Losses In Grain Yield Research Articles

RESPONSE OF SOME COMMERCIAL MAIZE HYBRIDS AND THEIR PARENTS TO DOWNY MILDEW DISEASE AND YIELD LOSSES

Thirty four white and yellow maize (Zea mays L.) inbred lines and hybrids were evaluated to downy mildew disease caused by Peronosclerospora sorghi (Weston and Uppal) C.G. Shaw. This study was performed in 2006 -20007 growing seasons at Gemmeiza Agricultural Research Station, El-Gharbea Governorate, Egypt. Out of the white maize genotypes, only the inbred lines Gm.22 and Gm.21were highly resistance( 0 and 0.48% disease infection, respectively) . The other inbred lines showed infection types ranged from resistance (Gm.4 and Gm.30), moderate resistance (Gm.14, Gm.27 and Sd.7). Both of Gm.2 and Sd.63 showed moderate to susceptible infection types. The white hybrids (S.c.11, S.c.12, S.c.13, S.c.14 and S.c.26 ) were moderately resistant, while, hybrids S.c.21, S.c.22, S.c.27, T.w.c.321, T.w.c.325 and T.w.c326were moderately susceptible then hybrids S.c.10, S.c.15, S.c.25, T.w.c.322 and T.w.c.327were susceptible. It can be concluded that inbred lines Gm.4, Gm.21, Gm.30 and Sd.7 play a role in conferring resistance in their hybrids and could be considered as sources of resistance to downy mildew. All the tested yellow maize inbred lines and hybrids showed moderately susceptible, and susceptible infection types. Losses in grain yield were in a parallel line with disease infection. The yellow maize genotypes scored the highest percentage of yield reduction compared with the white genotypes . All of the white inbreds and hybrids showed losses in grain yield except the inbred line Gm.22. The highest % of grain yield losses were detected in the inbred lines Sd.63 and Gm.2 (31.19 and 21.22%, respectively) as well as the hybrids S.c.10 (34.48%), S.c.21 (31.61%) and S.c.26 (31.26%). Concerning with yellow maize genotypes, the highest losses % were noticed in the inbred lines 1021 and 1002 (66.11 and 64.85%, respectively) as well as the hybrids T.w.c. 352 (87.47%), S.c.52 (63.79%), S.c.155 (73.77%) then T.w.c351 (51.93%).

Methyl Jasmonate Reduces Grain Yield by Mediating Stress Signals to Alter Spikelet Development in Rice

Jasmonic acid (JA) is involved in plant development and the defense response. Transgenic overexpression of the Arabidopsis (Arabidopsis thaliana) jasmonic acid carboxyl methyltransferase gene (AtJMT) linked to the Ubi1 promoter increased levels of methyl jasmonate (MeJA) by 6-fold in young panicles. Grain yield was greatly reduced in Ubi1:AtJMT plants due to a lower numbers of spikelets and lower filling rates than were observed for nontransgenic (NT) controls. Ubi1:AtJMT plants had altered numbers of spikelet organs, including the lemma/palea, lodicule, anther, and pistil. The loss of grain yield and alteration in spikelet organ numbers were reproduced by treating NT plants with exogenous MeJA, indicating that increased levels of MeJA in Ubi1:AtJMT panicles inhibited spikelet development. Interestingly, MeJA levels were increased by 19-fold in young NT panicles upon exposure to drought conditions, resulting in a loss of grain yield that was similar to that observed in Ubi1:AtJMT plants. Levels of abscisic acid (ABA) were increased by 1.9- and 1.4-fold in Ubi1:AtJMT and drought-treated NT panicles, respectively. The ABA increase in Ubi1:AtJMT panicles grown in nondrought conditions suggests that MeJA, rather than drought stress, induces ABA biosynthesis under drought conditions. Using microarray and quantitative polymerase chain reaction analyses, we identified seven genes that were regulated in both Ubi1:AtJMT and drought-treated NT panicles. Two genes, OsJMT1 and OsSDR (for short-chain alcohol dehydrogenase), are involved in MeJA and ABA biosynthesis, respectively, in rice (Oryza sativa). Overall, our results suggest that plants produce MeJA during drought stress, which in turn stimulates the production of ABA, together leading to a loss of grain yield.

Erratum to: Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: a review

Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.

Epidemiology and control of spot form of net blotch (Pyrenophora teres f. maculata) of barley: a review

Spot form of net blotch (SFNB), caused by the fungus Pyrenophora teres f. maculata, was first described in Denmark in the 1960s and is now a prevalent foliar disease of barley in many countries. This disease should be controlled as a separate disease-causing organism from the net form of net blotch (NFNB), which is caused by P. teres f. teres. The increase in prevalence of SFNB is primarily due to stubble retention and cultivation of susceptible varieties, which have resulted in increased inoculum. Infected barley stubble is the primary inoculum source for SFNB, producing both asexual spores (conidia) and sexual spores (ascospores) from pseudothecia. Spot form of net blotch causes significant losses in grain yield and quality in situations where inoculum is present, susceptible varieties are cultivated, and where the climate is cool and moist. Cultivation of resistant varieties is the most cost-effective method for control of SFNB and more than 12 different resistance sources have been identified in barley germplasm and wild barley relatives. The resistance loci of 11 of these have been mapped. Control of SFNB can also be achieved with application of foliar fungicides, crop rotation, and stubble destruction.

Genetic Mapping of Sheath Blight Resistance QTLs within Tropical Japonica Rice Cultivars

ABSTRACTMost commercial cultivars of rice (Oryza sativa L.) are susceptible to sheath blight (SB), a devastating fungal disease causing significant losses in grain yield and quality. There are limited sources of genetic resistance adapted to U.S. growing conditions, and no commercial long grain cultivar of rice is currently available in the United States with a high level of SB resistance. Sheath blight resistance has been reported to be horizontal and quantitative. A population of 279 F2:3 progeny rows derived from a cross between two tropical japonica U.S. rice cultivars, Rosemont (semi‐dwarf, SB susceptible) and Pecos (tall, SB resistant), was used to map SB resistance. Progeny families were evaluated for disease reactions, plant height (PH), and heading date (HD) in replicated field trials for 2 yr and genotyped with 149 simple sequence repeat markers. Correlation analysis between SB ratings with PH and HD showed that both agronomic traits were significantly correlated with SB resistance. Four significant (logarithm of odds ratio ≥ 3.6) quantitative trait loci (QTLs) were identified for SB resistance, with individual effects explaining 5.6 to 33.4% of the total phenotypic variation. Plant height appears to have a direct influence on SB resistance, with QTLs for these traits colocated on chromosome 1. Consistent results across years indicate the stability of the identified QTLs and their potential for improving rice SB resistance using marker‐assisted selection.

Effects of crop rotation, residue retention and sowing time on the incidence and survival of ascochyta blight and its effect on grain yield of field peas ( Pisum sativum L.)

Ascochyta blight is endemic in many regions where field pea ( Pisum sativum) is grown, causing significant losses in grain yield. Crop management is the main method used to reduce the severity of disease and minimise yield losses, but with varying degrees of success. This is likely to be due to variation in the production and survival of inoculum. A 6-year experiment was conducted in which disease pressure was manipulated by crop rotation, residue retention, time of sowing and fungicide treatment. The experiment measured the amount and persistence of inoculum on crop residues and in soil as well as its dispersal in the air during the growing season, and assessed disease development and yield. Aerial inoculum from infected pea residues was the main source of infection, followed by soil-borne inoculum. Soil-borne inoculum declined slowly. The average rate of decline in soil inoculum was 15% per year, suggesting that a break of 6 years is required to reduce soil inoculum by 90%. This slow decline meant that increasing the disease break from 2 to 4 years did not consistently reduce the severity of disease or improve grain yield. By comparison, inoculum on pea crop residues declined rapidly after one season. Aerial inoculum was released from residues in two main periods: in autumn, before the pea crop was sown, and also in spring. Very little aerial inoculum was measured in winter. Rainfall in summer and autumn influenced inoculum release prior to sowing and reduced the disease pressure during establishment of the crop. Aerial inoculum was exhausted once 193 mm of rainfall had been received after 1 December. Delayed sowing was the best strategy for reducing the level of disease by avoiding the autumn peak in aerial inoculum. Disease severity was more than halved and grain yield increased by 6% by delaying sowing by 3–4 weeks. However, in the absence of disease, grain yield of early-sown crops was 20% greater than that of late-sown crops. A strategy of early sowing and the strategic use of fungicide may enable the dual goals of reduced disease and improved yields to be achieved. Early sowing without the disease penalty may be possible in seasons that have high summer and autumn rainfall, which results in the release of ascospores prior to sowing.

Temperature dependence of wheat development

Among the abiotic stress factors influencing the growth and productivity of wheat varieties, extremely high temperatures have the most limiting effect. In an experiment set up in the gradient chamber of the Martonvásár phytotron to test the effect of various temperatures on four winter wheat varieties and one variety of spelt, substantial differences were observed in the heat stress tolerance of the varieties. There was a considerable reduction in the number of shoots and spikes as the result of heat stress, leading to a drastic loss of grain yield. It was clear from changes in the biomass and in the grain:straw ratio that extremely high temperatures led to a substantial reduction in the ratio of grain to straw in the varieties tested. In response to high temperature the wheat plants turned yellow earlier due to the rapid decomposition of the chlorophyll content. This resulted in a considerable shortening of the vegetation period and early ripening. Reductions in the parameters tested were observed at different temperature levels for each variety, indicating considerable differences in the ability of the varieties to adapt to abiotic stress factors.

Molecular breeding for wheat fusarium head blight resistance in China

Wheat Fusarium head blight (FHB) may cause serious losses in grain yield and quality in China. More than 7 million hectares which approximately accounts for 25% of the total areas in China is infected by the disease. The cultivation of wheat varieties with resistance to Fusarium head blight is recognized as one of the most important components to diminish losses due to this disease. Chinese wheat breeders have commenced the research on FHB since 1950s. Wheat cultivars with improved FHB resistance were developed through conventional breeding. Some famous resistant varieties such as Sumai 3, Yangmai 158 and Ning 7840 were released from Jiangsu Academy of Agricultural Sciences, these varieties were widely applied in wheat production and breeding programs. Significant achievements concerning molecular mapping and marker assisted selection have been made in the past decade. The major QTL on chromosome 3BS was identified and located in the same region on chromosome 3BS in Sumai 3, Ning 894037, Wangshuibai, and Chinese Spring. Using SSR marker in this QTL region for assisted selection, some lines with the same resistance to FHB were obtained. New STS markers and SSCP markers were developed and will be tested for the efficiency of MAS. However, further achievements are still hindered by a number of constraints. More FHB resistance genetic resources from landrace in middle to lower reaches of Yangtze River are necessary to be used for improving FHB resistant. The genetic mechanism of the varieties contributing the resistance to improved cultivars is needed to be understood. Development of functional markers for FHB is discussed.

The maize (Zea maysL.)roothairless3gene encodes a putative GPI‐anchored, monocot‐specific, COBRA‐like protein that significantly affects grain yield

SummaryThe rth3 (roothairless 3) mutant is specifically affected in root hair elongation. We report here the cloning of the rth3 gene via a PCR-based strategy (amplification of insertion mutagenized sites) and demonstrate that it encodes a COBRA-like protein that displays all the structural features of a glycosylphosphatidylinositol anchor. Genes of the COBRA family are involved in various types of cell expansion and cell wall biosynthesis. The rth3 gene belongs to a monocot-specific clade of the COBRA gene family comprising two maize and two rice genes. While the rice (Oryza sativa) gene OsBC1L1 appears to be orthologous to rth3 based on sequence similarity (86% identity at the protein level) and maize/rice synteny, the maize (Zea mays L.) rth3-like gene does not appear to be a functional homolog of rth3 based on their distinct expression profiles. Massively parallel signature sequencing analysis detected rth3 expression in all analyzed tissues, but at relatively low levels, with the most abundant expression in primary roots where the root hair phenotype is manifested. In situ hybridization experiments confine rth3 expression to root hair-forming epidermal cells and lateral root primordia. Remarkably, in replicated field trials involving near-isogenic lines, the rth3 mutant conferred significant losses in grain yield.

Análise de trilha para componentes do rendimento e caracteres agronômicos de trigo sob desfolha

O objetivo deste trabalho foi avaliar a influência dos componentes do rendimento e caracteres da planta, na produção de grãos, em trigo sob desfolha, por meio da decomposição das correlações por meio de análise de trilha. O experimento foi conduzido em Viçosa, MG, em 2004. Os tratamentos constituíram-se de três níveis de desfolha e uma testemunha, com três variedades de trigo - Anahuac, BRS 207 e BR 24 -, com quatro repetições. A desfolha foi realizada com a retirada do limbo da folha bandeira, das segunda e terceira folhas superiores. Avaliaram-se: rendimento de grãos, peso do hectolitro, massa de mil grãos, número de espigas por parcela, número de grãos por espiga, biomassa seca do colmo, biomassa seca da palha da espiga, biomassa seca total, rendimento de grãos por espiga, biomassa seca do colmo individual, biomassa seca da palha da espiga individual e biomassa seca total por planta individual. A redução da biomassa seca do colmo levou a menores perdas de rendimento de grãos, pela remobilização de fotoassimilados com a desfolha. A massa de mil grãos e o número de grãos por espiga foram os principais componentes de rendimento. A seleção direta para esses caracteres é estratégia eficiente para aumentar o rendimento de grãos em trigo sob desfolha.

Role of stalk-anatomy and yield parameters in development of charcoal rot caused byMacrophomina phaseolina in winter sorghum

Charcoal rot caused byMacrophomina phaseolina (Tassi) Goid. damages stalk tissue and weakens stalk strength, leading to lodging of crop and loss in grain yield in sorghum. In an attempt to understand the pathogenicity byM. phaseolina in relation to stalk characters and plant outputs, the effects of morphological (stalk-thickness), anatomical (bundle-number, bundle-density, and vascular tissue) and physiological characters (water and soluble sugar content) of the stalks of winter sorghum genotypes on charcoal rot development were analyzed. Bundle-number and stalk-thickness had a significant influence on internal spread of charcoal rot. A thicker stalk facilitated the spread of lesions more than did a thinner one. A stalk with densely packed vascular bundles inhibited lesion advancement. Field studies with 24 winter sorghum genotypes demonstrated that most of the parameters that could improve grain and stover yield also increased the length of charcoal rot lesions. Lesion development in stalks showed a high degree of association with grain yield (R2=0.51) and 100-grain weight (R2=0.42). The rate of symptom development in stalks differed during dough and maturity stages. It was concluded that anatomical characters of sorghum stalk, especially bundle-number, along with yield parameters played an important role in determining the extent of stalk damage by charcoal rot in winter sorghum.

Managing nematode pests in the southern and western regions of the Australian cereal industry: continuing progress in a challenging environment

Both cereal cyst (Heterodera avenae) and root-lesion nematode (Pratylenchus spp. ) are associated with loss of grain yield in south-eastern and western Australia. Cereal cyst nematode has been a major pest since the 1930s but losses have declined significantly in the last 15 years due to more effective rotations and the widespread adoption of well adapted cereal cultivars with nematode resistance — strategies that were developed during several decades of research by pathologists, nematologists, agronomists and plant breeders. Research efforts are now focussed on reducing crop losses associated with root-lesion nematode. Rotations that minimise losses from the nematode have been identified, but a better-resourced plant breeding program is required to develop resistant cereal cultivars adapted to environmental conditions across the region. This paper reviews 40 years of research on the epidemiology and management of these two important pests.

Root-lesion nematodes (Pratylenchus thorneiandP. neglectus): a review of recent progress in managing a significant pest of grain crops in northern Australia

Two species of root-lesion nematode (predominantly Pratylenchus thornei but also P. neglectus) are widespread pathogens of wheat and other crops in Australia's northern grain belt, a subtropical region with deep, fertile clay soils and a summer-dominant rainfall pattern. Losses in grain yield from P. thornei can be as high as 70% for intolerant wheat cultivars. This review focuses on research which has led to the development of effective integrated management programs for these nematodes. It highlights the importance of correct identification in managing Pratylenchus species, reviews the plant breeding work done in developing tolerant and resistant cultivars, outlines the methods used to screen for tolerance and resistance, and discusses how planned crop sequencing with tolerant and partially resistant wheat cultivars, together with crops such as sorghum, sunflower, millets and canaryseed, can be used to reduce nematode populations and limit crop damage. The declining levels of soil organic matter in cropped soils are also discussed with reference to their effect on soil health and biological suppression of root-lesion nematodes.

Mechanisms of resistance to Helicoverpa armigera and introgression of resistance genes into F1 hybrids in chickpea

The noctuid pod borer, Helicoverpa armigera is a major pest of chickpea, and host plant resistance is an important component for managing this pest. We evaluated a set of diverse chickpea genotypes with different levels of resistance to H. armigera, and their F1 hybrids for oviposition non-preference, antibiosis, and tolerance components of resistance under uniform insect infestation under greenhouse/laboratory conditions. The genotypes ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB were non-preferred for oviposition under no-choice, dual-choice, and multi-choice conditions, and also suffered lower leaf damage in no-choice tests as compared to the susceptible check, ICCC 37. Antibiosis expressed in terms of low larval weights was observed in insects reared on ICC 12476, ICC 12478, and ICC 506EB. Weight gain by the third-instars was also low on ICC 12476, ICC 12477, ICC 12478, ICC 12479, and ICC 506EB at the podding stage. Non-preference for oviposition and antibiosis (poor larval growth) were also expressed in hybrids based on ICC 12477, ICC 12476, ICC 12478, ICC 12479, and ICC 506EB as compared to the hybrids based on the susceptible check, ICCC 37, indicating that oviposition non-preference and antibiosis in the F1 hybrids is influenced by the parent genotype. Loss in grain yield was lower in ICC 12477, ICC 12478, ICC 12479, and ICC 506EB compared to that on ICCC 37. The genotypes ICC 12477, ICC 12478, ICC 12479, and ICC 506EB showing antixenosis, antibiosis, and tolerance mechanism of resistance to H. armigera can be used for developing chickpea cultivars for resistance to this pest.

Weed management in aerobic rice systems under varying establishment methods

Aerobic rice systems, wherein the crop is established via direct-seeding in non-puddled, non-flooded fields, are among the most promising approaches for saving water and labour. However, aerobic systems are subject to much higher weed pressure than conventionally puddled transplanted rice (CPTR). Experiments were conducted for 2 years to develop effective and economical methods for managing weeds in aerobic rice grown by direct-seeding or transplanting on flat land or furrow-irrigated raised-bed systems (FIRBS). Total weed dry weight and weed density were lower with CPTR and highest with aerobic direct-seeded rice on a FIRBS (ADSB), followed by aerobic direct-seeded rice (ADSR). In terms of weight grassy weed constituted 78–96% of total weed weight in all systems of rice establishment. Loss of grain yield of rice due to weed competition ranged from 38% to 92%, being the highest in ADSB. Both weed density and dry weight were negatively correlated with rice grain yield. ADSR treatment produced yield and net economic returns similar to CPTR treatment when weeds were controlled. Pretilachlor with safener at 500 g a.i. ha −1 applied 3 days after sowing (DAS)/ days after transplanting (DAT) followed by chlorimuron+metsulfuron at 4 g a.i. ha −1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/DAT could effectively control all the weeds. The next best treatment was cyhalofop-butyl at 120 g a.i. ha −1 applied 14 DAS/DAT followed by chlorimuron+metsulfuron at 4 g a.i. ha −1 applied 21 DAS/DAT followed by hand-weeding at 35 DAS/DAT. The ADSR was as effective as conventionally puddle-transplanted rice in attaining higher rice grain yield and net returns when weeds were kept under control.

Straighthead disease of rice ( Oryza sativa L.) induced by arsenic toxicity

Straighthead disease is a physiological disorder of rice ( Oryza sativa L.) characterized by sterility of the florates/spikelets leading to reduced grain yield. Though the exact cause of straighthead is unknown, a glass house experiment was conducted to investigate the effect of inorganic arsenic on straighthead disease in rice ( Oryza sativa L.). BRRI dhan 29, a popular Bangladeshi rice strain, was grown in soils spiked with arsenic (prepared from sodium arsenate, Na 2HAsO 4·7H 2O) at the rate of 10, 20, 30, 40, 50, 60, 70, 80 and 90 mg of As kg −1 and one control treatment was also run to compare the results. Although there may be some other soil physico-chemical factors involved, arsenic concentration was found to be closely associated with straighthead of rice. With the increase of soil arsenic concentration, the severity of straighthead increased significantly. Up to the 50 mg of As kg −1 soil treatments, the severity of straighthead incidences were not prevalent. Straighthead resulted in sterile florets with distorted lemma and palea, reduced plant height, tillering, panicle length and grain yield. Straighthead caused approximately 17–100% sterile florates/spikelets formation and about 16–100% loss of grain yield. Straighthead also causes the reduction of panicle formation and panicle length significantly ( p < 0.01). In the present study, panicle formation was found to be reduced by 21–95% by straighthead.

Dominance, diversity and species composition of the weeds of rice crop in Doon Valley

Weeds have a direct effect on crop yields when they compete with the crop for nutrients, moisture and light. It is found infested with a variety of ways, which compete with the crop and often cause losses in grain yield ranging from 20-30%. During this study dominance, diversity and species composition of the weeds of Rice field in Doon Valley was studied. The study was conducted in the various Villages viz. Babugarh, Doctorganj and Bawanpur of the Vikasnagar block of Doon Valley in the month of August and September. A total of 24 weeds of rice fields were recorded in the selected sites. Lindernia anagallis, Cyperus iria and Echinochloa colona are the dominant weed species in the month of August, with the heighest IVI values (73.36, 57.69 and 67.45) in Babugarh, Doctorganj and Bawanpur respectively. Meanwhile, in September the highest IVI values (65.84, 53.66 and 94.56) were reported for weed species Caesulia axillaris, Cyperus difformis and Fimbristylis miliacea for the selected villages of Vikasnagar block of the Valley. Maximum diversity 2.54 was reported in the village Doctorganj during the month of September.

Comparison of phenotypic and marker-based selection for Fusarium head blight resistance and DON content in spring wheat

Fusarium head blight (FHB) is one of the most economically important wheat diseases, resulting in losses in grain yield and quality as well as contamination with deoxynivalenol (DON). Cultivar Sumai 3 from China and its descendants as well as var. Frontana from Brazil have been identified as potent sources of resistance and subsequently mapped by molecular markers. The aim of the present study was to compare phenotypic and marker-based selection in spring wheat. In a double cross, we combined two donor-quantitative trat loci (QTL) alleles from CM82036 (Sumai 3/Thornbird) located on chromosomes 3B and 5A and one donor-QTL allele from var. Frontana on chromosome 3A with two high-yielding German spring wheat varieties. This initial population was selected phenotypically by a two- (CP1) and three-step procedure (CP1+) and by independent marker-based analysis using one to three flanking markers per QTL (CM). To estimate selection gain, the two phenotypically selected variants and the marker-selected variant as well as an unselected variant (C0) were inoculated with FHB in the field at four locations in 2004. Between 26 and 135 progeny were tested from each variant. FHB severity and DON content were significantly reduced by all selection variants. The highest total selection gain was obtained by the three-step phenotypic selection for both traits, although marker-based selection for the two donor-QTL alleles from CM82036 proved to be more powerful on an annual basis. The large range of variation for FHB resistance and, to a lesser extent, DON content within the marker-based variant, however, shows that an additional phenotypic selection will enhance selection gain.

Host resistance and fungicide control of leaf rust ( Puccinia hordei) in barley ( Hordeum vulgare) and effects on grain yield and yield components

The effectiveness of varying levels of host resistance in five barley ( Hordeum vulgare L.) genotypes and three fungicide application protocols on the control of leaf rust (caused by Puccinia hordei G. Otth) and losses in grain yield, test weight, and 1000-kernel weight was evaluated in field experiments at two locations over four crop years. Fungicide treatments applied to all barley entries at each location and each year included a non-treated control, a single threshold-based application of triadimefon (140 g a.i. ha −1), and a complete control treatment comprised of multiple applications of triadimefon to emulate a disease-free environment. Leaf rust severity was assessed using the James [1971. A Manual of Assessment Keys for Plant Diseases. Canada Dep. Agric. Publ. 1458. The American Phytopathological Society, St. Paul, MN.] scale (0–25%) at three to four plant growth stages and data were used to calculate mean rust severity (MRS) and area under the disease progress curve (AUDPC). Leaf rust epidemics were severe in 1 (1995) of the 4 years of the study, and the treatment effect on grain yield was significant at one location (Warsaw). The susceptible cv. Wysor had a grain yield loss of 33% and MRS was 9.25% (34.23% in modified Cobb scale) at this location. In 2 (1995 and 1997) of 4 years of study, significant ( P ⩽ 0.05 ) negative correlations were obtained between MRS and grain yield, test weight, and 1000-kernel weight of cv. Wysor at both locations. In the other 2 years (1994 and 1996) when leaf rust epidemics were mild, these correlations were mostly non-significant. In general, fungicide treatment significantly ( P ⩽ 0.05 ) reduced MRS and AUDPC and reduced losses in grain yield, test weight, and 1000-kernel weight for the susceptible and moderately susceptible cultivars compared with the non-treated control. The cv. Starling, possessing adult-plant resistance, did not consistently benefit from fungicide application. There was no benefit from fungicide application for control of leaf rust in the resistant line VA92-42-46. In general, the complete-control fungicide treatment did not result in further significant reduction in leaf rust or losses in grain yield compared to threshold-level fungicide applications.

Yield reduction in barley in relation to spot-type net blotch

To study the loss of grain yield associated with specific levels of spot-type net blotch of barley, experiments were conducted at three sites with between four and six different levels of application of the fungicide propiconazole or mixtures of propiconazole and iprodione applied to obtain a wide range of disease levels. Yield loss varied from 23 to 44%. There was a negative linear relationship between yield and the average disease severity on the top three leaves (flag, flag-1 and flag-2). The observed relationship was much stronger at the milk stage compared with early flag leaf emergence stage. On average, every 10% increase in disease severity on the top three leaves accounted for 0.4 t/ha yield loss. The yield response to disease was independent of locations and years. The disease affected grain quality, with grain protein and screenings consistently higher and grain size consistently lower than samples from undiseased barley.