Nitrogen fertilization rates in cereal production systems are generally determined by subtracting soil test N from a specified N requirement based on the grain yield goal, which represents the best achievable grain yield in the last 4 to 5 yr. If grain yield could be predicted in season, topdress N rates could be adjusted based on projected N removal. Our study was conducted to determine if the potential grain yield of winter wheat (Triticum aestivum L.) could be predicted using in-season spectral measurements collected between January and March. The normalized difference vegetation index (NDVI) was determined from reflectance measurements under daytime lighting in the red and near-infrared (NIR) regions of the spectra. In-season estimated yield (EY) was computed using the sum of two postdormancy NDVI measurements (Jan. and Mar.) divided by the cumulative growing degree days (GDD) from the first to second reading. A significant relationship between grain yield and EY was observed (R-2 = 0.50, P > 0.0001) when combining all nine locations across a 2-yr period. Our estimates of potential grain yield (made in early Mar.) differed from measured grain yield (mid-July) at three sites where yield-altering factors (e.g., late summer rains delayed harvest and increased grain yield loss due to lodging and shattering) were encountered after the final sensing. Evaluating data from six of the nine locations across a 2-yr period, EY values explained 83% of the variability in measured grain yield. Use of EY may assist in refining in-season application of fertilizer N based on predicted potential grain yield.
Knowledge of changes associated with advances in crop productivity is essential for understanding yield-limiting factors and developing strategies for future improvement. Our objective was to identify plant traits associated with gains in grain yield of winter wheat (Triticum aestivum L.) in the Great Plains. Twelve landmark cultivars and one experimental line were compared with 'Turkey' (introduced 1873) at Hutchinson (Clark-Ost complex soil) and Manhattan (Reading silt loam soil), KS. during 1996-1997 and 1998-1999. Agronomic traits, leaf rust infection (caused by Puccinia recondita Rob. ex Desm. f. sp. tritici), and grain yield and its components were measured. Grain yields ranged from 2718 kg ha(-1) for Turkey to 4987 kg ha(-1) for the experimental line, with mean genetic gains of 0.16% per year for early genotypes and 0.63% per year for recent genotypes. Kernel number per unit of soil area had the highest phenotypic correlation with grain yield and contributed most to its genetic gain. Gains in spike numbers per unit of soil area and above-ground biomass also contributed significantly to higher yields of some genotypes. Significant genetic changes over time and correlations with grain yield were observed for early heading, decreased height, and reduced lodging and leaf rust but not for kernel weight. Our results suggested that yield components that form during vegetative phases (spike numbers per unit of soil area and kernels per spike) when conditions for growth are generally favorable are more amenable to genetic improvement than kernel weight, which forms during maturation when moisture and temperature are often unfavorable.
An understanding of the causes of genotype x environment (GE) interaction can help identify traits that contribute to better cultivar performance and environments that facilitate cultivar evaluation. Through subjecting environment-centered yield of a multi-environment trial data to singular value decomposition, the portion of yield variation that is relevant to cultivar evaluation is partitioned into noncrossover and crossover GE interaction, quantified by the first two principal components (PC), respectively. Each PC is a set of genotypic scores multiplied by a set of environmental scores. By relating the PC scores to genotypic and environmental covariates, GE interaction represented by each PC can be interpreted in terms of trait X factor interactions. This strategy was employed in analysis of the 1992 to 1998 Ontario winter wheat (Triticum aestivum L,) performance trial data, Results indicated that plant height and maturity were the major genotypic causes of GE interaction, whereas cold temperature in the winter and hot temperature in the summer were the major environmental causes of GE interaction. Positive interactions were found between earlier maturity vs, warmer winters or hotter summers, and between shorter plant height vs, warmer winters or cooler summers. In addition, better resistance to septoria lear blotch (caused by Septoria secalis Frill, & Delacr,) was frequently associated with overall performance. The results of this study should help in determining breeding objectives and Tor selecting test sites or environments Tor winter wheat breeding in Ontario.
We developed a PCR-based assay to quantify trichothecene-producing Fusarium based on primers derived from the trichodiene synthase gene (Tri5). The primers were tested against a range of fusarium head blight (FHB) (also known as scab) pathogens and found to amplify specifically a 260-bp product from 25 isolates belonging to six trichothecene-producing Fusarium species. Amounts of the trichothecene-producing Fusarium and the trichothecene mycotoxin deoxynivalenol (DON) in harvested grain from a field trial designed to test the efficacies of the fungicides metconazole, azoxystrobin, and tebuconazole to control FHB were quantified. No correlation was found between FHB severity and DON in harvested grain, but a good correlation existed between the amount of trichothecene-producing Fusarium and DON present within grain. Azoxystrobin did not affect levels of trichothecene-producing Fusarium compared with those of untreated controls. Metconazole and tebuconazole significantly reduced the amount of trichothecene-producing Fusarium in harvested grain. We hypothesize that the fungicides affected the relationship between FHB severity and the amount of DON in harvested grain by altering the proportion of trichothecene-producing Fusarium within the FHB disease complex and not by altering the rate of DON production. The Tri5 quantitative PCR assay will aid research directed towards reducing amounts of trichothecene mycotoxins in food and animal feed.
Vernalization and photoperiod genes have wide-ranging effects on the timing of gene expression in plants. The objectives of this study were to (1) determine if expression of low-temperature (LT) tolerance genes is developmentally regulated and (2) establish the interrelationships among the developmental stages and LT tolerance gene expression. LT response curves were determined for three photoperiod-sensitive LT tolerant winter wheat (Triticum aestivum L. em Thell) genotypes acclimated at 4 °C under 8 h short-day (SD) and 20 h long-day (LD) photoperiods from 0 to 112 d. Also, three de-acclimation and re-acclimation cycles were used that bridged the vegetative/reproductive transition point for each LD and SD photoperiod treatment. A vernalization period of 49 d at 4 °C was sufficient for all genotypes to reach vernalization saturation as measured by minimum final leaf number (FLN) and confirmed by examination of shoot apices dissected from crowns that had been de-acclimated at 20 °C LD. Before the vegetative/reproductive transition, both the LD- and SD-treated plants were able to re-acclimate to similar LT50(temperature at which 50% of the plants are killed by LT stress)levels following de-acclimation at 20 °C. De-acclimation of LD plants after vernalization saturation resulted in rapid progression to the reproductive phase and limited ability to re-acclimate. The comparative development of the SD (non-flowering-inductive photoperiod) de-acclimated plants was greatly delayed relative to LD plants, and this delay in development was reflected in the ability of SD plants to re-acclimate to a lower temperature. These observations confirm the hypothesis that the point of transition to the reproductive stage is pivotal in the expression of LT tolerance genes, and the level and duration of LT acclimation are related to the stage of phenological development as regulated by vernalization and photoperiod requirements. Copyright 2001 Annals of Botany Company
In vitro conditions, the interactions betecen the fungi most frequently isolated from the stem base of winter wheat were determined. These were the species from genus Fusarium (F. culmorum, F. avenaceum and F. poae) and Rhizoctonia cerealis, Pseudocercosporella herpotrichoides, Alternaria alternata and Aureobasidium bolleyi. Some saprotrophes showed stimulating effect on R. cerealis, P. herpotrichoides and F. poae. Certain species in combined cultures showed exceptionally favourable relationships.
Winter wheat (Triticum aestivum L.) -fallow is the predominant cropping system in low-precipitation regions (< 250 mm annually) of the inland Pacific Northwest (PNW) in the USA. Wind erosion is a recurrent problem during and after fellow periods when inadequate crop residue amounts are retained on the soil surface. Management options that optimize both grain yield and straw production are needed. A 3-yr held study was conducted to determine sowing rate and sowing date effects on straw and grain yield, and grain yield components of winter wheat cultivars with semidwarf, standard height, or tall growth habit. Four winter wheat cultivars were evaluated at three sowing rates (65, 130, and 195 seeds m(-2)) and three sowing dates in August, September, and October. A split plot design was used, with sowing dates as main plots and sowing rate x cultivar combinations as subplots, The greatest effect of sowing date was on straw production. Straw biomass from mid-August sowing averaged 6.70 Mg ha(-1) compared with 4.65 and 2.78 Mg ha(-1) from mid-September and mid-October sowing, respectively. Grain yield was highest for mid-August sowing during two years and lowest for mid-October sowing all years. Averaged across years, the semidwarf cultivar produced the highest grain yield on all sowing dates and was equal to the standard height and tall cultivars for straw production. Path coefficient analysis showed that variation in grain yield was due primarily to differences in spikes per unit area (SPU) and kernels per spike (KPS), Late sowing resulted in a large reduction in SPU and, therefore, grain yield. For cropland susceptible to wind erosion in east-central Washington, early sowing results in increased wheat straw production and generally higher grain yield compared with mid-to-late sowing dates.
1. Spiders form a major component of the generalist predator fauna, potentially able to restrict pest population growth, but their populations may be food-limited under current farming regimes. This study aimed to quantify food availability to spiders in winter wheat and to determine whether spider web locations are positively associated with available food resources. 2. Mini-sticky traps (availability rate per 24 h, including prey falling from the crop) and mini-quadrats (instantaneous density on the ground by day) were used, in combination, to monitor the availability of potential prey to web-building species of money spider (Linyphiidae) in fields of winter wheat in Warwickshire, UK, 1997-98. 3. These methods were applied to web sites of individual spiders and to non-web sites located randomly up to 30 cm away from each web. A total of 18 546 invertebrates were captured using these methods. 4. Overall, significantly more potential prey were available in web sites than in non-web sites (both on sticky traps and in quadrats). 5. Prey availability in May and July was about a third of that in June (both on sticky traps and in quadrats) and may have been below that known to be necessary for spiders to realize their maximum population growth rate. 6. The peak rate of capture of linyphiid spiders on mini-sticky traps was 0.6 trap day at web sites, and approximately half this value at non-web sites. Numbers of spiders captured by mini-sticky traps and mini-quadrats increased exponentially as the season progressed. The high capture frequency in relation to population density, and the differential between web and non-web sites, points to a dynamic and aggregated distribution of spiders in winter wheat, which is consistent with what is known about mate-searching and web site abandonment rates by the Linyphiidae. 7. The combination of techniques described here is recommended for monitoring prey availability in prey-enhancement programmes and may prove useful in quantitative studies of both intra- and interspecific interactions between spiders.
The effects of the fungicides azoxystrobin (a strobilurin) and epoxiconazole (a sterol biosynthesis inhibitor) on phyllosphere fungi, senescence and yield were studied in winter wheat in field trials free of visible disease and under controlled environmental conditions. In two field trials, treatments with each of the two fungicides prolonged green leaf area retention and increased yield compared with untreated control plots. Azoxystrobin maintained green leaf area for longer than epoxiconazole and, in one trial, treatments with azoxystrobin gave a greater yield response than epoxiconazole. Mycelial growth on leaf surfaces, mainly originating from saprophytic fungi, was reduced by each of the fungicides. Papilla formation and hypersensitive reactions, almost exclusively against infection attempts by Mycosphaerella spp. (most probably M. graminicola ), occurred with high frequency in the leaves. These defence reactions presumably incurred a significant energy cost, accelerating plant senescence. Fewer defence reactions were recorded in azoxystrobin‐treated leaves than in epoxiconazole‐treated and untreated leaves. Inoculation in a glasshouse experiment with the saprophytic fungi Alternaria alternata and Cladosporium macrocarpum accelerated wheat senescence. Control of the saprophytes by azoxystrobin or epoxiconazole treatments caused a delay in the accelerated senescence, but without significant increase in above‐ground biomass and yield. Neither fungicide influenced senescence, above‐ground biomass or yield in noninoculated wheat plants. In growth chamber experiments azoxystrobin inhibited spore germination and mycelial growth of A. alternata and C. macrocarpum . Epoxiconazole had little inhibitory effect on spore germination, but strongly inhibited mycelial growth of both saprophytes. Both fungicides reduced A. alternata ‐induced papilla formation in wheat leaves, with epoxiconazole being more effective. Inoculation with either of the two saprophytes did not significantly increase wheat leaf respiration, in contrast to inoculation with the nonhost pathogen Erysiphe graminis f.sp. hordei . Treatment with azoxystrobin did not affect this latter increase in respiration whereas it was reduced by epoxiconazole treatment. It is proposed that the greater inhibition of infection attempts from Mycosphaerella spp. by azoxystrobin, compared with epoxiconazole, may account for the greater yield given by azoxystrobin in field plots.