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South Africa supports a rich floral diversity, with 21 643 native plant taxa that include a high proportion (76.3%) of endemic species, and many of these favoured as ornamentals, both locally and globally. Consequently, South Africa has contributed substantially to global plant invasions, with 1093 native taxa (5% of all species) naturalized in other countries. At least 80 taxa are invasive in natural or semi-natural ecosystems elsewhere, while an additional 132 taxa are potentially invasive. Of the global naturalized flora, 8.2% originate from South Africa and largely comprise species of Poaceae, Asteraceae, Iridaceae and Fabaceae. Australia, in particular, but also Europe and North America are major recipients of South African weeds. However, few countries have targeted South African plants for biological control (biocontrol), with most efforts undertaken by Australia. Previous and current targets have involved only 26 species with 17 agents (15 insects, one mite and one rust fungus) of South African origin released on five target species in Australia and the United States of America. South Africa's history of weed biocontrol, together with a large cohort of active scientists, is currently facilitating several internationally funded programmes targeting invasive plants of South African origin. In particular, the recently inaugurated Centre for Biological Control at Rhodes University and the University of KwaZulu-Natal have provided the impetus for novel efforts on five new target species and renewed efforts on four previously targeted species. In this contribution, we review the history of earlier biocontrol programmes against weeds of South African origin and the status of projects currently in progress in South Africa. [ABSTRACT FROM AUTHOR]

Seed number is the primary yield component in soybean [Glycine max (L.) Merrill], but the mechanisms responsible for the regulation of this component are not fully understood. Three soybean cultivars (Elgin 87, Emerald, and Essex) with genetic differences in seed growth rate and seed size were grown in the field in 1995 and 1996 to determine the relationship between photosynthesis, sink characteristics, and seed number at individual nodes. The sixth node from the bottom of the main stem was isolated by heat girdling the stem below the node to disrupt phloem continuity and by removing the part of the plant above the girdled node when flowers first opened at this node. Photosynthesis was varied by defoliating (removing approximately 0, 33, 66, 83, or 100% of the leaf area) the leaf at the girdled node. Carbon dioxide exchange rate (CER) was measured at approximately weekly intervals for up to 40 d after girdling. Girdling temporarily reduced CER in four of six comparisons and defoliation tended to increase CER. Defoliation produced large differences in nodal carbon input (NCI) per node and seed number increased rapidly as average NCI per node increased from 0 to approximately 0.10 µmol [CO.sub.2] [node .sup.-1] [s.sup.-2]. However, there was no further increase in seed number as average NCI continued to increase to 0.5 µmol [CO.sub.2] [node.sup.-1] [s.sup.-2], suggesting that isolated nodes respond differently than soybean communities. Maximum seed number per node was inversely related to cultivar differences in individual seed growth rate and seed size. The girdled node technique should prove useful to investigate seed number-photosynthesis relationships in soybean., THE YIELD OF GRAIN CROPS, including soybean, is a function of the number of seeds produced per unit area and the average weight of the individual seed (seed size) (Shibles [...]

Soybean [Glycine max (L.) Merr.] yield can be limited by the activity of the source (i.e., canopy photosynthesis) or by the ability of the seed (i.e., the sink) to utilize the assimilate produced by the source. An experiment was conducted for 3 yr at Lexington, KY, (38 ° N latitude) to evaluate potential source-sink limitations of early and late maturing cultivars. Two early maturing cultivars (Kasota and Hardin, Maturity Group I) and two late maturing cultivars (Essex and Hutcheson, Maturity Group V) were planted in mid-May in 0.38-m rows and the plots were irrigated to minimize water stress. Shade cloth that reduced irradiance by 63% was placed over half of the plots from approximately growth stage R6 (early seed filling) to maturity. Shade always significantly reduced the individual seed growth rate (9-32%) indicating that the plants were source limited. Leaf starch levels during seed filling were monitored to evaluate potential sink limitations. Starch levels in the late maturing cultivars usually remained constant or declined during seed filling, providing little evidence of a sink limitation. Starch levels in the early cultivars increased approximately 6-fold in the early stages of seed filling in 1 of 3 yr, suggesting that, in that year, the plants were sink limited, i.e., the seeds could not use all of the available assimilate. Source limitations during seed filling are apparently common in soybean, but sink limitations seem to occur infrequently in environments where water is not limiting., Yield of a grain crop is the net result of the production of assimilate by leaves (the source) and translocation of these assimilates to the developing seed (the sink) where [...]

Purpose: Human oocytes are arguably one of the most important cell types in humans, yet they are one of the least investigated cells. Because oocytes are limited in number, the use of high-quality oocytes is almost entirely in reproduction. Furthermore, regulatory hurdles for research on gametes and regulations on funding related to research on gametes present significant obstacles to research and the advancement of reproductive treatments. Here we report the outcomes of the largest compensated oocyte donation program for research in the USA to date, and probably worldwide.Methods: Women who participated in oocyte donation for research between 2008 and 2017 were contacted in a phone interview and completed a standardized questionnaire.Results: Of 114 participants, 98 oocyte donors completed donation, donating 1787 mature MII oocytes and a total of 86 skin biopsies. Complication rate, including minor complications, of oocyte donation was 8/98, or 8.1%, for which two involved follow-up. Fifty-seven donors answered questions about their experience. Participants were incentivized primarily by money and a desire to help others and reported an overall favorable experience. Most, but not all, human subjects recalled that they had donated for research, and approximately half recalled that their oocytes were being used specifically for stem cell research.Conclusions: Compensated oocyte donation provides a reliable path to obtaining high-quality oocytes for research and is reviewed favorably by oocyte donors. The continuation of programs that offer compensation for oocyte donation is invaluable to continued progress and advancements in stem cell research and human embryology, and for the advancement of novel reproductive treatments. [ABSTRACT FROM AUTHOR]

Developing cropping systems to maintain productivity in future environments will require a better understanding of crop species × environment interactions. The ratios of county corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields (corn/soybean) from three midwestern states (Kentucky [31 counties], Iowa [47 counties] and Nebraska [irrigated, 33 counties]) (1972 through 2015) were used to evaluate this interaction. Yield estimates (converted to a weight basis) were obtained from the National Agriculture Statistics Service. Average yield ratios were similar in Iowa (2.96) and Nebraska (3.00) in spite of higher yields in Nebraska. The highest average ratio (3.39) occurred in Kentucky counties where soybean double cropped after winter wheat (Triticum aestivium L.) predominated. Yield ratios were remarkably stable (low CVs) over time in high-yield environments, but stability decreased as county productivity (estimated by average corn yield) decreased (CVs increased from ~8 to 23%). The mean yield ratios in Kentucky and Nebraska decreased significantly as the proportion of continuous corn in a county increased. The largest yield ratios in non-double crop counties in Kentucky were associated with a larger proportion of continuous soybean in the rotation. Yield ratios increased significantly (p < 0.10) from 1972 to 2015 in only 37% of the counties (mostly in Iowa). The largest interactions between corn and soybean involved cropping systems and not fundamental physiological characteristics of these species. The consistency of mean yield ratios in rain fed and irrigated environments suggests that these crops may respond similarly to changes in precipitation. [ABSTRACT FROM AUTHOR]

The Mont Blanc and Aiguilles Rouges massifs, which form part of the external crystalline massifs of the western European Alps, record a young and fast exhumation history, as established by an extensive low-temperature thermochronology and geochronology data set. Various kinematic and dynamic models for Oligocene to Neogene deformation and exhumation of the Aiguilles Rouges-Mont Blanc system have been proposed. However, the timing of deformation along major shear zones in and around the massifs, which is crucial to these models, is still controversial. Our new 40Ar/39Ar data from key deformation zones in the Mont Blanc area show that NW directed thrusting lasted from Oligocene to mid-Miocene times in the Mont Blanc massif before a NW-ward jump of the deformation front to below the Aiguilles Rouges massif, which led to updoming of the Aiguilles Rouges and Mont Blanc massifs. This deactivated the main NW verging shear zones and caused back-folding and back thrusting east of the Mont Blanc, as well as upward extrusion of the Aiguilles Rouges massif. Subsequently, there was a switch to more coaxial shortening between the Aiguilles Rouges and Mont Blanc massifs associated with strain partitioning and related dextral strike-slip deformation on the eastern side of the Mont Blanc massif. [ABSTRACT FROM AUTHOR]

The most consistent change in management practices associated with the increase in maize (Zea mays L.) yield in the United States since 1930 has been a steady increase in plant population. populations increased from roughly 30,000 plants ha-1 at the beginning of the hybrid era to >75,000 plants ha-1 in recent years. The purpose of this review was to evaluate the potential role of sink size in historic maize yield-population relationships. The steady increase in yield (~4×) during the hybrid era required an increase in source activity since there was no change in harvest index. The increase in grain yield was associated with an increase in kernels per unit area, so there was a concomitant increase in both source and sink. Data collected from the literature and evaluations of hybrids from different eras demonstrate that ear size (kernels per ear) of U.S. and Canadian hybrids did not increase during the hybrid era. Ears per plant did not increase above an average of one. Since ear size and prolificacy did not change, higher plant populations were needed to increase sink size (ears and kernels per unit area). This approach to analyzing population-yield relationships suggests that higher populations didn't necessarily contribute directly to higher productivity; rather, the increase in sink size avoided a sink limitation and allowed the higher productivity of the source to be translated into grain yield. Future yield increases will, therefore, require even higher populations which could create new management challenges. [ABSTRACT FROM AUTHOR]

The ability of soybean \Glycine max (L.) Merr.] to adjust its pod load to environmental conditions is an important, but not well understood, part of the yield production process. To better understand this process at the whole plant level, a single-node model (SOYPOD) was extended to predict pod set of whole plants. Pod survival in SOYPODP was determined by comparing assimilate from photosynthesis (calculated from solar radiation) to pod requirements during initial pod growth. Measured profiles of flowers per node and pod and seed growth rates were used as input. Pods that do not receive adequate assimilate for a specified number of consecutive days do not survive. When inter-nodal movement of assimilate was prohibited and the nodal assimilate production profile matched the input flower profile, pod set on the stem matched measured profiles of two field-grown culti-vars. In this form, SOYPODP accurately mimicked known responses of pod number to variation in assimilate supply, nodes per plant and individual seed growth rate. Competition for assimilate at a node-controlled pod set, so increasing uniformity of pod development (more flowers or a shorter flowering period) increased pod set. Increasing nodal variation in the beginning of pod development reduced the sensitivity of the plant to short-term fluctuations in assimilate supply. Variation in uniformity of pod development at a node was responsible for increases in pod set with no change in assimilate availability. The value of these increases is not clear, but it seems unlikely that they would affect yield. [ABSTRACT FROM AUTHOR]

The magnitude of yield gaps (YGs) (potential yield -- farmer yield) provides some indication of the prospects for increasing crop yield. Quantile regression analysis was applied to county corn (Zea mays L.) yields (1972-2011) from Kentucky, Iowa, and Nebraska (irrigated) (total of 115 counties) to estimate the attainable potential yield (APY) (yield in the most favorable environments in the 40-yr record) for each county. The YG for each year was the difference between the APY and the county yield. Potential productivity (40-yr mean county yield) varied substantially within and among states (579-1001 g m-2). The mean relative yield gap (RYG) varied from 9 to 24% of APY and decreased linearly (p < 0.0001) as the mean county yield increased for each state. Large YGs were partially related to very low yields that occurred in some years and may reflect the ability of the soil to supply water to the crop; other soil or management factors may also be involved since irrigation did not reduce the RYG in Nebraska to zero. The highest mean county APY was 30% (Kentucky), 22% (Iowa) and 14% (Nebraska) higher than the lowest county APY. This second YG occurred in favorable environments. Reducing the first YG in Kentucky and Iowa will probably require irrigation. Reducing the second YG may be more difficult if it is related to intractable soil characteristics. These results suggest that soil conditions may play an important role in determining the size of YGs in Midwestern corn production systems. [ABSTRACT FROM AUTHOR]

The magnitude of yield gaps (YG) (potential yield--farmer yield) provides some indication of the prospects for increasing crop yield. Quantile regression analysis was applied to county soybean [Glycine max (L.) Merr.] yields (1972-2011) from Kentucky, Iowa, and Nebraska (irrigated) to estimate the attainable potential yield (APY) (yield in the most favorable environments in the 40-yr record). The YG for each year was the difference between the APY and the county yield. There was substantial variation in the 40-yr mean county yields (186-335 g m-2) within and among states. The mean county APY within each state increased linearly (P < 0.0001) in conjunction with mean county yields. The mean relative YGs varied from 9 to 24% of APY and were largest in the lowest yielding counties and they decreased linearly (P < 0.0001) as the mean county yield increased for each state. The large YGs were partially related to very low yields that occurred in some years during the 40-yr period and these YGs may partially reflect the ability of the soil to supply water to the crop. The difference between the maximum APY in each state and each county APY defined a second YG. The largest values ranged from 12 to 19% of the maximum APY. Irrigation should partially eliminate the first YG, but the second may be more intractable to the degree it is related to soil characteristics. These results suggest that soil conditions may play an important role in determining the size of YGs. [ABSTRACT FROM AUTHOR]

A method for predicting soybean [Glycine max (L.) Merr.] seed germination during storage would benefit seed producers and the seed industry. This investigation evaluated the ability of the Ellis and Roberts deterioration model to predict seed germination after warehouse storage and the accuracy of a rapid-aging test to estimate initial seed quality ([K.sub.i]). Seed lots with low levels of mechanical injury and Phomopsis longicolla (Hobbs) seed infection produced in 1990 and 1991 were stored more than 2 yr in multiwall paper bags in seed warehouses in Kentucky and Indiana. Warehouse temperature was monitored and seed moisture and germination were determined at 3-mo intervals. The rapid-aging test (40 ° C and 150 g [kg.sup.-1] seed moisture [fresh weight basis]) was used to estimate [K.sub.i] for each seed lot. The model accurately (± 10 percentage points) predicted germination of most seed lots after one carryover year of storage (1 yr after the first spring planting season, [approximately equals] 430 d), when little deterioration had occurred. After 2 yr of carryover storage ([approximately equals] 800 d), when germination had declined, the model accurately predicted the germination of only six of 16 seed lots. The inaccurate predictions may have been related to variation in [K.sub.i] (substantial variation occurred between repeated determinations on the same seed lot) or to variation among seed lots in the rate of deterioration at constant temperature and seed moisture. These results suggest that some of the assumptions underlying the Ellis-Roberts seed deterioration model may be invalid and require further evaluation., Soybean seed lots typically decline in quality faster than the seed of other agronomic crops (Delouche et al., 1973). Thus, a method of predicting declines in germination during storage and [...]

Soybean [Glycine max (L.) Merr.] yield is often associated with the number of pods per unit area, which can be construed to suggest that the number of pod bearing structures (nodes) plays a role in determining yield. This hypothesis was tested in a 2-yr field experiment at Lexington, KY (38° N latitude). Four cultivars that varied in relative maturity (0.7 to 5.3) and high and low populations (one cultivar) were used to create variation in nodes per square meter. The experiments were planted on 25 May 2010 and 31 May 2011 in 38-cm rows (19 cm for the high population) and the target populations were approximately 43 (four cultivars), 26 (low population), and 78 (high) plants m-2. Irrigation was used to minimize water stress. There were four replications of each treatment in a randomized complete block design. A 30-cm section of bordered row was harvested at maturity to determine flower scars, pods, and nodes. The photosynthetically active radiation interception was roughly 90% or above at R1 for all treatments and there was little difference in incident solar radiation or temperature among treatments during flowering and pod set. There was a two-fold variation in nodes per square meter in both years. Pods per square meter increased in concert with nodes per square meter up to approximately 70% of the maximum node number; above that level there was no change in pods per square meter. At low node levels, pods per square meter seems to be limited by the number of nodes, but at higher node levels there was no relationship between nodes and pods. [ABSTRACT FROM AUTHOR]

There is substantial variation in seed size (weight per seed) among the seeds produced by a soybean (Glycine max [L.] Merrill) plant. Five field experiments with two cultivars were conducted near Lexington, Kentucky, United States (38°N), to test the hypothesis that variation in seed size was related to the time of fruit initiation during the flowering period. All fruits ≥ 10 mm long on a plant were marked at three-day intervals, harvested at maturity, and separated by the time of marking before seed size was determined. There was substantial variation in seed size, but the time of fruit initiation accounted for only a small proportion of the variation. Fruits that initiated growth at different times often produced the same sized seeds, and there was always substantial variation in seed size among fruits initiated at the same time. The data provide little support to the hypothesis that seed size is related to the timing of fruit initiation. The data suggest that there may be several mechanisms responsible for the variation in seed size on soybean plants. [ABSTRACT FROM AUTHOR]

Seed vigor is defined as those "seed properties that determine the potential for rapid, uniform emergence and development of seedlings under a wide range of field conditions." Seedlings from high-vigor seed lots are expected to emerge more uniformly than those from low-vigor lots. We tested this hypothesis in a series of greenhouse and growth chamber experiments with several high- and low-vigor corn (Zea mays L.) samples that had high standard germination. Seed-vigor levels were estimated with the saturated cold test where the seeds were stressed with low temperature (10°C) and field soil for 7 d and then germination was measured after 5 d at 25°C. The uniformity index (UI) (time from 10 to 90% of final emergence) was estimated by planting seeds 3.8 cm deep in soil and counting emergence every 6 h in greenhouse and growth chamber experiments. Lowering the soil temperature from roughly 23 to 15°C increased the time to 10% of final emergence (T10) from about 100 to more than 300 h and increased the UI. Low-vigor seed always had a larger UI than high- vigor seed, but the difference was less when the seedlings emerged rapidly (Uls were 20 to 30 h) than when they emerged slowly (maximum of -80 h for high-vigor seed and 140 h for low-vigor seed). High-vigor seed had more uniform emergence, but soil temperature and the time to emergence also influenced uniformity. [ABSTRACT FROM AUTHOR]