Sugar characteristics of sweet corn populations from a sugary enhancer breeding program

Summary Endosperm sugars and sorbitol were determined on 18 sweet corn (Zea mays L.) populations from a breeding program undertaken to transfer the sugary enhacer (se) gene into diverse sugary (su) backgrounds. Three subpopulations of IL677a, the source of se, and six su Se inbreds were included for comparison. Mature dry kernels of between two and four successive generations of these populations were analyzed. Immature kernels at two developmental stages (21 and 35 days after pollination) were also analyzed for one generation.Eleven of the breeding populations closely resemble IL677a, with high sucrose at the edible stage (21 days after pollination) and maltose accumulating as the seeds matured. In most instances, the distinctive sugar profiles were observed consistently in dry seeds of various generations. Hence, it appears that the se trait can be transferred successfully into su cultivars having various genetic backgrounds. The remaining seven breeding populations possessed elevated sucrose and glucose compared to most of the standard su Se inbreds, but maltose did not accumulate during seed maturation. It is not clear whether se was transferred to these populations and its expression modified or whether another trait was responsible. There were also marked differences in glucose levels among the su Se populations examined.Supported by the National Science Foundation (Grant No. 7922 686) and the Illinois Agriculture Experiment Station (Project No. 65-0330).     

Radiation use efficiency and leaf photosynthesis of sweet corn in response to phosphorus in a cool temperate environment

Phosphorus (P) deficiency has been shown to decrease accumulated intercepted solar radiation (RI_cum) for sweet corn and in this paper the effects on radiation use efficiency (RUE) and leaf photosynthetic rate at 2000 μmol m⁻² s⁻¹ PPFD (P₂₀₀₀) are examined. Data from two consecutive field experiments on a low P site at Lincoln, New Zealand, were analyzed. In the first experiment (2001/2002) 0, 50, 100, 150 or 200 kg P ha⁻¹ was applied to sweet corn followed by an additional 0, 0, 10, 20 or 40 kg P ha⁻¹ in 2002/2003 applied to the same plots. Thus, total P applications were 0, 50, 110, 170, or 240 kg P ha⁻¹.There were no differences in RUE between P treatments but RUE changed with crop ontogeny. The RUE was 0.66 g MJ⁻¹ before each crop had 10 fully expanded leaves and RUE was 1.34 g MJ⁻¹ after this. The cause of this difference between development stages was unclear, but it was not related to air temperature. In contrast to RUE, there were clear differences in P₂₀₀₀ due to differences in specific leaf phosphorus (SLP). At a SLP of 0.12 g P m⁻² or greater, P₂₀₀₀ was a constant value of 34 μmol CO₂ m⁻² s⁻¹. When SLP was less than 0.12 g P m⁻² P₂₀₀₀ was reduced. The differences in P₂₀₀₀ between P treatments occurred when the plants were young (≤10 fully expanded leaves) and after this, SLP of all leaves exceeded 0.12 g P m⁻² and there were no differences in P₂₀₀₀. These early leaves were unimportant in determining crop RUE but are likely to have been important in establishing the hierarchies that led to the changes in RI_cum reported previously. These results demonstrate the importance of an adequate supply of P early in crop growth.     

磷肥对甜玉米籽粒植酸和锌有效性的影响

为明确磷肥对甜玉米籽粒营养特性的影响,利用不同品种的磷肥定位试验以及磷肥梯度水平试验,探讨甜玉米籽粒植酸、磷(P)、锌(Zn)含量及Zn有效性的时间(不同灌浆期)和空间(果穗上、中、下部;籽粒果皮、胚乳和胚)变化及其对外源磷肥的响应特性。试验结果表明,甜玉米籽粒的P和植酸含量随磷肥用量的增加而增加,Zn含量及其有效性则呈现下降趋势。磷肥投入对吐丝后16～24 d籽粒的植酸、P和Zn的积累(mg plant^–1)的影响最为显著,而对不同灌浆时期Zn有效性均表现出抑制效应。在中磷水平下,果穗不同穗位籽粒植酸(g kg^–1)和Zn有效性的差异并不显著。高磷水平显著提高了中、下部果穗植酸的含量,但对不同穗位籽粒Zn含量和Zn有效性均存在抑制效应。对籽粒内不同部位(果皮、胚乳和胚)进行比较,植酸、P以及Zn含量均以胚中含量最高,积累量占比则以胚乳中最高;而Zn有效性以胚中最高。高磷处理可显著提高籽粒内不同部位植酸和磷含量,降低Zn含量及其有效性。综上,合理磷肥施用可促进籽粒Zn积累,而过量磷肥投入会显著增加不同灌浆时期,以及胚乳和胚中的植酸含量和积累量...     

Solar radiation interception and canopy expansion of sweet corn in response to phosphorus

Insufficient phosphorus (P) availability decreases the yield of Zea mays, particularly for sweet corn crops grown in cool environments. This research examined the mechanisms of yield reductions with initial emphasis on canopy expansion processes that affect the interception of solar radiation. Experiments in two consecutive seasons (2001/2002 and 2002/2003) were grown at a low P site (Olsen P = 6 μg ml⁻¹) at Lincoln, New Zealand. Each experiment contained five rates of P application. In 2001/2002 rates of 0, 50, 100, 150, or 200 kg P ha⁻¹ were applied. In 2002/2003 an additional 0, 0, 10, 20 or 40 kg P ha⁻¹ was applied to the same plots producing total P treatments of 0, 50, 110, 170 or 240 kg P ha⁻¹ summed over the two seasons.When P availability was limited (0 or 50 kg P ha⁻¹) the rates of leaf tip and fully expanded leaf appearance were slower in both seasons. Phyllochrons (°Cd leaf tip⁻¹) were 5 °Cd longer in crops that received 0 kg P ha⁻¹ than those fertilised with ≥100 kg P ha⁻¹. The area of individual leaves was also reduced by low P inputs but the ranking of leaf area by main stem leaf position was conservative. The leaf area of the largest leaf of the unfertilised crops was at least 22% less than the maximum measured leaf area in both seasons. In contrast, P fertiliser application had no effect on leaf senescence.The rate of leaf appearance per plant, individual leaf area and plant population were integrated to calculate green leaf area index (GLAI) and to estimate accumulated radiation interception (RI_cum) for these crops. The total RI_cum throughout the season in the unfertilised crops was 12–28% less than for those crops that received ≥100 kg P ha⁻¹ in both seasons. This difference partly explained the differences in crop biomass production in response to P availability. A sensitivity analysis showed that RI_cum was equally sensitive to changes of the rate of leaf appearance and the area of individual leaves in response to P supply. Both processes need to be incorporated in mechanistic models of P effects on Z. mays which can be used to design efficient P fertiliser strategies.     

Genetic control of kernel modification found in South African quality protein maize inbred lines

Summary The genetic control of endosperm modification in 12 opaque-2 maize (Zea mays L.) inbred lines was investigated by means of a diallel cross experiment conducted across two environments. Kernel vitreousness and kernel hardness were determined by partially dominant genes. Additive gene action was largely responsible for kernel modification. A favourable general combining ability for kernel vitreousness and kernel hardness was positively correlated with an accumulation of dominant kernel modifying genes. South African sources of endosperm modifiers have been found to be similar to those used in other quality protein maize breeding programmes. Certain inbred lines displayed sufficient genetic potential for use in a quality protein maize hybrid breeding programme.     

Populations of maize with more rapid and reliable seedling emergence than cornbelt dents at low temperatures

Summary Selected races, populations and genotypes of maize (Zea mays L.) from regions where maize is sown under cool conditions were evaluated in controlled-environment rooms for time to seedling emergence and percentage emergence at low temperatures. The objective of the study was to identify populations with the ability to emerge more rapidly and more reliably than Cornbelt Dent, the race most widely used to produce cultivars for temperate regions.Several populations emerged markedly faster and more reliably than Cornbelt Dent populations. All of these populations contained germplasm of highland Mexican origin, except for Gaspé Flint, and the fastest population in each experiment always contained a high proportion of germplasm from the Cónico race. The advantage of populations containing Cónico germplasm was greatest in environments where emergence was slowest.     

甜玉米种子特性与全苗技术

甜玉米基因抑制籽粒淀粉合成,从而影响种子发芽出苗。提高发芽率、出苗率,促进全苗,确保单位面积基本株数是获得产量的基础。综述了甜玉米种子形成、苗期生长特点,播种出苗技术要领以及浸种、拌种,种子包衣,育苗移栽,地膜覆盖,种子储藏等相关研究结果。甜玉米的采收期影响着种子质量及发芽率;低温、安全含水量对于保存种子活力十分有利,植物生长延缓剂等处理对延缓种子老化有一定效果;三十烷醇、双氧水等浸种,植物生长调节物质、种子包衣技术等处理对甜玉米种子萌发及幼苗生长有促进作用;选择好种子和土壤,掌握播种温度、深度,施足基肥是促进甜玉米壮苗早发手段;育苗移栽、覆膜栽培技术能较好弥补甜玉米播种出苗方面的先天不足。     

Variation in cooking and eating quality traits in Japanese rice germplasm accessions

The eating quality of cooked rice is important and determines its market price and consumer acceptance. To comprehensively describe the variation of eating quality in 183 rice germplasm accessions, we evaluated 33 eating-quality traits including amylose and protein contents, pasting properties of rice flour, and texture of cooked rice grains. All eating-quality traits varied widely in the germplasm accessions. Principal-components analysis (PCA) revealed that allelic differences in the Wx gene explained the largest proportion of phenotypic variation of the eating-quality traits. In 146 accessions of non-glutinous temperate japonica rice, PCA revealed that protein content and surface texture of the cooked rice grains significantly explained phenotypic variations of the eating-quality traits. An allelic difference based on simple sequence repeats, which was located near a quantitative trait locus (QTL) on the short arm of chromosome 3, was associated with differences in the eating quality of non-glutinous temperate japonica rice. These results suggest that eating quality is controlled by genetic factors, including the Wx gene and the QTL on chromosome 3, in Japanese rice accessions. These genetic factors have been consciously selected for eating quality during rice breeding programs in Japan.     

甜玉米种子活力低下原因及其种子处理方法

综述有关甜玉米种子活力低下的生理、遗传和环境等因素的研究进展，种子引发，包衣和有机溶剂渗入等种子处理方法对提高甜玉米种子活力和田间出苗率的效果及其应用前景。     

Mid-parent heterosis and combining ability of European corn borer resistance in maize

Success in breeding maize resistant to the European corn borer has been limited, with the exception of leaf feeding resistance. The inheritance of resistance to leaf, sheath-collar and ear damage in four maize germplasms and their six F₁ crosses was evaluated by diallel analysis. Plants in a completely randomized design were artificially infested at the whorl, anthesis or full silk stage of plant development and were evaluated in the field for insect damage. A damage index based on size, number and location of lesions was calculated for each stage. Stowell's Evergreen (susceptible) had a mean damage index three to six times that of Maiz Amargo (resistant) at the whorl stage and the progeny plants were more resistant than the susceptible parent. Maiz Amargo and its crosses had significantly lower mean indices than Stowell's Evergreen for sheath-collar damage in Year 1 but not Year 2. Zapalote Chico, Maiz Amargo and their cross were significantly less damaged than other genotypes at the full silk stage. Heterosis values indicated an increase in resistance of crosses over the midparent average at all three stages of development. General combining ability (GCA) was highly significant for all types of damage, but specific combining ability was significant only for leaf damage. Based on estimates of GCA, Maiz Amargo was the best source of resistance to leaf and sheath-collar damage and both Zapalote Chico and Maiz Amargo would be good parents for ear damage resistance. Results suggest that resistance at different plant development stages can be combined.     

Variation in traits affecting nodulation of common bean under intercropping with maize and sole cropping

Common bean (Phaseolus vulgaris L.), an important food crop in Europe, America, Africa and Asia, is thought to fix only small amounts of atmospheric nitrogen. It contributes significantly to the sustainability of traditional cropping systems because of the predominance of small-scale farmers who cultivate beans in those areas. The objectives of this work were to evaluate bush bean varieties under common agronomic cropping systems and to evaluate breeding lines under low N-fertility sole cropping and intercropping systems. The purpose of the study was to characterize the genotype and cropping system's variability in symbiotic and plant characters and to identify the most suitable genotypes to establish an effective symbiosis with indigenous strains of Rhizobium. No significant differences among the bush bean varieties evaluated under typical fertilization practices were observed for N₂-fixation and plant traits except for seed nitrogen. Significant differences among the bean lines studied under low N-fertilization conditions were detected for plant growth,plant component and N₂-fixation traits. A significant interaction of bean genotype x cropping system was found for number of nodules per plant and nodule moisture on the bush bean varieties studied, and for days to emergence, days to flowering, end of flowering, shoot length, root dry weight and shoot nitrogen on the bean lines evaluated. Nodulation parameters were correlated positively with the yield components, shoot and root parts and duration of flowering, and correlated negatively with seed crude protein, pod and seed dimensions and seed dry weight. These observations indicate that it may be possible to increase both the symbiotic N₂-fixation and seed yield through plant breeding. This revised version was published online in August 2006 with corrections to the Cover Date.     

Variation in sweet potato for tolerance to some physical and biological stresses

Summary Sweet potato cultivars, breeding lines and unselected seedling clones were grown under 9 stress conditions in field and greenhouse; heavy soil, space competition, competition with maize, shading, flooding, drought, acidity, salinity, and weevil infestation. High root yield was considered to be a sign of stress tolerance. Stresses were shown to reduce the growth of shoots and roots, except flooding, which increased fibrous root production. The percentge of plants showing high stress tolerance varied from 0.35 to 30.90 for the different stress situations. Tolerances to stresses tended to occur together, as shown by low but significant correlations, significant chi-squares for numbers of plants with multiple stresses, and by low but significant correlations between yield and multiple stresses. Root flooding, space and fertility competition, and soil acidity appear to be the stress factors most closely related to production in heavy soils. Yet the magnitude of the correlations suggest that other factors or random variation also affect yield, and thus the predictive value of greenhouse stress test is presently limited.     

Variation of sweet potatoes with respect to source potentials and sink capacities

Summary By using four tester clones either as scions or stocks, source potentials and sink capacities of two groups of 13 and 20 sweet potato clones were measured in 1986 and 1987, respectively. Results obtained in the 1986 trial were generally consistent with those in the 1987 trial, though different clones were used in both trials. There were significant differences in source potentials and in sink capacities among tested clones. Responses of source to sink and of sink to source were also estimated using a regression method. No significant correlation was observed between source potential and response of source to sink. However, sink capacity showed significant relationship with response of sink to source.     

Nutritional and culinary quality of bush bean populations intercropped with maize

Summary The intereropping of common bean (Phaseolus vulgaris L.) and maize (Zea mays L.) is a common practice in the Northwest of the Iberian Peninsula. In this experiment, 25 populations of bush bean were evaluated for nutritional and culinary traits of dry seed and immature pod in sole crop and in intercrop in two years and in two locations, in order to determine whether selection of bush bean in sole crop can result in genetic progress for intercrop.There were no differences in the population means between cropping systems. Significant differences were detected among populations for all traits tudied except starch content, crude ash, water absorption and coat proportion. Population x environment interaction was significant for pod thickness. Bean populations did not interact with cropping systems for any trait, although there were differences between cropping systems for crude protein. These results suggest that a sole crop system provides sufficient information to select bean populations efficiently for the bush bean-maize intercropping system, although the advanced generations of the breeding program should be tested for quantitative traits such as protein content in the appropriate cropping system (intercropping) to know the competitive ability with the associated species. This would permit to choose bush bean populations which complement more efficiently and would be less competitive with the maize population.     

Genetic variation in maize (Zea mays L.) for germination and emergence at 10°C

Summary Full-sib, paternal half-sib and S1 families were derived from a population of maize, Pool 5, with a wide germplasm base. These families were used to study genetic variation for germination percentage, emergence percentage and time to emergence at 10°C.Genotypic variances were large for all characters, and the best families from the population were markedly superior to hybrids used as checks. Maternal effects appeared to be of overwhelming importance for germination percentage, but variances due to males were significant for emergence percentage and time to emergence. Inbreeding depression at the seedling level was also important for these two emergence characters. Germination and emergence characters were not correlated with seed weight.We concluded that Pool 5 should be a valuable source of genes for improving germination and emergence of maize at low temperatures.     

Mass selection for kernel depth in early maize

Summary Effectiveness of mass selection for kernel depth in an early maize (Zea mays L.) synthetic, i.e. NDSAB, was evaluated in eight North Dakato environments. Four cycles of selection for deeper kernels were evaluated for grain yield and associated traits by using corresponding randomly selected subpopulations of NDSAB to adjust out inbreeding effects on selected subpopulations. General combining ability (GCA) effects of selected subpopulations also were evaluated for these traits.Subpopulations selected from one to four cycles for deep kernels were reciprocally crossed to corresponding randomly selected subpopulations in a factorial mating design. Subpopulations, selfed subpopulations, and subpopulation crosses were evaluated for yield and associated traits. Subpopulations selected for deep kernels generally had deeper kernels, higher yields, heavier kernels, more kernel rows per ear, and lower test weights than corresponding randomly selected subpopulations. Differences in GCA effects among selected and unselected subpopulations generally corresponded to differences between selected and unselected parental subpopulations. Inbreeding effects from selfing were observed for all traits, but no average heterosis was detected when subpopulation crosses were compared to parental subpopulations. Reciprocal differences were observed for all traits except kernel depth, but these differences were inconsistent relative to whether deep kerneled females made superior hybrids to unselected females.Results supported the use of mass selection for kernel depth as a means of grain yield improvement in the short term for NDSAB. However, negative associations of kernel depth with test weight may restrict long term use of this procedure.Journal Article No. 1505 of the North Dakota Agric. Exp. Stn., Fargo     

Variation in the expression of specificity in two maize diseases

Summary Ten inbred lines from the open-pollinated maize variety Jarvis were selected from 51 randomly collected lines to represent a wide range of susceptibility to one isolate each of Bipolaris maydis or Colletotrichum graminicola. Ten isolates of each pathogen were selected for a range of virulence on a maize line with average resistance. Resistance and virulence ratings were based on lengths of lesions that developed on leaves of greenhouse-grown seedlings inoculated with 5 l droplets of suspensions of known spore concentrations. For each disease the ten maize lines were inoculated in all possible combinations with the ten pathogen isolates. The experiment was run six times with each pathogen. Analysis of variance for individual trials indicated a significant interaction between maize lines and B. maydis isolates in all six trials and between maize lines and C. graminicola isolates in four of six trials. For both diseases. the combined analysis over all six trials revealed no significant interaction. Apparently the expression of specificity in these host-pathogen interactions is variable.     

Variation and inheritance of response to acetochlor among maize inbred lines and hybrids

Summary The variation of response to acetochlor was studied in a two-year experiment carried out by subjecting 18 maize (Zea mays L.) inbred lines to three herbicide rates (0, 2.5 and 5 l a.i./ha). In both years some inbred lines consistently exhibited an evident susceptibility, with symptoms consisting of the seedling curling up below the soil surface and causing impaired field emergence. The results were poor plant density and lower grain yield in comparison to control. In contrast, other lines showed a satisfactory level of tolerance.Then, to gather data on the inheritance of response to acetochlor, four tolerant inbreds (T) and four susceptible inbreds (S) were crossed to obtain four T×T, four S×S, four S×T and the corresponding four T×S two-way hybrids. These hybrids were studied together with parental lines by applying the same herbicide rates used in the previous trial. The S×S hybrids showed susceptibility to the herbicide and the T×T were tolerant, whereas the S×T and the T× S hybrids showed a tolerance very close to that of the T×T hybrids. No difference was found between S×T and the corresponding T×S hybrids as to herbicide response. On average, the 16 hybrids exhibited greater tolerance than the eight parental lines, with each hybrid group being more tolerant than its parental line group. These results indicate that tolerance to acetochlor is prevailingly dominant, that action of extranuclear genes should be ruled out, and that the level of plant vigour can affect herbicide reactiveness.     

Variation among Andean races of maize for cold tolerance during heterotrophic and early autotrophic growth

Cold in the initial growth stages is an important stressfactor for maize grown in regions with a temperate climate,particularly in case of early sowing. Sources of tolerancehave been identified in adapted genotypes, but promisinggenes for cold tolerance should also be found in materialdeveloped under the lower-temperature margins of the cropdistribution. This research was conducted in order to testAndean maize accessions for cold tolerance expressed duringboth the heterotrophic and early autotrophic growth stages.Experiments were conducted in controlled environments tostudy cold tolerance traits (germination %, germinationindex and plant growth rate) at continuous 10^°C (heterotrophic growth) and at varying 10–16^°C (autotrophic growth). An experiment was also performed inthe field with early sowing (both heterotrophic and autotrophic growth). In each experiment, a control trialwas conducted in more favourable conditions (i.e. continuous25^°C in a controlled environment or late planting inthe field) so that cold tolerance traits could also beexamined as the ratio between the stress and the controltrial. None of the accessions was superior for all coldtolerance traits. However, several Andean maize accessionsoutperformed the US Corn-belt hybrid checks for one or moretraits, both in heterotrophic and autotrophic growth. Overall, BOZM 855, PMS 636, Poblacion D, Poblacion E andBOZM 696 were the best accessions, suggesting that they canbe a promising source of genes for improving cold toleranceof adapted maize genotypes.     

Seed quality differences between normal,floury-2 and opaque-2 maize inbreds

Summary 142 inbreds of maize (Zea mays L.) and their fl2 and o2 versions, have been compared for seed quality traits. On average, fl2 is superior to the normal and o2 maizes in protein and oil contents and intermediate between normal and o2 in tryptophan content and DBC value. The introduction of the two mutant alleles drastically enhances the variation of the quality traits DBC value and tryptophan content. In association with the higher protein content of the fl2 versions, this effect makes it possible to identify a group of fl2 genotypes with high protein content (14.06%) and high DBC value (65.55), tryptophan content (1.32%) and oil percentage (5.92%).Supported by the Commission of the European Communities, contracts no 437 and 438.