Horacio A. Acciaresi

Spatial pattern effect on corn (Zea mays) weeds competition in the humid Pampas of Argentina

Abstract The objectives of this study were to determine the effect of spatial pattern on corn above- and below-ground biomass, grain yield, weed above-ground biomass and soil water and photosynthetically active radiation (PAR) dynamics. Field studies were conducted in 2003 and 2004. Three corn hybrids with two spatial pattern (square and rectangular) under weed-free and weedy conditions were tested. Corn grain yield was greater in the square than in the rectangular pattern. This increase was related to better resources use while reducing the competition from weeds. Early in the growing season, there was greater moisture content in the intrarow at square pattern while a lower soil water content was observed at maturity. Conversely, the square pattern registered lower soil water content during the whole corn growing season in the interrow. This soil water profile was an outcome of the uniform corn below-ground biomass distribution. A greater PAR interception with a lower weed above-ground dry matter was obtained in square plant arrangement. The use of uniform spatial pattern appeared as an interesting alternative to increase both the grain yield potential and the corn suppressive ability against weeds in dry-land Argentinean production systems.

Traits Related to Competitive Ability of Wheat (Triticum aestivum) Varieties against Italian Ryegrass (Lolium multiflorum)

ABSTRACT The objective of this study was to determine which specific morphological characters are related with competitive ability and to establish their potential to suppress Lolium multiflorum growth while maintaining wheat grain yields. Field experiments were conducted at the La Plata National University Experimental Station (34°S 58°W), La Plata (Argentina) during 1997 and 1998. Wheat varieties used were Buck Charrúa, Klein Cacique and Pro Inta Super. A local ecotype of L. multiflorum was used. 280 plants m−2 of wheat and 50, 100 and 150 plants m−2 of Italian ryegrass were tested. The aggressivity index for aboveground dry matter and grain yield were used as a measure of competitive ability. A higher aggressivity of wheat varieties at first node, detectable up to 100 plants m−2 of weed was observed. For the 150 plants m−2 of weed, L. multiflorum had higher aggressivity than wheat varieties. At crop anthesis, weed aggressivity was higher than wheat varieties for the evaluated densities. No differences between varieties at 50 and 100 plant m−2 of L. multiflorum were observed. At first node detectable, aboveground dry matter and height of last expanded leaf of wheat, and photosynthetically active radiation interception were related with aggressivity. At anthesis, flag leaf length, flag leaf area, penultimate expanded leaf length and relative crop grain yield were positively correlated with aggressivity. This study demonstrates that variety differences in competitive ability of Argentinean wheat genotypes are significant at early crop stages up to 100 plants m−2 of L. multiflorum. Conversely there are no characters associated with wheat aggressivity at anthesis (for aboveground dry matter) and for grain yield.

Glyphosate Resistance in Perennial Ryegrass (Lolium perenne L.) is Associated with a Fitness Penalty

Abstract The net selection effect of herbicides on herbicide-resistance traits in weeds is conditioned by the fitness benefits and costs associated with resistance alleles. Fitness costs play an important evolutionary role preventing the fixation of adaptive alleles and contributing to the maintenance of genetic polymorphisms within populations. Glyphosate is widely used in world agriculture, which has led to the evolution of widespread glyphosate resistance in many weed species. The fitness of glyphosate-resistant and -susceptible perennial ryegrass plants selected from within a single population were studied in two field experiments conducted during 2011 and 2012 under different soil water availability. Glyphosate-resistant plants showed a reduction in height of 12 and 16%, leaf blade area of 16 and 33%, shoot biomass of 45 and 55%, seed number of 33 and 53%, and total seed mass of 16 and 5% compared to glyphosate-susceptible plants in 2011 and 2012, respectively. The reduction in seed number per plant resulted in a 40% fitness cost associated with the glyphosate-resistance trait in perennial ryegrass. Fitness costs of glyphosate-resistant plants were expressed under both conditions of water availability. These results could be useful for designing management strategies and exploiting the reduced glyphosate-resistant perennial ryegrass fitness in the absence of glyphosate selection. Nomenclature: Glyphosate; perennial ryegrass, Lolium perenne L., LOLPE.

Corn and Soybeans in a Strip Intercropping System: Crop Growth Rates, Radiation Interception, and Grain Yield Components

Crop growth rates (CGR), radiation interception (IPAR), yields, and their components were determined in two crops monocultures (using one corn and two soybean genotypes) and in intercropped “strips,” during three growing seasons. Corn yield in the strips significantly increased in the three seasons (13–16%) as compared to that in the monocultures. This response was due to increased yield in corn plants of the border rows of the strips, which was highly correlated to an increased IPAR, allowing high CGR at critical crop stages. As a result, more dry matter was partitioned to grain and also an increased number of ears per plant were generated. Conversely, yields of soybeans in the strips were 2 to 11% lower than that in the monocultures, with variable significance depending on soybean cultivar and/or year. Grain number per unit area was the yield component most closely associated to yield variation in both crops. We believe that if yield components of this system are more closely identified, more appropriate genotypes will fit into strip intercropping, thus contributing to the spread of this technique and thus to the sustainability of actual massive monocultured agricultural systems.

Response of weed populations to tillage, reduced herbicide and fertilizer rates in wheat (Triticum aestivum) production

Experimentos foram conduzidos sob condicoes de campo em 1999 e 2000 a fim de investigar os efeitos dos plantios convencional (PC) e direto (PD), em combinacao com tres doses de herbicidas e tres de nitrogenio (N), no crescimento de plantas daninhas e producao de duas variedades de trigo. Foi observada producao maior de graos PD, comparado ao PC, durante um ano. A biomassa das plantas daninhas no PC foi menor do que no PD, para as duas variedades. Nenhuma diferenca em biomassa e producao de graos de trigo foi observada entre as doses de herbicida integral e reduzida. N aumentou a biomassa do trigo e producao de graos significativamente. Apenas o nivel medio de N teve efeito sobre a biomassa das plantas daninhas em relacao a nao-aplicacao de N, enquanto uma taxa maior de N diminuiu a biomassa das plantas daninhas. No plantio convencional, doses reduzidas de herbicida e aplicacao de N foram efetivos na limitacao do crescimento das plantas daninhas no cultivo de trigo.

Effect of plant row spacing and herbicide use on weed aboveground biomass and corn grain yield

O uso de espacamento reduzido entre fileiras de milho foi sugerido como uma alternativa tecnologica para obter incrementos de producao de graos devido a um melhor uso de recursos. Os arranjos regulares das culturas podem diminuir a competicao entre as plantas da cultura, ao mesmo tempo que podem favorecer a competicao com as plantas daninhas. O objetivo deste estudo foi analisar o efeito da modificacao do espacamento em milho sobre a producao de biomassa da parte aerea das plantas daninhas e sobre a producao de graos da cultura. Foram conduzidos experimentos em campo durante duas estacoes de crescimento. Utilizaram-se tres hibridos de milho com dois espacamentos (0,70 e 0,35 m entre fileiras). Observou-se maior intercepcao da radiacao fotossinteticamente ativa, com menor producao de biomassa aerea das plantas daninhas no menor espacamento. Essa maior intercepcao da cultura produziu diminuicao da competicao das plantas daninhas, com incremento da producao de graos de milho. O uso de espacamento reduzido surge como uma alternativa interessante para incrementar o rendimento de milho e aumentar a habilidade da cultura em competir com plantas daninhas em sistemas produtivos nao-irrigados.

Genotype-environment interaction in avena sativa l: employing AMMI and factorial correspondence models

The objective of this study was (i) to determine the presence of genotype-environment interaction (GXE) in Avena sativa L. for above dry matter yield of Schizaphis graminun tolerant and non-tolerant genotypes according to two different models: additive main effects and multiplicative interaction (AMMI) and factorial correspondence analysis; and (ii) to study and compare the results obtained with these models. Twelve genotypes and 12 environments were conducted at La Dulce and La Plata (Argentina) during three years (1993, 1994 and 1995). The environment (E), genotype (G) and GxE factors explained a 41.15%, 7.88% and 36.36% of the total sum of square, respectively. The first three axes of principal component analysis of AMMI were highly significant (p<0.001), explaining a 57.99%, 29.03% and 6.27% of interaction sum of square. The first three factorial correspondence coordinates accounted for 58.98%, 29.58% and 5.60% of the interaction sum of square. The relation- ships between tolerant genotypes-first clipping environments and non-tolerant genotypes-second clipping environments were reflected in the biplots of both models. The simultaneous use of AMMI and factorial correspondence analysis appeared as a useful methodology for the study of GxE interaction in the oat breeding for tolerance to Schizaphis graminum.

Efecto del glifosato sobre el crecimiento y acumulación de azúcares libres en dos biotipos de lolium perenne de distinta sensibilidad al herbicida

El movimiento sistemico del glifosato esta determinado por el transporte de fotoasimilados. A su vez, la capacidad de un destino de consumir los asimilados esta condicionada por su actividad metabolica. Pese a su importancia, la relacion entre el glifosato y la sintesis de azucares en hojas fuente ha sido poco abordada. El objetivo del presente trabajo fue evaluar los efectos del glifosato sobre el crecimiento y la acumulacion de azucares libres en dos biotipos de Lolium perenne de baja y alta sensibilidad al herbicida. Se trabajo con clones de ambos tipos de plantas, en macollaje, tratados con 1.440 g e.a. ha-1 de glifosato y sin tratamiento herbicida como controles. Se evaluo periodicamente el efecto del glifosato sobre el rebrote de hojas hasta las 50 horas post-aplicacion y sobre los niveles de azucares libres totales, reductores y no reductores en hojas a 1, 2, 3 y 5 dias post-aplicacion. A partir de las 25 horas post-aplicacion, el glifosato provoco una disminucion del crecimiento del 58% en el biotipo susceptible, con una acumulacion de azucares libres superior al 90% con relacion al control, desde el primer dia post-aplicacion en adelante. La inhibicion del crecimiento, inducida por el glifosato en plantas susceptibles, no depende de la limitacion del traslado de fotoasimilados desde la parte aerea. Por tanto, la acumulacion de azucares libres en hojas podria explicarse por la caida en la tasa de crecimiento. En el biotipo de baja sensibilidad, en el que no se detecto inhibicion del crecimiento, estos efectos fueron limitados.

Shoot and root competition in a Lolium multiflorum-wheat association

ABSTRACT Three outdoor pot experiments with three wheat cultivars and Lolium multiflorum were conducted at La Plata National University (Argentina), where the effects of shoot and root competition were separated using aerial partitions. Root competition (RC) for both shoot dry matter yield (SDM) and grain yield was higher (p < 0.05) than shoot competition (SC). Cv. P.I. Super was most affected by SC while cvs. K. Cacique and B. Charrua were least affected. Crop competition caused a highly significant reduction of weed variables. RC had a greater effect on both weed SDM and weed seed yield than did SC. Cvs. B. Charrua and K. Cacique registered a higher photosynthetically active radiation interception (PAR) than cv. P.I. Super and L. multiflorum in SC treatment, but cv. P.I. Super intercepted more PAR than L. multiflorum and cvs. B. Charrua and K. Cacique in RC treatment. The resources complementarity for grain yield was obtained by means of relative yield total (RYT). There was resources complementarity when wheat and weed were in SC, but not in RC and full competition (FC), showing that the species were in full competition, despite the high nitrogen availability throughout the crop growing cycle. Cvs. B. Charrua and K. Cacique were more aggressive than the weed, while cv. P.I. Super was less aggressive than the weed in the SC treatment. Conversely, in both the RC and FC treatments, higher aggressivity than wheat cvs. was shown by the weed. This result could be ascribed to the lower shoot/root ratio and the higher nitrogen uptake of L. multiflorum. Despite the high availability of nitrogen, the results demonstrate that competition was mainly for soil nutrients, and wheat cvs. with a higher competitive ability in above-ground competition may have no competitive advantage when RC occurs. Because the experimental technique in pots does not reflect field conditions, caution is needed in extrapolating the results to a field situation.

Response of corn (Zea mays) and weeds to planting pattern and herbicide use

ABSTRACT The use of narrow row arrangement in corn (Zea mays) has been suggested as a technological alternative to obtain grain yield increases through a better use of the resources. The regular pattern could diminish intraspecific competition while favouring interspecific competition with weeds. The objective of this study was to analyse the effect of corn planting pattern and herbicide application on (i) soil water content and photosynthetically active radiation (PAR) dynamics, (ii) below ground and above ground corn biomass and grain yield and (iii) weed suppressive ability of dryland corn sown at square and rectangular plant arrangement. Field experiments were conducted during the growing seasons 2002/03 and 2003/04. Three corn hybrids with two plant arrangement (rectangular: 0.70 × 0.20 m and square: 0.35 × 0.35 m) and herbicide (2.25 kg ai ha−1 of atrazine and 2.32 kg ai ha−1 of metolachlor) use compared with no herbicide use were tested. In the initial stages of the crop there was greater moisture content in the row of corn sowed at square planting pattern while a lower soil water content at maturity was observed. Conversely, between rows, the square plant arrangement registered lower soil water content during the growing cycle of the crop. This soil water profile was a consequence of the uniform corn below ground dry matter distribution. A greater PAR interception with a lower weed above ground dry matter was obtained in square plant arrangement. Corn grain yield was greater in the square-planting pattern than in the rectangular ones. This increase in grain yield was related to better resources use i.e. soil moisture and PAR interception while reduces the competition from weeds. The use of equidistant plant arrangement appeared as an interesting alternative to increase both the grain yield potential and the corn suppressive ability against weeds in dryland Argentinean production systems.