Assessments and improvement of filter media cleanliness in rapid gravity sand filters

Introduction: Rapid sand filtration is an essential unit process in the water purification process. It captures and removes coagulated and flocculated material and other suspended matter not removed during the preceding treatment processes. The pores in the filter bed gradually become clogged and the media progressively collects deposit through the continuous use and life of the filter. During normal operations cleaning is initiated by excessive head loss, deterioration in filtrate quality or when the predetermined time for a filter run has elapsed. Air scour, to remove deposit from filter media by vigorous agitation, and wash water, to remove this deposit from the filter bed, are applied. The combined action of air and water should quickly return the media to its original perfectly clean state for the cycle to continue. However, on inspection it is often found that filter sand on purification plants is unacceptably dirty and backwash systems are clearly incapable of cleaning the media to its initial state of cleanliness. It is at times possible to relate the dirty filter media to faulty designs or poor operating procedures, but often the reasons for the media deterioration remain elusive and the media becomes dirtier the longer it is in use. As there was an almost complete lack of published or agreed upon procedures to measure the cleanliness of filter media, rudimentary methods for measuring filter media cleanliness and backwash efficiency were developed. Thereafter filter media from full-scale treatment plants was analyzed with these methods at regular intervals to establish some benchmarks for these determinants. These methods were also applied during the laboratory and pilot plant phases of the project

RESPONSE OF LOCALLY ADAPTED PEARL MILLET POPULATIONS TO S1 PROGENY RECURRENT SELECTION FOR GRAIN YIELD AND RESISTANCE TO RUST

In the semi-arid zones of Uganda, pearl millet ( Pennisetum glaucum (L.) R. Br.) is mainly grown for food and income; but rust (Puccinia substriata var indica (L.) R. Br.) is the main foliar constraint lowering yield. The objective of the study was to genetically improve grain yield and rust resistance of two locally adapted populations (Lam and Omoda), through two cycles of modified phenotypic S1 progeny recurrent selection. Treatments included three cycles of two locally adapted pearl millet populations, evaluated at three locations. Significant net genetic gain for grain yield (72 and 36%) were achieved in Lam and Omoda populations, respectively. This led to grain yield of 1,047 from 611 kg ha-1 in Lam population and 943 from 693 kg ha-1 in Omoda population. Significant improvement in rust resistance was achieved in the two populations, with a net genetic gain of -55 and -71% in Lam and Omoda populations, respectively. Rust severity reduced from 30 to 14% in Lam population and from 57 to 17% in Omoda population. Net positive genetic gains of 68 and 8% were also achieved for 1000-grain weight in Lam and Omoda, respectively. Traits with a net negative genetic gain in both populations were days to 50% flowering, days to 50% anthesis, days to 50% physiological maturity, flower-anthesis interval, plant height and leaf area.Dans la zones semi-arides en Ouganda, le milet perl\ue9 ( Pennisetum glaucum (L.) R. Br.) est principalement cultiv\ue9 comme culture vivri\ue8re et de rente, mais la maladie de rouille (Puccinia substriata var indica (L.) R. Br.) est la contrainte majeure affectant le rendement. L\u2019ojectif de l\u2019\ue9tude \ue9tait l\u2019am\ue9lioration du rendement en grains et la r\ue9sistance \ue0 la maladie de rouille chez deux populations localement adapt\ue9es milet perl\ue9 (Lam and Omoda), ceci \ue0 travers deux cycles de selection reccurente. Les traitements consistaient \ue0 trois cycles de deux populations localement adapt\ue9es de milet perl\ue9, \ue9valu\ue9es dans trois milieu diff\ue9rents. Un gain genetique significatif de 72 et 36% de rendements en grain a \ue9t\ue9 observe respectivement chez les populations de Lam et de Omoda. Ceci a occasionn\ue9 des rendements en grains de 1,047 kg ha-1 au lieu de 611 kg ha-1 chez la population de Lam et 943 kg ha-1 au lieu de 693 kg ha-1 chez la population de Omoda. Une am\ue9lioration significative de la r\ue9sistance \ue0 la maladie de rouille a \ue9t\ue9 obtenue au sein des deux populations, avec des gains g\ue9n\ue9tiques nets de -55 et -71% respectivement chez les populations de Lam et Omoda. La s\ue9v\ue9rit\ue9 de la maladie de rouille a \ue9t\ue9 de 30% \ue0 14% au sein de la population de Lam population et de 57% \ue0 17% au sein de la population de Omoda. Un gain g\ue9n\ue9tique positif net de 68 et 8% ont \ue9t\ue9 \ue9galement obtenu respectivement pour le poid de 1000 grains de Lam et 1000 de Omoda. Les caract\ue8res comme le nombre jours \ue0 50% de floraison, le nombre de jours \ue0 50% anth\ue8se, le nombre de jours \ue0 50% de maturit\ue9 physiologique, l\u2019intervalle de temps entre la floraison et l\u2019anth\ue8se, la hauteur des plants et la surface des feuilles

Assessment of genetic diversity of rice based on SNP markers for selection of parents for sheath rot (Sarocladium oryzae) resistance breeding

Sheath rot of rice, caused by Sarocladium oryzae, is an important emerging rice disease not only in Rwanda, but also in other rice-growing countries. Given that cultivar resistance is a sustainable management strategy for small-scale farmers, the aim of this study was to identify genetically distant parental materials for sheath rot resistance breeding. Ten resistant and fifteen susceptible accessions were analysed using 94 single nucleotide polymorphism (SNP) markers. The number of alleles amplified per locus ranged from 1 to 4 with a mean of 2.01 and a total of 189 alleles detected from the 25 genotypes. The number of observations per marker locus ranged from 11 to 25 with an average of 23. The mean major allele frequency was 76.2%, whereas the mean polymorphic information content was 0.263, and gene diversity was estimated at 0.325. Consequently, the markers were highly informative and revealed good estimates of genetic diversity among the studied accessions. Genetic distances ranged from 0 to 0.63 and a UPGMA dendrogram distinguished resistant and susceptible genotypes. This study revealed the possibility of improving resistance to sheath rot with minimum risk of genetic depression or reduced variability among progenies through hybridisation of locally adapted germplasm

Genetic analysis of mechanisms associated with inheritance of resistance to sheath rot of rice

Understanding genetic mechanisms controlling inheritance of disease resistance traits is essential in breeding investigations targeting development of resistant genotypes. Using North Carolina design II, 32 F1 hybrids were generated by crossing eight susceptible to four resistant parents and submitted for field evaluation. The analysis of general and specific combining ability (GCA and SCA) indicated involvement of additive and non-additive gene action controlling inheritance of horizontal resistance to sheath rot of rice. High GCA/SCA ratio and high heritability estimates revealed additive effects and were more predominant than none additive ones. The level of dominance indicated dominant genes was more important than recessive genes. Estimates of GCA and SCA analysis suggested that crop improvement programmes should be directed towards selection of superior parents or good combiners, emphasizing on GCA. As far as source of resistance is concerned, most promising genotypes were Cyicaro, Yunertian and Yunkeng. The predominance of additive genetic effects together with the relevance of dominant genes suggested possibilities of improving the resistance by introgression of resistance genes through recurrent selection coupled with phenotypic selection

Seed protein content and its relationships with agronomic traits in pigeonpea is controlled by both main and epistatic effects QTLs

The genetic architecture of seed protein content (SPC) and its relationships to agronomic traits in pigeonpea is poorly understood. Accordingly, five F2 populations segregating for SPC and four agronomic traits (seed weight (SW), seed yield (SY), growth habit (GH) and days to first flowering (DFF)) were phenotyped and genotyped using genotyping-by-sequencing approach. Five high-density population-specific genetic maps were constructed with an average inter-marker distance of 1.6 to 3.5 cM, and subsequently, integrated into a consensus map with average marker spacing of 1.6 cM. Based on analysis of phenotyping data and genotyping data, 192 main effect QTLs (M-QTLs) with phenotypic variation explained (PVE) of 0.7 to 91.3% were detected for the five traits across the five populations. Major effect (PVE ≥ 10%) M-QTLs included 14 M-QTLs for SPC, 16 M-QTLs for SW, 17 M-QTLs for SY, 19 M-QTLs for GH and 24 M-QTLs for DFF. Also, 573 epistatic QTLs (E-QTLs) were detected with PVE ranging from 6.3 to 99.4% across traits and populations. Colocalization of M-QTLs and E-QTLs explained the genetic basis of the significant (P < 0.05) correlations of SPC with SW, SY, DFF and GH. The nature of genetic architecture of SPC and its relationship with agronomic traits suggest that genomics-assisted breeding targeting genome-wide variations would be effective for the simultaneous improvement of SPC and other important traits

Assessment of genetic variability among groundnut accessions under natural rosette disease infestation in Malawi

Groundnut production in East and South African region is low due to several constraints. Success in development of resilient varieties rides on genetic diversity in available germplasm for key traits in question. This study was undertaken to dissect the magnitude of variability among groundnut accessions. The experimental design was an alpha lattice design replicated thrice. Significant differences in yield traits were observed among the accessions. There was high phenotypic (PCV) and genotypic (GCV) coefficient of variation in most of the traits except for the number of primary branches and shelling percentage. A combination of high heritability and genetic advance was recorded for the number of secondary branches, height, seed yield and rosette incidence. This indicates that it is possible to carry out phenotypic selection based on the mean for successful improvement of yield and resistance to rosette disease

Phenotypic correlation, path coefficient and multivariate analysis for yield and yield-associated traits in groundnut accessions

Yield is a complex quantitative trait largely influenced by the environment. Direct selection for grain yield is less efficient in improving groundnut productivity. The selection efficiency can be enhanced by exploiting the relationship between yield and its related traits. Moreover, the use of genetically diverse parents is essential to generate genetic variation for successful selection of genotypes in a breeding program. Therefore, the study aimed at analysing the relationship between grain yield and its related traits and determining the morphological diversity among selected groundnut genotypes under natural rosette disease (GRD) infestation. The genotypes were evaluated in a 7 × 4 alpha lattice design with three replications. Data were collected on yield and yield-related traits. Correlation, path coefficient and multivariate analyses were done. The results revealed that yield was directly associated with plant height, number of pods per plant, hundred seed weight, GRD incidence and number of secondary branches. Therefore, these traits should be considered in selection when improving groundnut for yield. Cluster analysis revealed existence of diversity among the evaluated groundnut genotypes with no influence of geographical origin to the clustering pattern. The Principal Components Analysis (PCA) biplot was effective in showing the genetic distance among the genotypes and the results were comparable with those of the cluster analysis. Moreover, Shannon-Weaver diversity indices revealed existence of high diversity among the genotypes, an implication that groundnut improvement for yield is possible through selection in breeding

Development of sequence-based markers for seed protein content in pigeonpea

Pigeonpea is an important source of dietary protein to over a billion people globally, but genetic enhancement of seed protein content (SPC) in the crop has received limited attention for a long time. Use of genomics-assisted breeding would facilitate accelerating genetic gain for SPC. However, neither genetic markers nor genes associated with this important trait have been identified in this crop. Therefore, the present study exploited whole genome re-sequencing (WGRS) data of four pigeonpea genotypes (~ 12X coverage) to identify sequence-based markers and associated candidate genes for SPC. By combining a common variant filtering strategy on available WGRS data with knowledge of gene functions in relation to SPC, 108 sequence variants from 57 genes were identified. These genes were assigned to 19 GO molecular function categories with 56% belonging to only two categories. Furthermore, Sanger sequencing confirmed presence of 75.4% of the variants in 37 genes. Out of 30 sequence variants converted into CAPS/dCAPS markers, 17 showed high level of polymorphism between low and high SPC genotypes. Assay of 16 of the polymorphic CAPS/dCAPS markers on an F2 population of the cross ICP 5529 (high SPC) × ICP 11605 (low SPC), resulted in four of the CAPS/dCAPS markers significantly (P < 0.05) co-segregated with SPC. In summary, four markers derived from mutations in four genes will be useful for enhancing/regulating SPC in pigeonpea crop improvement programs

Molecular mapping of seed protein content in pigeonpea – a drought tolerant crop of the semi-arid tropics

Pigeonpea is a uniquely drought and heat tolerant crop that provides a major source of dietary protein to nearly a billion people in the tropical and semi-arid tropics of the world. Despite its importance as a source of dietary protein the genetic control of its seed protein content (SPC) is poorly understood. The present study used high density linkage maps to identify quantitative trait loci (QTL) associated with SPC and its relationship with 100-seed weight (HSW), seed yield (SY), days to first flower (DTFF) and growth habit (GH). Five F2 mapping populations segregating for SPS including ICP 11605 × ICP 14209, ICP 8863 × ICP 11605, HPL 24 × ICP 11605, ICP 5529 × ICP 11605 and ICP 8863 × ICPL 87119 were genotyped using genotyping-by-sequencing and phenotyped for the traits. The average inter-marker distance on the population-specific maps varied from 1.6cM to 3.5cM.On the basis of the population-specific and consensus linkage maps, 48main effect QTLs (M-QTLs)with phenotypic variance explained (PVE) ranging from 0.7 to 23.5% were detected across five populations, of which 15 M-QTLs were major (PVE≥10). Twenty seven of the M-QTLs could be collapsed into six consensus QTL regions. In addition, 34 epistatic QTLs (E-QTLs) with PVE ranging from 6.3% to 69.8% were detected across populations. Co-localization of M-QTLs and E-QTLs affecting SPC and the agronomic traits explained the genetic basis of the significant (P < 0.05) correlations of SPC with HSW (r2 = 0.22 to 0.30), SY (r2 = -0.18 to -0.28), DTFF (r2 = -0.17 to -0.31) and GH (r2 = 0.18 to 0.34). The quantitative nature of genetic control of SPC and its relationship with agronomic traits suggest that marker-assisted recurrent selection or genomic selection would be effective for the simultaneous improvement of SPC and other important traits

Genetic variation and relationships of total seed protein content with some agronomic traits in pigeonpea (Cajanus cajan (L.) Millsp.)

Seed protein content (SPC) is an important grain quality trait, which impacts the nutritional importance of pigeonpea seed in the diet of over a billion people globally. The present study was carried out to determine variation in SPC and its relationships with some agronomic traits among 23 parental lines of different types of pigeonpea mapping populations. The parental lines were evaluated under field conditions during 2014-2015 growing season. A randomised complete block design in two replications was used. Data were recorded on SPC, days to first flower (DTF), plant height at maturity (PltH), number of pods per plant (NPP), number of seeds per pod (NSP), hundred-seed weight (SW) and seed yield per plant (SY). There were significant differences among genotypes for all traits. Broad-sense heritability was 0.693 for SPC but ranged from 0.519 (NPP) to 0.999 (DTF) while genetic advance was 2.4% for SPC but ranged from 1.2 % (NSP) to 141.2 % (SY), and genetic gain ranged from 11.0 % (SPC) to 230.0 % (SY). Simple correlation showed that SPC is only significantly but negatively correlated with SW (r = -0.30, P < 0.05), while path analyses revealed that SPC is negatively associated SW and NPP but positively with DTF, PltH, NSP and SY. It is concluded that genetic variation for SPC and agronomic traits exist among pigeonpea genotypes studied. The variation is accompanied by both favourable and unfavourable relationships of SPC with the agronomic traits