Relating estimates of wood properties of birch to stem form, age and species

Birch has long suffered from a lack of active forest management,leading many researchers to use mate-rial without a detailed management history.Data collected from three birch(Betula pendula Roth,B.pubescens Ehrh.)sites in southern Sweden were analyzed using regression analysis to detect any trends or differences in wood proper-ties that could be explained by stand history,tree age and stem form.All sites were genetics trials established in the same way.Estimates of acoustic velocity(AV)from non-destructive testing(NDT)and predicted AV had a higher correlation if data was pooled across sites and other stem form factors were considered.A subsample of stems had radial profiles of X-ray wood density and ring width by year created,and wood density was related to ring number from the pith and ring width.It seemed likely that wood density was negatively related to ring width for both birch species.Linear models had slight improvements if site and species were included,but only the youngest site with trees at age 15 had both birch species.This paper indicated that NDT values need to be considered separately,and any predictive models will likely be improved if they are specific to the site and birch species measured.

Inbreeding and genetic load in a pair of sibling grouse species:Tetrastes sewersowi and T.bonasia

Genetic load and inbreeding are recognized as important factors to be considered in conservation programs.Elevated levels of both can increase the risk of population extinction by negatively impacting fitness-related characters in many species of plants and animals,including humans(inbreeding depression).Genomic tech-niques are increasingly used in measuring and understanding genetic load and inbreeding and their importance in evolution and conservation.We used whole genome resequencing data from two sibling grouse species in subarctic Eurasia to quantify both.We found a large range of inbreeding measured as FROH(fraction of runs of homozygosity)in individuals from different populations of Chinese Grouse(Tetrastes sewerzowi)and Hazel Grouse(T.bonasia).FROH estimated from genome-wide runs of homozygosity(ROH)ranged from 0.02 to 0.24 among Chinese Grouse populations and from 0.01 to 0.44 in Hazel Grouse.Individuals from a population of Chinese Grouse residing in the Qilian mountains and from the European populations of Hazel Grouse(including samples from Sweden,Germany and Northeast Poland)were the most inbred(FROH ranged from 0.10 to 0.23 and 0.11 to 0.44,respectively).These levels are comparable to other highly inbred populations of birds.Hazel Grouse from northern China and Chinese Grouse residing in the Qinghai-Tibetan Plateau showed relatively lower inbreeding levels.Comparisons of the ratio between deleterious missense mutations and synonymous mutations revealed higher levels in Chinese Grouse as compared to Hazel Grouse.These results are possibly explained by higher fixation rates,mutational melt down,in the range-restricted Chinese Grouse compared to the wide-ranging Hazel Grouse.However,when we compared the relatively more severe class of loss-of-function muta-tions,Hazel Grouse had slightly higher levels than Chinese Grouse,a result which may indicate that purifying selection(purging)has been more efficient in Chinese Grouse on this class of mutations.

The Correlation between Synthetic Oxytocin Given during Labor and Women’s Personality Traits According to the SSP (Swedish University Scales of Personality) Survey: A Pilot Study

Background: In modern obstetric care, oxytocin is one of the most frequently used drugs, and the possible mental impact this drug has on women is very little studied. The objective of this study is to investigate whether women augmented with oxytocin during labor will rate their personality profile differently after childbirth than non-stimulated women. Methods: Prospective cohort study was performed at Women’s Clinic, Soder hospital, Stockholm.76 women received the SSP (Swedish University Scales of Personality) questionnaire to fill in during their stay in the post-maternity ward after labor. Information about the use of oxytocin was retrieved from the women’s medical records. Primary outcome: Differences in the SSP scores in the group augmented with synthetic oxytocin during labor compared with the non-augmented group. Results: Women with and without oxytocin estimates on the SSP subscale form differed regarding personality traits described as “lack of assertiveness” (p = 0.04), which means “lack of ability to speak up and to be self-assertive in social situations”. The result also showed that women that had a long time of augmentation with oxytocin (>5 h) scored higher for “social desirability” (p = 0.004), which was defined as being “socially adapted,” “friendly,” and “helpful”. A difference in “psychological anxiety” (p = 0.04) and “social desirability” (p = 0.004) was found among women who had oxytocin in a dose of at least 200 ImU/h for ≥1 hour. This group also had a lower rate of “mental anxiety” than those who received lower oxytocin doses. Conclusion: Synthetic oxytocin given during labor may affect the woman mentally. The total time and volume of given oxytocin seem to be essential factors when discussing augmentation’s maternal psychological response. We conclude that prolonged and extended use of synthetic oxytocin during labor should be avoided if possible.

Spatial Distribution of Heavy Metals in Agricultural Soils of an Industry-Based Peri-Urban Area in Wuxi, China

In industry-oriented peri-urban areas, the heavy metal accumulation in soils caused by industrialization has become a potential threat. The top soil samples from 27 paddy fields and 75 vegetable fields were collected from a typical industry-based peri-urban area of about 8 km2 in Wuxi, China, to study the accumulation and distribution of As, Hg, Cu, Zn, Pb, Cr, and Cd in comparison with heavy metal contents in soils near developed industrial sites (Guangzhou, China; Wallsend Burn of Tyneside, UK; and Osnabriick, Germany). Kriging interpolation was used to determine the metals' spatial distribution. The results showed that most soils, compared to the background values, contained elevated contents of As, Hg, Cu, Zn, and Pb with some having elevated contents of Cd and Cr. Except for less than 10% of the soil samples of Cu, Zn and Cd contents, these heavy metal contents were lower than the soil threshold levels of the Grade II criteria for the Chinese environmental quality standard. Probably, because of the scattered distribution and diversity of industries in the study area, spatial distributions of these heavy metals from Kriging interpolation indicated little similarity. Nevertheless, when compared with other areas in the Taihu Lake region, mean contents of Cu, Zn, Pb, and Cd were relatively high in the Wuxi peri-urban area. Additionally, compared to soils in agricultural areas around Guangzhou, Osnabriick, or Wallsend Burn, contents of most heavy metals in soils from this area were lower.

A chronosequence analysis of forest recovery on abandoned agricultural fields in Nicaragua

Species composition, diversity and population structure of woody species recovered on three abandoned agricultural fields after 4, 9 and 14 years were characterized. Seedlings, saplings/poles and mature trees were identified and counted in 70 plots of 100 m^2 in each abandoned site. A total of 13, 29 and 22 families represented by 17, 48 and 44 species were registered in 4-, 9- and 14-year-old stands, respectively. There was a shift in dominant species across successional stages. Lonchocarpus acuminatus had the highest importance value in the 4-year old stand, whereas, Myrospermun frutescens, Guazurna ulmifolia and Cordia alliodora had the highest importance value in the 9-year-old-stand and Caesaeria corymbosa, Muntingia calabura, Gliricidia sepium and Tabebuia rosea in the 14-year-old stand. The total stem density increased from 5011 to 9631 individuals per hectare as the age of abandonment increased from 4 to 14 years. The total basal area of individuals _〉 I cm d.b.h, also increased with the age of abandonment. Overall, small individuals （〈 10 cm dbh） contributed to more than half of the total basal area. Species diversity was the highest in the 9-year old stand followed by 14- and 4-year-old stands. We concluded that floristic composition of secondary forests recovers rapidly to the mature forest level compared to structural attributes, which is consistent with the general successional trajectories of tropical dry forest.

Comparison of genetic impact on growth and wood traits between seedlings and clones from the same plus trees of Pinus koraiensis

To evaluate the relationships among clones and open pollinated families from the same plus trees and to select elite breeding materials,growth,and wood characteristics of 33-year-old Pinus korainsis clones and families were measured and analyzed.The results show that growth and wood characters varied significantly.The variation due to clonal effects was higher than that of family effects.The ratio of genetic to phenotypic coefficient of variation of clones in growth and wood traits was above 90%,and the repeatability of these characteristics was more than 0.8,whereas the ratio of genetic to phenotypic coefficient of variation of families was above 90%.The broad-sense heritability of all characteristics exceeded 0.4,and the narrow-sense family heritability of growth traits was less than 0.3.Growth characteristics were positively correlated with each other,but most wood properties were weakly correlated in both clones and families.Fiber length and width were positively correlated between clones and families.Using the membership function method,eleven clones and four families were selected as superior material for improved diameter growth and wood production,and two families from clonal and open-pollinated trees showed consistently better performance.Generally,selection of the best clones is an effective alternative to deployment of families as the repeatability estimates from clonal trees were higher than narrow-sense heritability estimates from open pollinated families.The results provide valuable insight for improving P.koraiensis breeding programs and subsequent genetic improvement.

Why ecosystem characteristics predicted from remotely sensed data are unbiased and biased at the same time-and how this affects applications

Remotely sensed data are frequently used for predicting and mapping ecosystem characteristics,and spatially explicit wall-to-wall information is sometimes proposed as the best possible source of information for decisionmaking.However,wall-to-wall information typically relies on model-based prediction,and several features of model-based prediction should be understood before extensively relying on this type of information.One such feature is that model-based predictors can be considered both unbiased and biased at the same time,which has important implications in several areas of application.In this discussion paper,we first describe the conventional model-unbiasedness paradigm that underpins most prediction techniques using remotely sensed(or other)auxiliary data.From this point of view,model-based predictors are typically unbiased.Secondly,we show that for specific domains,identified based on their true values,the same model-based predictors can be considered biased,and sometimes severely so.We suggest distinguishing between conventional model-bias,defined in the statistical literature as the difference between the expected value of a predictor and the expected value of the quantity being predicted,and design-bias of model-based estimators,defined as the difference between the expected value of a model-based estimator and the true value of the quantity being predicted.We show that model-based estimators(or predictors)are typically design-biased,and that there is a trend in the design-bias from overestimating small true values to underestimating large true values.Further,we give examples of applications where this is important to acknowledge and to potentially make adjustments to correct for the design-bias trend.We argue that relying entirely on conventional model-unbiasedness may lead to mistakes in several areas of application that use predictions from remotely sensed data.

Species diversity and regeneration of old-growth seasonally dry Shorea robusta forests following gap formation

Diversity and regeneration of woody species were investigated in two ecological niches viz. gap and intact vegetation in old-growth seasonally dry Shorea robusta （Gaertn. f.） forests in Nepal. We also related varieties of diversity measures and regeneration at- tributes to gap characteristics. Stem density of tree and shrub components is higher in the gap than in the intact vegetation. Seedling densities of S. robusta and Terminalia alata （B. Heyne ex Roth.） are higher in the gap than in the intact vegetation, while contrary result is observed for T. bellirica （Gaertn. ex Roxb.） and Syzigium cumini （L. Skeels） in term of seedling density. The complement of Simpson index, Evenness index, and species-individual ratio in the seedling layer are lower in the gap than the intact vegetation. Gap size can explain species richness and species establishment rate. Gaps created by multiple tree falls in different years have higher seedling density of S. robusta than gaps created by single and/or multiple tree falls in the same year. In conclusion, gaps maintain species diversity by increasing seedling density, and favor regeneration of Sal forests. In addition to gap size, other gap attributes also affect species diversity and regeneration.

The importance of aboveground and belowground interspecific interactions in determining crop growth and advantages of peanut/maize intercropping

Intercropping of maize(Zea mays L.) and peanut(Arachis hypogaea L.) often results in greater yields than the respective sole crops. However, there is limited knowledge of aboveground and belowground interspecific interactions between maize and peanut in field. A two-year field experiment was conducted to investigate the effects of interspecific interactions on plant growth and grain yield for a peanut/maize intercropping system under different nitrogen(N) and phosphorus(P) levels. The method of root separation was employed to differentiate belowground from aboveground interspecific interactions. We observed that the global interspecific interaction effect on the shoot biomass of the intercropping system decreased with the coexistence period, and belowground interaction contributed more than aboveground interaction to advantages of the intercropping in terms of shoot biomass and grain yield. There was a positive effect from aboveground and belowground interspecific interactions on crop plant growth in the intercropping system, except that aboveground interaction had a negative effect on peanut during the late coexistence period. The advantage of intercropping on grain came mainly from increased maize yield(means 95%) due to aboveground interspecific competition for light and belowground interaction(61%–72% vs. 28%–39% in fertilizer treatments). There was a negative effect on grain yield from aboveground interaction for peanut, but belowground interspecific interaction positively affected peanut grain yield.The supply of N, P, or N + P increased grain yield of intercropped maize and the contribution from aboveground interspecific interaction. Our study suggests that the advantages of peanut/maize intercropping for yield mainly comes from aboveground interspecific competition for maize and belowground interspecific facilitation for peanut, and their respective yield can be enhanced by N and P. These findings are important for managing the intercropping system and optimizing the benefits from using this system.

Comparative growth, dry matter accumulation and photosynthetic rate of seven species of Eucalypt in response to phosphorus supply

Plantations of eucalypts as short-rotation tree crops are rapidly expanding in tropical and sub-tropical regions, including southern China, where the soils are acidic and available phosphorus （P） is limited. We investigated seedling growth, dry matter accumulation, and the dynamics of photosynthetic rate and chlorophyll content of seven Eucalyptus spe- cies/hybrids （E. dunnii, E. grandis, E. grandis x E. camaldulensis, E. urophylla x E. camaldulensis, E. urophylla x E. tereticornis, E. grandis x E. tereticornis, E. urophylla x E. grandis） in response to different levels of P supply （0, 6, 12 and 18 mg-kg-l KH2PO4）. The photosynthetic rate and the chlorophyll content significantly declined as the P supply declined in almost a linear fashion for all species as the P stress period extended. In the absence of P supply, height growth of seedlings of all species was significantly impaired, while root collar diameter growth and whole plant dry matter accumulation was not affected by the level of P supply in most of the species. Significant inter-species variations in growth, dry matter accumulation and photosynthetic rate in response to P supply were detected. Eucalyptus dunnii had the lowest growth perform- ance across all levels of P supply while E. urophylla x E. tereticornis showed superior growth performance. From a practical point of view, E. urophylla x E. tereticornis is suggested as a candidate hybrid for planting on slightly P-deficient sites in southern China while E. dunnii, being a slow-growing species, is not suitable for short-rotation plantation. On plantation sites where severe P deficiency exists, P fertilization needs to be considered to boost rapid growth of seedlings so as to meet the man- agement objectives of short-rotation plantation.

Genetic Diversity and Structure of Tunisian Local Pear Germplasm as Revealed by SSR Markers

Growing pear has a long tradition in Tunisia, and numerous local cultivars possessing an excellent adaptability and resilience potential to climatic variation are present. This large adaptability is associated with an important genetic diversity, which is threatened to erosion.Appropriate measures have to be taken in order to properly evaluate and conserve this local material. Microsatellite markers were used to assess the level of genetic diversity among Tunisian pear germplasm, and compare it with some European varieties and wild pear species. 61 pear accessions representing eight groups(six groups from Tunisia, one from Northern Europe and another group composed of wild pear) have been genotyped using SSR markers derived from apple and pear. The pear accessions showed a significant polymorphism and 95 polymorphic alleles were found. The number of alleles per locus varied from 5 for CH04e03 locus to 14 for CH01d09 locus with an average of 9.4 alleles per locus.Moreover, the mean gene diversity(H_e) per locus ranged from 0.192 to 0.752. Genetic distance values and cluster analyses revealed high genetic similarities among the Tunisian groups. Factorial correspondence analysis(FCA) categorized the accessions into three independent groups where Tunisian local accessions agglomerated together distantly from European and wild pear accessions. Additionally, UPGMA dendrogram grouped accessions into two clusters, confirmed thereafter by the Bayesian model-based Structure analysis. The results showed 16 putative triploid accessions found in the local germplasm. This study provides valuable information to develop strategies of local pear conservation and use.

Use of models in large-area forest surveys： comparing model-assisted, model-based and hybrid estimation

This paper focuses on the use of models for increasing the precision of estimators in large-area forest surveys. It is motivated by the increasing availability of remotely sensed data, which facilitates the development of models predicting the variables of interest in forest surveys. We present, review and compare three different estimation frameworks where models play a core role： model-assisted, model-based, and hybrid estimation. The first two are well known, whereas the third has only recently been introduced in forest surveys. Hybrid inference mixes design- based and model-based inference, since it relies on a probability sample of auxiliary data and a model predicting the target variable from the auxiliary data.We review studies on large-area forest surveys based on model-assisted, model- based, and hybrid estimation, and discuss advantages and disadvantages of the approaches. We conclude that no general recommendations can be made about whether model-assisted, model-based, or hybrid estimation should be preferred. The choice depends on the objective of the survey and the possibilities to acquire appropriate field and remotely sensed data. We also conclude that modelling approaches can only be successfully applied for estimating target variables such as growing stock volume or biomass, which are adequately related to commonly available remotely sensed data, and thus purely field based surveys remain important for several important forest parameters.

Progresses in restoration of post-mining landscape in Africa

Mining alters the natural landscape and discharges large volumes of wastes that pose serious pollution hazards to the environment, to human health and to agriculture. As a result, the recent 2 decades have witnessed a global surge in research on post-mining landscape restoration, yielding a suite of techniques including physical, chemical, biological(also known as phytoremediation) and combinations. Despite the long history of mining in Africa, no systematic review has summarized advances in restoration research and practices after mining disturbance. Thus, the aim of this review was to document the state-of-knowledge and identify gaps in restoration of postmining landscape in Africa through literature review. We found that:(1) there has been substantial progress in identifying species suitable for phytoremediation;(2) few studies evaluated the feasibility of organic amendments to promote autochthonous colonization of mine wastelands or growth of planted species; and(3) restoration of limestone quarries in Kenya, sand mining tailings in South Africa,and gold mine wasteland in Ghana are successful cases of large-scale post-mining restoration practices in Africa.However, the pace of post-mining landscape restoration research and practice in Africa is sluggish compared to other parts of the global south. We recommend:(1)mainstreaming the restoration of mine wastelands in national research strategies and increased development planning to make the mining sector ‘‘Green'';(2) inventory of the number, area, and current status of abandoned mine lands;(3) expanding the pool of candidate species for phytostabilization;(4) further evaluating the phytostabilization potential of organic amendments, e.g., biochar;(5)assessing the impacts of mining on regional biodiversity.

Longevity of Juniperus procera seed lots under different storage conditions: implications for ex situ conservation in seed banks

Juniperus procera Endl. is economically important timber species, but its populations are extremely small and fragmented in its natural habitat, thus, calling for immediate ex situ conservation. Here we examined the effects of seed sources and storage temperature on the longevity of Juniperus procera seed lots through collection and preservation of seeds in seed banks. Seeds were collected from nine sites across the species natural distribution in Ethiopia and stored in four warehouses： modern cold room （5℃）, mud house （15℃）, concrete block house （17℃ or corrugated iron house （20℃） for 42 months. Every three months, a random sample of stored seeds were drawn and tested for germination. A highly significant variation （p 0.01） in germination of stored seeds was observed among different storage environments, seed lots, and duration of storage. Over the storage period, seeds stored in the cold room had the highest mean percentage germination, followed by the mud house, corrugated house and blocket house. The cold room （41%） and the mud house （38%） maintained the same level of germination as the intitial germination of the seedlotds （42%）. The variation in longevity of stored seeds was significnatly correlated with the initial germination of seed lots （r 0.80; p 0.01）. Cold storage also resulted in enhancement of germination through its stratification effect that terminated the non-deepphysiological dormancy of juniper seeds. In conclusion, seed lots with good initial germination can be effectively stored in cold room （5℃） up to four years. In the absence of modern cold stores, mud houses can be used as a good alternative to store seeds at local level.

Biomass production of hybrid aspen growing on former farm land in Sweden

We construct dry weight equations for hybrid aspen growing on former farmland in Sweden. Dry weight equations for fractions of hybrid aspen trees were also made. We estimated biomass production in 24 stands. The stands were located in Sweden at latitudes ranging from 55 to 60o N. The mean age was 18 years （range 15-23）, the mean stand density 1090 stems·ha-1 （range 378 2374）, and the mean diameter at breast height （over bark） 178 mm （range 85 244 mm）. Soil types in the hybrid aspen stands were mainly clay （21 stands）, tills （2 stands） and other （1 stand）. The mean total standing dry weight above stump level （≈ 200 mm） for the hybrid aspen stands was 135±53 t·ha-1 with a range of 42 219 t·ha-1 . In addition to estimating conventional dry weights of trees and tree components, basic density, specific leaf area （SLA）, projected leaf area （PLA） and leaf area index （LAI） were estimated and were in agreement with published figures.

Physiological responses of needles of Pinus massoniana elite families to phosphorus stress in acid soil

Pinus massoniana Lamb. is a major timber species widely planted in the South China, where the soil is acidic and deficient in phosphorus （P） due to fixation by aluminum and iron. Understanding the physiological responses to rhizospheric insoluble P is essential for enhancing plantation productivity. Thus, a sand culture experiment was conducted with four levels of P treatment （0, 5, 20 g insoluble P and 10 g soluble P）, and 11 P. massoniana elite families. Physiological responses were measured after two months of stress. Compared to the normal soluble P treatment, the insoluble P treatment significantly reduced the proline content and the APase activity in the needles, while it significantly increased the catalase activity by 1.3-fold and malondialdehyde content by 1.2-fold. Soluble protein content was unaffected by the treatments, but chlorophyll content was significantly lower in P-deprived treatment compared with soluble and insoluble P treatments. These physiological responses also exhibited highly significant variation among families （p 〈 0.01）. The findings suggest that increased catalase activities in the presence of insoluble P might be involved in the activation of an anti-oxidation defense mechanism that scavenges the reactive oxygen species elicited by the stress. And this response has a strong genetic control that can be exploited to identify desirable genotypes.

Effects of biochar and litter on carbon and nitrogen mineralization and soil microbial community structure in a China fir plantation

To investigate the effects of biochar addition(1 or 3%)to the soil of a China fir plantation with or without litter,we conducted a 90-day incubation experiment.We also studied the C and N dynamics and the microbial community structure of the soil.In soil without litter,the application of biochar at a rate of 3%significantly decreased CO2 emissions,while addition of 1%biochar had no effect.Biochar application did not affect the net N mineralization rate but significantly reduced the NH4?concentration after 90 days.In litter-enriched soil,biochar application had no significant effect on total CO2 emissions;however,application of 3%biochar significantly reduced the net N mineralization rate.Biochar application to soil with or without litter immediately reduced the dissolved organic carbon(DOC)concentration independent of the application rate,which was primarily due to sorption of DOC by the biochar.Phospholipid fatty acid analysis demonstrated that both concentrations of added biochar to soil(with or without litter)altered the soil microbial community structure at the end of incubation,although the effect of biochar was not as strong as the effect of time or litter application.The effect of biochar addition alone on microbial community structure was inconsistent over time.Litter added to soil significantly increased fungi and reduced Gram-positive bacteria.In the presence of litter,biochar applied at both 1%and 3%significantly increased(p<0.05)the proportion of actinomycete only at day 90.Our results indicate biochar as a potentially effective measure for C sequestration in the test soil of a China fir plantation,even in the presence of litter.

Spatial analysis increases efficiency of progeny testing of Chinese fir

We used spatial, global trend and post-blocking analysis to examine the effectiveness of a progeny trial in a tree breeding program for Chinese fir （Cunninghamia lanceolata （Lamb.） Hook） on a hilly site with an environmental gradient from hill top to bottom. Diameter at breast height （DBH） and tree height data had significant spatial auto-correlations among rows and columns. Adding a firstorder separable autoregressive term more effectively modelled the spatial variation than did the incomplete block （IB） model used for the experimental design. The spatial model also accounted for effects of experimental design factors and greatly reduced residual variances. The spatial analysis rel- ative to the IB analysis improved estimation of genetic parameters with the residual variance reduced 13 and 19% for DBH and tree height, respectively; heritability increased 35 and 51% for DBH and tree height, respectively; and genetic gain improved 3-5%. Fitting global trend and postblocking did not improve the analyses under IB model. The use of a spatial model or combined with a design model is recommended for forest genetic trials, particularly with global trend and local spatial variation of hilly sites.

Assessment of EST-SSR Markers for Evaluating Genetic Diversity in Watermelon Accessions from Zimbabwe

Fifteen expressed sequence tag (EST)-derived simple sequence repeats (EST-SSRs) were used to investigate genetic diversity in 139 plants obtained from seeds of 35 watermelon accessions collected from all the geographical provinces of Zimbabwe. In addition, 15 plants representing three commercial varieties developed in the United States (USA) were analyzed for comparison. A total of 65 alleles were detected among all the watermelon accessions. For the 13 polymorphic EST-SSR loci, number of alleles per locus varied from 2 to 13, with an average of 5 alleles per locus. Values for the polymorphic information content increased as the number of alleles increased, and varied from 0.15 to 0.77 with an average of 0.54 suggesting sufficient discriminatory power. Both cluster analysis and principal coordinate analysis (PCA) produced two major clusters;one with the 22 cow-melon accessions and the other with the 16 sweet watermelon accessions. Within the sweet watermelon group, two distinct sub-clusters formed, one of which contained only two of the commercial varieties from USA. Partitioning of genetic variation in the Zimbabwean material using analysis of molecular variation (AMOVA) revealed that 64% of the total variation resides between the two major forms, i.e. sweet watermelons and cow-melons, 28% between accessions within forms and 8% within accessions. The EST-SSR markers revealed a somewhat higher diversity in sweet watermelon accessions compared to that of cow-melons. This finding is contrary to previous reports using other markers (genomic SSR loci or RAPD) and/or a plant material that is likely to have experienced more stringent selection procedures compared to the landraces analyzed in our study.