Joseph Martin Bell

Evidence of genomic exchanges between homeologous chromosomes in a cross of peanut with newly synthetized allotetraploid hybrids

Cultivated peanut and synthetics are allotetraploids (2n = 4x = 40) with two homeologous sets of chromosomes. Meiosis in allotetraploid peanut is generally thought to show diploid-like behavior. However, a recent study pointed out the occurrence of recombination between homeologous chromosomes, especially when synthetic allotetraploids are used, challenging the view of disomic inheritance in peanut. In this study, we investigated the meiotic behavior of allotetraploid peanut using 380 SSR markers and 90 F2 progeny derived from the cross between Arachis hypogaea cv Fleur 11 (AABB) and ISATGR278-18 (AAKK), a synthetic allotetraploid that harbors a K-genome that was reported to pair with the cultivated B-genome during meiosis. Segregation analysis of SSR markers showed 42 codominant SSRs with unexpected null bands among some progeny. Chi-square tests for these loci deviate from the expected 1:2:1 Mendelian ratio under disomic inheritance. A linkage map of 357 codominant loci aligned on 20 linkage groups (LGs) with a total length of 1728 cM, averaging 5.1 cM between markers, was developed. Among the 10 homeologous sets of LGs, one set consisted of markers that all segregated in a polysomic-like pattern, six in a likely disomic pattern and the three remaining in a mixed pattern with disomic and polysomic loci clustered on the same LG. Moreover, we reported a substitution of homeologous chromosomes in some progeny. Our results suggest that the homeologous recombination events occurred between the A and K genomes in the newly synthesized allotetraploid and have been highlighted in the progeny. Homeologous exchanges are rarely observed in tetraploid peanut and have not yet been reported for AAKK and AABB genomes. The implications of these results on peanut breeding are discussed.

Genetic architecture of some leaf yield and quality attributes in dual-purpose cowpea (Vigna unguiculata L. Walp.).

Aims: Cowpea’s use as leafy vegetable has been widely neglected in research. The present study was aimed at finding out the nature and magnitude of genetic variability in dual-purpose cowpea for leaf yield and quality attributes. Place and Duration of Study: Ngaoundere University (Cameroon), from 2008 to 2009. Study design and Methodology: Fourteen pure lines and ten F1 hybrids derived from a 5 x 5 half-diallel cross were grown in Randomized Complete Block Design (RCBD) with three replications to assess the genetic mechanism of leaf yield index (LYI), leaf area (LA), leaves per plant (NLP), leaf protein (LN) and phosphorus (LP) content. Results: Analysis of variance indicated significant differences (p<0.01) among genotypes for all traits. Moderate to high heritability in broad-sense (0.49-0.90) was recorded for the characters indicating major role of genetic variance in the expression of these polygenic traits. Diallel analysis showed significance (p<0.05) of the effects of general combining ability (GCA), specific combining ability (SCA), the involvement of additive and dominance genes. These genes were asymmetrically distributed among the parental genotypes. Dominant genes had an overall positive effect for leaves per plant, leaf yield index and phosphorus content while high protein content and surface area appeared to be associated Research Article American Journal of Experimental Agriculture, 1(4): 400-413, 2011 401 mostly with recessive genes. Correlations between the leaf attributes and seed yield components were significant only for leaves per plant and seeds per pod (-0.73), pods per plant (-0.69); leaf yield index and seed weight (0.69); leaf protein content and pods per plant (-0.77). Conclusion: These results could be exploited in breeding programs to develop nutritional superior cowpea varieties which could be used for harvesting of both leaves and seeds.

A review of main factors affecting palm oil acidity within the smallholder oil palm (Elaeis guineensis Jacq.) sector in Cameroon

Crude palm oil from the mesocarp of Elaeis guineensis Jacq fruits is one of the most consumed vegetable oil in the world. The quality of palm oil assessed mainly by its free fatty acids (FFA) content and impurities, varies between the artisanal and industrial extraction and supply systems. The objective of this paper is to highlight the main parameters that influence the acidity or FFA content of crude palm oil produced by the smallholder artisanal sector. Three parameters examined are: crude palm oil production and extraction methods, microbial activity and oil palm genotype. These three parameters strongly increase lipase activity and hence palm oil acidity. In addition to endogenous lipase in fruit mesocarp, microorganisms found in palm oil are also involved in lipase activity e.g. Aspergillus sp, Mucor sp, Penicillium and Candida for fungi; and bacteria such as Bacillus, Pseudomonas, Micrococcus, Staphylococcus and Enterobacter. To improve the quality of palm oil, smallholders must first seek oil palm progenies with low acidity oil and respect the standard cultural practices for palm oil production. Key words: Elaeis guineensis Jacq, palm oil acidity, microorganisms, production systems, genotype.

Evaluation of resistance to cassava mosaic disease in selected African cassava cultivars using combined molecular and greenhouse grafting tools

Cassava mosaic disease (CMD) threatens cassava (Manihot esculenta) production in Africa. A total of 24 selected cultivars were screened against CMD using combined molecular and greenhouse grafting tools. Disease severity was recorded for 10 weeks after inoculation and the molecular markers associated with CMD2 were detected by PCR. CMD severity significantly differed (P < 0.0001) among cultivars. Twelve cultivars were morphologically resistant and eight of these possessed CMD2 and four did not. These results suggest that there are several CMD-resistant cassava cultivars that could be recommended for on-farm production and for conservation and breeding programs.