温度对不同叶龄长雄野生稻及其后代化感作用的影响

掌握温度对长雄野生稻(Oryza longistaminata)及其后代化感作用的影响,对开发利用野生种质资源的化感抗草基因具有重要意义。采用直接树脂吸收法收集不同叶龄长雄野生稻及其后代在各温度条件下的根系分泌物,并以稗草作为受体,测定其化感作用。结果表明:1)温度、叶龄和温度×叶龄对水稻化感作用的影响与其自身化感潜力正相关,且对强化感和中化感潜力水稻(OL、F1、RL159和RL169)的化感作用影响极显著,而对弱化感水稻(RD23和RL219)的化感作用影响不显著。2)供试条件下长雄野生稻及其后代根系分泌物对稗草的化感作用均为抑制作用,其中,低温不利于水稻化感潜力的发挥。15℃时,强和中化感潜力水稻在不同叶龄对稗草的苗高、根长和生物量的抑制作用最弱,化感综合效应指数也显著大于同等叶龄的高温处理。3)高温有利于水稻化感潜力的发挥,但并非总是随温度的升高而增强。在6叶期和8叶期,水稻材料OL、F1、RL159和RL169随温度的升高化感作用逐渐增强,但在2叶期和4叶期则表现为先增强后减弱,在25℃时对稗草化感作用最强。4)在15℃时,强和中等化感潜力水稻在2叶期化感作用最弱,而在其他温度条件下,其化感作用随叶龄的增加表现为先减弱后增强,在2叶期化感作用最强。研究结果显示,温度对不同叶龄的水稻化感作用具有调控作用,幼苗阶段高温有利于强和中化感潜力水稻化感作用的发挥。     

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.     

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.     

Plant population density,row spacing and hybrid effects on maize canopy architecture and light attenuation

Light attenuation within a row crop such as maize is influenced by canopy architecture, which has to be defined in terms of the size, shape and orientation of shoot components. Cultural practices that improve the efficiency of light interception affect canopy architecture by modifying such components. Our objectives were to: (i) determine the nature and timing of leaf growth responses to plant population and row spacing; (ii) analyze light attenuation within fully developed maize canopies. Field experiments were conducted at Pergamino (33°56′S, 60°34′W) and Salto (34°33′S, 60°33′W), Argentina, during 1996/1997 and 1997/1998 on silty clay loam soils (Typic Argiudoll) that were well watered and fertilized. Four maize hybrids of contrasting plant type were grown at three plant populations (3, 9 and 12 plants m⁻²) and two row spacings (0.35 and 0.70 m). Plant population promoted larger changes in shoot organs than did row spacing. As from early stages of crop growth, leaf growth (V₆–V₈) and azimuthal orientation (V₁₀–V₁₁) were markedly affected by treatments. Modifications in shoot size and leaf orientation suggest shade avoidance reactions, probably triggered by a reduction in the red:far-red ratio of light within the canopy. An interaction between hybrid and plant rectangularity on leaf azimuthal distribution was determined, with one hybrid displaying a random azimuthal leaf distribution under most conditions. This type of hybrid was defined as rigid. The other hybrids showed modified azimuthal distribution of leaves in response to plant rectangularity, even at very low plant populations. These hybrids were defined as plastic. Once maximum leaf area index (LAI) was attained light attenuation did not vary among hybrids and row spacing for plant populations ≥9 plants m⁻² (k coefficient: 0.55 and 0.65 for 9 and 12 plants m⁻², respectively). A more uniform plant distribution increased light attenuation (k coefficient: 0.37–0.49) only when crop canopies did not reach the critical LAI.     

Duration of the grain-filling period in maize is not affected by photoperiod and incident PPFD during the vegetative phase

Total number of initiated leaves and duration from sowing to silking increases when photoperiod is increased during the photoperiod-sensitive phase in maize (Zea mays L.). Little is known, however, about possible other effects of photoperiod and incident photosynthetic photon flux density (PPFD) on rate of development and duration of life cycle. A study was undertaken to quantify effects of photoperiod and incident PPFD from sowing to the 15-leaf stage on rate of leaf appearance and duration of the grain-filling period. The short-season maize hybrid Pioneer 3902 was grown in growth cabinets from sowing to the 15-leaf stage with either (i) a 10 h photoperiod at high PPFD (650 μmol m⁻² s⁻¹), (ii) a 20 h photoperiod consisting of 10 h of high PPFD followed by 10 h of low PPFD (5–50 μmol m⁻² s⁻¹), or (iii) a 20 h photoperiod of high PPFD. From the 15-leaf stage to maturity the plants were placed under a 16 h photoperiod in a growth room. Increasing photoperiod from 10 to 20 h increased final number of initiated leaves and delayed silking but did not affect rate of leaf appearance. Doubling incident PPFD to a value similar to that under Ontario field conditions during the summer resulted in a 16% increase in rate of leaf appearance and in a significant increase in total number of initiated leaves. Differences in final number of initiated leaves and in rate of leaf appearance from sowing to the 15-leaf stage among treatments resulted in a 4-day difference in silking date between the 10 h photoperiod treatment and the two 20 h photoperiod treatments. Duration of the grain-filling period did not differ among the three treatments.     

Breeding for perennial growth and fertility in an Oryza sativa/O. longistaminata population

The development of perennial cultivars (CVs) of upland rice would give farmers a new tool to reduce soil erosion from hilly fields, thereby mitigating a problem of regional concern in Southeast Asia. Oryza longistaminata is an undomesticated, perennial, rhizomatous relative of domesticated Asian rice (Oryza sativa). Using five sets of 4 × 2 factorial mating designs, we crossed rhizomatous interspecific genotypes (IGs) from an intermated O. sativa/O. longistaminata population with male-fertile IG selections from the intermated population, and with O. sativa CVs. Parents and progeny were planted in an upland field at IRRI using a randomized complete block design and evaluated for rhizome expression, survival after 1 year, vigor of the survivors, and yield. For the IG parents, rhizome expression was variable and penetrance of most genotypes was incomplete, but genotypes that demonstrated the potential for moderate rhizome expression had high penetrance (89% average). The CV parents yielded 11.0 g/plant on average but none produced rhizomes or survived 1 year. The IG parents averaged yields of 3.1 g/plant, 57% rhizomatous and 36% survival. The IG/IG progeny averaged yields of 4.2 g/plant, 32% rhizomatous and 37% survival. The IG/CV progeny averaged yields of 6.0 g/plant, 18% rhizomatous and 16% survival. Nine IG/IG progeny and six IG/CV progeny were rhizomatous, perennial, and yielded at least 5 g/plant, and five of these yielded more than 10 g/plant. For the IG parents and IG/IG progeny, rhizome presence and expression were positively associated with survival and vigor of the survivors. General combining ability effects were significant for percent survival and yield but not percent rhizomatous. Specific combining ability effects were significant for percent rhizomatous, percent survival and yield. By selecting female parents for long rhizomes and male parents for fertility, considerable gains in rhizome expression, survival and yield were made. The development of perennial upland rice CVs should be feasible via introgression of genes from O. longistaminata.     

Effect of nitrogen supply on leaf appearance,leaf growth,leaf nitrogen economy and photosynthetic capacity in maize (Zea mays L.)

Leaf area growth and nitrogen concentration per unit leaf area, N_a (g m⁻² N) are two options plants can use to adapt to nitrogen limitation. Previous work indicated that potato (Solanum tuberosum L.) adapts the size of leaves to maintain N_a and photosynthetic capacity per unit leaf area. This paper reports on the effect of N limitation on leaf area production and photosynthetic capacity in maize, a C4 cereal. Maize was grown in two experiments in pots in glasshouses with three (0.84–6.0 g N pot⁻¹) and five rates (0.5–6.0 g pot⁻¹) of N. Leaf tip and ligule appearance were monitored and final individual leaf area was determined. Changes with leaf age in leaf area, leaf N content and light-saturated photosynthetic capacity, P_max, were measured on two leaves per plant in each experiment. The final area of the largest leaf and total plant leaf area differed by 16 and 29% from the lowest to highest N supply, but leaf appearance rate and the duration of leaf expansion were unaffected. The N concentration of expanding leaves (N_a or %N in dry matter) differed by at least a factor 2 from the lowest to highest N supply. A hyperbolic function described the relation between P_max and N_a. The results confirm the ‘maize strategy’: leaf N content, photosynthetic capacity, and ultimately radiation use efficiency is more sensitive to nitrogen limitation than are leaf area expansion and light interception. The generality of the findings is discussed and it is suggested that at canopy level species showing the ‘potato strategy’ can be recognized from little effect of nitrogen supply on radiation use efficiency, while the reverse is true for species showing the ‘maize strategy’ for adaptation to N limitation.     

Rice root morphological traits are related to isozyme group and adaptation

Rice accessions from the International Rice Research Institute (IRRI) germplasm bank were evaluated for root traits of 40-day-old plants grown in soil in the greenhouse. The 136 accessions represented six groups defined on the basis of isozyme classification, with isozyme group six further subdivided on the basis of origin and morphology. An additional 28 rice cultivars were evaluated for seminal root xylem vessel diameter when grown in pots in a growth chamber. Rice groups differed in root thickness, root xylem vessel diameter, root:shoot ratio, and patterns of root distribution. Isozyme group 1, which corresponds generally to the indica subspecies, had thin, superficial roots with narrow vessels and a low root:shoot ratio. The other major isozyme group, group 6, comprising japonica types, was characterized by thick roots with wider vessels, a greater proportion of the root weight below 15 cm, and a larger root:shoot ratio. On an average, the bulu and temperate group 6 accessions were similar to the non-bulu types except that their root:shoot ratios and proportion of root weight above 15 cm were more similar to group 1. Group 2, with aus types from South Asia, was characterized by intermediate root thickness, but vertical root distribution and root:shoot ratio were more similar to group 6. The minor isozyme groups 3–5 were represented by few accessions, and in general, they had root thickness and root distribution profiles more similar to group 1 than to group 6. While significant differences were observed among isozyme groups for all the traits under study, there was significant variation within groups and groups overlapped for all traits measured. This study highlights the wide range of variability for constitutive root traits in rice. For example, root thickness ranged from 0.68 to 1.04 mm, seminal root xylem vessel diameters from 30 to 58 μm, root:shoot ratios from 0.05 to 0.21, and accessions had from 44 to 73% of the total root weight concentrated in the surface 15 cm of soil. For the 28 cultivars evaluated, root xylem vessel diameter was highly correlated with reported values of leaf epicuticular wax content (r=0.89). These values indicate the range of genetic variation within the rice genome for root morphological traits.     

Effect of SWD irrigation on photosynthesis and grain yield of rice (Oryza sativa L.)

A study was conducted with the objective to determine the influence of (shallow water depth with wetting and drying) SWD on leaf photosynthesis of rice plants under field conditions. Experiments using SWD and traditional irrigations (TRI) were carried out at three transplanting densities, namely D1 (7.5 plants/m²), D2 (13.5 plants/m²) and D3 (19.5 plants/m²) with or without the addition of organic manure (0 and 15 t/ha). A significant increase in leaf net photosynthetic rate by SWD was observed with portable photosynthesis systems in two independent experiments. At both flowering and 20 DAF stages, photosynthetic rate was increased by 14.8% and 33.2% with D2 compared to control. SWD significantly increased specific leaf weight by 17.0% and 11.8% over the control at flowering and 20 DAF stages, respectively. LAI of D2 under SWD was significantly increased by 57.4% at 20 DAF. In addition, SWD with D2 significantly increased the leaf dry weight (DW) at both growing stages. At all the three densities, SWD increased the leaf N content and the increase was 18.9% at D2 density compared with the conventional control. In SWD irrigation, the leaf net photosynthetic rate was positively correlated with the leaf N content (R² = 0.9413), and the stomatal conductance was also positively correlated with leaf N content (R² = 0.7359). SWD enhanced sink size by increasing both panicle number and spikelet number per panicle. The increase in spikelet number per panicle was more pronounced in the 15 t ha⁻¹ manure treatment than in the zero-manure treatment. Grain yield was also significantly increased by SWD, with an average increase of 10% across all treatments. SWD with D2 had the highest grain yield under the both cultivars with or without 15 t ha⁻¹ manure treatment, which was 14.7% or 13.9% increase for Liangyoupeijiu and 11.3% or 11.2% for Zhongyou 6 over the control, respectively.     

Effect of growth regulators on yield and fiber quality in ramie (Boemheria nivea (L.) Gaud.), China grass

The effects of two mixtures of four plant growth regulators (choline chloride, gibberellin (GA₃), benzyladenine (6-BA) and NaHSO₃) at 20:9:5:800 mg kg⁻¹ (H1) and 20:42:43:2350 mg kg⁻¹ (H3) (active ingredients), respectively, were investigated on yield and fiber quality in ramie (Boehmeria nivea (L.) Gaud.). The mixtures were sprayed over the canopy at two growth stages (10 and 20 days after the previous cut) of field-grown ramie. The treatments increased raw fiber yield by 13–18%, and improved fiber fineness by 57–349 m g⁻¹, increased number of leaves per plant, and also improved all yield components. Treatment H1 resulted in a denser distribution, smaller diameters and greater quantity of fiber cells in stem cross-section. Physiological responses included improving leaf water status, increasing net photosynthetic rate, and decreasing electrolyte exosmosis rate.     

决明属（Chamaecrista spp）豆科牧草8个品种化感潜力的研究

研究决明属（Chamaecrista spp.）豆科牧草8个品种[圆叶决明（Chamaecrista rotundifolia）CPI86134、CPI34721、CPI86178、CPI3248、ATF2232、CPI57503和羽叶决明（Chamaecrasta nictitans）ATF2217、ATF2219]对禾本科牧草百喜草（Paspalum notatum）的化感作用,以确定该8个豆科牧草品种的化感潜力。结果表明,8个决明属豆科牧草品种具有较强的化感作用;随着浓度的逐渐降低,8个品种开花期浸提液的化感抑制作用逐渐减弱,结荚期浸提液的化感促进作用逐渐加强;同一品种,同一生长时期,不同浓度（5%、7.5%和10%）的化感作用综合效应表现不同;同一生长时期,同一浓度,不同品种的化感综合效应表现也不同。可见,决明属牧草8个品种的化感作用受浓度、生长时期和品种的影响。     

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).     

Fine Mapping of QTLs for Stigma Exsertion Rate from Oryza glaberrima by Chromosome Segment Substitution

Stigma exsertion is an important trait for outcrossing ability in rice. Stigma exsertion rate (SER) of male sterile lines (MSLs) is a key factor affecting F₁-seed production in hybrid rice. In this study, seven QTLs for SER were detected on five chromosomes using a set of single-segment substitution lines (SSSLs) derived from O. glaberrima. Three of the QTLs were mapped in the estimated intervals of 92.5–333.0 kb. qSER-5 was located in a substitution segment of 92.5 kb. qSER-1b and qSER-8b were respectively limited to 333.0 kb and 107.5 kb by secondary substitution mapping. qSER-1b and qSER-3 had bigger additive effects of 11.5% and 11.9%, respectively, while the other five QTLs had smaller additive effects from 5.7% to 8.6%. Open reading frames were identified in the regions of qSER-5 and qSER-8b in O. sativa and O. glaberrima genomes. Fine mapping of the QTLs laid a foundation for the cloning of genes, and QTLs for SER will be used to develop MSLs with strong ability of outcrossing.     

Long-term effects of inorganic and organic fertilizer sources on yield and nutrient accumulation of lowland rice

Deceleration in rice (Oryza sativa L.) yield over time under fixed management conditions is a concern for countries like Bangladesh, where rice is the primary source of calories for the human population. Field experiments were conducted from 1990 to 1999 on a Chhiata clay loam soil (Hyperthermic Vertic Endoaquept) in Bangladesh, to determine the effect of different doses of chemical fertilizers alone or in combination with cow dung (CD) and rice husk ash (ash) on yield of lowland rice. Two rice crops—dry season rice (December–May) and wet season rice (July–November) were grown in each year. Six treatments—absolute control (T₁), one-third of recommended fertilizer doses (T₂), two-thirds of recommended fertilizer doses (T₃), full doses of recommended fertilizers (T₄), T₂+5 t CD and 2.5 t ash ha⁻¹ (T₅) and T₃+5 t CD and 2.5 t ash ha⁻¹ (T₆) were compared. The CD and ash were applied on dry season rice only. The 10-year mean grain yield of rice with T₁ was 5.33 t ha⁻¹ per year, while the yield with T₂ was 6.86 t ha⁻¹ per year. Increased fertilizer doses with T₃ increased the grain yield to 8.07 t ha⁻¹ per year, while the application of recommended chemical fertilizer doses (T₄) gave 8.87 t ha⁻¹ per year. The application of CD and ash (T₅ and T₆) increased rice yield by about 1 t ha⁻¹ per year over that obtained with chemical fertilizer alone (T₂ and T₃, respectively). Over 10 years, the grain yield trend with the control plots was negative, but not significantly, both in the dry and wet seasons. Under T₃ through T₆, the yield trend was significantly positive in the dry season, but no significant trend was observed in the wet season. The treatments, which showed positive yield trend, also showed positive total P uptake trend. Positive yield trends were attributed to the increasing P supplying power of the soil.     

On-farm soil N supply and N nutrition in the rice–wheat system of Nepal and Bangladesh

On-farm research to evaluate the productivity and nitrogen (N) nutrition of a rice (Oryza sativa L.)–wheat (Triticum aestivum L.) cropping system was conducted with 21 farmers in the piedmont of Nepal and with 21 farmers in northwest Bangladesh. In Nepal, two levels of N-fertilizer (0–22–42 and 100–22–42 kg N–P–K ha⁻¹) and farmers’ nutrient management practices were tested in the rice season, and three levels of N (0–22–42, 70–22–42, and 100–22–42) and farmers’ practices were evaluated in the wheat season. The treatments in Bangladesh included a researchers managed minus-N plot (0–22–42) and the farmers’ practices. Rice and wheat yields were higher in all treatments than the 0–22–42 control plots, with the exception of rice with the farmers’ practices at one location in Bangladesh. The researchers’ treatment of 100–22–42 in Nepal resulted in larger yields of both rice and wheat than the farmers’ practices, indicating that farmers’ rates of N-fertilizer (mean 49 kg N ha⁻¹) were too low. Delaying wheat seeding reduced yields in the fertilized plots in both countries, especially as N-fertilizer dose increased. Soil N-supplying capacities (SNSC), measured as total N accumulation from the zero-N plots (0–22–42), and grain yields without N additions were greater for rice than for wheat in both Nepal and Bangladesh. Higher SNSC in rice was probably due to greater mineralization of soil organic N in the warm, moist conditions of the monsoon season than in the cooler, drier wheat season. However, SNSC was not correlated with total soil N, two soil N availability tests (hot KCl-extractable NH₄⁺ or 7-day anaerobic incubation), exchangeable NH₄⁺ or NO₃⁻. Wheat in Nepal had greater N-recovery efficiency, agronomic efficiency of N, and physiological efficiency of N than rice. Nitrogen internal-use efficiency of rice for all treatments in both countries was within published ranges of maximum sufficiency and maximum dilution. In wheat, the relationship between grain yield and N accumulation was linear indicating that mobilization of plant N to the grain was less affected by biotic and abiotic stresses than in rice.     

Seasonal changes in the effects of free-air CO2 enrichment (FACE) on dry matter production and distribution of rice (Oryza sativa L.)

It is reported that stimulating effect of elevated atmospheric [CO₂] on photosynthesis of rice (Oryza sativa L.) is likely to be reduced during the plant growth period. However, there is little information on seasonal changes in dry matter (DM) production and distribution of rice under elevated atmospheric [CO₂]. A free-air CO₂ enrichment (FACE) experiment was conducted at Wuxi, Jiangsu, China, in 2001–2003, using Wuxiangging 14, a japonica cultivar. The rice was grown at ambient or elevated (ca. 200 μmol mol⁻¹ above ambient) [CO₂] and supplied with 25 g N m², which is the normal N application rate for local farmers. DM accumulation of rice in FACE plots was significantly increased by 40, 30, 22, 26 and 16% on average at tillering, panicle initiation (PI), heading, mid-ripening and grain maturity, respectively. Rice DM production under FACE was significantly enhanced by 41, 27, 15 and 38% on average during the growth periods from transplanting to tillering (Period 1), tillering to PI (Period 2), PI to heading (Period 3) and heading to mid-ripening (Period 4), respectively, but significantly decreased by 25% in the period from mid-ripening to grain maturity (Period 5). In general, seasonal changes in crop response to FACE in both green leaf area index (GLAI) and net assimilation rate (NAR) followed a similar pattern to that of the DM production. Under FACE the leaves decreased significantly in proportion to the total above-ground DM over the season, the stems showed an opposite trend, while the spikes depended on crop development stage: showing no change at heading, significant increase (+4%) at mid-ripening and significant decrease (−3%) at grain maturity. Grain yield was stimulated by an average of 13% by FACE, due to increased total DM production rather than any changes in partitioning to the grain. We conclude that the gradual acclimation of rice growth to elevated [CO₂] do not occur inevitably, and it could also be altered by environmental conditions (e.g., cultivation technique).     

Effect of photoperiod on tuberization in the Livingstone potato (Plectranthus esculentus N.E.Br. Lamiaceae)

The Livingstone potato (Plectranthus esculentus N.E.Br.) produces a cluster of edible tubers at the base of the stem that are used as a potato substitute in many areas of Africa. No information is available on factors affecting tuberization in this species. Photoperiod is known to influence storage organ formation in a wide range of crops, and pilot trials indicated that it also played a role in tuberization in P. esculentus. The critical photoperiod for tuber induction, as well as the number of short-day cycles required to induce tubers, were investigated in glasshouse trials using in vitro plants. Nine photoperiod treatments (30-min intervals from 10 to 14 h of light) were applied in the critical photoperiod experiment. To determine the number of short-day cycles required to induce tuberization, plants were exposed to short days (10 h light) for periods ranging from 0 to 20 days at 2-day intervals. Data were collected from both intact plants and sub-apical two-node cuttings made after the experimental treatments were completed. The critical photoperiod for the specific genotype used in this study was between 12.5 and 13 h, with cuttings giving a slightly exaggerated result over that of intact plants. It was established that exposure to four short-day cycles was sufficient to induce tuberization in this species.     

Induced Effects of Exogenous Phenolic Acids on Allelopathy of a Wild Rice Accession （Oryza Iongistaminata, S37）

Four exogenous phenolic acids, including salicylic acid, fumalic acid, p-coumaric acid and p-hydroxybenzonic acid, were used to investigate the regulatory effects on allelopathy of a wild rice accession of S37 (Oryza longistaminata), which is a known allelopathic rice. The four exogenous phenolic acids induced the enhancement of the allelopathic potential of wild rice S37 in target weeds though the weed-suppressive activities were low, and the inducible effects were dependent on the specific phenolic acid, concentration and treatment time. After foliar application of exogenous phenolic acids, the inhibition rates for plant height, root length and fresh weight of barnyard grass (Echinochloa crus-galli) were significantly higher than those of the control. Especially at the concentration of 100 mg/L, the inhibition rates for plant height and fresh weight of barnyard grass by fumalic acid were 38.12% and 26.31% higher than those of the control, showing that fumalic acid was more effective compared with other phenolic acids in inhibiting monocotyledon weed growth. Furthermore, the weed-suppressive activity of aqueous extract from the leaves of wild rice S37 treated with exogenous phenolic acids was increased, and it peaked at 48 h after the treatment with the aqueous extract, and then gradually declined.     

Modeling chickpea growth and development: Leaf production and senescence

Quantitative information regarding leaf area development in chickpea (Cicer arietinum L.) is scarce. Data from four field experiments with a range of treatments including genotype, sowing date and plant density across four location-season combinations were analyzed to quantify main effects of temperature, photoperiod and plant population density on plant leaf area in chickpea. All experiments were conducted under well-watered conditions. Maximum rate of main stem node development was 0.72 nodes/d. Cardinal temperatures for node appearance were found as 6.0, 22.2 and 31.0 °C for base, optimum and ceiling temperatures, respectively. Plant density had no effect on cardinal temperatures for leaf appearance and phyllochron. Leaf senescence on the main stem started when the main stem had about 12 nodes and proceeded at a rate of 1.67% per each day increase in physiological day (a day with non-limiting temperature and photoperiod). Leaf production per plant versus main stem node number occurred in two phases; phase 1 when plant leaf number increased with a slower and density-independent rate (three leaves per node), and phase 2 with a higher and density-dependent rate of leaf production (8–15 leaves per node). A close relationship was found between the fraction of senesced leaves per plant and the same fraction on the main stem. The average leaf size per plant increased from 4 cm² when there were 10 nodes on the main stem and stabilized at 10.8 cm² when there were 21 nodes on the main stem. Plant density and sowing date did not affect leaf size. Plant leaf area was also predictable directly from main stem node number. The relationships found in this study can be used in simulation models of chickpea.     

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.