Search

In recent years, the application of remote sensing techniques is gaining a growing interest and importance in agriculture. Researchers often combine data from near-infrared and red spectral bands a...

Background: In breeding programs, the selection of cultivars with the highest yield potential consisted in the selection of the yield per se, which resulted in cultivars with higher grains per spike (GN) and occasionally increased grain weight (GW) (main numerical components of the yield). In this study, quantitative trait loci (QTL) for GW, GN and spike fertility traits related to GN determination were mapped using two doubled haploid (DH) populations (Baguette Premium 11 × BioINTA 2002 and Baguette 19 × BioINTA 2002). Results: In total 305 QTL were identified for 14 traits, out of which 12 QTL were identified in more than three environments and explained more than 10% of the phenotypic variation in at least one environment. Eight hotspot regions were detected on chromosomes 1A, 2B, 3A, 5A, 5B, 7A and 7B in which at least two major and stable QTL sheared confidence intervals. QTL on two of these regions (R5A.1 and R5A.2) have previously been described, but the other six regions are novel. Conclusions: Based on the pleiotropic analysis within a robust physiological model we conclude that two hotspot genomic regions (R5A.1 and R5A.2) together with the QGW.perg-6B are of high relevance to be used in marker assisted selection in order to improve the spike yield potential. All the QTL identified for the spike related traits are the first step to search for their candidate genes, which will allow their better manipulation in the future. EEA Marcos Juárez Fil: Pretini, Nicole. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina Fil: Pretini, Nicole. Universidad Nacional del Noroeste de la Provincia de Buenos Aires (UNNOBA). Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina. Fil: Vanzetti, Leonardo Sebastian. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Marcos Juárez; Argentina Fil: Vanzetti, Leonardo Sebastian. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Departamento de Trigo; Argentina Fil: Donaire, Guillermo. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Marcos Juarez; Argentina. Fil: González, Fernanda Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina. Fil: González, Fernanda Gabriela. Universidad Nacional del Noroeste de la Provincia de Buenos Aires (UNNOBA). Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino; Argentina.

Population growth has been closely associated with agricultural production, since the first famine predicted by Malthus (1798) up to the Green Revolution of the past century. Today, we continue to face increasing demand for food and crop production (Tilman et al., 2011). Considering the combined caloric or protein content of the 275 major crops used directly as human foods or as livestock and fish feeds, Tilman et al. (2011) forecast a 100% increase in global demand for crops from 2005 to 2050. Meeting this demand with the lowest impact on the environment could be achieved by sustainable intensification of existing cropland with reduced land clearing (Tilman et al., 2011; Fischer and Connor, 2018). EEA Pergamino Fil: González, Fernanda G. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Pergamino. Departamento de Ecofisiología; Argentina Fil: González, Fernanda G. Universidad Nacional del Noroeste de la Provincia de Buenos Aire. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires (CITNOBA, CONICET- UNNOBA-UNSADA); Argentina Fil: Manavella, Pablo A. Universidad Nacional del Litoral. Facultad de Bioquímica y Ciencias Biológicas. Instituto de Agrobiotecnología del Litoral (CONICET-UNL); Argentina

Fruiting efficiency (FE, grains per g of spike dry weight at anthesis) was proposed as a promising spike trait to improve wheat yield potential, based on its functional relationship with grain number determination and the evidence of trait variability in elite germplasm. During the last few years, we have witnessed great advances in the understanding of the physiological and genetic basis of this trait. The present review summarizes the recent heritability estimations and the genetic gains obtained when fruiting efficiency was measured at maturity (FEm, grains per g of chaff) and used as selection criterion. In addition, we propose spike ideotypes for contrasting fruiting efficiencies based on the fertile floret efficiency (FFE, fertile florets per g of spike dry weight at anthesis) and grain set (grains per fertile floret), together with other spike fertility-related traits. We also review novel genes and quantitative trait loci available for using marker-assisted selection for fruiting efficiency and other spike fertility traits. The possible trade-off between FE and grain weight and the genes reported to alter this relation are also considered. Finally, we discuss the benefits and future steps towards the use of fruiting efficiency as a selection criterion in breeding programs.

In breeding programs, the selection of cultivars with the highest yield potential consisted in the selection of the yield per se, which resulted in cultivars with a higher grain number per spike (GN) and occasionally higher grain weight (GW) (main numerical components of the yield). This task could be facilitated with the use of molecular markers such us single nucleotide polymorphism (SNP). In this study, quantitative trait loci (QTL) for GW, GN and spike fertility traits related to GN determination were mapped using two double haploid (DH) populations (Baguette Premium 11 x BioINTA 2002 and Baguette 19 x BioINTA 2002, BP11xB2002 and B19xB2002). Both populations were genotyped with the iSelect 90K SNP array and evaluated in four (BP11xB19) or five (B19xB2002) environments. We identify a total of 305 QTL for 14 traits, however 28 QTL for 12 traits were considered significant with an R2 > 10% and stable for being present at least in three environments. There were detected eight hotspot regions on chromosomes 1A, 2B, 3A, 5A, 5B, 7A and 7B were at least two major QTL sheared confident intervals. QTL on two of these regions have previously been described, but the other six regions were never observed, suggesting that these regions would be novel. The R5A1 (QSL.perg-5A, QCN.perg-5A,QGN.perg-5A) and R5A.2 (QFFTS.perg-5A, QGW.perg-5A) regions together with the QGW.perg-6B resulted in a final higher yield suggesting them to have high relevance as candidates to be used in MAS to improve yield.Author contribution statementKey message28 stable and major QTL for 12 traits associated to spike fertility, GN and GW were detected. Two regions on 5A Ch., and QGW.perg-6B showed direct pleiotropic effects on yield.

Spike fruiting efficiency (FE), defined as grains per unit of spike dry weight at anthesis (SDWa) is a promising trait for improving grain number (GN) in wheat (Triticum aestivum L.). It is often estimated at maturity as the grains per unit of chaff or FE at maturity (FEm). The fertile floret efficiency (FFE), defined as fertile florets per unit of SDWa, and grain set (GST), or the number of grains per floret, were studied to better understand FE determination for the first time. Two double haploid populations designed by crossing modern cultivars contrasting for FE [‘Baguette 19’ and ‘Baguette Premium 11’(high FE) × ‘BioINTA2002’ (low FE)] were sown in five environments. The FE and FEm showed an unstable correlation (low or high) among genotypes within environments (caused by variable SDWa–chaff associations), resulting in a worse correlation between GN and FEm than between GN and FE. Therefore, the use of FEm as a surrogate for FE to improve GN may yield lower gains than those expected if FE were used. The narrow-sense heritability of FFE was high but the variability in fertile florets per spike among genotypes within environments was correlated with FFE only in the environments with high SDWa. Despite the close association between FE and FFE, the former was not totally set at anthesis, as GST greatly affected FE and GN. Selecting for higher FFE and GST, where genotype × environment effects determine heavy spikes at anthesis, is an alternative to breeding for improved GN. Fil: Pretini, Nicole. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Gazaba, Luciana N.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Donaire, Guillermo M.. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuaria Marcos Juárez; Argentina Fil: Arisnabarreta Dupuy, Sebastián. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Vanzetti, Leonardo Sebastián. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Córdoba. Estación Experimental Agropecuaria Marcos Juárez; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina Fil: González, Fernanda Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina

This study identified and validated two QTL associated with spike fertile floret and fruiting efficiencies. They represent two new loci to use in MAS to improve wheat yield potential. The spike fruiting efficiency (FE—grains per unit spike dry weight at anthesis, GN/SDW) is a promising trait to improve wheat yield potential. It depends on fertile floret efficiency (fertile florets per unit SDW—FFE, FF/SDW) and grain set (grains per fertile floret—GST). Given its difficult measurement, it is often estimated as the grains per unit of nongrain spike dry weight at maturity (FEm). In this study, quantitative trait loci (QTL) were mapped using a double haploid population (Baguette 19/BIOINTA 2002, with high and low FE, respectively) genotyped with the iSelect 90 K SNP array and evaluated in five environments. We identified 37 QTL, but two were major with an R2 > 10% and stable for being at least present in three environments: the QFEm.perg-3A (on Chr. 3A, 51.6 cM, 685.12 Mb) for FEm and the QFFE.perg-5A (on Chr. 5A, 42.1 cM, 461.49 Mb) for FFE, FE and FEm. Both QTL were validated using two independent F2 populations and KASP markers. For the most promising QTL, QFFE.perg-5A, the presence of the allele for high FFE resulted in + 4% FF, + 9% GN, + 13% GST, + 16% yield gSDW−1 and + 5% yield spike−1. QFEm.perg-3A and QFFE.perg-5A represent two new loci to use in MAS to improve wheat yield potential.

Improvement of grain yield (GY) at farm level, which is closely related to GY potential, seems to be the main alternative to increase wheat (Triticum aestivum L) production. The aim of current research was to assess the genetic progress of GY potential and associated physiological traits as well as the GY stability under diverse environments of cultivars released to the Argentine market during the last five decades (1971–2011). Ten cultivars, classified into two groups of five according to the time to anthesis in late cycle (LC) and early cycle cultivars (EC), were grown under twelve environments (E1 to E12) in Pergamino, Argentina. The environmental index of GY (average of cultivar’s GY in each environment) ranged from 174 to 602 g m−2. Under potential conditions (E1 to E3, 602 to 548 g m−2), GY improved at 0.74 % per year of release (YOR) (or 4.20 g m−2 per YOR) across all cultivars. The harvest index (HI), particularly in LC, and total biomass produced at physiological maturity (BTPM), associated with crop growth rate during stem elongation (CGRSE) and total biomass produced at anthesis (BTA), particularly in EC, were improved by breeding explaining the GY potential increase. Maximum HI reached 0.46, suggesting it can be further improved in both groups, but pre-anthesis growth should continue increasing in EC, as it seemed to be a yield-limiting trait for these cultivars. Grain number per m−2 (GN) increased by recent breeding in both groups with no change in grain weight (GW). This was a consequence of greater grain number per spike (GNS) in EC, as expected, but higher spike number per m−2 (SN) in LC. Fruiting efficiency (FE, grains g−1 of spike dry weight at anthesis -SDWA-), rather than SDWA, seems to have been improved by recent breeding, turning it a key trait to further increase GN. Finally, modern cultivars out-yielded the old ones in a wide range of environments, suggesting that wide adaptation is a valid breeding strategy for Argentine conditions.

tThe use of physiological traits for indirect selection may help to increase wheat yield potential. Fruitingefficiency (FE, grain number per unit of spike dry weight at anthesis −SDWa-) may be an alternativeto increase grain number per unit area (GN), but the possible cross-over genotype (G) × environment(E) interaction and trade-off with SDWa and grain weight (GW) may limit its usefulness. The presentpaper aimed to determine (i) the degree of G × E interaction of FE at plot, main stem and tiller levels,(ii) the relationship between GN and FE, and (iii) the possible trade-off between FE and (a) SDWa, and(b) GW. Three FE contrasting genotypes (B11 and B19 ? high FE, and B2002 ? low FE) were grown underdifferent Nitrogen (N) availability at sowing [(i) low ? Ni: ca. 50 kg N ha−1; (ii) middle −130 kg N ha−1and (iii) high −200 kg N ha−1). Two other treatments were applied within the 200N: (iv) late sowing, i.e.delaying sowing 30 days in relation to optimum date (200N + LS) and (v) shading the canopy during stemelongation (200N + SH). The FE showed G × E interaction (year × genotype and genotype × treatment) butit only explained 13.4% of its variation. The environment (year) had similar impact than the genotype,explaining both ca. 38% of FE variation (19% each). The FE of tiller spikes was higher than that of mainstem spikes, but the difference among cultivars was maintained. Thus, canopies of the same genotypewith different proportion of main stem and tiller spikes may present different FE value at plot level.Nevertheless, a high correlation (r = 0.82, p < 0.0001) and a close 1:1 relationship was observed between FEat plot level and FE in main stems, for all treatments and cultivars, suggesting that sampling the main stemspikes represents the FE at plot level in dense canopies. A G × E cross-over interaction was observed whenthe sowing was delayed one month (200N + LS) from the optimum date because B19 reached anthesislater than B2002, exploring higher heat stress index (◦Ch > 27◦C) around anthesis, which reduced FE.The correlation of GN with FE was high and significant (r = 0.74, p < 0.00001) for all treatments and fora wide range of SDWa values (from 90 to 188 g m−2). The B19, selected as a high FE genotype, showedhigher GN than B2002 (selected as a low FE genotype) under all treatments, while B11 (also of high FE)showed similar or higher GN than B2002, depending on treatment. Thus, despite the G × E interaction, thegenotypes with higher FE had more GN under a wide range of environments. Nevertheless, the SDWa andGW were negatively correlated with FE (for SDWa r = −0.73 p < 0.005, without considering 200N + SH; andfor GW r = −0.48 p < 0.01 for all treatments or r = −0.75 p < 0.08 for genotypes only). Then, special attentionshould be given to SDWa and GW when selecting for higher FE in a breeding program. Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Miralles, Daniel Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina Fil: González, Fernanda Gabriela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina

Coupling anthesis date to the most suitable environmental conditions is critical for wheat (Triticum aestivum L.) adaptation and yield potential. Development to anthesis is controlled by temperature and photoperiod. Response to photoperiod is chiefly modulated by Ppd-1 genes, but their effect on the quantitative response to photoperiod of (i) time to anthesis and (ii) pre-anthesis phases remains largely unknown. A photoperiod-sensitive spring cultivar, Paragon, and near-isogenic lines of it carrying different combinations of Ppd-1a insensitivity alleles were tested under a wide range of photoperiods, including switches in photoperiod at the onset of stem elongation. Using multimodel inference we found that Ppd-1a alleles reduced photoperiod sensitivity of (i) emergence to anthesis and (ii) emergence to onset of stem elongation, both in a less than additive manner, while threshold photoperiod and intrinsic earliness were unaffected. Sensitivity to current photoperiod from onset of stem elongation to flag leaf and from then to anthesis was milder than for previous phases and was not related to variability in Ppd-1. However, 'memory' effects of previously experienced photoperiod on the duration from onset of stem elongation to flag leaf were related to variability in Ppd-1. The characterization and quantification provided here of the effects on development of Ppd-1 allelic combinations should help increase accuracy of genotype-to-phenotype models in predicting wheat phenology.

Transgenic wheat expressing the sunflower transcription factor HaHB4 outyields the wild type by 6% when tested in the field during 9 years across 37 contrasting environments., HaHB4 is a sunflower transcription factor belonging to the homeodomain-leucine zipper I family whose ectopic expression in Arabidopsis triggers drought tolerance. The use of PCR to clone the HaHB4 coding sequence for wheat transformation caused unprogrammed mutations producing subtle differences in its activation ability in yeast. Transgenic wheat plants carrying a mutated version of HaHB4 were tested in 37 field experiments. A selected transgenic line yielded 6% more (P

Water deficit has been signaled as an important determinant of grain yield (GY) gaps between potential and actual GYs. Breeding for improved water as well as solar radiation productivities is a sustainable means to reduce this gap. The aim of this study was to evaluate breeding effects on GY and its physiological determinants, including water (WUE) and radiation (RUE) use efficiencies, of temperate maize hybrids grown under a wide range of environmental conditions in Argentina. We hypothesized that breeding focused on GY performance and broad adaptation produced an increase in crop biomass linked to an increased tolerance to adverse growing conditions, a trend associated with an increase in WUE and/or RUE. For this purpose, hybrids were grown under three stand densities and eight environmental conditions in the main target environment for the production of temperate hybrids in Argentina. Analyzed traits were GY, total shoot biomass (BT) production, harvest index (HI = GY/BT), crop evapotranspiration (ETC), crop radiation interception (IPARC: cumulative amount of intercepted incident photosynthetically active radiation), radiation use efficiency (RUE = BT/IPARC), water use efficiency (WUE) for biomass production (WUEB,ETc= BT/ETC) and WUE for GY production (WUEGY,ETc= GY/ETC). No breeding effect was registered on ETC and IPARC, whereas significant breeding effects (P

The original article was corrected. Author Muhammad Kundi should instead read: Muhammad Sohail.

To accelerate genetic gains in breeding, physiological trait (PT) characterization of candidate parents can help make more strategic crosses, increasing the probability of accumulating favorable alleles compared to crossing relatively uncharacterized lines. In this study, crosses were designed to complement “source” with “sink” traits, where at least one parent was selected for favorable expression of biomass and/or radiation use efficiency—source—and the other for sink-related traits like harvest-index, kernel weight and grains per spike. Female parents were selected from among genetic resources—including landraces and products of wide-crossing (i.e. synthetic wheat)—that had been evaluated in Mexico at high yield potential or under heat stress, while elite lines were used as males. Progeny of crosses were advanced to the F4 generation within Mexico, and F4-derived F5 and F6 generations were yield tested to populate four international nurseries, targeted to high yield environments (2nd and 3rd WYCYT) for yield potential, and heat stressed environments (2nd and 4th SATYN) for climate resilience, respectively. Each nursery was grown as multi-location yield trials. Genetic gains were achieved in both temperate and hot environments, with most new PT-derived lines expressing superior yield and biomass compared to local checks at almost all international sites. Furthermore, the tendency across all four nurseries indicated either the superiority of the best new PT lines compared with the CIMMYT elite checks, or the superiority of all new PT lines as a group compared with all checks, and in some cases, both. Results support—in a realistic breeding context—the hypothesis that yield and radiation use efficiency can be increased by improving source:sink balance, and validate the feasibility of incorporating exotic germplasm into mainstream breeding efforts to accelerate genetic gains for yield potential and climate resilience.

The identification of physiological traits that determine grain number (and yield) in modern cultivars, and the possible tradeoffs among them, may help to detect promising traits for breeding to increase yield potential. High-yielding Argentinean wheat (Triticum aestivum L.) cultivars were grown under irrigated and high-input conditions during two seasons to study (i) yield and grain number m ―2 (GN) as a result of stover biomass at harvest (SH) and harvest index (HI); and (ii) spike dry weight at anthesis (SDW a ; g m ―2 ) and spike fertility index (SFI; grain number per gram of spike chaff or non-grain spike biomass). Duration of the stem elongation phase (SEP; first node detectable to anthesis) was analyzed as an alternative to increase SDW a . The HI was highly associated with yield differences between cultivars for both years, independently of stem height. In contrast, SH did not vary among cultivars in either season (P > 0.05). The GN determined yield differences between cultivars and was highly associated with SFI and SDW a for both years and cycles. Some cultivars with the same anthesis date showed stable variation for duration of the SEP between years (despite the year x cultivar interaction observed). As the SFI and duration of the SEP were not related, it seems promising to increase GN in a cultivar with high SFI through an increased duration of the SEP (which may yield higher SWD a ) or vice versa.

Further improvements in wheat yields are critical, for which increases in grain number would be required. In the recent past, higher grain number was achieved through increased growth of the juvenile spikes before anthesis, due to the reduction in stem growth. As current cultivars have already an optimum height, alternatives must be identifi ed for further increasing grain number. One of them is increasing fruiting effi ciency (grains set per unit of spike dry weight at anthesis). Fruiting effi ciency is the fi nal outcome of the fate of fl oret development and differences in this trait within modern cultivars would be related to higher survival of fl oret primordia. Then there are two alternative physiological pathways to improve fruiting effi ciency by allowing a normal development of most vulnerable fl oret primordia: an increased allocation of assimilates for the developing fl orets before anthesis, or reduced demand of the fl orets for maintaining their normal development. Both alternatives may be possible, and it might be critical to recognize which of them is the actual cause of differences in fruiting effi ciency. When considering this trait in breeding we must be aware of potential trade- offs and therefore it must be avoided that increases in fruiting effi ciency be constitutively related to decreases in either spike dry weight at anthesis or grain weight. In this review we described fruiting effi ciency and its physiological bases, analyzing genetic variation and considering potential drawbacks that must be taken into account to avoid increases in fruiting effi ciency being compensated by other traits Fil: Gustavo A. Slafer. AGROTECNIO; España. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. Institució Catalana de Recerca i Estudis Avançats; España Fil: Elia, Mónica. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. AGROTECNIO; España Fil: Savin, Roxana. Universidad de Lleida. Departamento de Producción Vegetal y Ciencia Forestal; España. AGROTECNIO; España Fil: García, Guillermo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina Fil: Terrile, Ignacio Ismael. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Ferrante, Ariel. The University of Queensland. Queensland Alliance for Agriculture and Food Innovation; Australia Fil: Miralles, Daniel Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal; Argentina Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Lengthening the late reproductive phase (LRP) of stem elongation in wheat (Triticum aestivumL.), by changing its photoperiod sensitivity independently of the preceding phases, would improve the yield potential through increasing spike weight and the number of fertile florets at anthesis. This paper presents results of a two-year field experiment designed to determine the impact of Ppd-D1and Ppd-B1on (i) the duration of three pre-anthesis developmental phases, and (ii) spike weight and the number of fertile florets at anthesis under two photoperiods during the LRP (natural and an extension of six hours over that). Near isogenic lines of Mercia and single chromosome recombinant lines of Cappelle Desprez were used. Under natural photoperiod, Ppd-D1hastened time to anthesis ca. 500∘C d in both backgrounds by reducing each of the three pre-anthesis phases. Ppd-B1hastened the time to anthesis under natural photoperiod by 178∘C d, mainly by reducing the early reproductive phase. The response to photoperiod of the LRP under extended daylength depended on the Ppdlocus present: Ppd-D1was insensitive while Ppd-B1and the recessive controls were sensitive. For all lines, photoperiod treatments and years, the number of fertile florets was associated with spike dry weight at anthesis (R 2≅ 80%, p< 0.01) which, in turn, was positively related to the intercepted radiation accumulated during the LRP (R 2 45%, p< 0.05). Changing the duration of the LRP through extended photoperiod or through Ppd-D1produced similar results in both backgrounds and years. Thus, altering the duration of the LRP by manipulating photoperiod sensitivity may be an alternative to changing the fertile floret number in wheat. Nevertheless, as no particular allele was responsible for the photoperiod sensitivity only during the LRP, new alleles should be studied to identify the control of photoperiod sensitivity of individual phases to fine-tune the pre-anthesis wheat development.

The manipulation of photoperiod sensitivity during stem elongation (terminal spikelet initiation—anthesis) has been suggested as a means to increase wheat yield potential. Nevertheless, photoperiod sensitivity and the interaction with vernalization during that phase have not been previously explored under field conditions. Thus, a field study was carried out (i) to assess whether duration of stem elongation is sensitive to photoperiod experienced only during that phase, and if so (ii) to evaluate whether vernalization interacts with this photoperiod response and (iii) to determine if altering duration of stem elongation may influence wheat yield and its components. The experiment was a factorial combination of two vernalization treatments (15 (V15) or 50 (V50) days at 4±1 °C and 8 h photoperiod), two photoperiod regimes during stem elongation (natural daylength in the field (NP+0) and one daylength extension of 6 h (NP+6)) and three cultivars (Buck Manantial (BM), Eureka Ferrocarril Sur (EFS), and ProINTA Puntal (PP)). The stem elongation phase responded to the actual photoperiod experienced during that phase in the three cultivars, increasing its duration with shorter photoperiod. In the vernalization-sensitive cultivars EFS and PP, plants vernalized 50 days showed greater response to photoperiod than those vernalized 15 days. In the most photoperiod-sensitive cultivar (BM), as duration of stem elongation lengthened by exposure to less inductive photoperiod, a higher number of fertile florets at anthesis was achieved leading to an increased grain number and thereby to a higher wheat yield. These results reinforce the idea that a longer duration of stem elongation may offer an alternative avenue to improve yield potential in wheat.

A longer duration of stem elongation (from terminal spikelet initiation to anthesis) would result in a higher wheat yield potential as a consequence of the increase in both spike dry weight and number of fertile florets at anthesis. It is not clearly understood, however, which processes are involved in the increased spike dry weight and whether this variable accounts for the higher number of fertile florets when duration of stem elongation is modified by photoperiod treatments. As vernalization interacts with photoperiod during the stem elongation phase, a better understanding of the role of vernalization is also required. A field experiment was carried out using two wheat cultivars (Buck Manantial (BM) and Eureka Ferrocarril Sur (EFS)) subjected to diverse periods of vernalization (V 15 and V 50 , plants vernalized for 15 and 50 days, respectively) and exposed to different photoperiods (NP+0 and NP+6, natural and 6 h extended photoperiod, respectively) only during the stem elongation phase. Floret development together with stem and spike growth during the stem elongation phase were studied. When the stem elongation phase was exposed to short photoperiod (i) duration of spike growth increased without any change in its growth rate, and (ii) most of the spike growth occurred during minimum stem growth rate as the onset of maximum stem growth rate was delayed. In EFS, the vernalization-sensitive cultivar, the former (i) and (ii) was true only when vernalization requirements were met. For both cultivars, the survival of the initiated floret primordia under short photoperiod increased, independently of vernalization. Both partitioning of assimilates to the spike and a direct photoperiod effect seemed to have been involved in the survival of floret primordia when the stem elongation phase was exposed to short photoperiod.

It has been established that photoperiod influences the rate of wheat development well beyond the end of the vegetative phase. Conversely, vernalization effects are still assumed to be mainly during the vegetative phase. The aim of the study was to assess the effects of different combinations of vernalization and photoperiods on the developmental characteristics of wheat pre-flowering reproductive phases under field conditions. For this purpose, three high yielding cultivars (ProINTA Puntal, ProINTA Super and Klein Pegaso) were subjected to two vernalization treatments (unvernalized (V0) and vernalized during 56 days in a cool chamber (V56)) and four photoperiod regimes. The photoperiod treatments consisted of the natural photoperiod of the season (NP+0) and daylength extensions over that of 2 (NP+2), 4 (NP+4), and 6 (NP+6) hours. Photoperiod influenced the duration of early (collar—first node detectable) and late (first node detectable—heading) pre-flowering reproductive phases, reducing their durations as photoperiod increased. When cultivars with strong vernalization response (ProINTA Puntal and ProINTA Super) were not vernalized, duration of the early and late pre-flowering reproductive phases increased and the rate of spikelet initiation decreased. Thus, when vernalization requirements were not satisfied, the spikelet initiation rate was even slower than the leaf initiation rate (both expressed in a thermal time base). Results showed significant interactions between photoperiod and vernalization (vegetative phase), or clear, though non-significant, trends to interactive effects (late pre-flowering reproductive phase). Thus, the length of vegetative and late pre-flowering reproductive phases changed in response to photoperiod depending on the level of satisfaction of the vernalization requirements. The relationship between the cumulative number of leaves on the main stem and thermal time fitted a bi-linear model whenever the final leaf number (LNf) was large, e.g. when photoperiod was not extended or vernalization requirements not satisfied. Thus, responses during the pre-flowering reproductive phases were accompanied by an increased phyllochron for leaves emerging after the first 7–8 leaves. This study demonstrated with field grown plants that the length of the late pre-flowering reproductive phase in wheat is sensitive to photoperiod and that the response to this environmental factor could be changed by the level of satisfaction of the vernalization requirements.

A detailed and accurate phenotyping of mapping populations is an important “bottleneck” for the understanding of the phenotype–genotype relationships. Grain number per unit area (GN), the main wheat yield component, can be analyzed through physiological components as spike dry weight at flowering, determined by crop growth rate and biomass partitioning to spike during stem elongation phase, and fruiting efficiency. The phenotypic variability of these physiological traits responsible for variation in GN and the relationships among them was analyzed in an elite wheat doubled-haploid (DH) population grown in two different environments. Positive transgressive segregation (i.e. DH lines that exceed parental phenotypic values) was observed for all GN determining traits, suggesting that increases in GN could be achieved through their improvement. However, focusing on top DH lines, which represent a feasible genetic improvement, fruiting efficiency was the most relevant physiological trait for consistently improving GN, and thereby grain yield, in both environments. Fil: García, Guillermo Ariel. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Serrago, Roman Augusto. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Slafer, Gustavo Ariel. Institució Catalana de Recerca i Estudis Avancats; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina Fil: Reynolds, Matthew P.. Centro Internacional de Mejoramiento de Maíz y Trigo; México Fil: Miralles, Daniel Julio. Universidad de Buenos Aires. Facultad de Agronomía. Departamento de Producción Vegetal. Cátedra de Cerealicultura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina

Improving wheat (Triticum aestivum L.) yield potential via higher grain number per unit area (GN) may reduce average grain weight and consequently the yield increment would be low. Thirty-nine high-yielding modern cultivars differing in spike fruiting efficiency (FE) (number of grains per gram of no-grain spike) were grown under potential conditions during two temperature-contrasting years to study the level of source limitation during grain filling and rank the main physiological determinants of potential grain weight (PGW) and actual grain weight. The response of grain weight to a 100% higher source ranged from 0 to 25%, depending on cultivar and year. No general relationship was observed between PGW and FE. The stabilized grain water content, which was partially correlated with the endosperm cell number per grain (r2 = 48%, p < 0.05), was the main variable associated to grain weight variation (r2 = 77%, p

Further improvements to wheat yield potential will be essential to meet future food demand. As yield is related to the number of fertile florets and grains, an understanding of the basis of their generation is instrumental to raising yield. Based on (i) a strong positive association between the number of fertile florets or grains and spike dry weight at anthesis; and (ii) the finding that floret death occurs when spikes grow at maximum rate, it was always assumed that floret survival depends on the growth of the spike. However, this assumption was recently questioned, suggesting that assimilates diverted to the spike do not determine the number of florets and grains and that the onset of floret death may instead be a developmental process that is not associated with spike growth. In this study, the relationships between the fate of floret primordia and spike growth from six independent experiments that included different growing conditions (greenhouse/field experiments, growing seasons, photoperiod/shading treatments during the floret primordia phase) and diverse cultivar types (winter/spring, semi-dwarf/standard-height, photoperiod sensitive/insensitive) were re-analysed together. Onset of floret death was associated with the beginning of spike growth at the maximum rate in c. 80% of the cases analysed; and the rate of floret death (the main determinant of floret survival) showed a negative quantitative relationship with spike weight at anthesis. As floret death and survival were shown to be linked to pre-anthesis spike growth, the strategy of focusing on traits associated with pre-anthesis spike growth when breeding to increase wheat yield potential further is valuable. Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Miralles, Daniel Julio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina Fil: Slafer, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Institució Catalana de Recerca i Estudis Avancats; España. Universidad de Lleida; España

The wheat spikelet meristem differentiates into up to 12 floret primordia, but many of them fail to reach the fertile floret stage at anthesis. We combined microarray, biochemical and anatomical studies to investigate floret development in wheat plants grown in the field under short or long days (short days extended with low-fluence light) after all the spikelets had already differentiated. Long days accelerated spike and floret development and greening, and the expression of genes involved in photosynthesis, photoprotection and carbohydrate metabolism. These changes started while the spike was in the light-depleted environment created by the surrounding leaf sheaths. Cell division ceased in the tissues of distal florets, which interrupted their normal developmental progression and initiated autophagy, thus decreasing the number of fertile florets at anthesis. A massive decrease in the expression of genes involved in cell proliferation, a decrease in soluble carbohydrate levels, and an increase in the expression of genes involved in programmed cell death accompanied anatomical signs of cell death, and these effects were stronger under long days. We propose a model in which developmentally generated sugar starvation triggers floret autophagy, and long days intensify these processes due to the increased carbohydrate consumption caused by the accelerated plant development. © 2008 The Authors.

Wheat breeding has improved yield potential increasing floret survival through higher dry matter partitioning to the spikes during the stem elongation phase (from terminal spikelet initiation to anthesis). We studied survival of floret primodia in different spikelet positions along the spike in relation to dynamics of spike growth, when dynamics of dry matter partitioning to the spike was altered by photoperiod and shading treatments applied during the stem elongation phase. The cultivar Buck Manantial was exposed to (1) NP+0 un-shaded (natural photoperiod and incoming radiation of the growing season), (2) NP+0 shaded (natural photoperiod but only 33% of the incoming radiation), and (3) NP+6 un-shaded (natural photoperiod extended 6 h and natural incoming radiation). Floret survival increased, depending on spikelet position, 1.1–2.5 fold under un-shaded v. shaded treatments (both under NP+0), and 1.3–1.8 fold under NP+0 v. NP+6 treatments (both un-shaded), without any impact of treatments on the total number of initiated floret primordia. The fate of the floret primordia and its final stage at anthesis were associated with duration of floret development within the stem elongation phase (R2 = 82%, P

Worldwide wheat yields have been only slightly, and non-significantly, increasing during the 90’s, suggesting that they may be levelling off. Considering that there is consensus that large new growing areas will be not introduced and management improvements will be increasingly harder to obtain, genetic improvement would play a more important role to keep rising wheat yields in the future than in the past. In this scenario, the use of physiological bases as a complementary tool to identifying alternative ways for breeding seems to be crucial for breaking the apparent barriers in wheat yields. In this presentation, we attempted to envisage, from published and recent unpublished evidences from our lab, using studies carried out under both controlled and field conditions, some opportunities to manipulate the rate of crop development during the late reproductive phase. This phase has been recognised as critical in terms of yield generation, and the idea of manipulating its response to photoperiod as a tool for increasing yield potential in wheat is reviewed.

Increasing duration of stem elongation by exposure to short photoperiod would result in higher spike dry weight at anthesis, which is positively associated with the number of fertile florets and grains in wheat. However, it is not easy to determine whether photoperiod effects on fertile florets and grains are only mediated by assimilate supply to the growing spike when spike weight variation is attained only with photoperiod treatments. The aim of this study was to determine whether photoperiod effects on number of fertile florets and grains may be direct, that is, not mediated by assimilate supply, by comparing the magnitude of photoperiod effects with those of shading the canopy. Spike dry weight at anthesis was changed through the factorial combination of different photoperiod (natural and 6 h extended photoperiod) and shading (un-shaded and 67 ± 3% shaded) treatments during stem elongation of Buck Manantial, a cultivar known for its photoperiod sensitivity in this phase. Both treatments modified spike dry weight at anthesis and the number of fertile florets and grains, independently. When duration of stem elongation was lengthened by exposure to natural photoperiod and when incident radiation was high, spike dry weight at anthesis increased by 33% (NP+0 v. NP+6) and 27% (un-shaded v. shaded), respectively. The number of fertile florets increased similarly to spike dry weight (34% NP+0 v. NP+6 and 28% un-shaded v. shaded) resulting in higher number of grains. Most photoperiod effects on the number of fertile florets and, consequently, on the number of grains, were mediated by assimilate supply to the growing spike as the same relationship between the number of fertile florets and spike dry weight at anthesis was observed for photoperiod and shading treatments (R2 = 0.99, P

Fine tuning wheat phenology is of paramount importance for adaptation. A better understanding of how genetic constitution modulates the developmental responses during pre-Anthesis phases would help to maintain or even increase yield potential as temperature increases due to climate change. The photoperiod-sensitive cultivar Paragon, and four near isogenic lines with different combinations of insensitivity alleles (Ppd-A1a, Ppd-B1a, Ppd-D1a or their triple stack) were evaluated under short (12 h) and long (16 h) photoperiods. Insensitivity alleles decreased time to anthesis and duration of the three pre-Anthesis phases (vegetative, early reproductive and late reproductive), following the Ppd-D1a > Ppd-A1a > Ppd-B1a ranking of strength. Stacking them intensified the insensitivity, but had no additive effect over that of Ppd-D1a. The late reproductive phase was the most responsive, even exhibiting a qualitative response. Leaf plastochron was not affected but spikelet plastochron increased according to Ppd-1a ranking of strength. Earlier anthesis resulted from less leaves differentiated and a fine tuning effect of accelerated rate of leaf appearance. None of the alleles affected development exclusively during any particular pre-Anthesis phase, which would be ideal for tailoring time to anthesis with specific partitioning of developmental time into particular phases. Other allelic variants should be further tested to this purpose. Fil: Pérez Gianmarco, Thomas Ignacio. Universidad de Lleida; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina Fil: Slafer, Gustavo Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Institució Catalana de Recerca i Estudis Avancats; España. Universidad de Lleida; España Fil: González, Fernanda Gabriela. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte. Estación Experimental Agropecuaria Pergamino; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires. Universidad Nacional del Noroeste de la Provincia de Buenos Aires. Centro de Investigaciones y Transferencia del Noroeste de la Provincia de Buenos Aires; Argentina

Higher photoperiod sensitivity in wheat is associated with more fertile florets per spike at anthesis due to a longer floret initiation phase, which results in higher numbers of initiated florets, and to increased floret survival., Lengthening the pre-anthesis period of stem elongation (or late-reproductive phase, LRP) through altering photoperiod sensitivity has been suggested as a potential means to increase the number of fertile florets at anthesis (NFF) in wheat. However, little is known about the effects that the Ppd-1 genes modulating plant response to photoperiod may have on reproductive development. Here, five genotypes with either sensitive (b) or insensitive (a) alleles were grown in chambers under contrasting photoperiods (12 h or 16 h) to assess their effects. The genotypes consisted of the control cultivar Paragon (three Ppd-1b) and four near-isogenic lines of Paragon with Ppd-1a alleles introgressed from: Chinese Spring (Ppd-B1a), GS-100 (Ppd-A1a), Sonora 64 (Ppd-D1a), and Triple Insensitive (three Ppd-1a). Under a 12-h photoperiod, NFF in the genotypes followed the order three Ppd-1b > Ppd-B1a > Ppd-A1a > Ppd-D1a > three Ppd-1a. Under a 16-h photoperiod the differences were milder, but three Ppd-1b still had a greater NFF than the rest. As Ppd-1a alleles shortened the LRP, spikes were lighter and the NFF decreased. The results demonstrated for the first time that Ppd-1a decreases the maximum number of florets initiated through shortening the floret initiation phase, and this partially explained the variations in NFF. The most important impact of Ppd-1a alleles, however, was related to a reduction in survival of floret primordia, which resulted in the lower NFF. These findings reinforce the idea that an increased duration of the LRP, achieved through photoperiod sensitivity, would be useful for increasing wheat yield potential.