Incidence and severity of cassava mosaic disease in farmer’s fields in Ghana

A survey of cassava mosaic disease (CMD) was carried out in Ghana from 2007-2008 to assess CMD incidence, infection type, severity and adult whitefly population. A total of 136 farmers’ fields across major cassava producing areas in the Brong Ahafo, Western, Northern, Ashanti and Volta regions were assessed. CMD was prevalent in most of the 136 fields surveyed. Frequently encountered local landraces were susceptible to the disease. CMD incidence reached 100% in farmers’ fields. Mean disease incidence ranged from 46% in the Ashanti region to 90% in the Western region of the country. CMD incidence averaged 66.0%, with cutting-borne infection and Whitefly-borne infections being 54.0% and 12.0%, respectively. CMD shoot symptom severity ranged from 2.0 to 3.7 in the farmers’ fields, with a mean of 2.9. Mean adult whitefly population was 0.47. The high prevalence of CMD requires a concerted effort in the management of CMD in the country

Molecular markers associated with a new source of resistance to the cassava mosaic disease

The predominant source of resistance to the cassava mosaic disease (CMD) is known to be polygenic requiring evaluation in multiple environments to characterise resistant genotypes, which makes the detection of genes for resistance using segregation analysis inefficient. Recently, some landraces have been identified which exhibit high levels of resistance to CMD. In this study, molecular markers associated with resistance to CMD in a resistant landrace were identified, using F1 progenies derived from a cross between the CMD resistant landrace TME7 and the susceptible line TMS30555, as a first step in marker assisted breeding for CMD resistance. Bulk segregant analysis (BSA) on the parents, resistant and susceptible DNA pools, using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers revealed that an SSR marker, SSRY28-180, donated by the resistant parent was linked with resistance to CMD. Marker-trait association detected by regression analysis showed that the marker, accounted for 57.41% of total phenotypic variation for resistance. The analysis furthershowed that another SSR marker, SSRY106-207 and an AFLP marker, E-ACC/M-CTC-225, accounted for 35.59% and 22.5% of the total phenotypic variation for resistance, respectively. The implication of the results in breeding for resistance to CMD is discussed

High-density DArTSeq SNP markers revealed wide genetic diversity and structured population in common bean (Phaseolus vulgaris L.) germplasm in Ethiopia

Abstract Introduction Common bean is one of the widely consumed food security crop in Africa, Asia, and South America. Understanding genetic diversity and population structure is crucial for designing breeding strategies. Materials Two hundred and eighty-nine germplasm were recently collected from different regions of Ethiopia and introduced from CIAT to estimate genetic diversity and population structure using 11,480 DArTSeq SNP markers. Results The overall mean genetic diversity and polymorphic information content (PIC) were 0.38 and 0.30, respectively, suggested the presence of adequate genetic diversity among the genotypes. Among the geographical regions, landraces collected from Oromia showed the highest diversity (0.39) and PIC (0.30). The highest genetic distance was observed between genotypes collected from SNNPR and CIAT (0.49). In addition, genotypes from CIAT were genetically more related to improved varieties than the landraces which could be due to sharing of parents in the improvement process. The analysis of molecular variance revealed that the largest proportion of variation was due to within the population both in geographical region (63.67%) and breeding status (61.3%) based classification. Model-based structure analysis delineated the 289 common bean genotypes into six hypothetical ancestoral populations. Conclusions The genotypes were not clustered based on geographical regions and they were not the main drivers for the differentiation. This indicated that selection of the parental lines should be based on systematic assessment of the diversity rather than geographical distance. This article provides new insights into the genetic diversity and population structure of common bean for association studies, designing effective collection and conservation for efficient utilization for the improvement of the crop

Introgression of drought tolerance traits into adapted Kenyan chickpea varieties using marker assisted backcrossing (MABC)

Drought is the major constraint causing considerable yield reduction in chickpea. Roots play a critical role in enhancing drought tolerance. The main objective of the study was to introgress drought tolerant root traits into Kenyan chickpea varieties through marker assisted breeding (MABC). Eight simple sequence repeat (SSR) markers, linked to quantitative trait loci (QTL) for root and yield traits, were used to screen the parents at ICRISAT, India. In addition, 1144 single nucleotide polymorphic markers (SNPs) were also used in genotyping these parents at Legume Genomics Center, United Kingdom. Crosses were made between two selected varieties, ICCV 92944 (Chania Desi II) and ICCV 00108 (LDT 068) and ‘QTL-hotspot’ donor parent ICC 4958 that has extensive rooting system. Polymor- In the face of increasing water scarcity, breeding for higher transpiration efficiency (TE), that is, the biomass produced per unit of water transpired, has become crucial. This could be achieved by reducing plant transpiration through a better closure of the stomatal pores at the leaf surface. However, this strategy generally also lowers growth, as stomatal opening is necessary for the capture of atmospheric CO2 that feeds daytime photosynthesis. Here, we considered the reduction in transpiration rate at night (En), when photosynthesis is inactive, as a possible strategy to limit water use without altering growth. We carried out a genetic analysis for En and TE in grapevine, a major crop in drought-prone areas. A 3 year experiment was conducted on the F1 progeny from a cross between Syrah and Grenache cultiphic SSR and SNP markers were used to select progenies with root QTL at F1, BC1F1 and BC2F1 that were later advanced to BC2F3. The BC2F3 populations were evaluated for root traits at Egerton University in randomized complete block design with two replications in pot experiment. The BC2F3 families were significantly different for root dry weight (RDW), shoot dry weight (SDW), total plant dry weight (PDW) and root to shoot dry weight (R/S) ratio (R/S) for Chania Desi II x ICC 4958 and R/S for LDT 068 x ICC 4958. These lineshad significantly improved root traits compared the recurrent parents. MABC is aneffective and efficient method of introgressing complex drought tolerant traits which leads to improvement in yield especially under drought conditions

Validierung des Tierstimmentests (mFAST)

Hintergrund: Die Ermittlung der frequenzspezifischen Hörschwelle mit Sinustönen (PTA) ist goldener Standard in der Audiometrie. Dennoch ist dieses Verfahren nicht ohne Probleme. Um mögliche Effekte der Feinstruktur der Hörschwelle zu reduzieren und alltagsrelevante Reize anzubieten, wird der Einsatz spektral komplexerer, breitbandigerer Stimuli postuliert. Besonders bei der Testung von jüngeren Kindern verspricht man sich dadurch Vorteile.Beim Tierstimmentest (mFAST: multi-Frequency Animal Sound Test) werden vier Tierstimmen (Kuh, Hund, Katze und Vogel) mit unterschiedlicher spektraler Zusammensetzung und mittlerer Frequenz (500, 1 k, 2 k, 4 kHz) verwendet, um die audiometrischen Hörschwellen in einem adaptiven Verfahren einzuschätzen.Material und Methoden: In einer ersten Validierung wurden die mFAST-Schwellen mit denen für äquivalente Rauschbänder und Reintöne verglichen (normalhörende Erwachsene). Zudem wurden die mFAST-Schwellen bei normalhörenden Kindern (4-6 Jahre) mit dem Tonaudiogramm (PTA) verglichen.Bei 45 normalhörenden Erwachsenen (89 Ohren, Alter: 20-30 J.) wurden die Hörschwellen mit dem AuriCheck® Handheld Audiometer gemessen. Neben mFAST wurde das duoTone Verfahren (Reintöne und Rauschbänder) eingesetzt, dem dasselbe adaptive Verfahren wie bei mFAST zugrunde liegt. 33 Kinder einer Kindertagesstätte (58 Ohren; 4-6 J.) wurden mit mFAST getestet, davon 28 Ohren zusätzlich spielaudiometrisch mit PTA.Ergebnisse: Bei den Erwachsenen zeigten sich keine signifikanten Unterschiede zwischen mFAST und duoTone bei Rauschen und Reintönen (mit Ausnahme von 7dB Unterschied bei 4 kHz Reintönen).Alle Kinder konnten mit mFAST getestet werden, während bei 20% eine Testung mit PTA nicht gelang. Die Hörschwellen waren altersabhängig und lagen bei mFAST durchschnittlich 6 dB über der PTA-Schwelle.Die Testdauer konnte mit einer kürzeren mFAST Version erheblich reduziert werden.Diskussion: Die Ergebnisse zeigen, dass mFAST als eine (bessere) Alternative zur Reintonaudiometrie bei Hörscreening und -testung jüngerer Kinder eingesetzt werden kann.Erste Ergebnisse der Validierung bei Hörgeschädigten werden präsentiert

Combining Ability Analysis of Resistance to Mosaic Virus Disease in Cassava

A North Carolina design II experiment, with three improved cassava ( Manihot esculenta Crantz) accessions as the female parents, 15 cassava landraces and three improved cassava accessions as the male parents (3 x 18), was evaluated in three environments in Nigeria to determine the mode of gene action and the combining ability, and also to estimate heterosis for resistance to cassava mosaic disease (CMD), in various sources of resistance. General combining ability (GCA) effect due to females and males was significant in each environment; while the GCA effect due to males and the specific combining ability (SCA) effect were significant across environments. The relative magnitude of the total GCA components to the total GCA plus SCA component, however, suggested that GCA was more important that SCA in controlling CMD resistance among the crosses. The test for heterosis was significant in the individual environments; one across, involving the best general combiner, exhibited significant heterosis for resistance in all three environments. The implication of the findings in breeding for resistance to CMD is discussed

Gene Complementarity of Resistance to the Cassava Mosaic Disease among African Cassava Accessions

The cassava mosaic virus disease (CMD) is the most important disease of cassava in Africa, causing severe economic losses. The genetic stock, clone 58308, has been extensively used in breeding for resistance to the disease, but recently, other sources of resistance to the disease have been identified among the landraces and could be used in breeding to diversify resistance to the disease. In this study, the progenies of 70 segregating F1 crosses of some resistant and susceptible landraces, clone 58308 and its derivatives, were evaluated in 3 environments for their reaction to CMD to determine the mode of inheritance and allelic relationships among the various resistant accessions. The results indicated a polygenic mode of inheritance, with both resistant and susceptible accession contributing effective factors towards CMD resistance in their progenies. Effective factors contributed by the susceptible parents were recessive. Among the resistant accessions, the results further showed that the genes for resistance are nonallelic and not linked. Positive transgressive segregants were also detected in several crosses. Significant differences in the mean distribution of F1 progeny disease severity scores further revealed allelic differences among the various sources of resistance. These results imply that the resistant landraces are potential new sources of resistance, which could be used in a breeding programme, together with the resistant improved clones derived from clone 58308 to diversity resistance, while developing new genotypes with enhanced resistance to CMD

Gene complementarity of resistance to the cassava mosaic disease among African cassava accessions

The cassava mosaic virus disease (CMD) is the most important disease o1'cassava in Africa, causing severe economic losses. The genetic stock, clone 58308, has been extensively used in breeding for resistance to the disease, but recently, other sources o1'resistance to the disease have been identified among the landraces and could be used in breeding to diversity resistance to the disease. In this study, the progenies o1'70 segregating F, crosses of some resistance and susceptible landraces, clone 58308 and its derivatives, were evaluated in 3 environments for their reaction to CMD to determine the mode of inheritance and allelic relationships among the various resistant accessions. The result indicated a polygenic mode of inheritance, with both resistant and susceptible accessions contributing effective factors towards CMD resistance in their progenies. Effective factors contributed by the susceptible parents were recessive. Among the resistant accessions, the results further showed that the genes for resistance are nonallelic and not linked. Positive transgressive segregants were also detected in several crosses. Significant differences in the mean distribution of progeny disease severity scores further revealed allegic differences among the various sources of resistance. These results imply that the resistant landraces are potential new sources of resistance, which could be used in a breeding programme, together with the resistant improved clones derived from clone 58308 to diversify resistance, while developing new genotypes with enhanced resistance to CMD

Combining ability analysis of resistance to mosaic virus disease in cassava

A North Carolina design II experiment, with three improved cassava (Mctnihot esculenta Crantz) accessions as the female parents, l5 cassava landraces and three improved cassava accessions as the male parents (3 x I 8), was evaluated in three environments in Nigeria to determine the mode of gene action and the combining ability, and also t() estimate heterosis for resistance to cassava mosaic disease (CMD), in various sources of resistance. General combining ability (GCA) effect clue to females and males was significant in each environment; while the GCA effect clue to males and the specific combining ability (scA) effect were significant across environments. The relative magnitude of the total GCA components to the total GCA plus SCA component, however, suggested that GCA was more important than SCA in controlling cMD resistance among the crosses. The test for heterosis was significant in the individual environments; one cross, involving the best general combiner, exhibited significant heterosis for resistance in all three environments. The implication of the findings in breeding for resistance to CMD is discussed

Molecular markers associated with a new source of resistance to the cassava mosaic disease

The predominant source of resistance to the cassava mosaic disease (CMD) is known to be polygenic requiring evaluation in multiple environments to characterise resistant genotypes, which makes the detection of genes for resistance using segregation analysis inefficient. Recently, some landraces have been identified which exhibit high levels of resistance to CMD. In this study, molecular markers associated with resistance to CMD in a resistant landrace were identified, using F1 progenies derived from a cross between the CMD resistant landrace TME7 and the susceptible line TMS30555, as a first step in marker assisted breeding for CMD resistance. Bulk segregant analysis (BSA) on the parents, resistant and susceptible DNA pools, using simple sequence repeat (SSR) and amplified fragment length polymorphism (AFLP) markers revealed that an SSR marker, SSRY28-180, donated by the resistant parent was linked with resistance to CMD. Marker-trait association detected by regression analysis showed that the marker, accounted for 57.41% of total phenotypic variation for resistance. The analysis furthershowed that another SSR marker, SSRY106-207 and an AFLP marker, E-ACC/M-CTC-225, accounted for 35.59% and 22.5% of the total phenotypic variation for resistance, respectively. The implication of the results in breeding for resistance to CMD is discussed