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Combining ability of cassava genotypes for cassava mosaic disease and cassava bacterial blight, yield and its related components in two ecological zones in Ghana
Written by Administrator   
Wednesday, 30 October 2013 14:52

Parkes EY, Fregene M, Dixon A, Boakye-Peprah B, Labuschagne MT

Abstract

Breeding for resistant genotypes is the best strategy to offset the destructive effects of cassava mosaic disease (CMD) and cassava bacterial blight (CBB). Two sets of diallel parents were selected for the forest and the savannah ecological zones in Ghana based on good levels of resistance to CMD and CBB. Both sets were crossed in a half-diallel design. The first set of seven progenitors and their 21 F1 progenies were planted in a randomised complete block design (RCBD) with three replications in two different locations for two seasons in the forest ecology. The second set of five progenitors and their 10 F1 progenies were planted in a RCBD with three replications in two locations in the coastal savannah ecological zone of Ghana. Both experiments were evaluated for CMD and CBB resistance, fresh root yield, dry root yield, root number, harvest index, dry matter content, plant height at maturity and height at first branching, levels of branching and plant vigour. Results of the combined analysis of variance revealed that the environment effect was significant for all the traits. General combining ability and specific combining ability effects were significant for most of the traits. Narrow sense heritability was significant for plant vigour, root number, CMD and CBB in both the zones. CMD and root number also had a predictability ratio of close to one, indicating the importance of additive gene effects.

*Corresponding author. E-mail:

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Written by Administrator   
Thursday, 12 September 2013 14:30

Bulked segregant analysis identifies molecular markers associated with early bulking in cassava (Manihot esculenta Crantz)

  • 1. Department of Agronomy, University of Ibadan, Ibadan, Nigeria. 2. International Centre for Tropical Agriculture (CIAT), Cali, Colombia. 3. National Root Crops Research Institute (NRCRI), Umudike, Nigeria. 4. Donald Danforth Plant Science Center, St. Louis, MO, 63132, USA

Abstract

Late root bulking is a major factor leading to rejection and abandoning of improved cassava genotypes isub-Saharan Africa. Early bulking (EB) varieties shorten the growth period from planting to harvesting, better fit into environments with short rainy season, and reduce exposure to biotic and abiotic stresses thereby increasing productivity. This study was carried out to identify molecular markers linked to EB in cassava. Nine cassava hybrid populations (COB-1–COB-9) were developed using six elite varieties (TMS 30572, TMS 97/2205, TMS 98/0505, TMS 30555, NR 8212 and NR 8083) from the African cassava germplasm as parents. The progeny in each of the nine populations (101–272 genotypes per population) were evaluated for EB at 7 months after planting at seedling, clonal, and preliminary stages of breeding evaluation at Umudike. The parameters measured are fresh root yield, harvest index, fresh shoot weight and number of storage roots per plant. The progeny in each of the nine populations were genotyped at 542 simple sequence repeat (SSR) marker loci. Bulked segregant analysis was used to identify the SSR markers associated with EB in the populations. Nine SSR markers (SSRY 106, (ESTs)SSRY 292, SSRY 239, (ESTs)SSRY 7, NS 194, (ESTs)SSRY 47, SSRY 63, SSRY 250, and NS 323) were found to be closely linked (r = 0.3–0.5; p < 0.05) to EB in six of the nine hybrid populations. Seven of the markers with 10 % or more coefficient of determination (R2) were linked to major quantitative trait loci associated with EB in cassava. The molecular markers identified in this study provide useful materials to select for EB in cassava and for further target-traits-improvement by pyramiding

*Corresponding author. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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Written by Administrator   
Wednesday, 31 July 2013 09:28

Genetic variability of three cassava traits across three

locations in Ghana

Peprah Bright Boakye1*, Ofori Kwadwo 2, Asante Isaac K. 3 and Elizabeth Yaa Parkes 1,4

1 Crops Research Institute, Fumesua, Kumasi, P. O. Box 3785, Ghana.
2 Department of Crops Science, University of Ghana, Legon.
3 Department of Botany, University of Ghana, Legon.
4 International Institute of Tropical Agriculture, Ibadan, Nigeria.


Accepted 27 May, 2013

A study was conducted to assess the extent of genetic variability, broad-sense heritability and correlations for fresh root weight, root number and top weight of five cassava genotypes across three locations in 2 years. Combined analysis of variance revealed highly significant genotypic effect for all the traits. Genotype x environment interaction was also significant for all the traits studied indicating considerable but, varying response of the genotypes to the environments. High broad-sense heritability and genetic advance as percent of the mean were observed for fresh root weight, suggesting that the trait is primarily under genetic control and that a simple recurrent phenotypic selection scheme would be rewarding. Phenotypic coefficients of variation values were larger than their corresponding
genotypic coefficient of variation values for all traits. Correlations between the three traits were highly significant and positive indicating that simultaneous progress for the three traits is feasible.

 

*Corresponding author. E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it .

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