Morphological and molecular diversity of Agave tequilana Weber var. Azul and Agave angustifolia Haw. var. Lineño

The genetic diversity in forty-nine Agave tequilana Weber var. Azul accessions from different regions of the Appellation of Origin Tequila, and eighteen Agave angustifolia Haw. var. Lineño accessions from the south of the state of Jalisco, were evaluated using morphological traits and RAPD (Randomly Amplified Polymorphic DNA) markers. Thirteen morphological characters and three different random 10-mer primers were used. Statistical analysis for these traits revealed that all of them were statistically different (α = 0.05). Three principal components (PC) accounted for 79.9% of the total variability. The number of teeth found in 10 cm, the distance between the last lateral and the apical spine, tooth length, tooth basal width, maximum distance between teeth and leaf width were the most important traits. Besides the wide morphological variation found in both varieties, we were able to separate A. angustifolia from A. tequilana in two main groups using the dendrogram (r = 0.82) and plot from the PCA analysis. The RAPD analysis generated 46 clear and reproducible fragments, 24 of them (52%) were polymorphic, and this polymorphism was higher in A. tequilana (35%) than in A. angustifolia (24%). The dendrogram that was based on RAPD data, revealed two main groups similar to the morphological analysis with some discrepancies. Despite the low correlation found between morphological and molecular data (r = 0.31), these analyses were able to separate the agave varieties used in this study and were informative and complementary.     

Essential oil variation among and within six Achillea species transferred from different ecological regions in Iran to the field conditions

The compositions of essential oils of 19 accessions belonging to six different Achillea species, transferred from the natural habitats in 10 provinces of Iran to the field conditions, were assessed. The relationship between the leaf areas of selected accessions with their essential oil content was also investigated. Essential oil yield of dried plants obtained by hydro-distillation ranged from 0.1 to 2.7% in leaves. Results indicated a significant variation in oil composition among and within species. Total of 94 compounds were identified in 19 accessions belonging to the six species of A. millefolium, A. filipendulina, A. tenuifolia, A. santolina, A. biebersteinii and A. eriophora. The major constituents of the leaves in the tested genotypes were determined as germacrene-D, bicyclogermacrene, camphor, borneol, 1,8-cineole, spathulenol and bornyl acetate. According to the major compounds, four chemotypes were defined as: (I) spathulenol (1.64–34.31%) + camphor (0.2–15.61%) (7 accessions); (II₁) germacrene-D (18.78–23.93%) + borneol (7.93–8.26%) + bornyl acetate (11.56–14.66%) (5 accessions); (II₂) germacrene-D (13.28–36.28%) + bicyclogermacrene (5.93–8.4%) + 1,8-cineole (15.26–19.41%) + camphor (14.95–23.32%) (2 accessions); (III) borneol + camphor (52.04–63.27) (2 accessions); (IV) germacrene-D (45.86–69.64%) (3 accessions). The relationships of chemotypes with soil type and climatic conditions of collected regions were assessed, as probable reasons of high variations in essential oil components, and discussed.     

Maximizing yields in rice–groundnut cropping sequence through integrated nutrient management

Integrated use of organic and inorganic fertilizers can improve crop productivity and sustain soil health and fertility. The present research was conducted to study the effects of application of green manures [sesbania (Sesbania aculeate Poiret) and crotalaria (Crotalaria juncea L.)] and farmyard manure on productivity of rice (Oryza sativa L.) and its residual effects on subsequent groundnut (Arachis hypogaea L.) crop. Rice and groundnut crops were grown in sequence during rainy and post-rainy seasons with and without green manure in combination with different fertilizer and spacing treatments under irrigated conditions. The results showed that application of green manures sesbania and crotalaria at 10 t ha⁻¹ to rice compared to no green manure application significantly increased grain yield of rice by 1.6 and 1.1 t ha⁻¹, and pod yields of groundnut crop succeeding rice by 0.25 and 0.16 t ha⁻¹, respectively. There was no significant difference between the application of crotalaria or farmyard manure at 10 t ha⁻¹ on grain yields of rice, but pod yields of subsequent groundnut crop were greater with application of green manure. There was no significant effect of different spacing 20×15,15×15,15×10 cm² (333 000; 444 000; 666 000 plant ha⁻¹, respectively) on grain yield of rice. Pod yields of groundnut were significantly greater with closer spacing 15×15 cm² (444 000 plants ha⁻¹) as compared to spacing of 30×10 cm² (333 000 plants ha⁻¹). Maximum grain of rice was obtained by application of 120:26:37 kg NPK ha⁻¹ in combination with green manures, whereas maximum pod yield of groundnut was obtained by residual effect of green manure applied to rice and application of 30:26:33 kg NPK ha⁻¹ in combination with gypsum applied to groundnut crop.     

Cardinal temperatures for germination and early growth of two Lesquerella species

Lesquerella (Lesquerella fendleri) is a potential alternative crop that is being studied for commercial oilseed production. Understanding the minimum temperatures for germination and seedling growth is important for determining potential areas for lesquerella production. The objectives of this study were to determine the cardinal temperatures for germination and seedling growth, and to screen ecotypes for germination and growth characteristics. A temperature gradient table arrangement was used to observe seed germination over a range of temperatures, and time to germination and shoot appearance. Times to 5 mm root length and 5 mm shoot length were also measured to assess cardinal temperatures for seedling survival and growth. Two different species were examined, L. fendleri and a species we refer to as ‘L. pallida aff.’ because it differed from typical L. pallida plants in chromosome number and in oil quality. We concluded that both germination and growth of L. pallida aff. occurred fastest at 22 °C, whereas L. fendleri germinated earlier at 18 °C, but grew faster at 22 °C. L. pallida aff. also had lower germination than L. fendleri over the range studied. Non-dormant seeds of improved lines of L. fendleri had better performance at temperatures above 22 °C than did unimproved accessions. Lines of L. fendleri selected for high oil content and salt tolerance had similar temperature requirements for germination except for improved line WCL-LO3, the current line being used in production. This line had optimal temperatures 6 °C higher for germination and growth than the other improved lines. Accessions of L. fendleri collected from elevations above 2000 m performed better at warmer temperatures, whereas those collected from elevations below 2000 m tended to perform better at cooler temperatures. Dormant seeds of L. fendleri germinated more quickly at low temperatures and had lower base (<3 °C) and optimal (22 °C) temperatures than non-dormant seeds (>7 °C and 28 °C, respectively). We speculate that this partial dormancy trait allows populations of L. fendleri to exploit a wider range of temperature conditions in the wild in order to thrive in extreme environments.     

Virulence response to the Mi.1 gene of Meloidogyne populations from tomato in greenhouses

In a comparison of reproductive traits of 29 field populations of Meloidogyne spp. on resistant and susceptible tomatoes, 48% of the populations were virulent against the Mi.1 gene. Virulent populations produced more (P < 0.05) egg masses/plant, eggs/plant, eggs/g root, and showed higher infection frequencies and multiplication rates than the avirulent populations. The fecundity of females did not differ between the resistant and susceptible genotype, and did not change with the virulence status of the populations. On the resistant genotype, the populations collected from the susceptible tomato showed lower (P < 0.05) reproductive traits than those collected from rootstocks followed by those from resistant tomato. Meloidogyne javanica produced more (P < 0.05) egg masses/plant and eggs/g root than Meloidogyne incognita on the resistant genotype. A time course experiment was conducted to determine if root penetration by M. javanica populations with different Mi.1 virulence status is conditioned by the expression of resistance on tomato. Significant differences between populations were observed as early as of 2 days post-inoculation on the susceptible genotype. On the resistant genotype, low juvenile numbers from populations with acquired virulence penetrated the roots up to 4 dpi, but their numbers significantly increased 7 dpi. Juveniles of the natural virulent population followed similar penetration pattern on the resistant and susceptible genotypes. Peroxidases are involved in the oxidative burst typically associated with the hypersensitive response in incompatible host–pathogen interactions. Isoelectrofocusing isozyme analysis revealed an increase in the peroxidase activity on the resistant genotype after inoculation with the avirulent population and to a lesser degree with the populations with acquired virulence in comparison with the natural virulent population.     

Yield traits of six clones of Miscanthus in the first 3 years following planting in Poland

Miscanthus species are highly productive with low inputs and are excellent candidates for bioenergy feedstock production. A field experiment was conducted to characterize phenotypic differences in selected clones generated from interspecific hybrids of Miscanthus sinensis × Miscanthus sacchariflorus and intraspecific hybrids within M. sinensis. The field experiment was planted in plots of 20 m² at a density of 1 plant m⁻² in three randomized blocks. The trial was monitored for 3 years for traits important to biomass production including plant height, tiller density, tuft diameter and shoot diameter. ANOVA showed significant genotypic variation in these traits once the stand was 2 years old. This study shows that tillering and tuft diameter in years 1 and 2 are the most important traits influencing biomass yield, but over 3 years when the highest yielding potential is reached, tillering and tuft diameter have the highest correlation with biomass yield. These results identifying high-yielding Miscanthus clones will be utilized in our plant improvement program.     

Relationship Between Allelopathic Effects and Functional Traits of Different Allelopathic Potential Rice Accessions at Different Growth Stages

In this study,effects of temperature,light and their interactions on allelopathic effects and the functional traits specific leaf area(SLA)and stem mass fraction(SMF)of different allelopathic potential rice accessions at different growth stages were analyzed.The main results were as follows:Allelopathic responses to temperature and light varied with different allelopathic potential rice accessions at different growth stages.With the rise of temperature and the extension of photoperiod,allelopathic effect increased firstly and then decreased at 2–3 leaf stage,but increased constantly at the 4–5 and 7–8 leaf stages in strong allelopathic rice accessions[O.longistaminata,F1(O.longistaminata×RD23),F2(RL159 and RL169)].Temperature had significant impact on allelopathic effect without considering light factors,but light showed little effect on rice allelopathy at the same temperature conditions.The greatest allelopathic effect was attained with moderate temperature and long photoperiod at 2–3 leaf stage in strong allelopathic rice accessions,but all the rice accessions showed weak allelopathic effects at the low temperature condition(15oC/10oC),and the influence of different factors on allelopathy followed a general trend as temperatureleaf stagelight,indicating that among the multiple factors impacting rice allelopathy,temperature was the main factor.Allelopathic characteristics of F1 and F2 to various temperature and light were similar to O.longistaminata,showing that allelopathic genes from wild rice can be expressed in its descendants.Temperature and light also had significant effects on SLA and SMF,and rice allelopathy was closely correlative to SLA in strong allelopathic rice accessions at the 4–5 and 7–8 leaf stages,but there was no correlation between rice allelopathy and SMF at different growth stages.These results suggested that rice adjust the relationship between allelopathy and SLA and adapt to the varied environments,and that high temperature and long photoperiod can enhance rice allelopathic activity.     

Will nutrient-efficient genotypes mine the soil? Effects of genetic differences in root architecture in common bean (Phaseolus vulgaris L.) on soil phosphorus depletion in a low-input agro-ecosystem in Central America

Crop genotypes with root traits permitting increased nutrient acquisition would increase yields in low fertility soils but have uncertain effects on soil fertility in the long term because of competing effects on nutrient removal vs. the soil conserving effects of greater crop biomass. This study evaluated the relative importance of phosphorus loss in crop extraction vs. phosphorus loss in soil erosion as influenced by genetic differences in root shallowness and therefore phosphorus uptake in common bean (Phaseolus vulgaris L.). Six recombinant inbred lines of varying root architecture and two commercial genotypes of bean were grown in unfertilized, steeply sloped (32%), low phosphorus (5.8 mg kg^?1, Fe-strip) Udults in Costa Rica. Fertilized (60 kg total phosphorus ha^?1) plots of commercial genotypes were also included in the study. Runoff was monitored throughout the bean growing season in 2005 and 2006, and in 2006, monitoring continued through the maize growing season. Phosphorus removed in plant biomass at harvest through the 2006 bean–maize crop cycle averaged 7.3 kg ha^?1 year^?1, greatly exceeding phosphorus loss due to erosion (0.15–0.53 kg ha^?1 year^?1) in unfertilized plots. In fertilized bean plots, total biomass phosphorus averaged 6.32 kg ha^?1 year^?1 and total eroded phosphorus averaged 0.038 kg ha^?1 year^?1, indicating rapid sorption of fertilizer phosphorus. Shoot growth of several recombinant inbred lines under low phosphorus was comparable to that of fertilized commercial genotypes, illustrating the effectiveness of selection for root traits for improving plant growth in low-phosphorus soils. Genotypic differences in root architecture of recombinant inbred lines led to 20–50% variation in groundcover by shoots, which was associated with 50–80% reduction in sediment loss. This study demonstrates that root architecture traits can affect nutrient cycling at the agro-ecosystem level, and that integrated nutrient management strategies are necessary to avoid soil nutrient depletion.     

Upland rice grown in soil-filled chambers and exposed to contrasting water-deficit regimes: II. Mapping quantitative trait loci for root morphology and distribution

Root morphological characteristics are known to be important in the drought resistance of some rice (Oryza sativa L.) varieties. The identification of quantitative trait loci (QTLs) associated with root morphology and other drought resistance-related traits should help breeders produce more drought resistant varieties. Stability in the expression of root growth QTL across rooting environments is critical for their use in breeding programs. A greenhouse experiment in which a mapping population of 140 recombinant inbred lines and the parental varieties Bala and Azucena were grown in glass-sided soil chambers and evaluated for root growth and water uptake was conducted. In each of 2 years, two treatments were used; an early water-deficit (WD0) in which seeds were sown into wet soil but received no more water, and a late water-deficit (WD49) in which the plants were watered for 49 days and then received no water for a week. The major differences between treatments and years in dry matter partitioning and root growth traits are reported elsewhere. Here, the identification of QTLs for root growth traits by composite interval mapping is described. At LOD>3.2, there were six QTLs for the weight of roots below 90 cm and maximum root length, 11 for root to shoot ratio, 12 for the number of roots past 100 cm, and 14 for root thickness. A total of 24 regions were identified as containing QTLs (these regions often contained several QTLs identified for different root traits). Some were revealed only in individual experiments and/or for individual traits, while others were common to different traits or experiments. Seven QTLs, on chromosomes 1, 2, 4, 7, 9 (two QTLs) and 11, where considered particularly noteworthy. The complex results are discussed in the context of previously reported QTLs for root growth in other populations, the interaction between QTL with the environment and the value of QTLs for breeding.     

Determination of selection criteria for seed yield and seed oil content in Vernonia (Vernonia galamensis variety ethiopica)

The magnitude of relationships among different traits is important in plant breeding programs to identify the best selection criteria and improve the efficiency of selection. This study was conducted to determine relationships between seed yield and seed oil content with other important agronomic traits among 36 diverse accessions of Vernonia (Vernonia galamensis variety ethiopica), a potentially novel industrial oilseed crop. Field evaluations were conducted during 2005, 2006 and 2007 at the Limpopo Province in South Africa using a partially balanced lattice design. Simple correlation and path analysis were performed to identify the best selection criteria for increased seed yield and seed oil content. Simple correlation and path analyses revealed that the formation of productive primary heads strongly associated with increased seed yield (r_g = 0.81, p < 0.001). Furthermore, path analysis indicated selection for increased number of primary heads would bring about simultaneous and favorable change towards reduced days to maturity and shorter plant height. Further associational study of traits with seed oil content showed a significant (p < 0.05) correlation between oil content with 1000 seed weight (r_g = 0.4). The path analysis, however, exposed seed yield followed by 1000 seed weight with significant direct effect on seed oil content. The study demonstrated that selection for increased number of productive primary heads is the principal selection criterion to improve seed yield. Whereas selection for 1000 seed weight and increased seed yield serve as major selection criteria to achieve increased oil content in V. galemanesis.     

Differences in tolerance to infertile acid soil stress among germplasm accessions and genetic recombinants of the tropical forage grass genus,Brachiaria

Several Brachiaria species are the most widely grown forages in tropical America. A field study was conducted during two seasons (1994, wet and 1995, dry) in a medium-textured Oxisol at Carimagua, Colombia. The main objective of the study was to evaluate genotypic variation in plant attributes for tolerance to low fertility, acid soil stress conditions (pH 4.9) among germplasm accessions and genetic recombinants of Brachiaria. The entries included 43 genetic recombinants selected from a breeding population, four parental accessions and an additional eight germplasm accessions. Small amounts of fertilizer were applied at establishment (kg ha⁻¹: 40 N, 20 P, 20 K, 14 Ca, 12 Mg and 12 S). A number of plant attributes including forage yield, leaf area, shoot nutrient composition and shoot nutrient uptake were measured during both seasons. Significant genetic variation was observed in several plant attributes such as leaf area, shoot nutrient content, nutrient partitioning to leaves, shoot nutrient uptake, and forage yield in both seasons. Forage yield ranged from 59 to 343 g plant⁻¹ in the wet season and 5 to 174 g plant⁻¹ in the dry season. Correlation between forage yield and shoot nutrient uptake indicated the importance of nutrient acquisition, particularly of phosphorus (r=0.90; P<0.0001), for adaptation to infertile acid soil stress. Two genetic recombinants (BRN093/3009, FM9201/1873) were productive when grown under infertile acid soil stress in both wet and dry seasons. But, neither of these two recombinants is highly resistant to xylem-feeding insects known as spittlebugs (Homoptera: Cercopidae). One spittlebug-resistant genetic recombinant (BRN093/1371) exhibited several desirable attributes such as superior leaf area and leaf biomass, greater N content in leaves, and greater partitioning of N and P to leaves that could contribute to adaptation and persistence in these soils. This recombinant is being utilized in a breeding program to develop superior Brachiaria lines.     

Analysis of QTLs for seed low temperature germinability and anoxia germinability in rice (Oryza sativa L.)

Direct seeding instead of transplanting for rice (Oryza sativa L.) has increasingly been used in northern and eastern China because of labor and cost saving. However, poor germinability is still one of the major problems faced in the adoption of direct seeding under low temperature (low temperature germinability: LTG) and anoxia (anoxia germinability: AG) condition. To gain an understanding of the genetic control of seed germinability under these unfavourable conditions, two rice lines, USSR5 (japonica type) and N22 (indica type) and F₂ individuals derived from the cross USSR5 × N22 were tested for LTG and AG. USSR5 and N22 differ significantly for both LTG and AG. The LTG of the F₂ individuals ranged from 0 to 100% after a 10 days incubation. AG ranged from 0.0 to 4.0 cm shoot length. Based on segregation in the F₂ population, a linkage map was constructed using 121 SSR markers. The map covered 1821.5 cM, with a mean inter-marker distance of 16.7 cM. Eleven putative QTLs for LTG were detected, one on each of chromosomes 3–5, 7, 9–11, and four on chromosome 5. The USSR5 alleles in all these QTLs acted to increase LTG. Two QTLs for AG were located on chromosomes 5 and 11, respectively, at both of which the USSR5 alleles acted to increase AG. We propose that USSR5 could make a major contribution to improving LTG and AG in rice breeding programs.     

Effects of Heat Stress at Vegetative and Reproductive Stages on Spikelet Fertility

Seed-setting rate, yield components and grain quality traits of 169 accessions from an exotic rice germplasm were tested under high temperatures from 40 °C to 45 °C for 6 h during the daytime at the vegetative and reproductive stages, respectively. The results showed that heat stress significantly decreased the seed-setting rate of all the accessions, but the heat stress effects varied among accessions. Based on the decreases in seed-setting rate at high temperatures, N22 was the most tolerant, followed by AUS17, M9962, SONALEE and AUS16. Moreover, the reductions in seed-setting rate and yield under heat stress were more serious at the vegetative stage (45 d before heading) than at the booting stage (15 d before heading). In addition, heat stress also affected grain quality, especially by conferring chalkiness to most of the accessions, but SONALEE did not change much. The heat-tolerant accessions identified here and the phenotype protocols developed could be used in future genetic studies and breeding programmes focused on heat tolerance.     

Yield and agronomic traits of Khorasan wheat (Triticum turanicum Jakubz.)

The consumer's interest in natural, unconventional and nutritional foods led to the development of new specialty foods based on grain blends. Components of such foods are often so-called ‘ancient wheats’ which were never the subject of modern plant breeding programmes. Khorasan or Oriental wheat (Triticum turanicum) is a neglected and underutilised tetraploid wheat species, which probably survived over the centuries in subsistence farming systems in the Near East and Central Asia. In the present study the agronomic potential of Khorasan wheat was evaluated under eastern Austrian conditions.Fourteen accessions of Khorasan wheat were investigated together with check durum wheat cultivars over a period of 4 years in the Marchfeld region, north-east of Vienna. The crops were sown both in autumn and spring.The investigated material was inferior to modern durum wheats in most agronomic traits. No accession was found to tolerate soil temperatures below −5 °C. Tolerance to drought and fungal diseases was limited and/or modest, and grain yields were significantly lower. While the best performing turanicum accessions yielded in average 385.8 and 233.8 g m⁻² for autumn and spring sowing, respectively, the check winter durum yielded 466.5 g m⁻² and the check spring durums between 351.5 and 391.8 g m⁻². Several characteristic and interesting features were observed which permit successful marketing of pure Khorasan grain or as a component in grain blends, despite possible flour quality traits. The grain has an impressive kernel size and thousand kernel weight, in most cases greater than 50 g and often even greater than 60 g. The high thousand kernel weight might be a valuable trait to transfer into durum wheat to improve grain yield. Moreover, the grain has an amber colour and high vitreousness.Due to higher plant height, low lodging tolerance and high susceptibility against powdery mildew, Khorasan wheat is more suitable for organic farming systems. Although there is evidence that Khorasan wheat has low adaptation, it is of interest as an alternative cereal to increase diversity both in the field and on the consumer's table. However, further experiments are necessary: on the one hand to study the interactions between sowing rates, sowing dates, weed suppression, thousand kernel weight and kernel plumpness in order to find out optimal production procedures, and on the other hand to find out areas/fields with the best growth conditions for Khorasan wheat.     

Verification of Glyphosate Resistance,Lepidopteran Resistance and Wide Compatibility of Male Sterile Line E1C4008S in Rice

Weeds and insect pests are two important biotic stresses resulting in yield loss in rice, and wide compatibility is the essential characteristic of breeding inter-subspecific hybrid rice. This study focused on glyphosate resistance, lepidopteran resistance and wide compatibility as well as identification of molecular and some agronomic characteristics of transgenic male sterile line E1 C4008 S. The results indicated that glyphosate resistance gene Epsps# and lepidopteran resistance gene Cry1 ca~# were transferred into japonica wide compatibility male sterile line 4008 S by Agrobacterium-mediated method, and four independent transformation events named E1 C4008 S-1, E1 C4008 S-2, E1 C4008 S-3 and E1 C4008 S-4 were obtained, in which E1 C4008 S-3 and E1 C4008 S-4 were of single copy insertion. The EPSPS protein contents of E1 C4008 S-3 and E1 C4008 S-4 in different organs were significantly different both in descending order of leaf stem root, and ranged from 300.58 to 1410.69 μg/g at the tillering stage. The glyphosate tolerable concentration(dosage) of E1 C4008 S-3 and E1 C4008 S-4 reached at least 16 g/L(54.42 kg/hm2), and the seeds of E1 C4008 S-4 can germinate normally on the medium containing 1 g/L glyphosate. The CRY1 C protein contents of E1 C4008 S-3 and E1 C4008 S-4 in different organs were significantly different both in descending order of leaf stem root, and ranged from 0.62 to 2.43 μg/g at the tillering stage. The larvae mortalities of rice leaf rollers fed on leaves of E1 C4008 S-3 and E1 C4008 S-4 for 5 d were 95.35% and 97.77%, respectively, while the average mortalities of silkworms fed with protein extracts from leaves of E1 C4008 S-3 and E1 C4008 S-4 reached 94.55% and 83.64%, respectively. The results suggested that wide compatibility and evaluated agronomic traits of E1 C4008 S-4 were not significantly changed by insertion of the exogenous genes. Overall, a novel male sterile germplasm with glyphosate resistance, lepidopteran resistance and wide compatibility was verified to be developed in rice.     

Analysis of cold tolerance in sorghum under controlled environment conditions

Grain sorghum (Sorghum bicolor (L.) Moench) originated in the semi-arid tropics and is generally sensitive to low-temperature stress. Early planting and use of minimum tillage necessitate the development of sorghum hybrids with early season cold tolerance. Genetic variability for cold tolerance exists in sorghum and has been detected by early planting under field conditions and by analysis of seeds and plants under growth chamber conditions. There is limited information on the efficiency of evaluating cold tolerance under growth chamber conditions and the relationship with field performance. The objectives of this study were to quantify the variability of cold tolerance in commercial hybrid seed lots under growth chamber conditions, to exam different components of cold tolerance and their relationships, and to evaluate the consistency of lab test results with data from field tests. Thirty commercial hybrid seed lots were evaluated by growing the entries under 15/10, 13/10, 11/8, and 25/20 °C day/night temperature in a 13/11 h cycle in a growth chamber. Traits measured included emergence percentage, emergence index, shoot and root dry weight, seedling height, and vigor score. Significant genotypic differences were detected for all traits. Correlations among the traits were significant and favorable, which confirmed that simultaneous improvement of these traits should be possible. The same seed lots were also evaluated in a soil-free plate-based assay, in which percent germination, and shoot and root elongation of the seed lots grown in dark at 15 °C were measured. Results from both laboratory tests, soil-based and plate-based, were correlated with data collected in a field study, which was conducted to evaluate cold tolerance of commercial sorghum hybrids at Manhattan, Hesston, Bellville, and Garden City, KS in 1998 and 1999. Single-trait correlations between lab and field studies were significant. Differentiation based on rank-summation index of common traits, rank-summation index correlations and the overlap of best entries, further provided strong support of the efficiency of predicting and identifying elite hybrids using growth chamber assays.     

Productivity and residual effects of legumes in rice-based cropping systems in a warm-temperate environment: II. Residual effects on rice

Field experiments were conducted over the period 1994–1996 to investigate the residual effect on rice of a wide range of temperate legume species, grown during the preceding winter season in a warm-temperate environment in Nepal. The incorporation of large quantities of above- and below-ground legume biomass (roots and foliage) resulted in substantial residual effects on the subsequent upland rice crop. The effects on rice yield in terms of percent increase over the control were more pronounced at a site of comparatively lower inherent soil fertility where grain yields of rice grown after high yielding legume crops such as bitter lupin (Lupinus mutabilis) and Persian clover (Trifolium resupinatum) were almost twice as high (up to 7.6 t DM ha⁻¹) than those of the control treatment (rice after wheat). In contrast, the residual effects of below-ground biomass (roots, nodules) on the following rice crop were not very pronounced and resulted in similar residual effects as rice, after fallow. Although up to 480 kg ha⁻¹ of legume foliage N had been applied to rice, only a small proportion of the legume N (up to 70 kg N ha⁻¹) was recovered by the following rice crop. Total rice dry matter yields were highly correlated with the amount of legume N applied, yet other factors such as residue quality and residue management practices appeared to also affect the magnitude of the residual effects. Future work should aim at investigating the effect of residue quality as affected by legume species and residue management practice on decomposition and N mineralisation processes in rice soils.     

Peroxidase isozyme variants as genetic markers for early evaluation of Fe-efficiency and Fe-nutritional status in maize lines

The Fe-efficient maize (Zea mays L.) cultivar Alice, the Fe-inefficient mutant yellow-stripe (ys1), and six additional local inbred lines were grown in a growth chamber at 60% relative humidity and 16 h 25°C, 8 h 22°C day–night regime, in nutrient solution with varied Fe supply (+Fe=0.1 mM) or (−Fe=0.01 mM) supplied as Fe(III)–EDTA. The study aimed to establish a genetic assay system for early evaluation of Fe-efficiency and Fe-nutritional status based on peroxidase isozyme variation in roots of maize lines. The wild-type peroxidase isozyme patterns revealed an extra band (C3) not present in the mutant patterns. Inbreds 51, 122, 126, and 137 had peroxidase isozymes similar to the Fe-efficient Alice, while inbreds 112 and 144 had nearly the same pattern as the Fe-inefficient mutant ys1. Sufficient Fe supply did not alter the isoperoxidase patterns of the ys1, but had significant effect on the activity of the (C3) band of the Fe-efficient Alice. On the other hand, the activity of the (C3) band for the inbreds 51, 122, 126 and 137 responded clearly to the sufficient level of iron in the media similar to the response of Alice, while inbreds 112 and 144 did not show any changes in C3 either in sufficient or deficient Fe supply, similar to ys1. The results indicate that the Fe-efficient maize lines may have an additional cathodal (C3) band of the root isoperoxidase and that changes in the activity of the band can reflect the Fe-nutritional status of maize lines.     

Water uptake of soybean (Glycine max L. Merr.) during exposure to O2 deficiency and field level CO2 concentration in the root zone

This study determined whether the field level concentration of root zone CO₂ affects transpiration rate and root water transport in soybean (Glycine max L. Merr.). In an upland field converted from a paddy field, topsoil CO₂ during the cropping season rose to 8 kPa of partial pressure after rainfall, whereas O₂ dropped only to a minimum of 7 kPa. An elevated root zone CO₂ pressure of 6 kPa significantly reduced transpiration rate. Although the transpiration rate of soybean plants exposed to hypoxia of 1.5 kPa O₂ alone was reduced by 52% of the aerated plant, the rate was more decreased by 33 by adding CO₂ gas to low root zone O₂. Similarly, the elevated root zone CO₂ significantly reduced hydraulic conductance of roots. The low transpiration rate with a high leaf water potential and low leaf greenness in the elevated root zone CO₂ indicated that stomatal closure in high root zone CO₂ may also occur irrespective of leaf water status and be involved in depressed nitrogen supply to a shoot. The results indicate that root zone CO₂ at the field level is a growth inhibitor of waterlogged soybean through decreasing water uptake and/or stomatal aperture.