Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Re... more Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro) of maize is increasing in importance in sub-Saharan Africa (SSA). However, there is still limited information on the combining ability for disease resistance of the germplasm that are adapted to African environments. Evaluating combining ability effects and their interactions with the environment would provide valuable information that can be used in the development of cultivars that are resistant to PLS. This study was therefore conducted to determine the combining ability, gene action and the relationship between grain yield and PLS disease severity among selected tropical advanced maize inbred lines. Forty five F 1 hybrids were generated by crossing 10 inbred lines in a half diallel mating scheme. The 45 hybrids along with the ten inbred parents were evaluated in four environments, with two replications each between 2007 and 2009. General and specific combining ability (GCA and SCA) effects were highly significant (P ≤ 0.001) for PLS, grain yield and days to anthesis. GCA effects accounted for 66-90% and SCA effects for 10-34% of the variation in the hybrids for PLS resistance, grain yield and days to anthesis. This indicated predominance of additive over non-additive gene action for the three traits in these inbred lines. The resistant inbred lines to PLS were A1220-4, N3-2-3-3, CML312, MP18 and CML488. These lines had good combining ability for PLS resistance and contributed towards resistance in their crosses. In general, resistant hybrids involved a susceptible and a resistant parent, where at least one of the parents had a negative GCA effect. In addition, lines A1220-4 and CML312 contributed towards high yield and were late maturing. Inbred line CZL00009 conferred genes for early maturity. Linear regression analysis indicated that grain yield of maize was suppressed by about 250 kg ha −1 per each increase in PLS disease severity score, underscoring the need to control the disease. Significant (P < 0.01), negative correlations (r = −0.29 to −0.43) between grain yield and PLS severity were also detected. This showed the potential of PLS to reduce yield when favourable conditions for disease development are present. By and large, highly significant additive gene action implied that progress would be made through selection. Although non-additive effects were small (±10%), observation of dominance effects which were associated with reduced disease levels in some hybrids may be exploited in developing single cross maize hybrids among these inbreds when one parent is resistant.
ABSTRACT The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tro... more ABSTRACT The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tropical and subtropical regions worldwide. As a further step towards finding maize genotypes with acceptable levels of resistance to the maize weevil, 53 experimental maize hybrids that were generated in a North Carolina design II mating scheme, were evaluated for grain weight loss due to maize weevil damage under ambient temperature and humidity (ATH) conditions, in the on-station stock room at Harare, Zimbabwe. The study indicated that genotypic variation for grain weevil resistance was large (19%–57%) after five months of infestation by the maize weevils. A few F2 populations with potential for use as sources of breeding new varieties for maize weevil resistance were identified. They displayed consistency of high performance (better than the standard control varieties) and showed a lower rate of grain weight loss due to the maize weevils over the five months in the stock room. The male and female GCA and SCA effects were highly significant (P ≤ 0.01) for maize weevil resistance, especially at two months after infestation, indicating that resistance was controlled by genes with both additive and non-additive effects, respectively. Further, the distribution of grain weight loss data for the hybrids was continuous and almost normal at the four intervals of data collection, clearly supporting that resistance was partial and possibly conditioned by minor genes with cumulative effects. Therefore, resistance could probably be improved by selection among the promising F2 populations identified in this study. Although resistance was partial, a plot of grain weight loss of hybrids from the different categories demonstrated the advantage to farmers for growing a resistant variety (low percentage loss over time) compared to the susceptible ones that incurred significant grain weight losses. However, grain weight loss data were not significantly correlated with yield (r = 0.14; P &gt; 0.05), suggesting that the traits are not mutually exclusive. Therefore, breeding for maize weevil resistance in these populations would not necessarily compromise grain yield. Our results demonstrate that there is potential in developing maize varieties with acceptable levels of maize weevil resistance through recurrent selection procedures which exploit both GCA and SCA effects with sustainable impact on food security and the environment.
Diseases and pests are among the major constraints limiting maize productivity in the smallholder... more Diseases and pests are among the major constraints limiting maize productivity in the smallholder (SH) farming sector of sub-Saharan Africa. The objectives of this study were therefore, to determine how SH farmers perceive and cope with diseases and pests, identify with farmersother constraints to maize production. Data were collected from three villages of KwaZulu-Natal (KZN) province in South Africa using surveys and participatory rural appraisal (PRA) methodology. Local maize varieties were further evaluated for disease resistance and grain yield potential at two locations in KZN. Cob rots, grey leaf spot (GLS), maize streak virus (MSV), northern leaf blight (NLB), phaeosphaeria leaf spot (PLS) and common rust were the main diseases identified by farmers, but their incidence was low and occurrence infrequent. More than 75% of the farmers did not control both insect pests and diseases, while the rest used chemicals or everyday household remedies for control. Stalk borers and cutworms were the most prevalent insect pests, where as drought, excessive rains, hail storms, and soil fertility were the most important abiotic constraints identified. Field trial results of local varieties indicated high yield potential and genetic variability for disease resistance to PLS, GLS, and NLB. These findings suggest that; if the main production constraints are addressed, farmers could realize high yields from their local varieties. Breeding opportunities, therefore, exist for incorporating resistance or tolerance to these stresses into the local varieties.
Early planting of bambara groundnuts (Vigna subterranea L. Verdc) in the southern Africa enables ... more Early planting of bambara groundnuts (Vigna subterranea L. Verdc) in the southern Africa enables farmers to fetch premium prices before the markets are flooded with produce from the main summer growing period. However, adaptation of the crop outside the main growing season has not been studied in Zimbabwe. Therefore, this study evaluated 20 varieties at four planting dates covering contrasting temperatures and daylength, at Harare Research Station, during 2000/2001. Planting date was the main plot factor replicated three times and cultivar the subplot. Standard agronomic practices were followed and adequate moisture supplied through supplementary irrigation. Both the planting dates and variety main effects were significant (P<0.05) for yield and most of the secondary traits. Planting date x genotype interaction (G x E) effects were not significant (P<0.05) for yield, suggesting that cultivars were relatively yield stable. However, G x E effects were significant (P<0.05) for days to 50% emergence and pod count plant -1 . Differences among varieties were attributable to genotypic effects and different photothermal conditions. August and September planting dates resulted in high dry pod yield. Varieties BS599, BS537, V2-17, BS520, and Variety-10, had high relative yield, and were the most promising for off-season planting.
... southern and eastern Africa, most maize breeding programmes which are hybrid oriented use eli... more ... southern and eastern Africa, most maize breeding programmes which are hybrid oriented use elite maize ... to other diseases and abiotic stresses, such as drought tolerance and low nitrogen (N). The ... Field weight was then used to estimate the grain yield (t ha −1 ) adjusted to 12.5 ...
... Numbers of days to 50% flowering (number of days taken for half of the plot to reach anthesis... more ... Numbers of days to 50% flowering (number of days taken for half of the plot to reach anthesis), number of days to 95% maturity (number of days taken for about 95% of the plants to reach the hard dough stage), number of tillers plant −1 (tillers that were taller than half of the main ...
Bioethanol production from sweet sorghum entails expansion and intensive production of the crop, ... more Bioethanol production from sweet sorghum entails expansion and intensive production of the crop, which may include off-season production in the warm tropical lowlands. However, suitable cultivars are currently not available for this environment, especially in southern Africa. Hybrid cultivars were long ago demonstrated to be more productive than pure line varieties. Therefore a study was conducted to determine heterosis of experimental hybrids, and combining ability of parental lines for stem sugar traits. Sixty-four hybrids were generated among 16 lines in accordance with North Carolina design II mating scheme. Eight parents were cytoplasmic male sterile lines which were designated as females and were crossed with eight male fertile lines. The hybrids were evaluated at two sites in Mozambique and South Africa under off-season production conditions. Row-column alpha designs with three replications were used and standard agronomic practices were followed at both sites. Data were analysed in GenStat computer package. There was significant (P=0.05) variation among genotypes for stem °brix and associated traits. The top 20 stem °brix performers were constituted by 17 hybrids, exhibiting heterosis of up to 112%, and three parents. General and specific combining ability effects were significant for stem °brix and associated traits implying that both additive and non-additive gene action, respectively, were important for controlling the traits. The lines ZLR1 and ICSVP3046 displayed significant and positive GCA effects for stem °brix, while 13 crosses showed positive and significant SCA effects. These lines and the crosses ISCVP3046×ICSA4, ICSV700×ICSA731, ICSR165×ICSA307, ZLR1×ICSA474 and ICSR57×ICSA479, which combined high mean performance with positive SCA effects, would be recommended for use in breeding new varieties for tropical lowland environments.
ABSTRACT Development of top cross varieties with downy mildew (DM) resistance is one approach to ... more ABSTRACT Development of top cross varieties with downy mildew (DM) resistance is one approach to enhance maize productivity in tropical lowland environments. The objective of this study was to determine heterotic orientation of 18 advanced maize inbred lines towards popular open pollinated synthetic populations ZM523 and Suwan-1 under the prevalence of DM. The 36 top crosses, four hybrid check varieties and two testers, ZM523 (Z) and Suwan-1 (S) were evaluated in a 6 x 7 alpha-lattice design with two replications across three environments. General combining ability effects were significant (P&lt; 0.05) for DM resistance and grain yield, suggesting that genes with additive effects were important in controlling the traits. Specific combining ability (SCA) effects were not significant for DM suggesting small influence of DM resistance by the genes with non-additive effects; but SCA effects were significant for grain yield, indicating that non-additive gene effects played a significant role in governing the grain yield. Based on the SCA data, ten lines were grouped with Suwan-1 and eight lines with ZM523. Using the heterosis data, the lines were fitted into three groups that were designated as S, Z and SZ orientation. The lines ML2, ML30 and ML42, which displayed positive heterosis with both testers for grain yield, were allocated to the SZ-group. The lines ML8, ML10, ML25, ML45, and ML48 exhibited positive heterosis with Suwan-1 and were therefore, classified in the Z-group, and line ML19 that showed positive heterosis with ZM523 was fitted in the S-group. The remaining eight lines did not show any significant and positive heterosis with both testers hence they could not be classified based on heterosis data, suggesting that hybrid breeding efficiency could be improved by expanding the number of testers. Line ML42 displayed the highest level of heterosiswith both Suwan-1 (32 %) andZM523 (29 %) and outperformed all the standard check varieties qualifying it as a potential candidate for further testing. Generally, there was consistency of heterotic grouping of the lines using SCA and heterosis data.
Breeding for resistance to Angular Leaf spot (ALS), a fungal disease caused by Pseudocercospora g... more Breeding for resistance to Angular Leaf spot (ALS), a fungal disease caused by Pseudocercospora griseola (Sacc), is faced with a challenge of the existence of a few resistance sources that are exotic and not well adapted to environmental conditions in Uganda. In addition, P. griseola is a highly variable pathogen that co-evolves with its host, therefore necessitating the continuous identification of new and stronger sources of resistance. Identification of local bean landraces/adapted bean varieties with resistance to ALS would probably quicken the progress of development of resistant cultivars, and reduce yield losses. Seventy four landraces, four commercial varieties, and two controls were screened with four P. griseola pathotypes 1:6, 17:39, 21:39, and 61:63 to determine their ALS resistance levels. One landrace, U00297, showed consistent and strong resistance to the four pathotypes. The inheritance of resistance in U00297 was established from three individual populations derived from crosses with three susceptible cultivars, K132, K131, and Kanyebwa, commercially grown in Uganda. The allelic relationships between U00297 and two existing ALS resistance sources, AND277 and G5686 were tested. Segregation ratios of F 2 populations revealed that U00297 resistance to pathotype 17:39 is conferred by a single dominant gene, while digenic epistatic gene interactions were suggested for resistance to other pathotypes. The general and specific combining abilities were significant for resistance revealing the importance of additive and dominant components in the inheritance of ALS resistance. As a resistant parent, U00297 was a good combiner for resistance to pathotype 17:39, and effective resistance source to pathotypes 17:39 and 61:63. The allelic test indicated that the dominant gene in U00297 is independent of resistance genes harboured by resistance sources AND277 and G5686. The information generated is useful to breeding programs targeting developing bean cultivars carrying novel ALS resistance based on genes derived from U00297.
Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Re... more Phaeosphaeria leaf spot (PLS) disease (causal agent Phaeosphaeria maydis (Henn.) Rane, Payak & Renfro) of maize is increasing in importance in sub-Saharan Africa (SSA). However, there is still limited information on the combining ability for disease resistance of the germplasm that are adapted to African environments. Evaluating combining ability effects and their interactions with the environment would provide valuable information that can be used in the development of cultivars that are resistant to PLS. This study was therefore conducted to determine the combining ability, gene action and the relationship between grain yield and PLS disease severity among selected tropical advanced maize inbred lines. Forty five F 1 hybrids were generated by crossing 10 inbred lines in a half diallel mating scheme. The 45 hybrids along with the ten inbred parents were evaluated in four environments, with two replications each between 2007 and 2009. General and specific combining ability (GCA and SCA) effects were highly significant (P ≤ 0.001) for PLS, grain yield and days to anthesis. GCA effects accounted for 66-90% and SCA effects for 10-34% of the variation in the hybrids for PLS resistance, grain yield and days to anthesis. This indicated predominance of additive over non-additive gene action for the three traits in these inbred lines. The resistant inbred lines to PLS were A1220-4, N3-2-3-3, CML312, MP18 and CML488. These lines had good combining ability for PLS resistance and contributed towards resistance in their crosses. In general, resistant hybrids involved a susceptible and a resistant parent, where at least one of the parents had a negative GCA effect. In addition, lines A1220-4 and CML312 contributed towards high yield and were late maturing. Inbred line CZL00009 conferred genes for early maturity. Linear regression analysis indicated that grain yield of maize was suppressed by about 250 kg ha −1 per each increase in PLS disease severity score, underscoring the need to control the disease. Significant (P < 0.01), negative correlations (r = −0.29 to −0.43) between grain yield and PLS severity were also detected. This showed the potential of PLS to reduce yield when favourable conditions for disease development are present. By and large, highly significant additive gene action implied that progress would be made through selection. Although non-additive effects were small (±10%), observation of dominance effects which were associated with reduced disease levels in some hybrids may be exploited in developing single cross maize hybrids among these inbreds when one parent is resistant.
ABSTRACT The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tro... more ABSTRACT The maize weevil (Sitophilus zeamais) is a significant pest of stored maize grain in tropical and subtropical regions worldwide. As a further step towards finding maize genotypes with acceptable levels of resistance to the maize weevil, 53 experimental maize hybrids that were generated in a North Carolina design II mating scheme, were evaluated for grain weight loss due to maize weevil damage under ambient temperature and humidity (ATH) conditions, in the on-station stock room at Harare, Zimbabwe. The study indicated that genotypic variation for grain weevil resistance was large (19%–57%) after five months of infestation by the maize weevils. A few F2 populations with potential for use as sources of breeding new varieties for maize weevil resistance were identified. They displayed consistency of high performance (better than the standard control varieties) and showed a lower rate of grain weight loss due to the maize weevils over the five months in the stock room. The male and female GCA and SCA effects were highly significant (P ≤ 0.01) for maize weevil resistance, especially at two months after infestation, indicating that resistance was controlled by genes with both additive and non-additive effects, respectively. Further, the distribution of grain weight loss data for the hybrids was continuous and almost normal at the four intervals of data collection, clearly supporting that resistance was partial and possibly conditioned by minor genes with cumulative effects. Therefore, resistance could probably be improved by selection among the promising F2 populations identified in this study. Although resistance was partial, a plot of grain weight loss of hybrids from the different categories demonstrated the advantage to farmers for growing a resistant variety (low percentage loss over time) compared to the susceptible ones that incurred significant grain weight losses. However, grain weight loss data were not significantly correlated with yield (r = 0.14; P &gt; 0.05), suggesting that the traits are not mutually exclusive. Therefore, breeding for maize weevil resistance in these populations would not necessarily compromise grain yield. Our results demonstrate that there is potential in developing maize varieties with acceptable levels of maize weevil resistance through recurrent selection procedures which exploit both GCA and SCA effects with sustainable impact on food security and the environment.
Diseases and pests are among the major constraints limiting maize productivity in the smallholder... more Diseases and pests are among the major constraints limiting maize productivity in the smallholder (SH) farming sector of sub-Saharan Africa. The objectives of this study were therefore, to determine how SH farmers perceive and cope with diseases and pests, identify with farmersother constraints to maize production. Data were collected from three villages of KwaZulu-Natal (KZN) province in South Africa using surveys and participatory rural appraisal (PRA) methodology. Local maize varieties were further evaluated for disease resistance and grain yield potential at two locations in KZN. Cob rots, grey leaf spot (GLS), maize streak virus (MSV), northern leaf blight (NLB), phaeosphaeria leaf spot (PLS) and common rust were the main diseases identified by farmers, but their incidence was low and occurrence infrequent. More than 75% of the farmers did not control both insect pests and diseases, while the rest used chemicals or everyday household remedies for control. Stalk borers and cutworms were the most prevalent insect pests, where as drought, excessive rains, hail storms, and soil fertility were the most important abiotic constraints identified. Field trial results of local varieties indicated high yield potential and genetic variability for disease resistance to PLS, GLS, and NLB. These findings suggest that; if the main production constraints are addressed, farmers could realize high yields from their local varieties. Breeding opportunities, therefore, exist for incorporating resistance or tolerance to these stresses into the local varieties.
Early planting of bambara groundnuts (Vigna subterranea L. Verdc) in the southern Africa enables ... more Early planting of bambara groundnuts (Vigna subterranea L. Verdc) in the southern Africa enables farmers to fetch premium prices before the markets are flooded with produce from the main summer growing period. However, adaptation of the crop outside the main growing season has not been studied in Zimbabwe. Therefore, this study evaluated 20 varieties at four planting dates covering contrasting temperatures and daylength, at Harare Research Station, during 2000/2001. Planting date was the main plot factor replicated three times and cultivar the subplot. Standard agronomic practices were followed and adequate moisture supplied through supplementary irrigation. Both the planting dates and variety main effects were significant (P<0.05) for yield and most of the secondary traits. Planting date x genotype interaction (G x E) effects were not significant (P<0.05) for yield, suggesting that cultivars were relatively yield stable. However, G x E effects were significant (P<0.05) for days to 50% emergence and pod count plant -1 . Differences among varieties were attributable to genotypic effects and different photothermal conditions. August and September planting dates resulted in high dry pod yield. Varieties BS599, BS537, V2-17, BS520, and Variety-10, had high relative yield, and were the most promising for off-season planting.
... southern and eastern Africa, most maize breeding programmes which are hybrid oriented use eli... more ... southern and eastern Africa, most maize breeding programmes which are hybrid oriented use elite maize ... to other diseases and abiotic stresses, such as drought tolerance and low nitrogen (N). The ... Field weight was then used to estimate the grain yield (t ha −1 ) adjusted to 12.5 ...
... Numbers of days to 50% flowering (number of days taken for half of the plot to reach anthesis... more ... Numbers of days to 50% flowering (number of days taken for half of the plot to reach anthesis), number of days to 95% maturity (number of days taken for about 95% of the plants to reach the hard dough stage), number of tillers plant −1 (tillers that were taller than half of the main ...
Bioethanol production from sweet sorghum entails expansion and intensive production of the crop, ... more Bioethanol production from sweet sorghum entails expansion and intensive production of the crop, which may include off-season production in the warm tropical lowlands. However, suitable cultivars are currently not available for this environment, especially in southern Africa. Hybrid cultivars were long ago demonstrated to be more productive than pure line varieties. Therefore a study was conducted to determine heterosis of experimental hybrids, and combining ability of parental lines for stem sugar traits. Sixty-four hybrids were generated among 16 lines in accordance with North Carolina design II mating scheme. Eight parents were cytoplasmic male sterile lines which were designated as females and were crossed with eight male fertile lines. The hybrids were evaluated at two sites in Mozambique and South Africa under off-season production conditions. Row-column alpha designs with three replications were used and standard agronomic practices were followed at both sites. Data were analysed in GenStat computer package. There was significant (P=0.05) variation among genotypes for stem °brix and associated traits. The top 20 stem °brix performers were constituted by 17 hybrids, exhibiting heterosis of up to 112%, and three parents. General and specific combining ability effects were significant for stem °brix and associated traits implying that both additive and non-additive gene action, respectively, were important for controlling the traits. The lines ZLR1 and ICSVP3046 displayed significant and positive GCA effects for stem °brix, while 13 crosses showed positive and significant SCA effects. These lines and the crosses ISCVP3046×ICSA4, ICSV700×ICSA731, ICSR165×ICSA307, ZLR1×ICSA474 and ICSR57×ICSA479, which combined high mean performance with positive SCA effects, would be recommended for use in breeding new varieties for tropical lowland environments.
ABSTRACT Development of top cross varieties with downy mildew (DM) resistance is one approach to ... more ABSTRACT Development of top cross varieties with downy mildew (DM) resistance is one approach to enhance maize productivity in tropical lowland environments. The objective of this study was to determine heterotic orientation of 18 advanced maize inbred lines towards popular open pollinated synthetic populations ZM523 and Suwan-1 under the prevalence of DM. The 36 top crosses, four hybrid check varieties and two testers, ZM523 (Z) and Suwan-1 (S) were evaluated in a 6 x 7 alpha-lattice design with two replications across three environments. General combining ability effects were significant (P&lt; 0.05) for DM resistance and grain yield, suggesting that genes with additive effects were important in controlling the traits. Specific combining ability (SCA) effects were not significant for DM suggesting small influence of DM resistance by the genes with non-additive effects; but SCA effects were significant for grain yield, indicating that non-additive gene effects played a significant role in governing the grain yield. Based on the SCA data, ten lines were grouped with Suwan-1 and eight lines with ZM523. Using the heterosis data, the lines were fitted into three groups that were designated as S, Z and SZ orientation. The lines ML2, ML30 and ML42, which displayed positive heterosis with both testers for grain yield, were allocated to the SZ-group. The lines ML8, ML10, ML25, ML45, and ML48 exhibited positive heterosis with Suwan-1 and were therefore, classified in the Z-group, and line ML19 that showed positive heterosis with ZM523 was fitted in the S-group. The remaining eight lines did not show any significant and positive heterosis with both testers hence they could not be classified based on heterosis data, suggesting that hybrid breeding efficiency could be improved by expanding the number of testers. Line ML42 displayed the highest level of heterosiswith both Suwan-1 (32 %) andZM523 (29 %) and outperformed all the standard check varieties qualifying it as a potential candidate for further testing. Generally, there was consistency of heterotic grouping of the lines using SCA and heterosis data.
Breeding for resistance to Angular Leaf spot (ALS), a fungal disease caused by Pseudocercospora g... more Breeding for resistance to Angular Leaf spot (ALS), a fungal disease caused by Pseudocercospora griseola (Sacc), is faced with a challenge of the existence of a few resistance sources that are exotic and not well adapted to environmental conditions in Uganda. In addition, P. griseola is a highly variable pathogen that co-evolves with its host, therefore necessitating the continuous identification of new and stronger sources of resistance. Identification of local bean landraces/adapted bean varieties with resistance to ALS would probably quicken the progress of development of resistant cultivars, and reduce yield losses. Seventy four landraces, four commercial varieties, and two controls were screened with four P. griseola pathotypes 1:6, 17:39, 21:39, and 61:63 to determine their ALS resistance levels. One landrace, U00297, showed consistent and strong resistance to the four pathotypes. The inheritance of resistance in U00297 was established from three individual populations derived from crosses with three susceptible cultivars, K132, K131, and Kanyebwa, commercially grown in Uganda. The allelic relationships between U00297 and two existing ALS resistance sources, AND277 and G5686 were tested. Segregation ratios of F 2 populations revealed that U00297 resistance to pathotype 17:39 is conferred by a single dominant gene, while digenic epistatic gene interactions were suggested for resistance to other pathotypes. The general and specific combining abilities were significant for resistance revealing the importance of additive and dominant components in the inheritance of ALS resistance. As a resistant parent, U00297 was a good combiner for resistance to pathotype 17:39, and effective resistance source to pathotypes 17:39 and 61:63. The allelic test indicated that the dominant gene in U00297 is independent of resistance genes harboured by resistance sources AND277 and G5686. The information generated is useful to breeding programs targeting developing bean cultivars carrying novel ALS resistance based on genes derived from U00297.
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