Normal Planting Dates Research Articles

Effects of different planting dates and low light on cotton fibre length formation

Declining temperature and low light often appear together to affect cotton (Gossypium hirsutum L.) growth and development. To investigate the interaction on fibre elongation, two cultivars were grown in fields in 2010 and 2011 and in pots in 2011 under three shading levels for three planting dates, and the differences of environmental conditions between different planting dates were primarily on temperature. Fibre length in the late planting date 25 May was the longest instead of the normal planting date. Late planting prolonged fibre elongation period and the effect of late planting on fibre length formation was greater than low light. In the normal planting date, shading increased fibre length through delaying the peak of β-1,3-glucanase gene expression and bringing the peak of β-1,3-glucan synthase gene expression forward, leading to a longer duration of plasmodesmata(PD) closure to increase fibre length, instead of changing sucrose contents or relate enzyme activities. However, in the late planting dates, the difference of the duration of PD closure between shading treatments was not obvious, but low light had a negative impact on sucrose contents, sucrose synthase (SuSy) and vacuolar invertase(VIN) activities during fibre rapid elongation period, leading to the decline of fibre length. Due to late planting and low light, the decreased extent of fibre length of Sumian 15 was larger than Kemian 1. Under the combined condition, Sumian 15 had a shorter gene expression of Expansin, and more sensitive sucrose content, VIN and SuSy activity during fibre rapid elongation period. This resulted in the length formation of Sumian 15 which was more sensitive than Kemian 1, when the cotton suffered the combined effects.

Analyses of sorghum [Sorghum bicolor (L.) Moench] lines and hybrids in response to early-season planting and cool conditions

Kapanigowda, M., H., Perumal, R., Aiken, R. M., Herald, T. J., Bean, S. R. and Little, C. R. 2013. Analyses of sorghum [ Sorghum bicolor (L.) Moench] lines and hybrids in response to early-season planting and cool conditions. Can. J. Plant Sci. 93: 773–784. Early-season cold tolerance in sorghum contributes to emergence, seedling establishment, and early vegetative growth, and reduces damping-off diseases under chilling conditions. The objectives of this study were to identify cold-tolerant sources and to evaluate and optimize rapid screening techniques under a controlled environment. Field studies involving 48 genotypes, representing phases of the hybrid development process (landraces, elite and advanced breeding lines, recombinant inbred lines (RILs) and hybrids were conducted with early and normal planting dates in 2011 at Hays and Colby, Kansas. Studies under controlled environments were conducted at both locations using 18 genotypes that differ for emergence index (EI) and 30 d after emergence (DAE) shoot biomass based on field studies during 2011. Significant differences among the genotypes were recorded for all seedling traits (emergence percentage, EI, shoot biomass, plant height, and leaf number measured 30 DAE), and agronomic traits (days to 50% flowering, panicle exsertion, panicle length, and plant height at maturity). Eight advanced breeding lines: ARCH10731, ARCH10732, ARCH10736, ARCH10737, ARCH10738, ARCH10739, ARCH10744 and ARCH10749 and one RIL (RTx430/SQR-2) were found to be potential sources of cold tolerance with early EI, higher biomass and relatively early flowering. These genotypes are free from tannin, which helps to increase the feed grain efficiency of livestock, and hence were selected for test hybrid evaluation to assess fertility status, combining ability and yield performance. Significant correlation was observed between EI and biomass during early planting, which indicated that late-emerging genotypes produced greater biomass (30 DAE) compared with early-emerged genotypes. Significant correlation between growth chamber and field study for EI offers a potential and fast preliminary high-throughput screening technique for identification of cold-tolerant sorghum.

Characterization of genetic coefficients of durum wheat (Triticum turgidum L. ssp. durum) ‘Llareta-INIA’ and ‘Corcolén-INIA’

The genetic coefficients, representative of a crop, are necessary to use growth models; in many cases the range of the species is known, but there are no specific values for varieties. Durum wheat ( Triticum turgidum L. ssp. durum ) ‘Llareta- INIA’ and ‘Corcolen-INIA’ were sown under irrigation in the experiment station Antumapu of the Universidad de Chile on 29 June 2007, 19 May 2009, and 15 June 2010 in order to determinate four genetic coefficients: developmental thermal time, phyllochron (PHLN), extinction coefficient (k), and radiation use efficiency (RUE), and to evaluate the performance of these coefficients. Thermal times to anthesis and from anthesis to physiological maturity were 652 and 541° C d, respectively. Two PHLN values were found, 46.6° C d leaf-1 from emergence to fifth leaf and 102.9 ° C d leaf-1 from fifth to eighth leaf. In both cases neither variety nor sowing date was significant. The value of k did not vary among sowing dates for ‘Llareta-INIA’ and was not significantly different from that of ‘Corcolen-INIA’ for normal planting date, due to which a single fit for the two varieties was adjusted, obtaining a value of 0.46. However, ‘Corcolen-INIA’ had a lower value of k for later sowing dates. RUE did not vary between varieties or sowing dates; its estimated value was 2.83 g MJ-1. The evaluation of the coefficients obtained showed coherent results, thus they can be used in model simulations.

Diallel Analysis and Biochemical Genetic Markers for Heterosis and Combining Ability under Two Sowing Dates of Maize Inbred Lines

The study was undertaken to estimate heterosis and combining ability of new maize inbred lines in F1 combinations for some agronomic traits under two sowing dates for developing superior hybrids. Also this investigation studied the possibility of predicting heterosis and combining ability in maize inbred lines via protein electrophoresis. A half diallel set of crosses involving eight maize inbred lines were evaluated under two different sowing dates and the inbred lines were used for protein electrophoresis study. The obtained data revealed highly significant differences between sowing dates for all studied traits except number of rows per ear. The mean squares due to General Combining Ability (GCA) and Specific Combining Ability (SCA) were significant for all studied traits under both planting dates except 100 kernel weight under late planting date for SCA. GCA/SCA ratios were less than unity for plant height, days to 50% silking, 100 kernel weight and grain yield per plant under normal sowing date and ear height, plant height, number of kernel per row, 100 kernel weight and grain yield per plant under late sowing date and the other traits were more than unity. The hybrids P1 × P2, P1 × P6, P1 × P8, P2 × P5, P2 × P6, P3 × P6, P5 × P6, P5 × P7 and P6 × P7 under normal sowing date and P2 × P4, P2 × P5, P4 × P6 and P5 × P6 under late sowing date out yielded the check hybrid. The parental lines P2, P5 and P6 seemed to be the best combiners for grain yield per plant and most of the studied traits under normal and late planting dates. Twenty one out of the twenty eight crosses showed desirable significant SCA effects under normal and late sowing dates for grain yield per plant and most of the other studied traits. The electrophoresis patterns could be useful tools for the identification and characterization of these inbred lines and could be used as biochemical genetic markers associated with hybrid vigor and SCA in maize

Can planting date and cultivar selection improve resource use efficiency of cotton systems?

Water is an increasingly valuable resource and there is uncertainty about future rainfall patterns in a changing climate. Similarly, there are concerns with nitrogenous fertiliser use due to risks of greenhouse gas emissions and rising costs. Hence, it is timely to revisit and develop crop management strategies to balance economic, social and environmental impacts to determine if greater efficiencies can be attained. We investigated the potential to manipulate resource use efficiency with planting date and cultivar in cotton farming systems. Flexibility in planting date in some environments is now more practical because transgenic cotton provides better insect control, resulting in higher fruit retention and a shorter fruiting cycle. This allows later plantings to maintain yield and fibre quality. This is the first study to examine cotton planting date effect on resource use efficiency in Australia. Field experiments were conducted over two seasons at Narrabri, New South Wales, Australia (30°S, 150°E) to investigate the effect of delayed planting date and cultivar (differing in plant morphology and yield potential) on lint yield and quality, and resource use efficiency (water and nitrogen). Lint yield and resource use efficiency were not statistically decreased if planting occurred more than 30 days from the normal target planting date of 15 October. Studies using the OZCOT cotton crop simulation using 53 seasons of climate data confirmed the opportunity for improved water use efficiency with planting delayed to 15 November in warmer long-season Australian cotton regions.

PARAMETRIC MODEL BASED ASSESSMENT OF GENOTYPE X ENVIRONMENT INTERACTIONS FOR GRAIN YIELD IN DURUM WHEAT UNDER IRRIGATION

The objectives of this study were to assess the genotype (G) by environment (E) interaction of grain yield of durum wheat(Triticum durum Desf.) based on parametric models, additive main effects and multiplicative interaction (AMMI) and joint linear regression models; and compare the relative efficiency of the two models in explaining the GE effects. Twenty-three genotypes were evaluated across 12 environments (location-year combinations) in 2003 and 2004. Combined analysis of variance showed that the environment (E) accounted for a high percentage of sums of squares (remaining after removing the sums of squares due to error and replications). The genotypic variability of grain yield among genotypes was small. The best genotype 6 (DBSP02/8) out yielded the check by 0.24 ton/ha. Based on full AMMI model analysis, AMMI-1 was found to explain up to 94% of the main and interaction effects, and AMMI-2 was found to fully capture target percentage sums of squares in the GE interaction pattern. The biplot based on the first bilinear AMMI model terms indicated that genotype 7 (DBSP02/9) and genotype 19 (DBSP03/16) could be suited for cultivation across the test environments. However, no genotype had superior performance in all environments. Reitrivier normal planting date in 2003 (E403) was the most favorable environment for yield, whereas, Upington in 2003 (E603) was the least favorable one. Model comparison criteria showed that AMMI model was superior to joint regression model in terms of its predictive accuracy and efficiency of explaining the pattern of GE sum of squares. It was concluded that AMMI biplot clearly facilitate identification of mega-environments and cultivars for specific recommendations. The differential response of genotypes observed in this study reaffirms the necessity of multi location evaluations to identify superior and stable genotypes. However, trends in specific adaptation could be detected using the which-won-where pattern of the AMMI analysis, and site-specific breeding may be exploited when feasible.

RESPONSE OF COTTON GROWTH AND PRODUCTIVITY TO APPLICATION OF POTASSIUM AND ZINC UNDER NORMAL AND LATE SOWING DATES

Two field experiments were carried out in Sakha Agric. Res. Sta., Kafr El-Sheikh Governorate, Egypt during two growing seasons (2007 and 2008) using the Egyptian cotton cultivar Giza 86 (G. barbadense, L.), to study the response of cotton growth and productivity to application of potassium and zinc under two planting dates. The experimental design was split-plot with four replications. The main-plots were assigned to two planting dates, i.e., normal planting date on March 30th and late planting date on April 30th. The sub-plots included six potassium and zinc fertilization treatments i.e., two soil application levels (24 and 48 kg K2O/fed.) alone or with the foliar application of zinc at the level of 0.5 g Zn SO4/liter. Potassium was also tried as foliar application at the level of 5 kg K2SO4/fed. alone or with the abovementioned level of zinc. Soil added potassium was applied at thinning, while foliar added one was partly sprayed at the beginning of flowering and two weeks later. Zinc was sprayed once at beginning of flowering. The results indicated that sowing date gave significant effects on all growth parameters; no. of open bolls/plant, boll weight, no. of plants/fed. at harvest, seed index and seed cotton yield/fed., upper half mean length, micronaire reading, reflectance and yellowness in favour of early planting. Sowing date did not exhibit any significant on lint %, uniformity index, fiber strength and fiber elongation % in both seasons. Foliar application of potassium along with the foliar application of zinc gave a significant increase in plant height at harvest, no. of nodes/plant, no. of sympodia/plant, no. of open bolls/plant, boll weight, seed index and seed cotton yield (ken./fed.) as compared with the other fertilization treatments. The efficiency use of heat units by cotton plants increased in favour of normal sowing rather than in late sowings. The foliar application of potassium and zinc treatments did not exhibit any significant effect on all fiber quality traits in both seasons. It could be concluded that the foliar application of 5 Kg K2SO4/fed. sprayed partly twice + foliar application of 0.5 g ZnSO4/L once at beginning of flowering stage could be recommended to increase the yield and its components under normal or late sowing dates., for Giza 86 variety, under Sakha region condition at Kafr El-Sheikh Governorate.

INHERITANCE OF YIELD AND ITS COMPONENTS IN SOME BREAD WHEAT ( TRITICUM A ESTIVUM) CROSSES UNDER HEAT STRESS

Six bread wheat genotypes namely Giza164, Giza168, Sidsl, Sids7, Sahka93 and Debeira were used to study. The inheritance of grain yield and its components i.e. number of spikes/plant, number of kernels/spike and kernels weight, using a half-diallel cross in the F1 and F2 generations. The parental genotypes, F1 hybrids and F2 populations were grown in a randomized complete block design with three replicates under normal and Late sowing conditions (heat stress). Results exhibited that late sowing reduced number of spikes/plant, number of kernels/plant, kernels weight and grain yield/plant by (13.17 and 11.65 %), (11.76 and 7.50 %), (9.98 and 15.78%) and (21.82 and 27.27 %) for FI and F2 generation, respectively as compared with normal planting date. The best parents under the two sowing dates were Debeira for number of spikes /plant, Skis 7 for number of kernels /spike and kernels weight, Sids 1 for grain yield and Sakha 93 under the recommended planting date. The most promising F2 populations in grain yield were (P1xP3), (PixPe.), (P3xP6) and. (P.,x1,5) under normal conditions. Heat stress index values showed that the heat tolerant parents were Sids 7, Giza 164 for number of spikes/plant, Sids 1 and Debelra for number of kemels/spike, Sids 1 for kernels weight and Sids 7 for grain yield. The promising F2 populations for heat tolerance were (P1xP6), (PixPs), (P2xPs) and (P2xP3) and selection could be practiced in these populations for grain yield and/or its components. Both additive and non-additive gene effects were important in the genetic system for yield and its components. The additive gene effects were the most prevalent type under both sowing dates for these characters except for grain yield in F1 under late sowing and in F2 populations under both sowing dates. The parents showed more positive alleles for all traits in both generations under both sowing dates except for kernels weight in the Fr and F2 generations under recommended planting. Broad-sense heritability values varied from intermediate to high in all characters. Narrow-sense heritability values intermediate to low in all characters. These results indicate that these characters could be affected by dominance effects and environmental factors. From the previous results we can conduded that selection in segregation generation could be effective to produce lines have high grain yield under heat stress.

Growing degree day and sunshine radiation effects on peanut pod yield and growth

Growth and development of peanut (Arachis hypogaea L.) are affected by different uncontrollable environmental conditions. The objective of this work was to investigate the effect of different planting dates, thermal temperatures (growing degree days, GDD) and daily sunshine duration on morphological and agronomic traits of three commercial peanut cultivars (Gazipasa, Florispan, and NC-7) and a local cultivar. Experiments were carried out at four different planting dates in the Aegean region of Turkey during 2004 and 2005. The experimental design was a split-plot design with three replications. Planting date affected emergence, beginning of flowering, beginning gynophore formation, primary branch number, primary branch length, days to maturity and pod yield. Pod yield was significantly correlated with the primary branch length, GDD, sunshine radiation during gynophore formation, time to maturity and days from emergence to flowering. The Aegean climate has a long growing period and is a suitable environment for peanut growth. Peanut cultivars are exposed to suitable temperature regimes and sunshine during the vegetative and reproductive growth stages in the early and normal planting dates in the Aegean region. On the contrary, the peanut cultivars planted in the late planting stage were negatively affected in the vegetative and reproductive growth stages. The peanut cultivars were stressed in the late planting because of the shortened growth period and unsuitable growing conditions. Early planting, ranging from May 5 – 20, provided the essential 1450 and 1600°C GDD and 893 – 978 h of sunshine during the reproductive stage for peanuts grown in the Aegean region. The best suitable planting date was May 20 and Gazipa
a and the Local cultivar were the most promising cultivars for conditions typical of the Aegean region.

Evapotranspiration and responses to irrigation of broccoli

In cold, semi-arid areas, the options for crop diversification are limited by climate and by the water supply available. Growing irrigated crops outside the main season is not easy, because of climatic and market constraints. We carried out an experiment in Albacete, Central Spain, to measure the water use (evapotranspiration, ET) of broccoli ( Brassica oleracea L. var . italica Plenck) planted in late summer and harvested at the end of fall. A weighing lysimeter was used to measure the seasonal ET under sprinkler irrigation. Consumptive use reached 359 mm for a period of 109 days after transplanting. The crop coefficient ( K c) for broccoli was obtained and compared to the standard recommendations for normal planting dates. Dual crop coefficient computations of the lysimeter ET data indicated that evaporation represented 31% of seasonal ET. An analysis of the variation in daily K c values at a time of full cover suggested that the use of a grass lysimeter as a reference ET (ET o) was superior to using the ASCE Penman–Monteith (ASCE PM) equation at hourly time steps, which in turn caused less variability in K c than when using the FAO-56 Penman–Monteith (FAO-56 PM) equation at daily time steps for the ET o calculation. An additional experiment aimed at evaluating the yield response to applied irrigation water by the drip method (seven treatments, from 59 to 108% of ET c) generated a production function that gave maximum yields of near 12 t ha −1 at an irrigation level of 345 mm, and a water use efficiency of 3.37 kg m −3. It is concluded that growing broccoli in the fall season is a viable alternative for crop diversification, as the lower yields obtained here may be more than compensated for by the higher produce prices in autumn, at a time of the year where irrigation water demand for other crops is very low.

Soybean Response to Plant Population at Early and Late Planting Dates in the Mid‐South

The widespread adoption of glyphosate [N‐(phosphonylmethyl)‐glycine]‐resistant soybean [Glycine max (L.) Merr.] and the increased cost of soybean seed have generated interest in determining the minimum plant population needed for maximum yield. The objective of this study was to determine yield and economic return responses to plant population for normal and late planting dates. Cultivars with relative maturities of 2.8 to 4.9 were planted at five seeding rates (43,000 to 560,000 seeds ha−1) in May and/or June in 38‐cm rows during 2003 to 2005. The effect of plant population on both yield and economic return was explained with a variation of a Mitscherlich equation. Optimum plant population (OPP) and economically optimum plant population (EOPP) were defined as those resulting in 95% of the estimated yield or estimated economic return, respectively, at the maximum plant population. Optimum plant population ranged from 108,000 to 232,000 plants ha−1 for May planting dates and 238,000 to 282,000 plants ha−1 for June planting dates. Economically optimum plant populations were 7 to 33% less than OPPs. Complete canopy cover at R1 produced maximum yield in 8 of 10 comparisons. These results suggest that seeding rates below those that are currently recommended could lower seed costs without reducing yield.

Nitrogen Fertility and Planting Date Effects on Lint Yield and Cry1Ac (Bt) Endotoxin Production

Early planted cotton (Gossypium hirsutum L.) and varieties expressing the Bacillus thuringiensis (Bt) gene offer improved yield potential. It is not clear whether the current N recommendations remain appropriate for these new production options. The objectives were to determine how varying rates, application timing, and sources of N affected cotton dry matter partitioning, leaf chlorophyll (Chl) concentration, leaf Bt (Cry1Ac) endotoxin concentration, lint yield, and fiber quality. Four N treatments (112 kg N ha−1 anhydrous; 112 kg N ha−1 liquid; 112/56 kg N ha−1 split; 56/56 kg N ha−1 split) were applied to three cotton varieties (PM 1218BR, STV 4691B, and FM 832) planted on either an early or normal planting date from 2001 through 2004. The N response was consistent across planting dates and varieties for all data collected as shown by the lack of any interactions with these variables. Although N treatments had no effect on lint yield or any dry matter partitioning components, plants receiving the 112/56 kg N ha−1 split application treatment exhibited 14% greater leaf Cry1Ac concentration and a 3% greater leaf Chl concentration than the other N treatments. Early planted cotton had 5% greater leaf Chl concentration but a 12% lower leaf Cry1Ac concentration than normal planted cotton. Lower Cry1Ac levels may reflect enhanced remobilization of the leaf protein to feed the faster developing boll load of the early planted cotton. Early planted cotton yielded 10% more than normal planted cotton because it produced 9% more bolls. Current N recommendations for normal planted cotton also appear sufficient for early planted cotton.

Potential impacts of climate change on the grain yield of maize for the midlands of KwaZulu-Natal, South Africa

Abstract The increase in atmospheric carbon dioxide concentration and changes in associated climatic variables will likely have a major influence on regional as well as international crop production. This study describes an assessment of simulated potential maize ( Zea mays ) grain yield using (i) generated weather data and (ii) generated weather data modified by plausible future climate changes under a normal planting date and dates 15 days earlier and 15 days later using CropSyst, a cropping systems simulation model. The analysis is for maize production at Cedara, a summer rainfall location within the midlands of KwaZulu-Natal, South Africa. Baseline weather data input series were generated by a stochastic weather generator, ClimGen, using 30 years of observed weather data (1971–2000). The generated baseline weather data series was similar to the observed for its distributions of daily rainfall and wet and dry day series, monthly total rainfall and its variances, daily and monthly mean and variance of precipitation, minimum and maximum air temperatures, and solar radiant density. In addition, Penman-Monteith daily grass reference evaporation (ET o ) calculated using the observed and generated weather data series were similar except that the ET o values between 2 and 3 mm were less for the observed than for the corresponding generated values. Maize grain yields simulated using the observed and generated weather data series with different planting dates were compared. The simulated grain yields for the respective planting dates were not statistically different from each other. However, the grain yields simulated using the generated weather data had a significantly smaller variance than the grain yields simulated using the observed weather data series. The generated baseline weather data were modified by synthesized climate projections to create a number of climatic scenarios. The climate changes corresponded to a doubling of carbon dioxide concentration to 700 μl l −1 without air temperature and water regime changes, and a doubling of carbon dioxide concentration accompanied by mean daily air temperature and precipitation increases of 2 °C and 10%, 2 °C and 20%, 4 °C and 10%, and 4 °C and 20%, respectively. The increase in the daily mean minimum air temperature was taken as three times the increase in daily mean maximum air temperature. Input crop parameters of radiation use and biomass transpiration efficiencies were modified for maize in CropSyst, to account for physiological changes due to increased carbon dioxide concentration. Under increased carbon dioxide concentration regimes, maize grain yields are much more affected by changes in mean air temperature than by precipitation. The results indicate that analysis of the implications of variations in the planting date on maize production may be most useful for site-specific analyses of possible mitigation of the impacts of climate change through alteration of crop management practices.

GENETIC PARAMETERS OF SOME AGRONOMIC TRAITS IN YELLOW MAIZE UNDER TWO PLANTING DATES

Six population’s seeds of four yellow maize crosses were formed during 2001 and 2002 growing seasons. Their plants were evaluated during 2003 growing season under two planting dates (14th May and 29th June) for six agronomic traits at the Agric. Res. Stat. of Fac. of Agric., Ain Shams Univ., Shalakan, Kalubia Gover-norate, Egypt. The present work aimed to determine the genetic parameters and their interactions with planting dates for grain yield per plant, 100-kernel weight, number of kernels per row, ear length, ear diameter, and days to silking in the six popula-tions (P1, P2, F1, F2, BC1 and BC2). Mean values of the six populations for all studied traits in all crosses were higher under normal planting date than those under late one. Therefore, normal planting date seemed to be non-stress environment. The potence ratio for all traits in the four crosses exceeded (+1) except days to silking where it was less (-1). The highest heterosis percentage relative to mid and better parent reached 192.06% and 152.01% in cross 1 for grain yield per plant under late plant-ing date. Inbreeding depression values were not-significant in all studied traits ex-cept ear diameter and 100-kernel weight in crosses 1 and 3 as well as grain yield per plant in all crosses also, it was positive for most studied characters in the four cross-es except days to silking trait. Dominance occupied the first rank, additive or domi-nance type of epistasis occupied the second or the third contributor to the genetic ef-fects in order of importance according to cross with exception of days to silking, where additive and additive occupied the first and the second ranks. Narrow sense heritability was relatively high for yield attributes whereas it was low for grain yield per plant. Meantime, expected genetic advance was relatively moderate or low for all traits. Therefore, it could be suggested that selection for most studied traits in the subsequent generations will be relatively more effective than in the early genera-tions.

CORRELATION AND PATH COFFICIENT ANALYSIS IN FOUR YELLOW MAIZE CROSSES UNDER TWO PLANTING DATES

F1 and F2 seeds of four crosses were formed during 2001 and 2002 growing sea-sons. The F2 population’s plants were evaluated during 2003 growing season under the two planting dates (14th May and 29th June) to estimate the phenotypic correla-tion coefficients among eight plants characters and their contributions in the varia-tion of grain yield/ plant at the Agric. Res. Stat. of Fac. of Agric., Ain Shams Univ., Shalakan, Kalubia Governorate, Egypt. Results showed that grain yield/ plant under normal planting date correlated positively and significantly - in most cases - with each of ear diameter, ear length, number of kernels/ row, 100-kernel weight, number of rows/ ear, ear height, plant height and days to silking, while under late planting date, it correlated with each of number of kernels/ row, ear diameter, 100-kernel weight, ear length, number of rows/ ear, ear height and days to silking. Path coeffi-cient analysis estimates indicated that ear diameter; ear length and number of ker-nels/ row can be considered as the most important sources of plant grain yield varia-tion under normal planting date while, under late planting date they were number of kernels/ row, ear diameter, 100-kernel weight and ear length. It was concluded that each of ear diameter, ear length and ear length through its indirect effects via ear di-ameter are considered as the most important sources of plant grain yield variation.

Effects of Planting Date, Genotype, and Their Interactions on Sunflower Yield

Sunflower (Helianthus annuus L.) yields are strongly reduced by late sowing dates. The objectives of this study were to investigate the physiological bases of the sowing date (S), genotype (G), and genotype × sowing date (G × S) interaction effects on sunflower yield and contribute to development of ideotype-based selection strategies for improving yield at late plantings. Nine differentially adapted hybrids were evaluated during two seasons at normal and late planting dates at Venado Tuerto, Argentina, by means of the framework that defines oil yield as the product of grain number and weight and oil concentration. Sowing date was the major source of variation for oil yield. The G × S interaction, in turn, accounted for a portion of the total variability four times higher than the contribution of G. The S and G × S interaction effects on grain number were mostly determined by grain set in the central portion of the capitulum. Duration of grain filling was the main determinant of the S and G × S interaction effects on grain weight and grain oil concentration. Variation in grain oil concentration between sowing dates was largely due to changes in kernel oil proportion, rather than changes in kernel percentage. Relative changes in rate of grain filling and kernel percentage also contributed to the observed G × S interactions for grain weight and oil concentration, respectively. Although some degree of compensation among oil yield components underlie the observed G × S interactions, it was found that seed set in the central portion of the head can be used as an indicator of adaptation to late planting dates.

Genotype by environment interaction and indirect selection for yield in sunflower: I. Two-mode pattern analysis of oil and biomass yield across environments in Argentina

A reference set of 10 sunflower hybrids was evaluated in 21 subtropical (northern), temperate (central), and managed environments of Argentina, to identify patterns of genotype-by-environment interaction and opportunities for indirect selection. Pattern analyses showed that the average genotypic discrimination effects of the central and northern regions for oil yield are strongly orthogonal. Photoperiod and minimum temperature would be partially underlying the observed interactions. These patterns are repeatable over seasons, which suggests that central and northern regions are different mega-environments and that selection for specific adaptation to each region would result in a faster genetic progress than selecting for wide adaptation to both regions. Cluster analysis revealed three genotypic groups: northern, central and broadly adapted. All central environments discriminated among genotypes in a similar fashion; discrimination in northern environments was more divergent across years and locations. Late planting dates in a central location associated positively with the northern environments. This represents an opportunity for indirect selection for the northern region from the breeding program headquarters in central Argentina. When photoperiod was extended to 15.5 h in these trials, genotypes exhibited responses similar to those of normal planting dates in central environments, indicating that photoperiod could be a central factor underlying this association. Analysis of specific genotype responses to photoperiod in terms of oil yield showed that these involved traits or processes distinct from time to flowering. Pattern analyses of physiological determinants and components of yield revealed the existence of different specific genotype responses to specific environmental challenges within the same genotype group.

Influence of row spacing reduction on maize grain yield in regions with a short summer

The interest in reducing maize row spacing in the short growing season regions of Brazil is increasing due to potential advantages such as higher radiation use efficiency. This experiment was conducted to evaluate the effect of row spacing reduction on grain yield of different maize cultivars planted at different dates. The trial was conducted in Lages, in the State of Santa Catarina, Brazil, during 1996/97 and 1997/98 growing seasons, in a split-split plot design. Early (October 1st) and normal (November 15) planting dates were tested in the main plot; two morphologically contrasting cultivars (an early single-cross and a late double-cross hybrids) were evaluated in the split plots and three row widths (100, 75 and 50 cm) were studied in the split-split plots. The reduction of row spacing from 100 to 50 cm increased linearly maize grain yield. The yield edge provided by narrow rows was higher when maize was sown earlier in the season. Differences in hybrid cycle and plant architecture did not alter maize response to the reduction of row spacing.

Effects of shading and seed tuber spacing on initiation and number of tubers in potato crops (Solanum tuberosum)

Twelve field experiments, carried out over 7 years, examined effects of shading and seed tuber spacing on plant growth, initiation and retention of tubers in four cultivars: Estima, Maris Piper, Maris Peer and Record. Ten of the experiments were carried out at Cambridge and two near Valencia, Spain. Other treatments included in some experiments were floating polythene mulch and planting date.Shading by up to 75% did not affect the timing of onset or cessation of tuber initiation in Estima but shading by 50% or more delayed the completion of tuber initiation in Maris Piper compared with less severe shading. Except for intensely shaded treatments (50% or more), the majority of tubers were initiated in a very short period (4–7 days). Shading by 37% or more during the period of tuber initiation and increasing planting density, decreased number of tubers per stem initiated in all experiments, but number of tubers was not affected by shading at other stages of growth. At Cambridge, effects of shading on number of tubers >10 mm retained later in growth from normal planting dates (March to early May) were similar to effects on number of tubers initiated, but effects were much reduced or absent following later plantings at Cambridge and in both experiments in Valencia. The decreased effects of shading on number of tubers >10 mm at late plantings at Cambridge were associated with the initiation of fewer tubers at these plantings. Effects of shading, planting density and planting date on number of tubers were a consequence of changes in the frequency of occurrence and tuberization of different stolon types. Increasing shading and planting density and delaying planting reduced the number of lateral and branch stolons and the frequency of their tuberization but there were no effects on number of primary stolons or their tuberization. Consequently, at Cambridge a similar number of tubers was borne on primary stolons in shaded and unshaded crops. In Valencia a greater proportion of initiated tubers was retained at final harvest from shaded treatments than at Cambridge, which accounts for the absence of effects of shading on number of tubers >10 mm. The greater retention of tubers late in growth in Spain may have been associated with the higher peak growth rates achieved in higher radiation fluxes than at Cambridge.Linear regressions of the data for normal planting dates at Cambridge and from Valencia indicated that the number of tubers >10 mm late in growth was dependent on the radiation environment during the period of tuber initiation. Radiation flux during the brightest period of the first few days of initiation appeared to be the most crucial aspect of radiation affecting number of tubers. As incident radiation can vary greatly over the short period of tuber initiation, it is potentially an important factor affecting number of tubers in field crops.

Genetic Progress in Reducing Losses to Leaf Rust in CIMMYT‐Derived Mexican Spring Wheat Cultivars

Leaf rust, caused by Puccinia recondita Roberge ex Desmaz., is an important disease of wheat (Triticum aestivum L.) worldwide. To estimate the genetic progress in reducing grain yield losses through breeding for resistance to leaf rust, replicated trials including 15 popular CIMMYT germplasm‐derived wheat cultivars released between 1966 and 1988 in northwestern Mexico were sown in that same area; normal and late planting dates were used for four and two seasons, respectively. Leaf rust epidemics were established by inoculating spreader rows planted adjacent to plots of the cultivars which were not protected by fungicide. Average losses in grain yields of the cultivars due to leaf rust ranged between 6.6 and 62.7% and were highly correlated with final disease severity (r = 0.898, P < 0.01) and relative area under the disease progress curve (r = 0.917, P < 0.01). The losses in grain yield were mostly due to reductions in kernel weight, kernels per square meter, and grain fill rate. Grain yield losses (7.7–10.4%) in slow rusting cultivars Cocoraque 75, Nacozari 76, Opata 85, and Bacanora 88 were similar to those observed in the immune ‘Oasis 86’ (6.6%) or resistant ‘Ciano 79’ (10.2%). The average annual progress in grain yield potential achieved through breeding averaged over the six trials was estimated to be 0.48% (r2 = 0.38, P < 0.01) for fungicide protected and 2.21% (r2 = 0.47, P < 0.01) when not protected by fungicide. We conclude that while the grain yield potential of CIMMYT‐derived cultivars has increased significantly over the years, progress in protecting this yield potential through the incorporation of genes that confer slow rusting resistance has been more dramatic.