Assessment of genetic diversity among African cassava Manihot esculenta Grantz accessions resistant to the cassava mosaic virus disease using SSR markers

A study was conducted to determine the extent of genetic diversity among African cassava (Manihot esculenta Crantz) accessions resistant to the cassava mosaic virus disease (CMD), using simple sequence repeat (SSR) markers. The accessions included a breeding stock (clone 58308), five improved lines, 62 CMD resistant and 10 CMD susceptible landraces. Genetic diversity was assessed among accessions in five cluster groups derived from UPGMA analysis on data from 18 SSR primer pairs. Average gene diversity, He, was high in all cluster groups, with an average heterozygosity of 0.591 ± 0.061. The estimator of inbreeding Fis revealed a low level of inbreeding within groups and averaged −0.262 ± 0.142. Gene diversity among all accessions was 51.4% and gene diversity within cluster groups was 46.6%, while 4.8% was due to diversity between the different cluster groups. The amount of genetic differentiation measured by Gst and Fst were 9.6% and 12.1% respectively, indicating a weak genetic structure.     

Heterosis and combining ability for yield and resistance to grain mold in tannin-free photoperiod-insensitive sorghum [Sorghum bicolor (L) Moench] in Senegal

Journal of Crop Science and Biotechnology - Increasing sorghum production per unit area in the farmer’s field by developing high yielding tannin-free and grain mold tolerant varieties in...     

The genetic diversity of Jatropha Curcas (L.) germplasm in Ghana as revealed by random amplified polymorphic DNA (RAPD) primers

Jatropha curcas (L.) has gained popularity as a biodiesel plant to serve as an alternative fuel source and generate income to small landholders. The success of J. curcas as alternative fuel source and income generation depends on the identification of genetically divergent materials of the plant and developing superior planting stocks for farmers. This paper presents genetic diversity assessment of 40 representative accessions drawn from 90 accessions collected from ten regions of Ghana based on their seed yield performance. Random Amplified Polymorphic DNA (RAPD) analysis on the 40 accessions with ten primers revealed an average polymorphism of 24.99%. Genotype Genotype*Environmental biplot analysis which incorporates divergence effects due to genotype (PC1) and interactions between genotype and field parameters (PC2) was 44.7%. Hence the RAPD information indicates narrow genetic diversity among the accessions used in the study and J. curcas germplasm in Ghana. It is therefore recommended that local germplasm of J. curcas should be officially conserved and immediate efforts be made to widen the genetic base through research and introduction from other regions.     

Stability of <Emphasis Type="Italic">Solanum aethiopicum</Emphasis> Shum accessions under varied water deficit stress levels and identification of pertinent breeding traits for resistance to water shortage

Drought is a major constraint to productivity of Solanum aethiopicum ‘Shum’ group due to loss in market and nutrient value of stressed plants. This study evaluated S. aethiopicum Shum group accessions to identify genotypes (G) that excel across moisture deficit stress levels (WLs). A split-plot arrangement composed of four WLs and twenty accessions of S. aethiopicum as main plot and sub-plot factors, respectively, was implemented in a screenhouse, and repeated for two experiments. In each experiment, there was a highly significant effect of at least two WLs on mean performance among at least two accessions for most of the traits at p < 0.05. Further, very highly significant WL × G interactions were obtained for leaf relative water content (LRWC), leaves per plant (LPP) and plant height (PH), and non-significant for leaf blade length and leaf blade width. The order of priority as breeding traits for stability superiority across WLs was suggested as LRWC > PH > LPP. Consequently, based on LRWC, the most superiorly stable accessions were identified as accession 160 followed by accessions 145, 137, 108P and 184G while the least stable ones were identified as accessions 163G, 141, 163 and 108. The broad sense heritability (H ²) for each of the three recommended traits for drought resistance breeding was above 0.9 thus supportive for a good response to selection. Drought stress negatively affected the performance of S. aethiopicum Shum group but the exhibited variation allowed for selection of superiorly stable genotypes.     

Genetics of anther indehiscence with exerted stigmas and its application in hybrid rice breeding

Complete indehiscence of anthers accompanied with exerted stigmas outside the hull could be useful in hybrid rice breeding if the genetics and possible environmental effects are well understood. Studies were undertaken to identify the sources, confirm the mode of inheritance, and examine the possible environmental effects and potential application of anther indehiscence with exerted stigmas in hybrid rice breeding. Direct and reciprocal crosses were made between Jasmine 85, selected interspecific and intersubspecific lines and two wide compatibility varieties. The resulting F₁ progenies were evaluated for their expression of anther indehiscence and exerted stigmas. Expression of anther indehiscence with exerted stigmas by both direct and reciprocal crosses suggested no effect of cytoplasmic factors on the expression of the trait. Segregation analysis supported the 7:1 (indehiscence:dehiscence) mode of inheritance. Temperature and relative humidity could not modulate the fertility/sterility status of anther indehiscent plants. Utilization of anther indehiscence with exerted stigmas in hybrid rice breeding was hindered by trait fixation and propagation.     

Phenotypic characterization and validation of provitamin A functional genes in early maturing provitamin A-quality protein maize (Zea mays) inbred lines

The number of drought and low-N tolerant hybrids with elevated levels of provitamin A (PVA) in sub-Saharan Africa could increase when PVA genes are optimized and validated for developed drought and low-N tolerant inbred lines. This study aimed to (a) determine the levels of drought and low-N tolerance, and PVA concentrations in early maturing PVA-quality protein maize (QPM) inbred lines, and (b) identify lines harbouring the crtRB1 and LcyE genes as sources of favourable alleles of PVA. Seventy early maturing PVA-QPM inbreds were evaluated under drought, low-N and optimal environments in Nigeria for two years. The inbreds were assayed for PVA levels and the presence of PVA genes using allele-specific PCR markers. Moderate range of PVA contents was observed for the inbreds. Nonetheless, TZEIORQ 55 combined high PVA concentration with drought and low-N tolerance. The crtRB1-3′TE primer and the KASP SNP (snpZM0015) consistently identified nine inbreds including TZEIORQ 55 harbouring the favourable alleles of the crtRB1 gene. These inbreds could serve as donor parents of the favourable crtRB1-3′TE allele for PVA breeding in maize.     

Combining ability and heterosis of elite drought-tolerant maize inbred lines evaluated in diverse environments of lowland tropics

Estimates of combining abilities and heterosis of inbred lines are imperative for selection of suitable parents of maize hybrids. This study examined the combining ability of 24 drought-tolerant maize inbred lines, 12 each from International Centre for Maize and Wheat Improvement (CIMMYT) and International Institute of Tropical Agriculture (IITA). The lines were allotted into six groups each comprising four lines. The four lines in one group were used as females and crossed to the four lines in another group as males in six different sets using a North Carolina Design II mating scheme to generate 96 hybrids. The hybrids were evaluated together with four checks across six environments in the rainforest and savannah agro-ecologies of Nigeria between 2011 and 2012. The parental inbred lines were also evaluated in separate trial in each location. Significant hybrids × environment interaction was observed for grain yield and other measured traits. GCA effects accounted for 83.3% of the variation for grain yield at Bagauda, 78.1% at Saminaka, and 77.7% at Ikenne. GCA also contributed 91.1 and 80.0% to the variation observed for plant height and ear aspect, respectively, across the environments. Significant SCA × environment interaction detected for grain yield suggests that hybrids were not stable across test environments. Prediction of grain yield in hybrids using midparent values resulted in a R ² value of 0.13. Midparent heterosis for grain yield varied from 80 to 411%, with the top 36 hybrids recording >200%. Four CIMMYT (EXL02, EXL06, EXL04 and EXL16) and three IITA (ADL33, ADL41, and ADL32) inbred lines had positive and significant GCA effects for grain yield across environments. The novel alleles present in the CIMMYT lines will improve the adapted IITA germplasm in a new population for extracting new set of more productive inbred lines for developing adapted high yielding drought-tolerant maize hybrids.     

Genetic diversity in Echinochloa spp. collected from different geographic origins and within rice fields in Côte d'Ivoire

Summary Diversity studies of Echinochloa spp. are complicated by problems in taxonomy and species identification, caused by the existence of morphologically intergrading types. Six amplified fragment length polymorphism (AFLP) primer combinations and five microsatellites were used to assess variation in 24 samples morphologically identified as E. crus-galli , E. colona and E. crus-pavonis , from Bangladesh, India, Colombia, Costa Rica, Côte d'Ivoire and Philippines. Out of 909 AFLP bands generated, 775 were polymorphic. Genotype diversity for the microsatellites ranged from 0.28 to 0.72. Similarity matrices were calculated using Jaccard coefficient, and input into cluster and principal coordinates analyses. AFLP and microsatellite results were highly correlated. Echinochloa crus-pavonis and E. crus-galli were intermixed, consistent with the view that E. crus-galli occurs as numerous intergrading races in the four countries (Bangladesh, India, Côte d'Ivoire and Philippines). The E. colona samples clustered as a distinct group. In 15 samples of E. crus-pavonis collected from rice fields in a valley in Côte d'Ivoire (over a 2-km distance), four different genotypes were found in a 4 m × 4 m area. These results suggest that AFLPs and SSRs may be useful not only for discriminating genotypes and studying population structure but also for helping to resolve taxonomic relationships in Echinochloa spp.     

Genetic analysis of drought tolerance in adapted × exotic crosses of maize inbred lines under managed stress conditions

Introduced maize (Zea mays L.) germplasm can serve as sources of favorable alleles to enhance performance in new maize varieties and hybrids under drought stress conditions. In the present study, the combining abilities of 12 exotic maize inbred lines from CIMMYT and 12 adapted maize inbred lines from IITA were studied for grain yield and other traits under controlled drought stress. The inbred lines from each institution were separated into groups using SSR-based genetic diversity and were intercrossed using a factorial mating scheme to generate 96 hybrids. These hybrids were evaluated under both controlled drought stress and well-watered conditions at Ikenne in Nigeria in 2010 and 2011. Average mean yields of hybrids under drought stress represented 23 % of the average yield of hybrids under full irrigation. General combining ability (GCA) effects accounted for 49–85 % of the observed variation for several traits recorded under both well-watered and drought stress conditions. Specific combining ability effects for grain yield, though positive in most hybrids, were not significant under drought stress conditions. All the twelve exotic and nine adapted lines had positive GCA effects (female, male, or both) for grain yield under either drought stress or full irrigation, or both environments. EXL03 and EXL15 that had positive and significant female and male GCA effects for grain yield under both environments can be used to improve their adapted counterparts for grain yield and drought tolerance. Normalized difference vegetation index had weak but significant correlation with grain yield.     

Identification of CMS maintainers and restorers for hybrid rice development in Ghana

The cytoplasmic-genetic male sterility is the most widely used system for hybrid rice (Oryza sativa) seed production. It requires three lines: the two hybrid parents (A and R lines) and a third line (maintainer (B line)), which maintains the sterility of the female parent during seed increase. Studies were undertaken to identify maintainers and restorers for introduced cytoplasmic male sterile (CMS) lines using simple sequence repeat (SSR) markers and testcrosses. Molecular screening with SSR marker RM6100 grouped the assembled inbred lines into 30 potential restorers and 55 potential maintainers. One maintainer (WAS 127 -12-1-6-3-1) and 16 restorers were confirmed by testcrosses. WAS 127-12-1-2-3 had higher grain yield per plant in crosses with CMS1 (IR69625A) than the local checks (AgraRice and Jasmine 85) and could be used as a restorer to develop a locally adapted, high-yielding hybrid. Conversion of WAS 127 -12-1-6-3-1 into a local CMS line was stopped because of sterility instability in the BC₁F₁ generation. Continued testcrosses to the set of identified potential maintainers could help identify a stable one that can successfully be converted into a locally adapted CMS line.