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We used the ‘Baronesse’/‘Full Pint’ doubled haploid population to analyse the genetic factors controlling flowering date under South American conditions. Both parents have similar heading dates, but the population shows transgressive segregation. Two genes, eps2S on chromosome 2H and sdw1 on chromosome 3H, explained most of the phenotypic variation for anthesis date, with the later allele carried by ‘Baronesse’ and ‘Full Pint’ , respectively. Both effects were completely additive with no interaction. We studied three plant developmental periods: seedling emergence to tillering (Z10–Z20), tillering (Z20–Z30) and end of tillering to anthesis (Z30–Z49) under field conditions at three contrasting planting dates. Z10–Z20 was also measured under semi-controlled conditions. eps2S controlled Z30–Z49 periods, while sdw1 controlled Z20–Z30. Each of the two genes for the end-point phenotype—anthesis date—was a determinant of flowering at a different developmental stage. No gene x planting date interactions were detected.

Aim of the study: To analyze the course of leaf water status, water-use efficiency and growth in Eucalyptus grandis and hybrids throughout seasons with different rainfall.Area of study: The study was conducted in northern Uruguay.Methods: A randomized block trial was established containing E. grandis (ABH17), E. grandis × Eucalyptus camaldulensis (GC172), E. grandis × Eucalyptus tereticornis (GT529), and E. grandis × Eucalyptus urophylla (GU08). Predawn leaf water potential (Ψpd) and midday leaf water potential (Ψmd) were measured every six weeks from the age of 16 months, throughout two growing seasons. Stomatal conductance (gs), net photosynthetic rate (A), and leaf-level transpiration (E) were measured once in each growing season, along with leaf carbon isotope discrimination (∆13C) and tree growth. Stomatal density and distribution were studied.Results: ABH17 and GU08 had the lowest daily fluctuation of leaf water potential and showed stronger stomatal regulation; they were hypostomatic, and stomata on the adaxial leaf surfaces remained immature. GC172 and GT529 (Red-Gum hybrids) were amphistomatic and transpired more intensively; they were less efficient in instantaneous and intrinsic water use and grew faster under high soil moisture (inferred from rainfall). Under such conditions, GC172 reached the highest gas-exchange rate due to an increase in tree hydraulic conductance. ABH17 and GU08 were hypostomatic and used water more efficiently because of stronger stomatal regulation.Research highlights: Red-Gum hybrids evidenced less water use efficiency due to lower stomatal regulation, different stomatal features, and distinct growth patterns as a function of soil moisture (inferred from rainfall).Keywords: Eucalypt hybrids; stomatal conductance; water-use efficiency; transpiration.Abbreviations used: Ψpd:predawn leaf water potential;Ψmd: midday leaf water potential; ΔΨ: daily fluctuation of leaf water potential ( ; A: net photosynthetic rate, E: leaf transpiration rate, gs: stomatal conductance, WUE: instantaneous water-use efficiency; WUEi: integrated water-use efficiency; A/E: leaf photosynthesis-to-leaf transpiration ratio; ∆13C: leaf carbon isotope discrimination; K: tree hydraulic conductance; E/∆Ψ: ratio between leaf transpiration and daily fluctuation of leaf water potential; δ13C: natural abundance of 13C.

Paspalum dilatatum Poir. is a promising perennial summer grass forage for temperate regions, but among other factors, slow stand establishment has hindered its adoption. One of the reasons may be seed dormancy. Intraspecific variability in seed dormancy has been reported in P. dilatatum, but the mechanisms underlying this variability remain unclear. In this paper, we focus on the role of seed external covering structures on germination, particularly the lemma. Seeds of apomictic and sexual biotypes of P. dilatatum were subjected to acid scarification and removal of the lemma to study their germination, imbibition rate and sensitivity to ABA. Seeds without lemma showed higher germination than other treatments in dormant genotypes. We found that the lemma delayed but did not prevent water uptake in any genotype. Comparing sexual biotypes, P. dilatatum subsp. flavescens showed higher lemma-imposed dormancy than P. dilatatum “Virasoro”, and also higher seed dormancy at the caryopsis level. The thickness of the lemma was not different between these biotypes, so this trait did not explain differences in dormancy. Intraspecific variability of seed dormancy in this species may be attributable to the lemma incidence, however differences in the caryopsis component of seed dormancy should be considered. Resumo: Paspalum dilatatum Poir. é uma gramínea forrageira perene de regiões temperadas, mas sua utilização é limitada pelo seu estabelecimento lento, entre outros fatores. Uma razão pode ser a dormência das sementes. Tem sido relatada variabilidade intraespecífica da dormência em P. dilatatum, mas os mecanismos envolvidos nesta variabilidade não são claros. Neste trabalho estudamos o papel das coberturas externas sobre a germinação, particularmente da lema. Sementes de biótipos sexuais e apomíticos de P. dilatatum foram submetidos à escarificação ácida e remoção da lema para estudar a germinação, a taxa de embebição e a sensibilidade ao ABA. As sementes sem lema mostraram maior germinação que outros tratamentos em genótipos com dormência. Ainda, a lema retarda, mas não impede a entrada de água. Comparando genótipos sexuais, P. dilatatum subsp. flavescens apresentou uma maior dormência imposta pela lema que P. dilatatum “Virasoro”, e também dormência mais elevada ao nível do cariopse. A espessura da lema não foi diferente entre estes genótipos, e portanto esta não explicou as diferenças na dormência. A variabilidade intraespecífica da dormência nesta gramínea panicóide pode ser atribuída às diferenças na incidência da lema. Contudo, diferenças na dormência ao nível da cariopse devem ser consideradas.

Dallisgrass (Paspalum dilatatum Poir.) is a warm-season grass, native to South America. Its adoption as a pasture crop has been hindered by low seed germination and slow establishment. However, variability in germination behaviour for this species has never been systematically analysed. For Paspalum spp., dry-storage and moist cold or warm pre-conditioning treatments have been reported as effective for the relief or breaking of seed dormancy. In the present work, seed germination responses at 32°C were assayed for sixteen P. dilatatum genotypes, representing its known natural genetic variability, to two moist pre-conditioning treatments (at 5 and 20°C) and without pre-conditioning, and three seed storage periods (0, 3 and 6 months). Pre-conditioning at 20°C showed high germination percentages (>80%), with ratios equal to or higher than pre-conditioning at 5°C, suggesting that cold is not required to break dormancy. Longer storage times resulted in increases in germination responses for most of the genotypes, while other biotypes showed no effect. Biotypes Virasoro and Chiru showed a remarkably different behaviour with higher germination percentages of untreated freshly harvested seeds. Our results show that diversity for traits involved in seed germination exists among naturally occurring P. dilatatum genotypes and the characterization of these traits should be addressed during ecotype characterization and evaluation of potential domesticates of this species.

Barley spot blotch (SB), caused by Cochliobolus sativus, is an important barley disease which causes extensive grain yield losses. These losses may not always correlate directly with the amount of diseased leaf area. Two barley cultivars, Quebracho (susceptible to SB) and Carumbe (with intermediate susceptibility to SB), were compared in field experiments in 2003, 2004 and 2006. Plots of each cultivar were either inoculated with C. sativus or protected with fungicide under field conditions to generate contrasting treatments: i) diseased, and ii) free of disease, respectively. SB severity over the growing season, photosynthetic rate on leaves with no visible symptoms and grain yield were assessed for each treatment and year. There was no treatment effect on cv. Carumbe, while cv. Quebracho showed a significant yield reduction, even though SB severity during the grain filling period was

Quantitative trait loci (QTL) analysis can contribute to a deeper understanding of crop phenology. The parents of a barley mapping population have similar growth and development profiles, but the progeny show transgressive segregation for phenological traits. These phenotypes were measured in eight field experiments, using different planting dates over 3 years. Five QTL, on four chromosomes, were detected for anthesis date. The four maturity QTL were on the same chromosomes as the anthesis QTL. Five QTL for grain filling were detected on all chromosomes. Three QTL, on chromosomes 1H and 2H, were detected for photoperiod sensitivity. Both parents contributed higher value alleles for all traits, except for photoperiod sensitivity. QTL epistasis was not significant. Two QTL explained most of the phenotypic variation for anthesis and physiological maturity. Non-parental combinations of alleles at these loci account for the phenotypic transgressive segregation. Candidate genes for these QTL effects are eps2S (2H) and denso (3H). QTL for other traits had smaller effects and were coincident with genes and/or QTL for the same traits reported in other germplasm.

Several methods have been proposed to simulate yield in crop simulation models. In this work, we present a simple method to estimate harvest index (HI) of grain crops based on fractional post-anthesis phase growth (f G = fraction of biomass accumulation that occurred in the post-anthesis phase). We propose that HI increases in a linear or curvilinear fashion in response to f G. The linear model has two parameters, the intercept (HIo) and the slope (s). The curvilinear model was assumed to be monotonic: HI = HIx � (HIxHIo) � exp(� kf G); where HIx is the asymptote, HIo is the intercept andk is a constant modulating the rate of HI increase. The models were tested for barley (Pullman, WA and Uruguay), wheat (Pullman, WA) and sorghum (Australia). A positive relationship between HI and f G was in general evident. For barley, the linear model appropriately represented the response of HI to fG, with both HIo and s in the vicinity of 0.3. For wheat HIo and s were 0.34 and 0.21, respectively, but the curvilinear model yielded a slightly better fitting than the linear model. For sorghum, both linear and linear-plateau models fitted data reasonably well. It is shown that the models work well in crops source-limited or source-sink co-limited during grain filling, but in sink-limited conditions the magnitude of the limitation needs to be characterized to compute HI. A major advantage of this method is that the parameters of the linear or curvilinear model are readily calibrated from yield data and biomass measurements at anthesis and harvest. # 2007 Elsevier B.V. All rights reserved.

El raleo y la poda afectan la disponibilidad hídrica y en consecuencia el crecimiento de las plantaciones forestales, aunque no es claro que el manejo silvícola afecte de igual manera a plantaciones con diferentes grados de disponibilidad hídrica en los suelos. En un rodal de Pinus taeda L. de cinco años en Tacuarembó (Uruguay, 31º 38’S, 55º 41’W) se evaluaron los efectos del primer raleo (40 %) y poda (50 %) (mayo/2008) sobre el potencial hídrico y el crecimiento posterior. En tres sitios, dos sobre suelos profundos y uno sobre suelos superficiales, se instalaron parcelas con sus respectivas áreas testigo. En cada parcela se midió: potencial hídrico foliar base (Yb) y mediodía (Ymd), diámetro a la altura del pecho y altura de fuste cada seis semanas entre julio/2008 y enero/2010. Se calculó el déficit de presión de vapor (Dpv) del rodal y la evapotranspiración relativa (ETR) por sitio. El tratamiento redujo el Yb durante los meses con mayor déficit de ETR y este efecto fue más prolongado sobre suelos superficiales. El Ymd fue menor en suelos profundos (-2,51 vs -2,09 ± 0,34 MPa), posiblemente por una mayor actividad transpiratoria (DYw). Ymd y Yb se relacionaron linealmente hasta valores de Yb próximos a -1,00 MPa, aunque no hubo asociación durante el período de alta deficiencia de ETR. Existió una asociación positiva entre la tasa de crecimiento relativo (TCR) y DYw pero TCR no fue afectada por sitio ni manejo. Los resultados sugieren que el raleo y la poda incrementaron la actividad transpiratoria. Thinning and pruning modify water availability, and therefore growth of forest plantations, although it is not clear that the silvicultural management would affect equally stands with different levels of soil water availability. The effect of first thinning (40 %) and pruning (50 %) (May/2008) on water potential and growth were evaluated in a five-year-old stand of Pinus taeda L. in Tacuarembó, Uruguay (31º 38’S, 55º 41’W). Experimental and control plots were installed at three sites, two with deep soils and one with shallow soils. Predawn (Ypd) and midday (Ymd) needle water potential, diameter at breast height, and stem height were measured in each plot every six weeks, from July/2008 to January/2010. Vapor pressure deficit (Vpd) on stand basis and relative evapotranspiration (RET) on site basis were calculated. Treatment reduced Ypd during the highest RET-deficit period (autumn/2009) and its effect lasted longer on plots with shallow soils. Ymd was lower on deeper-soil plots (-2.51 vs -2.09 ± 0.34 MPa) probably due to higher water availability and therefore, higher transpiration rates (DYw). Ypd and Ymd were linearly related up to Ypd values near -1.00 MPa but there was no relationship during the highest RET-deficit period. Relative growth rate (RGR) and DYw were linearly related but RGR was not modified either by site or silvicultural treatment. These results suggest that thinning and pruning increased transpiration activity.

A degree of seed dormancy (SD) is required for malting barley varieties in Uruguay, and many other parts of the world, in order to prevent pre-harvest sprouting. Water sensitivity (WS) (a decrease in germination under excess water) is a related trait that can create problems at the malthouse. Both traits are affected by environmental conditions during grain filling. We used a population of 100 doubled haploid lines derived from the cross BCD47 × Baronesse to map quantitative trait loci (QTL) affecting SD, WS, and malting quality traits. Preliminary experiments revealed that BCD47 has low SD and Baronesse has high SD. WS for these accessions was not known before this research. A major SD QTL – detected in four experiments – is on chromosome 5H, with BCD47 contributing the low dormancy allele. Four other regions with QTL effects for SD were mapped, but these QTL were significant in data from only one or two environments. Four regions were detected with QTL effects for WS, but only two – in 5H coincident with the SD QTL, and 3H – were significant in more than one environment. SD and WS were affected by the average temperature at the end of the grain-filling period, with higher temperatures associated with lower values for SD. At the same region on 5H where SD and WS QTL were detected, we found significant QTL for malt extract, α-amylase activity, β-glucans, FAN, Kolbach index, wort turbidity and protein content, with BCD47 contributing favourable alleles for all traits. These results underscore the importance of environmental effects on both SD and WS as well as the difficulties of combining good malting quality with adequate levels of SD and WS.