High Input Conditions Research Articles

Effect of Low-Input Management on Pest Damage to Rice (<i>Oryza Sativa</i> L) Under Natural Infestation in Southeastern Nigeria

Seven rice lines, selected for their good performance under Low-input management condition, were studied under low and high-input management conditions in Umudike in Abia State and Uyo in Akwa-Ibom State , to establish the effect of low-input management on diseases and pests of rice under natural infection and infestation in the humid zone of Southeastern Nigeria. The experiment was laid out in a randomized complete block design (RCBD) with three replications. Data were collected on leaf blast, glume discoloration, brown leaf spot, kernel smut, and stem borer infestations under both low and high-input management conditions. Glume discoloration was most severe under zero fertilizer rate. However, there were no clear trends in the attack by diseases and insect pests based on management levels. Damage level by insects were not significantly different under low-input and high-input management conditions and infection levels by diseases were also not significantly different under low-input and high-input conditions. Therefore low-input cannot be said to aggravate pest infestation or disease infection in rice. Keywords: Low-input, High-input, management, diseases, insect pests and rodents.Journal of Agriculture and Food Sciences Vol. 5 (1) 2007: pp. 1-10

Changes in allele frequencies in landraces, old and modern barley cultivars of marker loci close to QTL for grain yield under high and low input conditions

Changes in alleles frequencies of marker loci linked to yield quantitative trait loci (QTL) were studied in 188 barley entries (landraces, old and modern cultivars) grown in six trials representing low and high yielding conditions in Spain (2004) and Syria (2004, 2005). A genome wise association analysis was performed per trial, using 811 DArT® markers of known map position. At the first stage of analysis, spatially adjusted genotypic means were created per trial by fitting mixed models. At the second stage, single QTL models were fitted with correction for population substructure, using regression models. Finally, multiple QTL models were constructed by backward selection from a regression model containing all significant markers from the single QTL analyses. In addition to the association analyses per trial, genotype by environment interaction was investigated across the six trials. Landraces seemed best adapted to low yielding environments, while old and modern entries adapted better to high yielding environments. The number of QTL and the magnitude of their effects were comparable for low and high input conditions. However, none of the QTL were found within a given bin at any chromosome in more than two of the six trials. Changes in allele frequencies of marker loci close to QTL for grain yield in landraces, old and modern barley cultivars could be attributed to selection exercised in breeding, suggesting that modern breeding may have increased frequencies of marker alleles close to QTL that favour production particularly under high yield potential environments. Moreover, these results also indicate that there may be scope for improving yield under low input systems, as breeding so far has hardly changed allele frequencies at marker loci close to QTL for low yielding conditions.

Interactions of sunflower ( Helianthus annuus) and sunflower broomrape ( Orobanche cumana) as affected by sowing date, resource supply and infestation level

The holoparasitic weed Orobanche cumana (sunflower broomrape) constrains sunflower ( Helianthus annuus) production in many countries. The development of efficient control strategies requires an understanding of the processes underlying the complex environment–host–parasite interrelations. Growth and development of O. cumana and sunflower were quantified under field conditions in southeastern Romania. Sunflower hybrid Florom 350 was sown at two dates, in plots infested with 0, 50, 200 and 1600 viable O. cumana seeds kg −1 dry soil, under low-input (rainfed, low nitrogen supply) and high-input (irrigated, high nitrogen supply) conditions. Sunflower shoot biomass reached peak values of 760–1287 g m −2 between the end of anthesis and physiological maturity. Seed yield varied from 221 to 446 g m −2. Sunflower biomass and yield were affected by all experimental factors. Seed yield responded positively to delaying sowing from early April to late May as well as to irrigation and fertilisation, and negatively to O. cumana infestation. Yield reductions, which were a product of reduced seed number and size, amounted to 13%, 25% and 37% at parasite seed densities of 50, 200 and 1600 viable seeds kg −1 soil, respectively. Maximum O. cumana attachment numbers, recorded in late-sown high-input crops in 2004, ranged from 11 m −2 in plots with 50 parasite seeds kg −1 soil to 188 m −2 with 1600 seeds kg −1 soil. Parasite attachment number was a function of crop sowing date, water and nutrient supply, seedbank density, and sunflower biomass and root length density, via mechanisms of parasite seed stimulation, host carrying capacity and intraspecific competition. Delayed sowing and improved water and nitrogen supply were associated with increases in parasite number that neutralised yield-boosting effects of irrigation and fertilisation at the highest infestation level. Sunflower shoot biomass was significantly reduced by O. cumana infection, with reductions affecting organs in the order head > stem > leaves. Most of the discrepancy between infected and non-infected plants was accounted for by O. cumana biomass. Parasites mainly acted as an extra sink for assimilates during sunflower generative growth and impaired host photosynthesis to a much lesser degree. Results suggest that similar mechanisms govern infection level and host–parasite biomass partitioning across different Orobanche–host systems.

An induced brachytic mutant of chickpea and its possible use in ideotype breeding

Mutations were induced in chickpea (Cicer arietinum L.) cultivar ‘JG 315’ through treatment of seeds with ethyl methane sulphonate (EMS). One of the mutants, named JGM 1, had brachytic growth (compact growth), characterized by erect growth habit, thick and sturdy stem, short internodal and interleaflet distances and few tertiary and later order branches. It was isolated from M2 derived from seeds treated with 0.6% EMS for 6 h. Segregation analyses in F2 progenies of its crosses with normal chickpea genotypes (JG 315, ICC 4929, and ICC 10301) suggested that a single recessive gene controlled brachytic growth in JGM 1. This gene was not allelic to the br gene for brachytic growth in spontaneous brachytic mutant E100YM. Thus, the gene for brachytic growth in JGM 1 was designated br2 and the br gene of E100YM was redesignated br1. Efforts are being made to use JGM 1 in development of a plant type with short internodes and erect growth habit. Such plant type may resist excessive vegetative growth in high input (irrigation and fertility) conditions and accommodate more plants per unit area.

Decline in the growth of a sugarcane crop with age under high input conditions

In Australian sugarcane crops, growth in terms of radiation use efficiency (RUE) can appear to slow down well before final crops are harvested, despite conditions that are considered favourable for growth. In order to assess the extent and cause of this reduced growth phenomenon (RGP), 14 experiments conducted in Australia were examined. From these experiments, 34 treatments were selected where nutrients and water were likely to be non-limiting and consequently the yields obtained were likely to be limited only by temperature and radiation. Radiation use efficiency is defined as the measured amount of net biomass accumulated above ground per unit radiation intercepted. Accumulated biomass may have been lost through loss of stalks. In almost half of the treatments RUE significantly declined between approximately 223 and 665 days after crop start. The high incidence of RGP found in the analyses (a) challenges the previously held assumption that a constant value of RUE can be used to adequately describe biomass accumulation in sugarcane as a function of cumulative radiation interception and (b) suggests that relatively low growth rates during the later phases of the cropping season are frequently experienced throughout the Australian sugar industry. Reduced growth phenomenon resulted in actual biomass at final harvest being on average 21% less than potential yield, compared with 5% in crops that did not display a slowdown in growth. Mean maximum RUE in the plant crop was greater than in ratoon crops, at 1.37 and 1.19 g MJ −1, respectively. As there was no effect of location, cultivar, crop duration, ratoon crop class or fumigation treatment on RUE for the periods either before or after the onset of reduced growth, it would appear that the value of RUE is predominantly influenced by crop class. Despite the differences in RUE between the two crop classes, RGP occurred at a similar frequency in both plant and ratoon crops. In order to gain a greater mechanistic understanding of the factors likely to be associated with the onset of the RGP, the relative time of lodging, specific leaf nitrogen (SLN), number of stalks and seasonal temperature were all considered individually. Whilst declining SLN and increasing stalk loss were associated with reductions in growth during the later periods of crop growth, it is likely that lodging also contributed to the widespread slowdown in biomass accumulation, whereas photosynthetic stress, as a result of extreme temperatures, did not play a substantive role in reducing growth.

Wear, Debris, and Biologic Activity of Cross-linked Polyethylene in the Knee

Cross-linked polyethylene currently is being introduced in knee prostheses. The wear rates, wear debris, and biologic reactivity of non cross-linked, moderately cross-linked, and highly cross-linked polyethylene have been compared in multidirectional wear tests and knee simulators. Multidirectional pin-on-plate wear studies of noncross-linked, moderately cross-linked (5 Mrad), and highly cross-linked (10 Mrad) polyethylene showed a 75% reduction in wear with the highly cross-linked material under kinematics found in the hip, but only a 33% reduction under wear in kinematics representative of the knee. In knee simulator studies, with the fixed-bearing press-fit, condylar Sigma cruciate-retaining knee under high kinematic input conditions, the wear of 5 Mrad moderately cross-linked polyethylene was 13 +/- 4 mm per 1 million cycles, which was lower (p < 0.05) than the wear of clinically used, gamma vacuum foil GUR 1020 polyethylene (23 +/- 6 mm/1 million cycles). For the low-contact stress mobile-bearing knee, the wear of moderately cross-linked polyethylene was 2 +/- 1 mm per 1 million cycles, which was lower (p < 0.05) than GVF GUR 1020 polyethylene (5 +/- 2 mm/1 million cycles). The wear debris isolated from the fixed-bearing knees showed the moderately cross-linked material had a larger percentage volume of particles smaller than 1 mum in size, compared with GVF GUR 1020 polyethylene. Direct cell culture studies of wear debris generated in sterile wear simulators using multidirectional motion showed a increase (p < 0.05) in tumor necrosis factor-alpha levels and reactivity for GUR 1050 cross-linked polyethylene debris compared with an equivalent volume of noncross-linked GUR 1050 polyethylene. The use of cross-linked polyethylene in the knee reduces the volumetric wear rate. However, the clinical significance of reduced fracture toughness, elevated wear in abrasive conditions, and the elevated tumor necrosis factor-alpha release from smaller more reactive particles warrant further investigation.

Adaptive Coincidence Detection and Dynamic Gain Control in Visual Cortical Neurons In Vivo

Several theories have proposed a functional role for response synchronization in sensory perception. Critics of these theories have argued that selective synchronization is physiologically implausible when cortical networks operate at high levels of activity. Using intracellular recordings from visual cortex in vivo, in combination with numerical simulations, we find dynamic changes in spike threshold that reduce cellular sensitivity to slow depolarizations and concurrently increase the relative sensitivity to rapid depolarizations. Consistent with this, we find that spike activity and high-frequency fluctuations in membrane potential are closely correlated and that both are more tightly tuned for stimulus orientation than the mean membrane potential. These findings suggest that under high-input conditions the spike-generating mechanism adaptively enhances the sensitivity to synchronous inputs while simultaneously decreasing the sensitivity to temporally uncorrelated inputs.

Genetic diversity among European cultivated spelt revealed by microsatellites

Spelt and common wheat constitute two of the six groups of the hexaploid wheats with an AABBDD genome. Spelt culture has been progressively replaced by that of common wheat which out-yields spelt under high-input conditions. In the last decades, spelt breeders intended to introduce the yield-potential and bread-making qualities of common wheat into spelt, by frequent crossings between accessions of these two different groups. The present study aims at determining the genetic basis of modern spelt cultivars in terms of intra-group variability and inter-group (spelt vs common wheat) distances, by using microsatellite markers developed for common wheat. The allelic composition of 30 spelt and nine common wheat accessions was determined at 17 microsatellite loci. The coefficient of co-ancestry (ƒ) and the genetic distances (1 - proportion of shared alleles) based upon allelic composition were calculated for all pairs of accessions. Two dendrograms were constructed using the UPGMA method. Amplification products were found for all loci on most accessions. A total of 113 alleles was identified, of which 60.2% were specific to spelt or common wheat. The correlation between (1 –ƒ ) and the genetic distance was high (0.701***). The mean pairwise genetic distance was 0.656 ± 0.181 over the 39 accessions, 0.706 ± 0.14 among common wheat and 0.573 ± 0.172 among spelt. The mean genetic distance between spelt and wheat was 0.782 ± 0.113. The two dendrograms were in accordance with each other and clearly separated the spelt from the common wheat accessions. It is concluded that microsatellites developed for common wheat and distances based on the proportion of shared alleles are powerful tools for reconstructing phylogenies in spelt, and that the genetic basis of modern spelt cultivars is narrow despite frequent crosses made with bread wheat.

Adaptabilidade e estabilidade de comportamento de cultivares de milho em treze ambientes nos tabuleiros costeiros do nordeste brasileiro

Dezesseis cultivares de milho foram avaliadas em treze ambientes dos tabuleiros costeiros do Nordeste brasileiro, no período de 1994/95, em blocos ao acaso, com três repetições, visando conhecer o potencial dessa região para a produção do milho e a adaptabilidade e a estabilidade desses materiais para recomendação. As produtividades médias alcançadas, especialmente com os híbridos, mostraram o grande potencial dessa faixa costeira do Nordeste para a produção do milho, sobressaindo os tabuleiros costeiros do Piauí, Sergipe e Bahia, onde o milho poderá se tornar uma grande alternativa para os produtores. A análise de variância conjunta mostrou diferenças entre os locais e as cultivares, e a inconsistência das cultivares em face das variações ambientais. Usou-se o método de Cruz et al. para atenuar o efeito da interação cultivares x ambientes, de modo a permitir uma recomendação com mais segurança. Os híbridos mostraram melhor adaptação que as variedades e populações, e são recomendados para exploração em ambientes mais tecnificados. O AG 510, por mostrar adaptação em ambiente desfavorável, é também recomendado para esta condição. As variedades BR 5011, BR 5028, BR 106 e BR 5033, de bons rendimentos, constituem alternativas importantes para pequenos e médios produtores de milho.

Genotypic variation for grain yield and grain nitrogen concentration among sorghum hybrids under different levels of nitrogen fertiliser and water supply

Sorghum [Sorghum bicolor (L.) Moench] is often grown under nitrogen- or water-limited conditions, but there is little information on genotypic variation for grain yield and grain nitrogen (N) concentration under these conditions. This study examined the expression of specific adaptation of hybrids to these stress conditions and, secondly, the effect of N fertiliser application on yield and grain N concentration of the hybrids. Two experiments, one irrigated and the other under rainfed conditions, were conducted in 2 seasons to examine 14 hybrids grown under 3 levels of fertiliser N supply (0, 60, and 240 kg/ha). Genotypic variation for yield and grain N concentration was generally larger than the in˚uence of genotype environment (predominantly N and water) interactions. Genotypic variation for phenology was important in determining variation for yield and grain N concentration in high-input and rainfed conditions when N was not the limiting factor, but not under N-limiting conditions. Under high-input conditions (240 kg/ha of N fertiliser and irrigated), maturity date accounted for about 50% of the genotypic variation for grain yield (798-1049 g/m2), with later maturing hybrids having a higher yield. Maturity date had little effect on plant N content at maturity or N harvest index, and hence grain N concentration (1·67-2·01%) was negatively correlated with grain yield. Under N-limiting conditions, N fertiliser application had large effects on yield and/or grain N concentration in both well-watered and pre-anthesis water stress conditions. In the irrigated experiment, when N was limiting (0 and 60 kg/ha of N fertiliser), genotypic variation for grain yield (225-729 g/m2) was not related to that for maturity date. It was, however, related to the variation in N uptake and dry matter growth by anthesis in the non-fertilised treatment. There was significant genotypic variation for grain N concentration (0·94-1·26%), which was not explained by variation for grain yield. Under rainfed conditions, where severe pre-anthesis water stress occurred, phenology was important in determining about 40% of the genotypic variation for yield (69-286 g/m2). The late-flowering hybrids escaped the major impact of the pre-anthesis water stress, had reduced damage to panicle development, and had higher N utilisation, consequently producing higher grain yield. Grain N concentration (1·09-2·85%) was again negatively related with grain yield. Genetic improvement of N uptake is identified as a possible breeding strategy for raising productivity and quality of grain sorghum under N-limiting conditions.

Effect of the timing of water deficit on growth, phenology and yield of pearl millet (Pennisetum glaucum(L.) R. Br.) grown in Sahelian conditions

Several studies conducted under high input conditions have indicated little susceptibility of pearl millet to water deficit untill early grain filling, because the losses in main shoot production were fully compensated by increased tiller fertility. The present study assessed the impact of water deficits at three development stages: prior to flowering (S30), at the beginning of flowering (S45), and at the end of flowering (S60) in pearl millet grown in experimental conditions similar to Sahelian farming conditions. It included a control irrigation treatment simulating the natural distribution of rainfall throughout the cropping season. Both biomass production and grain yield were severely reduced by S30 and S45, while S60 had no effect. In S30 and S45, the flowering of tillers was delayed or totally inhibited. In both of these treatments, the low number of productive tillers did not compensate for damage to panicle initiation and flowering of the main shoot. All treatments maintained green leaves on the main shoot during the grain filling period, and in S30 leaf growth recovered from mid-season drought. These results illustrate how pearl millet mostly escapes drought by matching its phenology to the mean rainfall distribution in the Sahel. In the case of mid-season drought, some late productive tillers and the maintenance of green leaf biomass of the main shoots limited, but did not overcome, the yield losses. This study stresses the importance of agro-ecological conditions in control treatments, particularly the water regime and crop density, when assessing crop drought resistance.

Growth of sugarcane under high input conditions in tropical Australia. III. Accumulation, partitioning and use of nitrogen

Leaf nitrogen (g N m −2 leaf) is an important determinant of crop radiation-use efficiency. It is not known to what extent sugarcane can maintain high leaf N over its long growth duration. This study analyses the accumulation of N in two contrasting cultivars of sugarcane (Q117, Q138) under plant and ratoon crop conditions, and the partitioning of N to the various plant components, including the leaf. The crops were grown for 15 months under irrigated conditions in the same season and received 34.4 g N m −2 as fertiliser over the first 100–120 days of the season. Higher early N accumulation by the ratoon crop was associated with higher early biomass production. However, maximum N accumulation was unrelated to maximum biomass accumulation, with the plant crop (25.9 g N m −2) accumulating more than the ratoon crop (21.3 g N m −2), which resulted in widely varying values for biomass/N ratio. N accumulation ceased later in the plant (200 days) than in the ratoon (150 days) crop, and this occurred 100–140 days before maximum biomass. More work is needed to determine if this is due to exhaustion of soil N supply, reduced root activity, or a lowered crop N requirement. Leaf N was maintained above 1.2 g N m −2 for 300 days of the 450 day season. Decline in leaf N below 1.2 g N m −2 at the end of the season was associated with loss in leaf and total crop N accumulation, and apparently unrelated to the timing of cessation in biomass accumulation. Throughout the season, leaf N was higher in the plant than the ratoon crop (averaged over cultivars), and Q117 versus Q138 (averaged over crop classes), however these differences could not explain crop-class differences in RUE. Cultivar differences in leaf N were due to higher N accumulation because specific leaf area and partitioning of biomass and N to leaf were unaffected by crop class or cultivar. The biomass/N ratio varied with cultivar and crop class, and increased with crop age.

Growth of sugarcane under high input conditions in tropical Australia. I. Radiation use, biomass accumulation and partitioning

There is little detailed information on yield accumulation in sugarcane under high-input conditions, which can be used to quantify the key physiological parameters contributing to yield variation. Sugarcane is grown under plant and ratoon crop conditions. This study analysed canopy development, radiation interception and biomass accumulation of two contrasting cultivars of sugarcane under irrigation during the same season under plant and ratoon crop conditions. Over the 15 month season, 11 crop samplings were conducted. Biomass partitioning to stalk was also measured to determine to what extent differences in partitioning between cultivars under ratoon and plant crop conditions contribute to differential productivity. The key findings were: (1) The ratoon crop accumulated biomass more quickly than the plant crop during the first 100 days of growth due to higher stalk number, faster canopy development and greater radiation interception. For similar reasons, cultivar Q138 had higher early biomass production than cultivar Q117 in the plant crop. (2) Early differences in biomass accumulation due to crop class became negligible at about 220 days because maximum RUE of the plant crop (1.72 ± 0.01 g MJ −1) was 8% higher than in the first ratoon crop (1.59 ± 0.08 g MJ −1). The higher maximum RUE in the plant crop was consistent with a higher crop growth rate (35.1 ± 2.3 versus 31.0 ± 3.4 g m −2 d −1) during the linear phase of biomass accumulation. (3) Biomass accumulation, which ceased about 300 days after planting/ratooning and 140 days before final harvest, attained similar levels of 53–58 t ha −1 in all four crops. (4) The plateau in biomass was associated with loss of live millable stalks, and not a cessation in the growth rate of individual stalks. The crops continued to intercept radiation while on the biomass plateau, so that average RUEs at final harvest were much lower than the maximum values. (5) There was no effect of crop class or cultivar on the fraction of biomass in the leaf and millable stalk components. This study emphasizes that maximising early radiation interception and biomass accumulation will not necessarily lead to higher yield in an environment where biomass production reaches a plateau well before final harvest. Loss of live millable stalks late in the crop cycle results in poor utilisation of intercepted radiation.

Growth of sugarcane under high input conditions in tropical Australia. II. Sucrose accumulation and commercial yield

Information on the processes controlling the accumulation of sucrose over time can be used to assess the physiological basis of yield variation and consequently the scope for yield improvement in sugarcane. As commercial yield is commonly expressed on a fresh weight basis, and dry weight measures of sucrose accumulation aid biological interpretation, there is a need to study yield accumulation on both a fresh and dry weight basis. This study analysed the pattern of sucrose accumulation in the stalk in relation to crop biomass, and the concentration of sucrose in the stalk on a fresh and dry weight basis of two contrasting cultivars (Q117 and Q138) of sugarcane during the same season in tropical Australia, with irrigation and under plant and ratoon crop conditions. Over the 15 month season, 11 crop samplings were conducted. The key findings were that (1) greater than 95% of the aboveground sucrose accumulation is in the stalk; (2) a logistic relationship described the time trend in stalk sucrose accumulation, with maximum sucrose yield occurring 100 days before final harvest; (3) stalk biomass rather than stalk sucrose concentration was the major determinant of stalk sucrose accumulation; (4) maximum stalk sucrose concentration was stable across cultivars and crop classes at a value of 0.48 g g −1 stalk dry weight; (5) commercial yield expressed as the fresh millable stalk yield plateaued up to 230 days before final harvest and well before the attainment of maximum stalk biomass and sucrose yield due to increases in dry matter content during growth; (6) maximum stalk sucrose concentration on a fresh weight basis was obtained at a later crop age and was more variable across crops than maximum stalk sucrose concentration on a dry weight basis. The study highlighted the major influence that stalk dry matter content has on the relationship between sucrose yield and commercial yield, and that biological interpretation of crop response to climatic and management factors is difficult based on commonly available fresh weight measures of productivity. Optimising economic return from commercial sugarcane production requires further understanding on the factors controlling the dynamics of stalk dry matter content.

Breeding crop varieties for low-input agriculture

AbstractFew plant breeding programs involve attempts to develop varieties specifically adapted to low-input cropping systems. Plant breeders generally select varieties in highly fertile, weed-free, densely seeded environments. However, alleles needed for achieving maximum yield in low-input environments often differ from those required in highinput conditions. Thus, when effective selection can be undertaken under low-input conditions, breeding programs specifically targeted at low-input environments should produce the best varieties for those environments. Experimental protocols for identifying such situations are described in this review. These involve (a) testing breeding lines under low- and high-input conditions, (b) estimating both the degree to which yields from the two types of environment are controlled by the same alleles and the relative accuracy with which superior genotypes can be identified in low- and high-input environments, and (c) predicting the direct and indirect responses to selection at each input level. On the basis of published data, it seems feasible to develop corn hybrids specifically adapted to production with lower rates of N application than are now commonly used in the United States.

A post‐Green Revolution strategy for the improvement of small farmer‐grown common beans

Abstract Since 1973, the CIAT Bean Progam has focused on disease resistance breeding, with selection for performance under low input conditions and adaptation to farmers’ current production systems. This strategy was chosen to make new bean technology more accessible to resource poor farmers in low income countries than had been the products of the Green Revolution approach of selecting for maximum yield under optimum high input conditions. A case study of adoption of new disease resistant bean varieties among small farmers in Costa Rica shows that the disease resistance strategy has resulted in varieties that improve productivity even in farmers’ traditional shifting cultivation system. However, many small farmers are finding it advantageous to intensify management in order to raise the gains from the new varieties. Such success in a disease resistance, small farm‐oriented crop improvement program, depends critically on strong national agricultural research capacity, and a continuing commitment to deploy...

Anomalous behavior of molybdenum oxide as a fire retardant for polyvinyl chloride

The widespread application of polyvinyl chloride (PVC) as wire and cable insulation in the communication and electrical industries is due in part to its inherent fire retardant properties, which are improved by the addition of antimony oxide. This addition also increases somewhat the already high rate of smoke formation. Molybdenum trioxide, used either with or instead of Sb 2O 3, has been reported to be a smoke suppressant as well as a flame retardant. This is corroborated by laboratory-scale measurements reported here. However, in a large-scale test under high enthalpy input conditions, MoO 3 appeared to be ineffective in limiting the flame spread. A detailed investigation of the pyrolysis of PVC by thermogravimetric analysis and mass spectroscopy showed that the addition of MoO 3 results in the reduction of the temperature at which HCl is evolved, an increase in the temperature at which the organic pyrolyzate is produced, and a change in compostion of this pyrolyzate from aromatic to aliphatic. The underlying chemical mechanism is explained by the action of MoO 3 as a Lewis acid: 1. 1. The dehydrochlorination of PVC is catalyzed and occurs at a lower temperature; 2. 2. This process yields trans polyenes, either directly or via rapid isomerization of cis polyenes; 3. 3. The trans polyenes, being unable to cyclize and split off benzene, are stable to higher temperatures, at which a different mechanism obtains to give aliphatic products. The ineffectiveness of MoO 3 is ascribed to the difference in flame characteristics between aliphatic and aromatic fuels. The disagreement between laboratory and large-scale tests is attributed to the higher temperature at which the aliphatic pyrolyzate appears, which is reached only under conditions of higher enthalpy input that prevail in the large-scale tests.