moderate for SF (= 0.72). Trait–trait genetic correlation estimates were strong and positive among growth traits, but between growth traits and SF they were mostly negligible albeit positive. Overall, results suggest that genetic selection will be effective for growth traits but much less so for reducing stem forking in New Brunswick’s black spruce.

Genetic Variation, Heritability and Genotype × Environment Interactions of Resin Yield, Growth Traits and Morphologic Traits for Pinus elliottii at Three Progeny Trials

To better understand the genetic control of resin yield, growth traits and morphologic traits for Pinus elliottii families, genetic relationships among these traits were examined in three 27-year-old progeny trials located in Jingdezhen, Jian and Ganzhou, Jiangxi Province, China. In total, 3695 trees from 112 families were assessed at the three sites. Significant site, family and family × site effects were found for resin yield, growth traits and morphologic traits. Resin yield and growth traits were found to be under moderate genetic control for the three sites combined, with family heritability and individual narrow-sense heritability ranging from 0.41 to 0.55 and 0.11 to 0.27, respectively. The coefficient of genotypic variation (CVG) of stem volume (SV) and crown surface area (CSA) were higher than those of other traits at each site. Genetic correlation estimates indicated that selection for growth traits might lead to a large increment in resin yield (RY), and most morphologic traits had moderate to strong correlations with growth traits at each individual site. One possible strategy in tree breeding would be to maximize resin production through selection for growth traits.

Adaptive genetic variability and differentiation of Croatian and Austrian Quercus robur L. populations at a drought prone field trial

Provenance trials, where populations of different geographical origin are tested in a common environment (common garden test), are a tool suited to allow the study of intraspecific adaptive genetic variation. Research of pedunculate oak (Quercus robur L.) adaptive genetic variability through analyses of populations in common garden tests has a long tradition. However, pedunculated oak populations originating south-eastern from the Alps have been scarcely studied in this way. This study addresses the adaptive genetic variability and differentiation of pedunculate oak populations originating from Austria and Croatia in a provenance/progeny field trial. Studied plants were six years old and were growing at the trial for three years. After two years of unusually low precipitations height and survival were analysed. The total mean height of all plants in the trial was 137.8 cm and ranged from 123.0 cm to 151.8 cm. The overall mean survival rate was rather high (0.85). Mean population survival ranged from 0.64 to 0.94. Individual narrow-sense heritabilities (hi2), family mean heritabilities (hf2), the coefficients of additive genetic variation (CVA) and quantitative genetic differentiation coefficients (QST) were calculated. A multivariate regression tree (MRT) analysis was used to determine the pattern of genetic differentiation of the populations. Individual heritabilities for height ranged between 0.00 and 0.39. Family mean heritabilities for height were rather low in most populations as well (<0.5). Family mean heritabilities for survival were higher than for height (ranging between 0.00 and 0.77). Calculated QST coefficients (0.25 for height and 0.14 for survival) indicated between-population genetic differentiation. The populations were separated into two clusters by MRT analysis regarding a climatic variable, namely Hargreaves’ reference evapotranspiration. Populations originating from comparatively more humid habitats were grouped in the first cluster. The first cluster had a lower mean height and survival compared to the second one. The differences between these clusters were highly statistically significant. The observed quantitative genetic differentiation might have been driven by natural selection caused by differences in the relative moisture of the habitats from which the progeny populations originate. The results suggest ecotypic pattern of the quantitative genetic differentiation among studied populations.

Genetic variation of wood and resin production inPinus caribaeavar.hondurensisBarret &amp; Golfari

AbstractThe purpose of this work was to estimate genetic parameters and selection gain ofPinus caribaeavar.hondurensisprogeny trial for wood and resin production as well as correlation between them. Experiment was established in complete lattice square 10 × 10 (triple), 100 treatments, 10 plants per plot, 3 m × 3 m spacing. Twelve years after planting the trial had thinned considerably leaving six plants per plot. Twenty-seven years after planting height, diameter at breast height (dbh) and resin production were measured. Deviance analysis, genetic parameter estimates, selection expected gain, genetic and phenotypic correlation were based on REML/BLUP method. Significant phenotypic differences were observed among and within families for all traits. The thinning at 12 years after planting, contributed positively to dbh increase and resin production, with an average of 30.60 cm and 4.83 kg tree−1year−1. The individual narrow sense heritability ranged from 0.25 to 0.38 for dbh and volume. Genetic and phenotypic correlation between growth traits were positive, and significant. Therefore, different selection strategies will be proposed separately for both traits (resin and wood). The selection gains were significant, especially with 10 % selection intensity (individual selection) for dbh (7.53 %) and resin (13.49 %). The trial has had good performance for growth, resin and genetic variability to support the next breeding generation

Flowering traits in tetraploid Brachiaria ruziziensis breeding

Tetraploid Brachiaria ruziziensis genotypes which reproduce sexually are essential for the breeding of other species of the Brachiaria genus which reproduce by apomixis. Aiming at studying the available phenotypic and genetic variability in the breeding population of B. ruziziensis, it was estimated the parameters heritability and genetic and phenotypic correlations between the traits associated with flowering, and the traits responsible for forage yield and nutritional quality. Seventeen traits in 1180 individuals from 59 open pollinated families were studied, and the data were analyzed by mixed model methods. Individuals with sparse flowering presented higher breeding values for total dry matter, yield, and total number of panicles per plant than individuals with early or late flowering. Considering breeding population differences on flowering behavior, on individual narrow sense heritability and on genetic correlations between flowering, agronomic quality and nutritional quality traits have to be considered in intrapopulation breeding and in intrapopulational recurrent selection.

New accuracy estimators for genomic selection with application in a cassava (Manihot esculenta) breeding program.

Genomic selection is the main force driving applied breeding programs and accuracy is the main measure for evaluating its efficiency. The traditional estimator (TE) of experimental accuracy is not fully adequate. This study proposes and evaluates the performance and efficiency of two new accuracy estimators, called regularized estimator (RE) and hybrid estimator (HE), which were applied to a practical cassava breeding program and also to simulated data. The simulation study considered two individual narrow sense heritability levels and two genetic architectures for traits. TE, RE, and HE were compared under four validation procedures: without validation (WV), independent validation, ten-fold validation through jacknife allowing different markers, and with the same markers selected in each cycle. RE presented accuracies closer to the parametric ones and less biased and more precise ones than TE. HE proved to be very effective in the WV procedure. The estimators were applied to five traits evaluated in a cassava experiment, including 358 clones genotyped for 390 SNPs. Accuracies ranged from 0.67 to 1.12 with TE and from 0.22 to 0.51 with RE. These results indicated that TE overestimated the accuracy and led to one accuracy estimate (1.12) higher than one, which is outside of the parameter space. Use of RE turned the accuracy into the parameter space. Cassava breeding programs can be more realistically implemented using the new estimators proposed in this study, providing less risky practical inferences.

Genetic and correlation analysis of oleoresin chemical components in slash pine.

This is the first comprehensive study of the genetic analysis of the majority of oleoresin components of slash pine (Pinus elliottii). Pine oleoresin, the resin secreted from the pine tree, is a raw material widely used in industrial products. The objective of this study was to explore the genetic variation and correlation between the major oleoresin components of 50 open pollinated families of slash pine. The individual narrow-sense heritability of the 23 oleoresin components and genetic correlations between them were estimated using the residual maximum likelihood in the flexible mixed modeling program, ASReml-R. A high heritability of 0.424 was observed for β-pinene. Moderate levels of heritability were estimated for β-phellandrene, methyl abietate, estragole, 15-hydroxy-dehydroabietic acid, and isopimaric acid methyl ester at 0.303, 0.294, 0.27, 0.258, and 0.2, respectively. The heritabilities for pimaric acid methyl ester, abieta-8, 13-diene-18-oic acid methyl ester, sandaracopimaric acid, methyl ester, and camphene were relatively low and ranged from 0.11 to 0.17. Many negative genetic correlations were observed as unfavorable while the corresponding phenotypic correlations presented no significant relationships or positive phenotypic correlations. However, the heritabilities and genetic correlations showed that single or multiple component selections and improvement, directly or indirectly, were effective. We postulate that genetic parameters estimated in this study will work as a reference in breeding programs of oleoresin components, especially in slash pine.

Estimation of genetic parameters for height using spatial analysis in Tsuga heterophylla full-sibling family trials in British Columbia

Abstract Non-spatial and spatial analyses were carried out to study the effects on genetic parameters in ten-year height growth data across two series of 10 large second-generation full-sib progeny trials of western hemlock [Tsuga heterophylla (Raf.) Sarg.] in British Columbia. To account for different and complex patterns of environmental heterogeneity, spatial single trial analyses were conducted using an individual-tree mixed model with a two-dimensional smoothing surface with tensor product of B-spline bases. The spatial single trial analysis, in all cases, showed sizeable lower Deviance Information Criterion values relative to the non-spatial analysis. Also, fitting a surface displayed a consistent reduction in the posterior mean as well as a decrease in the standard deviations of error variance, no appreciable changes in the additive variance, an increase of individual narrow-sense heritability, and accuracy of breeding values. The tensor product of cubic basis functions of B-spline based on a mixed model framework does provide a useful new alternative to model different and complex patterns of spatial variability within sites in forest genetic trials. Individual narrow-sense heritabilities estimates from the spatial single trial analyses were low (average of 0.06), but typical of this species. Estimated dominance relative to additive variances were unstable across sites (from 0.00 to 1.59). The implications of these estimations will be discussed with respect to the western hemlock genetic improvement program in British Columbia.

Comparison between different selection methods of rubber trees

The purpose of this study was to compare estimates of genetic gain using three different selection methods (between and within, combined selection and Multi-Effect Index) for the cultivation of rubber trees (Hevea brasiliensis), analyzing the variables rubber yield and the annual girth growth, evaluated at three locations. The population and consisted of 22 open pollinate progenies from different regions of rubber cultivation in the State of São Paulo (Jaú, Pindorama and Votuporanga). The experiment was arranged in a randomized block design with 6 replications, 10 plants per plot and spacing of 2m×2m. The individual narrow-sense heritability (hˆr2) and heritability of progeny means (hˆmp2) were mean and high, respectively, for all variables at the three sites, indicating little environmental influence on the variables. The within and between selection method proved more promising in Jaú, while at the other locations, gains were higher by the Multi-Effect Index, with genetic gain of over 100%. The combined selection obtained medium gains, in some cases very close to those of the Multi-Effect Index. The multi-effect selection index can increase the genetic gains, maximizing selection and enabling a reduction in the breeding cycle of the species.

Susceptibility to Teratosphaeria nubilosa and precocity of vegetative phase change in Eucalyptus globulus and E. maidenii (Myrtaceae)

Since the first report of Teratosphaeria nubilosa (Cooke) Crous &amp; U.Braun in Uruguay in 2007, young plantations of Eucalyptus globulus Labill. and E. maidenii F.Muell. have been severely damaged by Mycosphaerella leaf disease. The genetic variation in disease resistance and in the timing of heteroblastic phase change was examined in 194 open-pollinated families of E. globulus and 86 families of E. maidenii growing in a field trial in south-eastern Uruguay, naturally infected by T. nubilosa. Disease severity, precocity of vegetative phase change and tree growth were assessed at 14 months. E. globulus was significantly more susceptible to T. nubilosa than was E. maidenii, presenting higher severity of leaf spots (10.6% and 5.6%, respectively), higher defoliation (31.9% and 22.9%, respectively) and higher crown-damage index (39.1% and 27.4%, respectively). However, the heteroblastic transition began significantly earlier in E. globulus than in E. maidenii, with 34.1% and 2.8% of the trees having some proportion of their crown with adult foliage at 14 months, respectively. Significant individual narrow-sense heritabilities were found in E. globulus for severity of leaf spots (0.40), defoliation (0.24), crown-damage index (0.30) and proportion of adult foliage (0.64). Additive genetic variation in E. maidenii was significant only for defoliation and crown-damage index, with a moderate heritability (0.21 and 0.20, respectively). Although E. maidenii was more resistant to T. nubilosa than was E. globulus, the degree of resistance was not enough to consider this species as an alternative to E. globulus for high-risk disease sites. In addition, the small genetic variability for resistance on the juvenile foliage and the late transition to adult foliage suggested that the chances for early selection in E. maidenii are quite limited. By contrast, the genetic variation in E. globulus clearly indicated that through selection for resistance of the juvenile foliage, and especially by selecting for early phase change, it is possible to obtain genetic stock suitable for sites with high risk of T. nubilosa infection.

Genetic variation among and within provenances of Adansonia digitata L. (Baobab) in seed germination and seedling growth from selected natural populations in Malawi

Baobab (Adansonia digitata L.) trees have a wide variety of subsistence and economic values across sub-Saharan Africa. Knowledge of the genetic variation within and between the species is essential for management and designing domestication, improvement and conservation strategies. Fifty-nine half-sib families were evaluated in the nursery to determine the genetic variation and control within and between the populations from four silvicultural zones. Seed germination and seven seedling growth parameters were assessed. Total phenotypic variance, family variance, within family variance, individual narrow sense heritability, and additive genetic coefficient of variation (AGCV) were derived from observed and expected mean squares. There were highly significant differences in seed germination, plant height, root collar diameter, number of leaves, shoot height and diameter, tuber diameter and weight. Provenance variation in germination ranged from 46.7 ± 3.3 to 68.7 ± 3.3% while tree-to-tree variation ranged from 6.3 ± 8.6 to 95.5 ± 8.6%. Coefficient of variation in seedling growth variables ranged from 18.6 to 43.6%. Individual narrow sense heritabilities (h2) ranged from 0.07 to 0.71. AGCV ranged from 3.21 to 14.67%. Morphological traits showed that mainland populations were genetically distant from the island one. High and moderate additive genetic control of traits and AGCV show the potential that Baobab can also respond well to tree improvement. High phenotypic variation found in the study offers an opportunity to effect selection of superior attributes at both provenance and individual tree-to-tree level.