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Ceballos H.,Aereo | Kawuki R.S.,National Crops Resources Research Institute NaCRRI | Gracen V.E.,Cornell University | Yencho G.C.,North Carolina State University | Hershey C.H.,Aereo
Theoretical and Applied Genetics | Year: 2015

Key message: Consolidates relevant molecular and phenotypic information on cassava to demonstrate relevance of heterosis, and alternatives to exploit it by integrating different tools. Ideas are useful to other asexually reproduced crops. Abstract: Asexually propagated crops offer the advantage that all genetic effects can be exploited in farmers’ production fields. However, non-additive effects complicate selection because, while influencing the performance of the materials under evaluation, they cannot be transmitted efficiently to the following cycle of selection. Cassava can be used as a model crop for asexually propagated crops because of its diploid nature and the absence of (known) incompatibility effects. New technologies such as genomic selection (GS), use of inbred progenitors based on doubled haploids and induction of flowering can be employed for accelerating genetic gains in cassava. Available information suggests that heterosis, non-additive genetic effects and within-family variation are relatively large for complex traits such as fresh root yield, moderate for dry matter or starch content in the roots, and low for defensive traits (pest and disease resistance) and plant architecture. The present article considers the potential impact of different technologies for maximizing gains for key traits in cassava, and highlights the advantages of integrating them. Exploiting heterosis would be optimized through the implementation of reciprocal recurrent selection. The advantages of using inbred progenitors would allow shifting the current cassava phenotypic recurrent selection method into line improvement, which in turn would allow designing outstanding hybrids rather than finding them by trial and error. © 2015, The Author(s).

Cervantes-Flores J.C.,North Carolina State University | Cervantes-Flores J.C.,Vilmorin Inc. | Sosinski B.,North Carolina State University | Pecota K.V.,North Carolina State University | And 7 more authors.
Molecular Breeding | Year: 2011

Development of orange-fleshed sweetpotatoes (OFSP) is desired for the improvement of the food supply and nutritional status of millions of people in developing countries, particularly in sub-Saharan Africa. However, sweetpotato [Ipomoea batatas (L.) Lam] breeding is challenging due to its genetic complexity, and marker-assisted breeding tools are needed to facilitate crop improvement. We identified quantitative trait loci (QTL) for dry-matter, starch, and β-carotene content in a hexaploid sweetpotato mapping population derived from a cross between Tanzania, a white-fleshed, high dry-matter African landrace, and Beauregard, an orange-fleshed, low dry-matter sweetpotato cultivar popular in the USA. Two parental maps were constructed using a population of 240 clones. Strong correlations were observed between starch and dry-matter content (r > 0.8, P < 0.0001) in the storage roots, while moderate correlations (r = -0.6, P < 0. 0001) were observed for β-carotene and starch content. In both parental maps, QTL analysis revealed the presence of 13 QTL for storage root dry-matter content, 12 QTL for starch content, and 8 QTL for β-carotene content. Multiple QTL regression models developed for segregation of alleles in each parent explained 15-24% of the variation in dry-matter content, 17-30% of the starch content, and 17-35% of β-carotene content. To the best of our knowledge, this research presents the only QTL mapping study published to date for dry-matter, starch, and β-carotene content in sweetpotato. This work improves our understanding of the inheritance of these important traits in sweetpotato, and represents a first step toward the long-term goal of developing marker-assisted breeding tools to facilitate sweetpotato breeding efforts. © 2010 US Government.

Sseruwu G.,University of KwaZulu - Natal | Sseruwu G.,Mukono Zonal Agricultural Research and Development Institute MUZARDI | Shanahan P.,University of KwaZulu - Natal | Melis R.,University of KwaZulu - Natal | Ssemakula G.,National Crops Resources Research Institute NaCRRI
Euphytica | Year: 2016

Alternaria blight (Alternaria spp.) is an important sweetpotato disease in Uganda causing yield losses of over 50 % in susceptible genotypes. In Uganda, Alternaria bataticola and Alternaria alternata are the major species with A. bataticola the more aggressive of the two. The most effective control measure for this disease is the use of resistant genotypes. This study was conducted to determine the inheritance of resistance to Alternaria blight and the general and specific combining abilities of the available germplasm. Sixteen parental clones varying in reaction to Alternaria blight were crossed using the North Carolina II mating scheme. Due to incompatibility of some parents, two sets of compatible parents were formed. Differences among the families for Alternaria blight severity were significant while general combining ability (GCA) and specific combining ability (SCA) mean squares were highly significant (P < 0.001) for the disease with GCA sum of squares (SS) being more predominant at 67.4 % of the treatment SS for Set 1 and the SCA SS predominant at 54.0 % of the treatment SS for Set 2. This indicated that both additive and non-additive effects are important in controlling this trait. Some parents with high, negative GCA effects produced families with undesirable SCA effects and the reverse was also true. This implies that the best parents should not be chosen on GCA alone but also on SCA of their best crosses. The wide range in the area under disease progress curve for the families indicated that it was possible to select for highly resistant genotypes. © 2016 Springer Science+Business Media Dordrecht

Ochola D.,National Crops Resources Research Institute NaCRRI | Ochola D.,Makerere University | Tusiime G.,Makerere University
Asian Journal of Plant Pathology | Year: 2011

In the present study, we assessed the pathogenicity of the prevalent strains of Rice Yellow Mottle Virus (RYMV) present in Eastern Uganda and identified suitable donors for durable resistance among rice cultivars. Screenhouse studies were conducted using eight isolates of the virus against 16 rice cultivars. Isolate aggressiveness and cultivar resistance were assessed in terms of disease severity and percentage stunting following mechanical inoculation by the finger-rub technique. Highly significant differences (p<0.001) between rice cultivars for both parameters revealed the occurrence of different genetic factors for resistance among the rice cultivars. Mean disease severity and percentage stunting ranged between 0.9-9.0 and -1.1-32.4%, respectively for individual cultivars. The absence of significant isolate-by-cultivar interaction suggests a race-non-specific resistance. No significant differences in aggressiveness were obtained between isolates, indicating limited pathotype diversity in Eastern Uganda as evidenced by the absence of mega-environments among the prevalent strains. Based on cultivar resistance ranking, three O. sativa subspecies japonica (NERICA6, ITA257 and ITA325) and two O. sativa subspecies indica (WAC116 and WAC117) were identified as the potential sources of resistance for improving susceptible local varieties. The confirmed resistance breakdown in GIGANTE has important implications for plant breeding and disease control strategies. Therefore, pyramiding different sources of resistance is recommended for enhanced durability of resistance. In addition, the use of sufficient prerelease challenge by the combination of isolates with different levels of aggressiveness will delay the rise of susceptibility in deployed resistant cultivars. © 2011 Academic Journals Inc.

Alibu S.,Tokyo University of Agriculture | Alibu S.,National Crops Resources Research Institute NaCRRI | Saito Y.,Tokyo University of Agriculture | Shiwachi H.,Tokyo University of Agriculture | Irie K.,Tokyo University of Agriculture
African Journal of Agricultural Research | Year: 2011

In rice, the coleoptile and mesocotyl are two morphologically important structures for seedling emergence. After germination, coleoptile and or mesocotyl elongation projects the seedling tip out of the soil and water in which it is planted, allowing the leaves to make contact with the atmosphere thus enabling the seedling to develop into a normal rice plant. Rice genotypes with inherently longer coleoptiles and or mesocotyls are thought to emerge better than those with shorter ones. However, the patterns of elongation under submergence and in soil-sand culture remain unclear especially for upland rice. This study examined coleoptile and mesocotyl elongation in 63 upland rice genotypes comparing elongation patterns under submergence to elongation in soil-sand culture. Coleoptile and mesocotyl elongation in soil-sand culture differed from elongation under submergence. Coleoptile lengths were enhanced more under submergence and mesocotyls grew longer in soil-sand culture. This appeared to link seedling emergence under submergence more to coleoptile elongation, and emergence in drained soil-sand culture largely to mesocotyl elongation. We found no obvious relationship between coleoptile and mesocotyl elongation under submergence. But in soil-sand culture, increases in coleoptile length corresponded to increases in mesocotyl length, suggesting that simultaneously coleoptile and mesocotyl elongation contribute to seedling emergence in drained soils. © 2011 Academic Journals.

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