Radiation‐Use Efficiency,Biomass Production,and Grain Yield in Two Maize Hybrids Differing in Drought Tolerance

Drought‐tolerant (DT) maize (Zea mays L.) hybrids have potential to increase yield under drought conditions. However, little information is known about the physiological determinations of yield in DT hybrids. Our objective was to assess radiation‐use efficiency (RUE), biomass production, and yield in two hybrids differing in drought tolerance. Field experiments were conducted in 2013 and 2014 with two hybrids, P1151HR (DT hybrid) and 33D49 (conventional hybrid) under well‐watered (I₁₀₀) and drought (I₅₀) conditions. I₁₀₀ and I₅₀ refer to 100 % and 50 % evapotranspiration requirement, respectively. On average, P1151HR yielded 11–27 % greater than 33D49 at I₁₀₀ and about 40 % greater at I₅₀, At I₁₀₀, greater yield in P1151HR was due to greater biomass at physiological maturity (BM_pm) resulting from greater post‐silking biomass accumulation (BM_post). At I₅₀, both hybrids had similar BM_pm but P1151HR showed a higher harvest index and greater BM_post. RUE differed significantly (P < 0.05) between the hybrids at I₁₀₀, but not at I₅₀. At I₁₀₀, the RUE values for P1151HR and 33D49 were 4.87 and 4.28 g MJ^?1 in 2013, and 3.71 and 3.48 g MJ^?1 in 2014. At I₅₀, the mean RUE was 3.89 g MJ^?1 in 2013 and 3.16 g MJ^?1 in 2014. Results indicate that BM_post is important for maintaining high yield in DT maize.     

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.     

Influence of harvest time and frequency on light interception and biomass yield of festulolium and tall fescue cultivated on a peatland

In this study, we report efficiencies of light capture and biomass yield of festulolium and tall fescue cultivated on a riparian fen in Denmark under different harvesting managements. Green biomass targeted for biogas production was harvested either as two cuts (2C) or three cuts (3C) in a year. Three different timings of the first cut in the 2C systems were included as early (2C-early), middle (2C-mid) and late (2C-late) cuts corresponding to pre-heading, inflorescence emergence and flowering stages, respectively. The fraction of intercepted photosynthetically active radiation (f_PAR) was derived from the canopy reflectance measured on 61 dates throughout a year, and cumulative interception of PAR (IPAR) and radiation use efficiency (RUE) was calculated. The dynamics of f_PAR and biomass accumulations was similar for both crops before the first cuts in all managements. Festulolium f_PAR in 2C-early and 2C-mid managements declined faster than in 2C-late and 3C managements in the second growth period and thus growing period IPAR of 2C-early and 2C-mid declined by 8% as compared to 3C management where IPAR was 925 MJ m⁻². Annual festulolium dry matter (DM) yield in 2C-early and 2C-mid managements (average 14.1 Mg DM ha⁻¹) decreased by 22% compared to 3C management (18.2 Mg DM ha⁻¹). The highest and the lowest RUE of festulolium were observed in 3C and 2C-mid managements as 1.97 and 1.59 g MJ⁻¹, respectively. For tall fescue f_PAR declined rather slowly in the second growing period in all 2C managements, which contributed to similar IPAR (908–919 MJ m⁻²), total biomass yield (16.4–18.8 Mg DM ha⁻¹ yr⁻¹) and RUE (1.80–2.07 g MJ⁻¹) for all managements. Whereas both crops were highly productive under both 3C management and 2C management with first harvest after flowering (i.e., 2C-late), the 2C-late strategy is recommended as the least intensive of the two management systems.     

Shading,Defoliation and Light Enrichment Effects on Chickpea in Northern Latitudes

Chickpea (Cicer arietinum L.) has an indeterminate growth nature, and the plant canopy with an improved light environment during critical growth stages may increase biomass (BM) production and improve crop yield. This study examined (i) the effects of shading, light enrichment and defoliation applied at various growth stages on BM and seed yield of chickpea in northern latitudes; and (ii) the difference between cultivars with fern‐ vs. unfoliate‐leaf type in responding to the altered canopy light environments. Field studies were conducted at Saskatoon and Swift Current, Saskatchewan in 2004 and 2005. Different light environments were created by 50 % defoliation at vegetative growth and at first flower, 50 % shading from vegetative growth to first flower, and two light enrichment treatments initiated at the first flower and pod formation stages. The 50 % shade treatment prior to flowering significantly decreased harvest index (HI) and seed yield. Light enrichments increased seed yield only one of three location‐years (the fourth site excluded because of disease damage). Defoliation at vegetative growth or first flower had a marginal effect on seed yield, largely as a result of the regrowth of vegetative tissues compensating for the lost plant tissues. The cultivar CDC Yuma (fern‐leaf type) exhibited consistently greater maximum light interception (LI), cumulative intercepted radiation, HI and seed yield than the cultivar Sanford (unifoliate‐leaf type) across all location‐years. Selective use of chickpea cultivars with improved morphological traits such as fern‐leaf type will likely improve LI and increase crop yield for chickpea in northern latitudes. Moreover, optimized crop management practices should be adopted to ensure that chickpea be grown under conditions with minimum shading before flowering and optimum light environment within the canopy especially during reproductive growth period.     

Light interception and radiation use efficiency in temperate quinoa (Chenopodium quinoa Willd.) cultivars

Sea level quinoas are grown at low altitudes in Central and Southern Chile. Both sensitivity to photoperiod and response to temperature largely determine quinoa adaptation, but crop biomass production must be quantified to evaluate agronomic performance. The objectives of this work are: (i) to characterize development effects on leaf area evolution for genotypes of sea level quinoa differing in cycle length, (ii) to quantify the extinction coefficient (k) for photosynthetically active radiation (PAR) and radiation use efficiency (RUE) from emergence up to the beginning of grain filling and (iii) to identify which crop attributes related to canopy architecture should be considered to improve biomass production. Four cultivars (NL-6, RU-5, CO-407 and Faro) were cropped in Pergamino (33°56′S, 60°35′W, 65 m a.s.l.), Argentina, at three densities (from 22 to 66 plants m⁻²) in two consecutive years under field conditions with adequate water and nutrient supply. Thermal time to first anthesis and maximum leaf number on the main stem were linearly correlated (r² = 0.87; p < 0.0001). Leaf area continued to increase during the flowering phase, notably in NL-6, the earliest genotype. There were significant differences in maximum plant leaf area between cultivars. Increasing density reduced plant leaf area but effects were comparatively small. Estimated k was 0.59 ± 0.02 across genotypes and was higher (p < 0.05) for 66 plants m⁻². Values for RUE changed as cumulative intercepted PAR (IPAR) increased; at initial stages of development RUE was 1.25 ± 0.09 g MJ IPAR⁻¹, but if cumulative IPAR was higher than 107.5 ± 10.4 MJ IPAR m⁻², RUE was 2.68 ± 0.15 g MJ IPAR⁻¹. That change occurred when leaf area index (LAI) and fraction of PAR intercepted were still low and ranged from 0.61 to 1.38 and from 0.33 to 0.51, respectively. No significant association was found with any developmental stage. Our results agreed to the notion that RUE variation during pre-anthesis phases is largely determined by LAI through its effect on radiation distribution within the canopy. Biomass production could be improved if periods of interception below 50% of incoming PAR were reduced to ensure high RUE. This seems to be possible in temperate areas both by the use of late genotypes with a higher number of leaves on the main stem and by early genotypes provided adequate plant density is chosen. Early increment in LAI and overlapping of the leaf area increase period with the flowering phase are desirable strategies for earliest genotypes to maximize yield.     

Radiation use efficiency,chemical composition,and methane yield of biogas crops under rainfed and irrigated conditions

For biomethane production, the cup plant (Silphium perfoliatum L.) is considered a promising alternative substrate to silage maize (Zea mays L.) due to its high biomass potential and associated ecological and environmental benefits. It has also been suggested to grow cup plant on less productive soils because of its presumed drought tolerance, but robust information on the impact of water shortage on biomass growth and substrate quality of cup plant is rare. Therefore, this study assesses the effects of soil water availability on the chemical composition and specific methane yield (SMY) of cup plant. Furthermore above-ground dry matter yield (DMY) was analysed as a function of intercepted photosynthetic active radiation (PAR) and radiation use efficiency (RUE). Data were collected in a two-year field experiment under rainfed and irrigated conditions with cup plant, maize, and lucerne-grass (Medicago sativa L., Festuca pratensis Huds., Phleum pratense L.). The cup plant revealed a slight decrease of −6% in the SMY in response to water shortage (less than 50% of plant available water capacity). The average SMY of cup plant [306 l (kg volatile solids (VS))⁻¹] was lower than that of maize [362 l (kg VS)⁻¹] and lucerne-grass [334 l (kg VS)⁻¹]. The mean drought-related reduction of the methane hectare yield (MHY) was significantly greater for cup plant (−40%) than for maize (−17%) and lucerne-grass (−13%). The DMY reduction in rainfed cup plant was mainly attributed to a more severe decrease in RUE (−29%) than for maize (−16%) and lucerne-grass (−12%). Under water stress, the mean cup plant RUE (1.3 g MJ⁻¹) was significantly lower than that of maize (2.9 g MJ⁻¹) and lucerne-grass (1.4 g MJ⁻¹). Compared to RUE, the reduced PAR interception was less meaningful for DMY in rainfed crops. Hence, the cup plant is not suitable for growing on drought prone lands due to its high water demand required to produce reasonably high MHYs.     

Water yam (Dioscorea alata L.) growth and yield as affected by the planting date: Experiment and modelling

Tubers of water yam (Dioscorea alata L.) are an important source of carbohydrates for millions of people throughout the tropics. Planting of the crop in the Caribbean and Central America is usually carried out between March and July. As water yam is very sensitive to small variations in photoperiod, changes in the planting date may greatly affect crop development and growth. The aim of this study was to assess the change in the radiation use efficiency (RUE) as a function of the planting date, and its effect on yam growth and yields. For this, we adapted the CropSyst model to simulate yam development and growth. The model was modified, calibrated and tested using two independent data sets from field experiments carried out in Guadeloupe (French Antilles) under non-limiting conditions for water and nutrients and over a wide range of planting dates and photoperiods (e.g. from 12.9 h in March to 11.3 h in October). The planting-harvest period varied from 4.4 months for the late planting dates to 9.1 months for the early planting dates. The RUE was relatively stable in the vegetative phase, increased after tuber initiation (TI) to reach a maximum value during the exponential phase of tuber growth, and then decreased towards the end of growth. The mean value of RUE increased from the early (March, 1.4 g MJ^?1) to the intermediate planting dates (July, 2.7 g MJ^?1), and then decreased for the late planting dates (October, 1.3 g MJ^?1). Maximum RUE was negatively correlated with photoperiod. This particular behaviour of RUE was induced by a source–sink interaction which was controlled by crop development and photoperiod. The model described yam development and growth satisfactorily for all the planting dates: e.g. R² > 0.92 for the correlation between modelled and measured tuber biomass. Yields varied little from the early to the intermediate planting dates because of an offset between the length of the vegetative phase, which determined leaf area, and the level of RUE after TI, which determined the capacity of the crop to fill tubers. Growth and yield drastically decreased for the late planting dates because photoperiod induced fast TI which strongly affected the leaf area. The model was a powerful tool to identify the underlying mechanisms affecting yam yields for some early planting dates, and to assess the factors involved in the high year-to-year variability currently observed in water yam yields.     

Water Deficit during the Reproductive Period of Grass Pea (Lathyrus sativus L.) Reduced Grain Yield but Maintained Seed Size

The grain legume grass pea (Lathyrus sativus L.) is adapted to drought‐prone environments, but the extent and mechanisms of its tolerance are not well understood. In a pot experiment, water deficit was imposed on plants by withholding water from first flowering until predawn leaf water potential (LWP_pd) was ?3.12 MPa. Water deficit reduced dry matter, seed yield, harvest index and water use efficiency by 60 %, 87 %, 67 % and 75 %, respectively, when compared with the controls. Flower production stopped when LWP_pd fell to ?1.8 MPa. At LWP_pd?1.5 MPa, only 25 % of flowers resulted in filled pods (compared with 95 % filled pods in the control) with the rest aborted as flowers (48 %) or pods (27 %). Filled pods had more aborted ovules than controls, resulting in 29 % less seeds per pod. Water deficit reduced pollen viability, germination and the number of pollen tubes reaching the ovary by 13 %, 25 % and 31 %, respectively. Emergence from seeds produced from water‐deficient plants was 21 % less than controls, but seedling shoot dry mass was 18 % higher, in accordance with the 19 % higher seed mass. The sensitivity of flowering to drought limited pod numbers but enabled plants to retain existing pods and develop near‐normal seeds with low β‐N‐oxalyl‐l ‐α‐β‐diaminopropionic acid toxin concentrations. This trait is useful for farming systems reliant on harvested seed for the next crop and in cases where seed size influences the value of the product.     

Shade Effects on Phaseolus vulgaris L. Intercropped with Zea mays L. under Well-Watered Conditions

Field experiments were carried out under unstressed conditions of soil water during two summer crop growing seasons (1998–99 and 1999–2000 seasons) in a South African semi‐arid region (Bloemfontein, Free State, South Africa). The aim of this study was to investigate shade effects on beans intercropped with maize in terms of plant mass and radiation use. The experimental treatments were two cropping systems (no shading/sole cropping and shading/intercropping) and two row orientations (north–south and east–west). At the top of bean canopies shaded by maize, incident radiation was reduced by up to 90 %. Shading reduced total dry matter of beans by 67 % at the end of the growing season, resulting in yield losses. The dry matter partitioning into leaf and stem (the ratios of leaf and stem to total biomass) was about 50 % higher in intercropping than sole cropping. In contrast, intercropped beans had 40 % lower dry matter partitioning into pod (the ratio of pod to total biomass). Fraction of radiation intercepted by sole‐cropped beans steeply increased until canopy closure (0.9) and then slowly decreased, while fraction of radiation intercepted by intercropped beans remained constant between 0.0 and 0.2 throughout the growing seasons. However, intercropped beans had 77 % higher radiation use efficiency (RUE) than sole‐cropped beans. In contrast, for maize, no effect of intercropping (shading) was found on growth, partitioning, yield, radiation interception or RUE. Consequently, lower bean yield losses can be attained in association with late shading rather than early shading. This can be controlled by growing crops with different temporal and spatial treatments. As regards row treatment, no effect of row direction was found on growth, partitioning, yield, radiation interception or RUE.     

Physiological basis of yield gains in wheat associated with the LR19 translocation from Agropyron elongatum

The physiological and genetic basis of yield improvement in wheat isonly partially understood. Nonetheless, a significant increase in yield andbiomass has been observed in several backgrounds when alien chromatinassociated with Lr19 was introgressed from Agropyronelongatum. Theoretically, higher yield and biomass may be achievedthrough (i) greater interception of incident radiation, (ii) increasedradiation use efficiency, (iii) a more optimal source-sink balance permittinghigher sink demand and/or a higher partitioning of assimilates to yield. Theobjectives of the current study were to evaluate the performance of nearisogenic lines differing in Lr19 to observe the physiological basis ofsuperior performance. Lr19 was associated with increases in yield(average 13%), final biomass (10%) and grain number (15%) in allbackgrounds studied. Differences were not associated with improved lightinterception based on measurements of biomass shortly after canopyclosure, nor with improved radiation use efficiency (RUE) prior to grainfilling based on biomass accumulation rate and direct measurement offlag-leaf photosynthetic rate prior to anthesis. Lr19 was associatedwith an increased partitioning of biomass to spike growth at anthesis(13%), a higher grain number per spike, and higher RUE and flag-leafphotosynthetic rate during grain filling. The mechanism causing increasedpartitioning of assimilates to spikes relative to the rest of the plant in Lr19 isolines was apparently not related to phenology or assimilationcapacity.     

Effect of Irrigation on Winter-Sown Chickpea in a Mediterranean Environment*

In the dry Mediterranean environments of the West Asia and North Africa region, irrigation is frequently used to supplement rainfall to increase crop productivity and yield stability. Chickpea (Cicer arietinum L.), an important pulse crop of the region, often suffers from drought and can benefit from such a practice. To investigate the response of chickpea to irrigation, experiments were conducted in the field at Tel Hadya, Syria, from 1985 to 1988 using 24 improved chickpea genotypes sown in winter. Irrigation scheduling was done using the daily water balance computed from rainfall and pan evaporation data. Yearly rainfall was 316, 358, and 504 mm and supplemental irrigation amount was 130, 120, and 80 mm in 1985–86, 1986–87, and 1987–88, respectively. Irrigation increased seed yield by 916 kg ha^?1 (44.0%) over the 3-year period. Irrigation requirement for chickpea coincided with flowering and seed development period. The top 10 highest-yielding genotypes under irrigated conditions were ILC 464, ILC 1272, ILC 237, ILC 613, ILC 95, ILC 4291, ILC 142, ILC 147, ILC 295, and ILC 3256. Their mean seed yields ranged from 3877 to 3208 kg ha^?1. Among these four genotypes, ILC 464, ILC 1272, ILC 3256, and ILC 4291 with mean seed yields of 3877, 3726, 3208, and 3266 kg ha^?1, respectively, were with predictable response to favourable conditions. Aboveground biomass contributed 49% of the total increase in seed yield from irrigation followed by plant height (26%) and early maturity (16%). These results indicate that it may be possible to breed chickpea for improved response to irrigation, and irrigation can enhance the yields of winter-sown chickpea grown in the lowland Mediterranean drylands.     

Allelic relationship between spontaneous and induced mutant genes for stem fasciation in chickpea

Stem fasciation is a morphological abnormality observed in plants where the stem is widened and leaves and flowers or pods are clustered at the apex. Several spontaneous mutants and one induced mutant for stem fasciation are found in chickpea (Cicer arietinum L.). This study was aimed at determining allelic relationship between spontaneous and induced mutant genes controlling stem fasciation and effects of stem fasciation on grain yield. Two spontaneous (ICC 2042 and ICC 5645) and one induced (JGM 2) stem fasciation mutants were crossed in all combinations, excluding reciprocals. The F₁ and F₂ plants from a cross between the two spontaneous mutants had fasciated stem. This indicated the presence of a common gene (designated fas1) for stem fasciation in the two spontaneous mutants. The F₁s of the crosses of the induced mutant JGM 2 with both spontaneous mutants had normal plants and segregated in a ratio of 9 normal : 7 fasciated plants in F₂. Thus, the gene for stem fasciation in the induced mutant JGM 2 (designated fas2) is not allelic to the common gene for stem fasciation in spontaneous mutants. The two genes in dominant condition produced normal non‐fasciated stem. The fasciated and the non‐fasciated F₂ plants did not differ significantly for number of pods per plant, number of seeds per plant, grain yield per plant and seed size, suggesting that it is possible to exploit the fasciated trait in chickpea breeding without compromising on yield.     

Determining relationships among yield and some yield components using path coefficient analysis in chickpea (Cicer arietinum L.)

Chickpea is an important source of protein and has a major role at human nutrition and it is essential to know the relationships between yield and its components in chickpea breeding programs. In this study, five chickpea lines provided from the chickpea breeding program of Field Crops Department, Faculty of Agriculture, Ankara University were used. In the examined characteristics, positive and significant relationships were found statistically between the number of seeds pod⁻¹ and the number of pods plant⁻¹, between the number of seeds plant⁻¹ and the number of pods plant⁻¹ and the number of seeds pod⁻¹, between seed yield plant⁻¹ and the number of pods plant⁻¹, the number of seeds pod⁻¹, the number of seeds plant⁻¹; between the number of seeds pod⁻¹ and seed yield unit⁻¹ area; between the number of seeds plant⁻¹ and seed yield unit⁻¹ area. Negative and significant relationships were determined statistically between the number of pods plant⁻¹ and 100 seed weight, between the number of seeds pod⁻¹ and 100 seed weight, between the number of seeds plant⁻¹ and 100 seed weight, between seed yield unit⁻¹ area and 100 seed weight. The total determining coefficient linking seed yield plant⁻¹ and seed yield unit⁻¹ area are 0.773 (77.3%) and 0.488 (48.8%) respectively in the model which were used in our research. And also total determining coefficient related to 100 seed weight was 0.896 (89.6%) in the same model.     

Nutrient Management Effects on Light Interception, Photosynthesis, Growth, Dry-matter Production and Yield of Indian Mustard (Brassica juncea)

A field experiment was conducted on sandy loam acidic soil to study the effect of nutrient managements on light interception, photosynthesis, growth, biomass production and yield of Indian mustard [Brassica juncea (L.) Czern & Coss.]. Plant height, number of branches per plant, number of siliqua per plant, number of seeds per siliquae, 1000‐seed weight, seed and oil yield of Indian mustard improved at 100 % recommended rates of NPK (N‐P‐K at 80‐17.2‐33.2 kg ha^?1) + 10 t ha^?1 farmyard manure (FYM) (T₃) compared with 100 % NPK rate (T₂). It was also at par with 100 % NPK + 10 kg ha^?1 borax + 20 kg ha^?1 ZnSO₄ (T₆) and 50 % NPK + 10 t ha^?1 FYM +10 kg ha^?1 borax + 20 kg ha^?1 ZnSO₄ (T₁₀). The rate of photosynthesis increased due to appropriate nutrient management treatments (T₃, T₆ or T₁₀) with concomitant increase in photosynthetically active radiation, internal CO₂ concentration and rate of transpiration and decrease in stomatal resistance. Consequent upon the higher rate of photosynthesis, dry‐matter accumulation increased. The crop receiving nutrient treatment T₃ or T₆ maintained higher light interception ratio (LIR), leaf area index (LAI), biomass production, crop growth rate (CGR) and net assimilation rate (NAR) that resulted in greater rate of photosynthesis, harvest index and seed yield. Similarly, T₁₀ was equally efficient in registering greater LIR, LAI, CGR, NAR and seed yield of mustard. The average seed yields were 1692, 1683 and 1668 kg ha^?1 in T₃, T₆ and T₁₀, respectively, and these three treatments were significantly superior to T₂ (1332 kg ha^?1), control (723 kg ha^?1) and other treatments. Significantly greater seed oil contents of 41.30, 40.60 and 41.07 % were recorded in T₃, T₆ and T₁₀, respectively. Thus, significant improvement due to appropriate combination of NPK, FYM, borax and ZnSO₄ was observed for uptake of nutrients.     

Salt Stress Delayed Flowering and Reduced Reproductive Success of Chickpea (Cicer arietinum L.), A Response Associated with Na+ Accumulation in Leaves

Salinity is known to reduce chickpea yields in several regions of the world. Although ion toxicity associated with salinity leads to yield reductions in a number of other crops, its role in reducing yields in chickpea growing in saline soils is unclear. The purpose of this study was to (i) identify the phenological and yield parameters associated with salt stress tolerance and sensitivity in chickpea and (ii) identify any pattern of tissue ion accumulation that could relate to salt tolerance of chickpea exposed to saline soil in an outdoor pot experiment. Fourteen genotypes of chickpea (Cicer arietinum L.) were used to study yield parameters, of which eight were selected for ion analysis after being grown in soil treated with 0 and 80 mm NaCl. Salinity delayed flowering and the delay was greater in sensitive than tolerant genotypes under salt stress. Filled pod and seed numbers, but not seed size, were associated with seed yield in saline conditions, suggesting that salinity impaired reproductive success more in sensitive than tolerant lines. Of the various tissues measured for concentrations of Cl^?, Na⁺ and K⁺, higher seed yields in saline conditions were positively correlated with higher K⁺ concentration in seeds at the mid‐filling stage (R² = 0.55), a higher K⁺/Na⁺ ratio in the laminae of fully expanded young leaves (R² = 0.50), a lower Na⁺ concentration in old green leaves (R² = 0.50) and a higher Cl^? concentration in mature seeds. The delay in flowering was associated with higher concentrations of Na⁺ in the laminae of fully expanded young leaves (R² = 0.61) and old green leaves (R² = 0.51). We conclude that although none of the ions appeared to have any toxic effect, Na⁺ accumulation in leaves was associated with delayed flowering that in turn could have played a role in the lower reproductive success in the sensitive lines.     

Exploitation of wild annual Cicer species for widening the gene pool of chickpea cultivars

Introgression of unadapted genes from the wild Cicer species could contribute to the widening of genetic base of important traits such as yield, yield attributes and resistance to major biotic and abiotic stresses. An attempt was made successfully to intercross two wild annual Cicer species with three cultivated chickpea cultivars. Four interspecific cross‐combinations were made, and their true hybridity was ascertained through morphological and molecular markers. These cross‐combinations were also studied for some important quantitative traits under real field conditions. The range, mean and coefficient of variation of agro‐morphological traits were assessed in the parental lines, their F₁ and F₂ generations to determine the extent of variability generated in cultivated chickpea varieties. A high level of heterosis was recorded for number of pods/plant and seed yield/plant in F₁ generation. Three cross‐combinations of ‘Pusa 1103’ × ILWC 46, ‘Pusa 256’ × ILWC 46 and ‘Pusa 256’ × ILWC 239 exhibited substantially higher variability for important yield‐related traits. The present research findings indicate that these wild annual Cicer species can be easily exploited to broaden the genetic base of cultivated gene pool for improving seed yield as well as adaptation.     

Chemical Manipulation of Reproductive Efficiency of Chickpea (Cicer arietinnum L.) by Triadimefon in Relation to Changes in Ethylene

Reproductive efficiency was successfully manipulated by the application of different concentrations of triadimefon at pre‐flowering, flowering and post‐flowering stages in chickpea (Cicer arietinum L.). Triadimefon improved the parameters determining reproductive efficiency. Yield was significantly improved due to reductions in flower and pod abscission by the application of triadimefon, which also lowered the ethylene levels in leaves, flowers and pods and delayed senescence. These findings suggest a relationship between ethylene level and reproductive efficiency in chickpea. Further, they indicate that triadimefon can be used for chemical manipulation of the reproductive efficiency of chickpea under field conditions.     

Mapping genes for double podding and other morphological traits in chickpea

Seed traits are important considerations for improving yield and product quality of chickpea (Cicer arietinum L.). The purpose of this study was to construct an intraspecific genetic linkage map and determine map positions of genes that confer double podding and seed traits using a population of 76 F₁₀ derived recombinant inbred lines (RILs) from the cross of ‘ICCV-2’ (large seeds and single pods) × ‘JG-62’ (small seeds and double podded). We used 55 sequence-tagged microsatellite sites (STMS), 20 random amplified polymorphic DNAs (RAPDs), 3inter-simple sequence repeats (ISSR) and 2 phenotypic markers to develop a genetic map that comprised 14 linkage groups covering297.5 cM. The gene for double podding (s) was mapped to linkage group 6 and linked to Tr44 and Tr35 at a distance of7.8 cM and 11.5 cM, respectively. The major gene for pigmentation, C, was mapped to linkage group 8 and was loosely linked to Tr33 at a distance of 13.5 cM. Four QTLs for 100 seed weight (located on LG4 and LG9), seed number plant^-1 (LG4), days to 50% flower (LG3) were identified. This intraspecific map of cultivated chickpea is the first that includes genes for important morphological traits. Synteny relationships among STMS markers appeared to be conserved on six linkage groups when our map was compared to the interspecific map presented by Winter et al. (2000). This revised version was published online in August 2006 with corrections to the Cover Date.     

Yield,water use and radiation use efficiencies of kenaf (Hibiscus cannabinus L.) under reduced water and nitrogen soil availability in a semi-arid Mediterranean area

Kenaf is a warm-season species that recently has been proved to be a good source of biomass for cellulose pulp for the paper industry in Mediterranean countries, where the use of hemp is problematic for legal reasons. A two-year research program aiming at studying the effects of different water regimes and nitrogen fertilization levels, upon plant growth, leaf area index, biomass accumulation, water and radiation use efficiency, was carried out on kenaf under a typically semi-arid Mediterranean climate of South Italy. In cv. Tainung 2, four different water regimes (I₀ = no irrigation, I₂₅, I₅₀ and I₁₀₀ = 25, 50 and 100% ETc restoration, respectively) and three nitrogen levels (N₀ = no nitrogen, N₇₅ and N₁₅₀ = 75 and 150 kg ha⁻¹ of N, respectively) were studied. The amount of water applied strongly affected plant growth (in terms of LAI, plant height and biomass) and final total and stem dry yield, which significantly increased from I₀ to I₁₀₀. Nitrogen did not exert any beneficial effect upon dry yield. Radiation Use Efficiency (RUE), calculated in the second year only, was the highest (1.95 g DM MJ⁻¹) in fully irrigated treatment (I₁₀₀) and the lowest (0.86 g DM MJ⁻¹) in the dry control.Water use efficiency (WUE) was rather similar among water regimes, whilst irrigation water use efficiency (IWUE) progressively increased with the decrease of total volume of water distributed to the crop by irrigation, from 3.47 to 12.45 kg m⁻³ in 2004 and from 4.27 to 7.72 kg m⁻³ in 2005. The results obtained from this research demonstrate that in semi-arid areas of South Italy, irrigation at a reduced rate (50% ETc restoration) may be advantageous, since it allowed a 42–45% irrigation water saving, when compared to the fully irrigation treatment, against a 23% (in 2004) and 36% (in 2005) yield reduction, and a still good efficiency (near that potential) in transforming the solar radiation in dry biomass was maintained (RUE = 1.76 g DM MJ⁻¹, against 1.95 g DM MJ⁻¹ in fully irrigated treatment).     

Crop and Weed Growth in a Sequence of Spring Barley and Winter Wheat Crops Established Together from a Spring Sowing (Relay Cropping)

A relay cropping system of cereals, whereby winter wheat (Triticum aestivum L.) was undersown in two‐row spring barley (Hordeum distichum L.), was established in a field trial in central Sweden in 1999 and continued until 2000. The purpose of the study was to examine crop and weed responses to different plant densities of the undersown winter crop. Winter wheat was sown at four seed rates (187, 94, 47 and 0 kg ha^?1) immediately after the sowing of barley. Barley was harvested in the first autumn after sowing and winter wheat in the second autumn. The grain yield of barley was not affected by the seed rate of wheat, and averaged 4580 kg ha^?1. Winter wheat did not vernalize during the first growing season but remained at the vegetative stage. The grain yield of wheat was 1990 kg ha^?1 for the lowest and 5610 kg ha^?1 for the highest seed rate of wheat. Whilst the undersowing process itself stimulated weed emergence in this experiment, increasing the undersowing seed rate reduced the population of perennial weeds by 40–70 %. In the second growing season, the total biomass of weeds was 66 % higher at the highest seed rate compared with the lowest seed rate.