Genetic variation among and within populations of <Emphasis Type="Italic">Cordia africana</Emphasis> in seed size and germination responses to constant temperatures

Cordia africana Lam. is a commercial timber species that grows naturally throughout sub-Saharan Africa and tropical Arabia. At present very little is known about genetic variation in this species and baseline information is needed to initiate improvement programs in Ethiopia. Thus, the objectives of the study were to quantify the inter- and intra-population variations in seed size traits and germination responses to different constant temperature regimes. Seeds were collected from 30 open-pollinated families within each of the five populations representing the natural distribution of the species in Ethiopia. To examine seed size variations, seed length, seed width, and 1,000-seed weight were quantified. Inter- and intra-population variations in seed germination were investigated under different constant temperature regimes from 20 to 35°C in climate chambers. Significant variations in seed length, width and weight were detected both at inter- and intra-population levels, and family heritabilities of 0.63–0.76 showed that much of the phenotypic variation in seed size traits were additive genetic variation. Significant variation in germination was also found among and within populations as well as between the different constant temperature regimes. Generally the variation in germination was considerably higher within population than between populations. The optimal temperature for germination of C. africana seeds was 25–30°C with family heritabilities for germination ranging between 0.20 and 0.33, depending on the germination temperature.     

Flotation techniques to improve viability of <Emphasis Type="Italic">Juniperus polycarpos</Emphasis> seed lots

The germination of freshly collected Juniperus polycarpos (K. Koch) seeds is very low and attributed to the large proportion of nonviable seeds in the seed lots. Thus, the aim of this study was to improve seed lot quality by removing nonviable seeds using two flotation techniques: incubation-drying-separation (IDS) and modified specific gravity (MSG) separation. We examined different IDS conditions (the specific incubation time, subsequent drying time and sorting media) for effectively sorting out nonviable seeds; and tested the feasibility of modified SG separation, which involved soaking seeds in water for a certain period before sorting in different concentrations of sucrose solution. Viable seeds were expected to absorb and metabolically bind more water during soaking than dead seeds could, and hence be sorted effectively depending on the viscosity of the sucrose solution. The viability of the seeds that floated or sank was determined in a topographical tetrazolium chloride (TTC) test. For the IDS trial, 7 days incubation followed by 9 h of drying and sedimentation in pure water or 200 g·L^?1 sucrose solution identified, respectively, 75 and 82 % of the seeds as viable (sunken) seeds. For the MSG trail, 77 % viable seeds were recovered in the sunken fraction when seeds were soaked for 48 h then immediately sorted in 600 g·L^?1 sucrose solution. In both cases, the loss of viable seeds in the discarded floating fraction was only 4 %. The results demonstrate that both IDS and MSG separation techniques substantially improved seed lot viability, but MSG separation is simple and needs no modern seed handling facility, and its efficacy relies on seed mass (due to the initial soaking) and the specific density and viscosity of the flotation medium.     

Coppicing ability of dry miombo woodland species harvested for traditional charcoal production in Zambia:a win–win strategy for sustaining rural livelihoods and recovering a woodland ecosystem

The miombo woodland is one of the most extensive woodlands in Africa, supporting livelihoods based on biomass fuel for millions of rural people. However, there are growing concerns about the sustainability of harvesting for biomass fuel(mainly charcoal). Thus, the aim of this study was to examine whether regeneration by coppice is a viable option for sustainably managing miombo woodlands for biomass fuel production. We tested the hypotheses that(1) species, stump diameter, stump height and time since cutting significantly affect the number of sprouts per cut stump(coppice density) and mean sprout height(shoot vigour) and(2) higher coppice density reduces shoot vigour due to competition among coppice shoots in a given stump. In an inventory in areas that were harvested for charcoal production by the local people, 369 stumps of 11 species were recorded with mean coppice stumps ranged from 6 to 84. The mean coppice density ranged from 5 to 8 shoots per stump while the mean height of coppice shoots ranged from 46 to 118 cm with marked interspecific variations. Stump size was significantly and positively correlated with coppice density for some of the species, but not with shoot vigour for the majority of the species. However, shoot vigour was significantly positively correlated to time since cutting of trees for nearly half of the species. Coppice density had a significant negative correlation with shoot vigour for two species, and a positive correlation for one species. In conclusion, the results provide evidence about the importance of coppice management as a win–win strategy for sustaining charcoal-based rural livelihoods and recovering the miombo woodland ecosystem.     

Rapid and non-destructive evaluation of seed quality of Chinese fir by near infrared spectroscopy and multivariate discriminant analysis

New Forests - Chinese fir (Cunninghamia lanceolata (Lamb) Hook) is a promising timber species for planting in the sub-tropical ecosystem. However, the germination rate of Chinese fir seed lots is...     

Discrimination of viable and empty seeds of Pinus patula Schiede & Deppe with near-infrared spectroscopy

Sustainable forest production demands a continuous supply of high quality seeds for the production of seedlings in the nursery or for direct sowing. Here, we demonstrated the potential of near infrared spectroscopy as a rapid technique to discriminate viable and empty seeds of Pinus patula Schiede & Deppe. Near infrared spectra were collected from single seeds in transmittance and reflectance modes. To discriminate viable and empty seeds, multivariate classification models were developed with partial least squares (PLS) regression using the digitized spectra as a regressor and a y-vector of artificial values (1 for viable and –1 for empty seeds) as a regressand. Viable and empty seeds were perfectly distinguished by PLS models computed on full and selected transmittance spectroscopy data, while those derived from full NIR reflectance spectra recognized 96 % of viable and 88 % of empty seeds. Analyses made on selected NIR reflectance spectra improved the classification rate of empty seeds to 100%. Difference spectra and PLS weights indicated that the origin of spectral differences between viable and empty seeds was attributed to differences in fatty acids and proteins that were totally absent in empty seeds. The result shows the prospect of developing rapid filter-based sorting equipment that can easily be automated.     

Effects of presowing treatments, desiccation and storage conditions on germination of Strychnos nux-vomica seeds, a valuable medicinal plant

Seeds of Strychnos nux-vomica have slow and erratic germination; thus different presowing treatments were applied to enhance the germination of its seeds collected from Tamaraikulam, Tamil Nadu, India. In addition, the effects of desiccation and different storage conditions on the germination of S. nux-vomica seeds were investigated. The results show that soaking in 500 ppm gibberellic acid (GA₃) for 24 h, incubation of seeds at 40 °C for 3 days and alternate water soaking (16 h) and drying (8 h) for 14 days significantly increased the percentage germination compared to the control. Desiccation of seeds down to 10% moisture content resulted in better germination. Germination of S. nux-vomica seeds differed significantly between different storage periods, moisture contents of the seed and for first and second order interactions (p<0.001). The highest germination (92%) was achieved when seeds with 10% moisture content were stored at ambient temperature for 30 weeks. Evidence from the present study indicates that S. nux-vomica seeds possess physiological dormancy that can be broken effectively by after-ripening. As seeds of S. nux-vomica are found to be desiccation tolerant, dry seed (10% moisture content) can be hermitically stored at ambient temperature for 30 weeks without losing their viability.     

Predispersal seed predation in Acacia macrostachya,its impact on seed viability,and germination responses to scarification and dry heat treatments

Predispersal seed predation among individual Acacia macrostachya trees over two sites in Burkina Faso was assessed. In addition, the effects of seed predation on seed viability; germination responses to scarification (mechanical, hot water at 60, 70 and 80°C, and sulphuric acid for 10, 20 and 30 min) and dry heat (at 60, 70 and 80°C for 15, 30 and 60 min each) treatments were investigated under laboratory conditions. The results indicated a large difference in predation intensity among individual trees, as well as between sites. Predispersal predation significantly decreased seed germination, particularly when the number of insect larvae per seed increased. Scarified and unscarified seeds germinated equally well, except for hot water treatments of high temperature. This indicates lack of physical dormancy and dispersed seeds can readily germinate provided that conditions for germination are conducive. Seeds exposed to dry heat treatments also germinated close to 97% under low intensity and short exposure times. This suggests that fire, under natural condition, plays a key role in triggering germination of A. macrostachya seeds.     

Enhancing germinability of Schinus molle L. seed lot from Ethiopia with specific gravity and IDS techniques

The IDS (Incubation, Drying and Separation) method was tested on Schinus molle L. seeds collected from Ethiopia in an attempt to sort non-viable from viable seeds. Seeds were incubated for 24 h followed by one, three, four, five, six, nine and twelve hours of drying and then separated in water. All IDS treatments gave 80.5–93.5% germination in the sunken fraction compared with 61% for untreated seeds. The mean germination time of sunken seeds reduced from 11.2 (control) to 8.9–9.2 days (IDS-treated). Specific gravity separation in water of untreated seeds was also tested, and the germination capacity of sunken fraction was 83.5% with a mean germination time of 9.3 days. IDS method can, therefore, be used to enhance both percentage and rate of germination of a seed lot of Schinus molle, which is desirable to produce uniform and vigorous seedlings in the nursery or out in the field.     

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 species/hybrids(E. dunnii, E. grandis, E. grandis × E. camaldulensis, E. urophylla × E. camaldulensis, E. urophylla × E. tereticornis, E. grandis × E. tereticornis, E. urophylla × E. grandis) in response to different levels of P supply(0, 6, 12 and 18 mg?kg-1 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 performance across all levels of P supply while E. urophylla × E. tereticornis showed superior growth performance. From a practical point of view, E. urophylla × 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 management objectives of short-rotation plantation.