Adaptation and yield of pigeonpea in different environments in Tanzania

Pigeonpea is grown in wide range of cropping systems and environments, both in East Africa and internationally. An important feature of adaptation to these diverse systems and environments is the timing of flowering and maturity. Most traditional cultivars grown in Tanzania are medium to late flowering types (>150 days), although extra-early flowering cultivars are now available. The aim of the present investigation was to measure biomass (BY) and seed (SY) yield of a set of phenologically diverse cultivars to determine their adaptation to contrasting environments in Tanzania. Ten cultivars, from extra-early (60 days) to late (>180 days) flowering, were planted at six locations varying in mean temperature, photoperiod and rainfall. Days to flowering (DTF) and maturity, and above-ground BY and SY at maturity, were measured. A stress index (ETr:ETm ratio, 100 = no stress) was computed for each site. Rainfall and the stress index at the different sites varied from 322 to 1297 mm and 57 to 89, respectively. Among cultivars, DTF varied from 55 to 320 days, the stress index from 3 to 98, BY from 700 to 25,000 kg ha⁻¹, and SY from 0 to 4000 kg ha⁻¹. The highest yielding environment was at Selian, where mean temperatures were favourable (19 °C) and no stress occurred. At all sites there was an optimum DTF, which for SY varied from <100 to 150 days. The best adapted cultivars were ICP 7035, ICPL 90094, Kat 50 and QP37, which were all medium flowering (c. 150 day) types. Extra-early cultivars such as ICPL 86005 also showed considerable potential, especially in short-season environments.     

Divergent selection at ultra-low plant density for seed protein and oil content within soybean cultivars

Soybean [Glycine max (L.) Merr.] seed is a major source of protein for animal feed and oil for human consumption. Selection within elite soybean cultivars for the improvement of agronomic and seed traits is assumed to be ineffective due to the belief that cultivars are highly homogeneous. Previously reported data suggest that latent variation among the single plant selections within a cultivar exists and that mechanisms that generate de novo variation may also be present. The main objective of this study was to perform divergent single-plant selection at ultra-low plant density and investigate the presence of genetic variation for seed protein and oil within three elite soybean cultivars. A secondary objective was to investigate the variation for fatty acid composition. In 1995, single plants from the three cultivars were grown in a honeycomb design using a plant-to-plant spacing of 0.9 m. A total of 333 plants from ‘Benning’, 392 plants from ‘Haskell’, and 371 plants from ‘Cook’ were evaluated. Divergent single-plant selection for protein and oil content was performed to select a total of 20 plants for high or low protein and 20 plants for high or low oil from each cultivar. The selected plants were further evaluated in replicated row-plot experiments for 3 years. Our results indicate that single-plant selection at low plant density was successful in discovering significant variation for seed protein and oil within each of the three soybean cultivars. For protein content, the magnitude of intra-cultivar variation between the highest- and lowest-protein lines averaged 19 g kg⁻¹ across the three cultivars and ranged from 13 to 24 g kg⁻¹. For oil composition, the magnitude of variation between the most divergent lines averaged 12 g kg⁻¹ across the three cultivars and ranged from 9 to 14 g kg⁻¹. Significant variation among the selected progeny lines was also discovered for specific fatty acid composition. The magnitude of intra-cultivar variation averaged from 6 to 29 g kg⁻¹ across the five fatty acids of soybean. The genetic variation discovered within the soybean cultivars is most likely due to latent variation and/or newly created variation. Our data provide evidence that single-plant selection at ultra-low plant density within elite cultivars can be effective in improving the seed composition of a soybean cultivar.     

Population density and row spacing effects on dry matter yield and bark content of kenaf (Hibiscus cannabinus L.)

Efforts to bring kenaf from experimental crop status to an accepted alternative in established cropping systems have been ongoing for years. To compete with existing crops and maximize monetary returns, the effects of agronomic practices on yield and crop quality must be better understood. Row spacing and population density are implicated in dry matter yield, and therefore, bast fiber production. Four row spacings, four population densities, and two cultivars were examined to determine these effects on dry matter accumulation and bark content. Of all factors evaluated, only row spacing significantly affected dry matter yield. Yield was greatest at the 35.5-cm row spacing, and lowest at the 71- and 101.6-cm row spacings. With regard to bast yield, calculated as a percentage of total sample dry weight, a significant cultivar × row spacing interaction occurred. However, data indicate that manipulating row spacing to maximize total stalk yield per hectare resulted in the highest bast fiber yield for the two cultivars tested. The narrowest row spacing of 35.5 cm, gave the greatest biomass yield as well as the highest bark yield per hectare.     

Grain concentrations of protein and mineral nutrients in a large collection of spelt wheat grown under different environments

A large number of spelt wheat genotypes (ranging from 373 to 772) were evaluated for grain concentrations of protein and mineral nutrients under 6 different environments. There was a substantial genotypic variation for the concentration of mineral nutrients in grain and also for the total amount of nutrients per grain (e.g., content). Zinc (Zn) showed the largest genotypic variation both in concentration (ranging from 19 to 145 mg kg⁻¹) and content (ranging from 0.4 to 4.1 μg per grain). The environment effect was the most important source of variation for grain protein concentration (GPC) and for many mineral nutrients, explaining between 37 and 69% of the total sums of squares. Genotype by environment (G × E) interaction accounted for between 17 and 58% of the total variation across the minerals. GPC and sulfur correlated very significantly with iron (Fe) and Zn. Various spelt genotypes have been identified containing very high grain concentrations of Zn (up to 70 mg kg⁻¹), Fe (up to 60 mg kg⁻¹) and protein (up to 30%) and showing high stability across various environments. The results indicated that spelt is a highly promising source of genetic diversity for grain protein and mineral nutrients, particularly for Zn and Fe.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Developing rice cultivars for high-fertility upland systems in the Asian tropics

Traditionally, upland rice is grown in Asia in low-input, subsistence systems. More productive upland systems, using more fertilizer and improved varieties, are emerging in China and Philippines, and could contribute to productivity increases in rainfed environments in other countries. Here, we evaluate, on-station and on-farm, the yield under upland management of improved indica upland cultivars selected for yield under high-fertility conditions. These cultivars are compared with traditional and improved tropical japonica upland varieties, and with elite indica high-yielding varieties (HYV) developed for irrigated lowland production, to characterize the features of varieties that produce high yields in favorable upland environments. Forty-four improved and traditional varieties and experimental lines were evaluated in irrigated lowland, non-stressed upland, moderately stressed upland, severely water-stressed upland, and low-fertility upland environments in southern Luzon, Philippines. Correlations between yields in non-stress and mild-stress environments were low but positive. Some cultivars, like IR55423-01, were among the highest yielding under both conditions, indicating that high yield and moderate water-stress tolerance can be combined. Upland-selected indica varieties yielded 3.56 t ha⁻¹ in favorable upland environments on-station in southern Luzon, outperforming improved tropical japonica and irrigated varieties by 23 and 69%, respectively. They were also the highest-yielding class in infertile, acid soils. The improved upland indica cultivars are about 110 cm tall under favorable upland conditions and maintain a harvest index of nearly 0.4, or about one-third higher than other cultivar types. The best upland-adapted rice varieties produced average yields on-farm of 3.3 and 4.1 t ha⁻¹ in southern Luzon and Yunnan, respectively, outyielding traditional checks by 30–50% with moderate N application. Screening under both high-fertility, non-stress conditions and moderate reproductive-stage stress appears to be needed to develop cultivars combining high-yield potential with drought tolerance. Upland-adapted indica cultivars offer a new approach to increasing productivity and reducing risk in Asian rainfed rice systems.     

Large applications of fertilizer N at planting affects seed protein and oil concentration and yield in the Early Soybean Production System

An inverse relationship between soybean [Glycine max (L.) Merr.] seed protein and oil concentration is well documented in the literature. A negative correlation between protein and yield is also often reported. The objective of this study was to determine the effect of high rates of N applied at planting on seed protein and oil. Nitrogen was surface-applied at soybean emergence at rates of 290 kg ha⁻¹ in 2002, 310 kg ha⁻¹ in 2003, and 360 kg ha⁻¹ in 2004. Eight cultivars ranging from Maturity Group II–IV were evaluated under the Early Soybean Production System (ESPS). However, not all cultivars were evaluated in all 3 years. Glyphosate herbicide was used in all 3 years and a non-glyphosate herbicide treatment was applied in 2002. Cultivars grown in 2003 were also evaluated under an application of 21.3 kg ha⁻¹ of Mn. All cultivar, herbicide, and Mn treatments were evaluated in irrigated and non-irrigated environments with fertilizer N (PlusN treatment) or without fertilizer N (ZeroN treatment). When analyzed over all management practices (years, cultivars, herbicide, and Mn treatments), the PlusN treatment resulted in a significant decrease in protein concentration (2.7 and 1.9%), an increase in oil concentration (2.2 and 2.7%), and a decrease in the protein/oil ratio (4.7 and 4.6%) for the irrigated and non-irrigated environments, respectively. However, the overall protein and oil yield increased with the application of fertilizer N at planting (protein: 5.0% irrigated, 12.7% non-irrigated and oil: 9.9% irrigated and 18.9% non-irrigated). These increases were due to the increase in seed yield with the application of large amounts of fertilizer at planting. Additionally, a significant correlation (r = 0.45, P = 0.0001) was found between seed protein concentration and seed yield. No significant correlation was found between seed oil concentration and seed yield. The data demonstrate the inverse relationship between protein and oil and indicate that large amounts of N applied at planting do not change this relationship.     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: I. Legume biomass production and N fixation

Field experiments were conducted to investigate the performance of temperate legume species in rice-based cropping systems in a warm-temperate environment in Nepal. Over the period 1994–1996, various legume species were grown during the winter season (October–May) in the Kathmandu valley (27° N, 1350 m asl) with the aim of evaluating their biomass production and N fixation. A wide range of legume species including food, feed and green manure crops proved to be very well adapted to the winter growing conditions in this environment. The cultivation of temperate legume crops therefore, constitutes an alternative to traditional cropping practices such as growing wheat or leaving the land fallow. The temperate species appeared to capitalise on generally favourable growing conditions such as long growing season, low pest and disease pressure, high radiant energy receipt and cool night temperatures. However, performance varied greatly between species and years. Total dry matter yields ranged from 2 to 20 t ha⁻¹ obtained with lentil (Lens culinaris Medic) and bitter lupin (Lupinus mutabilis), respectively. Highest seed yields were produced by fababean (Vicia faba) (5 t ha⁻¹) and field pea (Pisum sativum var. arvense) (3 t ha⁻¹) in the first season. Nitrogen yields and quantities of N fixed ranged from 18 to 481 kg ha⁻¹ and from 0 to 463 kg ha⁻¹, respectively. Large amounts of N were fixed by species such as fababean, Persian clover (Trifolium resupinatum) and bitter lupin. Early sowing in autumn was shown to be beneficial for some crops such as fababean, vetch (Vicia benghalensis) and Persian clover. In these cases, it is, therefore, important to reduce the turn-around interval after rice. Further research is required to fully determine the potential of temperate legume species in these environments with particular emphasis given to the identification of the most adapted cultivars and to reduce the need for irrigation of these winter crops.     

Seed yield components,oil content,and fatty acid composition of two cultivars of moringa (Moringa oleifera Lam.) growing in the Arid Chaco of Argentina

Moringa oleifera Lam. (M. pterygosperma Gaertn [Moringaceae]) is a fast-growing small tree native to the sub-Himalayan tracts of Northern India. The recognition that moringa oil has value in cosmetics has increased interest in cultivating it for seed-oil. The experimental trials were conducted in a semi-commercial moringa plantation in the subtropical northwestern region of Argentina, considering the similar climate conditions to the plant native region. Pods per tree, seeds per pod, weight of seed per pod, kernel weight, kernels oil content and fatty acid composition of PKM-1 and African cultivars were determined. One individual, E₄-9, a PKM-1 plant, had significantly (P < 0.05) higher production than all other plants. In addition, this individual was the highest extrapolated oil producer in both 2003 and 2004, with 595 and 564 kg ha^?1, respectively (ave. 580 kg ha^?1). Seed weight (200-seed wt.) was significantly greater in 2003 than 2004; no other traits studied showed significant differences between years. Both cultivars produced-oil with practically identical fatty acid composition, and the monounsaturated ω-9 oleic fatty acid accounted for more than 70% of the total for both cultivars. The polyunsaturated ω-6 linoleic fatty acid content of the African cultivar was slightly, but significantly (P < 0.05), higher than that of PKM-1.     

Consistent differences among wheat cultivars in osmotic adjustment and their relationship to plant production

Osmotic adjustment (OA) is generally considered an important component of drought resistance. Several reports by J.M. Morgan [Morgan, J.M., 1983. Osmoregulation as a selection criterion for drought tolerance in wheat. Aust. J. Agric. Res. 34, 607–614; 1992. Osmotic components and properties associated with genotypic differences in osmoregulation in wheat. Aust. J. Plant Physiol. 19, 67–76; 1995. Growth and yield of wheat lines with differing osmoregulative capacity at high soil water deficit in seasons of varying evaporative demand. Field Crops Res. 40, 143–152; Morgan, J.M., Condon, A.G., 1986. Water-use, grain yield and osmoregulation in wheat. Aust. J. Plant Physiol. 13, 523–532] from Australia concluded that consistent genetic differences in OA existed among wheat cultivars and that high OA cultivars tended to yield better than low OA cultivars under drought stress. Our study was performed to assess his results with his and other genetic materials.Two of Morgan’s spring wheat lines with high OA (‘H.Osm-134’) and low OA (‘L.Osm-136’) capacity in addition to eight other diverse spring wheat cultivars were tested for OA and plant production when grown in small plots under a rain exclusion shelter at Bet Dagan, Israel in 1996. OA of five of these cultivars (including Morgan’s lines) was also measured in two independent greenhouse tests in 1997 (Israel) and 1998 (Texas).The five cultivars differed significantly and ranked consistently for OA in all tests. No significant cultivar by test interaction for OA was revealed. OA was well correlated across cultivars between tests. The significantly higher OA capacity of H.Osm-134 as compared with L.Osm-136 was repeated in all tests. OA of all ten cultivars was positively correlated with biomass (r = 0.73; p = 0.02) and yield (r = 0.55; p = 0.09) under pre-flowering drought stress in the rain exclusion shelter. H.Osm-134 line performed significantly (p ≤ 0.05) better than L.Osm-136 line for both biomass and yield under drought stress. We therefore support Morgan’s results and conclude that consistent differences in OA exist among wheat cultivars and that these differences can be associated with plant production under pre-flowering drought stress.     

Modelling photoperiod and temperature responses of flowering in quinoa (Chenopodium quinoa Willd.)

Two modelling approaches were used to quantify photoperiod and temperature responses of time from emergence to visible flower buds in nine quinoa (Chenopodium quinoa Willd.) cultivars. The first, non-interactive model, considers temperature and photoperiod responses as independent, and the threshold photoperiod, critical photoperiod, and base temperatures as constants. The second, interactive model, considers these attributes as variable, and allows for interaction between photoperiod and temperature responses. Controlled-environment experiments with a factorial combination of temperature and photoperiod provided information on responses, and data from field experiments were utilized in tests of the predictive capacity of the models.The two models were very similar in their goodness of fit and predictive capacity, but testing revealed that some assumptions about the interactive model were not fulfilled, whereas the non-interactive model is more consistent with the data. Both the models failed to predict dates of visible flower buds when average temperatures during the phase were >20°C; it is proposed that interaction between irradiance receipt and high temperature in controlled environments result in lower optimum temperatures there than in the field. Differences between field data and predicted values were eliminated when predictions were recalculated assuming no optimum for the temperature response.All nine cultivars examined are short-day plants. A juvenile sub-phase was observed in the six cultivars for which it was tested; and its duration was negatively associated with the latitude of origin of the lines (R² = 0.9, p < 0.05). Photoperiod sensitivity was negatively associated with the latitude of origin of the lines (R² = 0.55, p < 0.05) and positively associated with duration of the basic vegetative phase (minimal time between emergence and visible flower buds) (R² = 0.55, p < 0.05) using the non-interactive model. Photoperiod and temperature response parameters were not significantly associated with the latitude of origin for the interactive model (p > 0.05).     

Elastic properties of gluten representing different wheat classes

Traditional instruments used to evaluate dough and/or gluten rheological properties do not provide unambiguous separation of elastic and viscous behaviors. Recovery after shear creep and cyclic large deformation cyclic tensile testing were used here to decouple elastic and viscous effects. A large variation in the recoverable shear strain (∼7.2% to ∼28%) was seen for glutens from 15 U.S. popular common wheat cultivars with varying HMW subunits. Sedimentation values ranged from 29 to 57 ml for 12 hard wheat cultivars and 15 to 22 ml for three soft wheat cultivars. The tensile force at 500% extension ranged from 0.12 to 0.67 N for hard wheat glutens and from 0.10 to 0.20 for soft wheat glutens. However, the recoverable work after large extension was less than 40% of the total work of extension. In addition, recoverable work in tensile testing was highly correlated with the total work of extension (r² = 0.97) and mixograph mix times (r² = 0.81). Good to excellent bread volume was obtained for several cultivars from this sample set. This suggests that optimizing water absorption for mixing doughs to achieve maximal bread volume compensates for the wide range of viscoelastic behaviors of gluten.     

The influence of environment and season on stalk yield in kenaf

Kenaf is an important fiber crop worldwide. It was recently introduced to South Africa as a commercial fiber crop. The aim of this study was to determine how different environments and seasons influence stalk yield. Nine kenaf cultivars from various countries were analysed in two environments, over two consecutive seasons, where one location was irrigated and the other not. Data were recorded for total fresh yield, defoliated stalk yield and dry stalk yield. Yield stability was analysed with four different statistical models. The dry stalk yield varied from 15.33 to 17.78 ton/ha. El Salvador and Tainung 2 had high dry stalk yields in the favourable environments, but Tainung 2 did not have stable yield across all trials. Everglades 41 and El Salvador were the most stable of the varieties across both environments and seasons. El Salvador was the cultivar that had the highest and most stable dry stalk yield in the two seasons and two locations in South Africa, and should perform well in commercial production.     

Selecting for increased barley grain size

In this study, 120–144 commercial varieties and breeding lines were assessed for grain size attributes including plump grain (>2.8 mm) and retention (>2.5 mm+>2.8 mm). Grain samples were produced from replicated trials at 25 sites across four years. Climatic conditions varied between years as well as between sites. Several of the trial sites were irrigated while the remaining were produced under dryland conditions. A number of the dryland sites suffered severe drought stress. The grain size data was analysed for genetic (G), environmental (E) and genotype by environment (G×E) interactions. All analyses included maturity as a covariate. The genetic effect on grain size was greater than environmental or maturity effects despite some sites suffering terminal moisture stress. The model was used to calculate heritability values for each site used in the study. These values ranged from 89 to 98% for plump grain and 88 to 96% for retention. The results demonstrated that removing the sources of non-heritable variation, such as maturity and field effects, can improve genetic estimates of the retention and plump grain fractions. By partitioning all variance components, and thereby having more robust estimates of genetic differences, plant breeders can have greater confidence in selecting barley genotypes which maintain large, stable grain size across a range of environments.     

Growth and distribution of maize roots under nitrogen fertilization in plinthite soil

To improve efficiency of soil N and water use in the savanna, maize (Zea mays L.) cultivars with improved root systems are required. Two rainfed field experiments were conducted in Samaru, Nigeria in the 1993 and 1994 growing seasons with five maize cultivars under various rates of nitrogen fertilizer. The capacity of maize for rapid early root growth and to later develop a deep, dense root system was assessed. In addition, the effect of N fertilization on root growth of maize was studied in 1994. The widely cultivated cultivar TZB-SR had a poor root system in the surface soil layer and was more susceptible to early-season drought, as indicated by low plant vigor and aboveground dry matter yield during that time. It had a lower grain yield and a relatively small harvest index, but ranked among the highest in total aboveground dry matter production compared to other cultivars. The size of root system alone did not always relate well with grain yield among cultivars. Partitioning of dry matter within the plant was important in determining differences in grain yield and N stress tolerance between cultivars. A semiprolific cultivar (SPL) had high seedling vigour and a dense root system in the surface soil layer that conferred a greater tolerance to early-season drought stress and improved uptake of the early-season N flush, as indicated by a greater dry matter yield at 35 days after sowing (DAS). It also had a fine, deep, dense root system at flowering that could have improved water- and N-use efficiency in the subsoil (> 45 cm), thereby avoiding midseason drought stress in 1994. SPL had a large harvest index and the greatest yield among cultivars in 1994. Averaged across cultivars, greater root growth and distribution was observed at a moderate N rate of 0.56 g plant⁻¹ than at zero-N or high N (2.26 g plant⁻¹). Differences in root morphology could be valuable as selection criteria for N-efficient and drought-tolerant maize.     

Responses of field-grown irrigated rice cultivars to varying levels of floodwater salinity in a semi-arid environment

Shallow saline water tables, naturally saline soils and variations in climatic conditions over the two growing seasons, create a harsh environment for irrigated rice production in the Senegal River Delta. At the onset of the growing season, salts accumulated by capillary rise in the topsoil are released into the soil solution and floodwater. Rice fields often lack drainage facilities, or drain from one field to the other, thus building up salt levels during the season. Salt stress may, therefore, occur throughout the growing season and may coincide with susceptible growth stages of the rice crop. The objectives of the present study were to (i) determine varietal responses to seasonal salinity in both the hot dry season (HDS) and the wet season (WS) and (ii) derive guidelines for surface water drainage at critical growth stages. We evaluated responses of three rice cultivars grown in the region to floodwater salinity (0–2, 4, 6, 8 mS cm⁻¹), applied either at germination, during 2 weeks at crop establishment, during 2 weeks around panicle initiation (PI), or during 2 weeks around flowering. Floodwater electrical conductivity (EC) reduced germination rate for the most susceptible cultivar by as much as 50% and yield by 80% for the highest salinity level imposed. Salinity strongly reduced spikelet number per panicle, 1000 grain weight and increased sterility, regardless of season and development stage. The strongest salinity effects on yield were observed around PI, whereas plants recovered best from stress at seedling stage. Floodwater EC <2 mS cm⁻¹ hardly affected rice yield. For floodwater EC levels >2 mS cm⁻¹, a yield loss of up to 1 t ha⁻¹ per unit EC (mS cm⁻¹) was observed for salinity stress around PI (at fresh water yields of about 8 t ha⁻¹). Use of a salinity tolerant cultivar reduced maximum yield losses to about 0.6 t ha⁻¹ per unit EC. It is concluded that use of salinity tolerant cultivars, drainage if floodwater EC >2 mS cm⁻¹ at critical growth stages, and early sowing in the WS to avoid periods of low air humidity during the crop cycle, are ways to increase rice productivity in the Senegal River Delta.     

Intraspecific responses in crop growth and yield of 20 soybean cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in crop growth and grain yield of 20 soybean cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The supplemental UV-B radiation was 5.00 kJ m⁻², simulating a depletion of 20% stratospheric ozone at Kunming (25°N, 1950 m). Out of the 20 soybean cultivars tested, 17 and 15 showed significant change in plant height at 80 DAP (days after planting) and ripening stages, respectively. Sensitivity in plant height was greater at 80 DAP than at ripening. The plant height of 3 cultivars increased, and that of 17 cultivars decreased. Under UV-B radiation, LAI (leaf area index), biomass and grain yield decreased, respectively. The greatest percent decrease was 95.7, 93.9 and 92.8, respectively. RI (response index) was the sum of percent change in plant height at ripening, LAI, biomass and grain yield. The results showed that all 20 soybean cultivars had a negative RI, indicating inhibition by UV-B radiation on soybean growth. The RI of 6 tolerant cultivars was higher than −163.1 and 5 out of 6 originated from south China (low latitude). The RI of the most tolerant cultivars, Yunnan 97801, was −72.4. Meanwhile, the RI of 5 sensitive cultivars was lower than −256.9 and 4 out of the 5 originated from north China (high latitude). The RI of the most sensitive cultivar, Huanxianhuangdou, was −295.7. These UV-B tolerant cultivars identified in this study might be useful in breeding programs.     

The effects of cultivar and prophylactic fungicide spray for leaf diseases on colonisation of maize ears by fumonisin producing Fusarium spp. and fumonisin synthesis in South Africa

Fumonisins are mycotoxins produced primarily by Fusarium verticillioides and Fusarium proliferatum on maize. These are secondary, carcinogenic metabolites and have been reported on maize worldwide. Field trials were conducted during 2010/2011 and 2011/2012 in six diverse maize production areas of South Africa to study the efficacy of an existing prophylactic fungicide regime for the control of foliar diseases, on the infection of grains of seven cultivars by fumonisin producing Fusarium spp. and fumonisin synthesis. Seven cultivars were selected to include both yellow and white, Bt and non-Bt and regionally adapted varieties. Azoxystrobin + difenoconazole (strobilurin, 200 g/L + triazole, 125 g/L) was applied 40–45 days after planting followed by flusilazole + carbendazim (silicone triazole, 125 g/L + benzimidazole, 250 g/L) with petroleum as adjuvant, 28–30 days later. Fumonisins in harvested kernels were analysed using High Performance Liquid Chromatography (HPLC) and fumonisin producing Fusarium spp. were quantified by means of quantitative Real Time PCR (qPCR). Mean natural colonisation of maize kernels by fumonisin producing Fusarium spp. was highest at Makhathini (33,696 pg/0.5 g of milled maize kernels) and the lowest at Potchefstroom (179 pg/0.5 g of milled maize kernels). Cultivars differed in susceptibility to fungal colonisation and fumonisin synthesis with PAN6P-110, DKC80-10 and CRN3505 proving most susceptible and LS8521B and DKC78-15B most resistant. Mean fumonisin contamination was highest at Makhathini (23.62 ppm) and lowest at Buffelsvlei (1.50 ppm). Analysis of variance showed no significant differences in colonisation of grain by fumonisin producing Fusarium spp. between sprayed and control treatments. Sprayed treatments had significantly higher fumonisin levels compared with unsprayed treatments. A highly significant cultivar × environment interaction was recorded for fungal colonisation. Highly significant environment × fungicide-treatment × cultivar interactions were recorded for fumonisin production. The strong interaction between cultivar and environment may be due to cultivar adaptation/behaviour under different environmental conditions. The use of a prophylactic fungicide spray regime for control of leaf diseases in maize did not reduce Fusarium ear rot in maize, however, significantly elevated fumonisin levels were recorded.