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Restricted genetic variability in elite tropical maize germplasm has raised concerns about the potential to develop higher yielding and stress-tolerant varieties. Elite temperate germplasm has high levels of genetic diversity for yield, drought tolerance and earliness. The objective of this study was to identify temperate maize inbreds that could enhance the grain yield potential, drought tolerance and high plant density tolerance of adapted tropical germplasm. Two hundred and forty-three temperate inbreds with expired Plant Variety Protection Act certificates from the USA were crossed to three CIMMYT single-cross testers. The three-way testcrosses were evaluated under high density, optimal, low nitrogen and managed drought conditions. Among the outstanding exotic temperate inbreds were HB8229, W8304, LH198 and PJH40 from the stiff stalk group, and LH159, LH214, and LH23Ht from the non-stiff stalk group. Of the highest yielding testcrosses, 65% were heterotic group A-lines, 30% heterotic group B-lines, and 5% were AB-lines. Although the testcrosses were more susceptible to diseases, their grain yield was comparable to the commercial checks, especially under managed drought and high-density conditions. Temperate lines also induced earliness and shorter plant stature to the three-way crosses. [ABSTRACT FROM AUTHOR]

Despite the development of quality protein maize (QPM) genotypes with increased lysine and tryptophan levels, there is still a controversy on the yield potential of QPM genotypes compared to non-QPM genotypes. The objective of this study was to compare the QPM hybrids with non-QPM hybrids for grain yield and related traits and to determine if the QPM trait caused yield reduction in tested environments. A total of 126 hybrids were developed by crossing 32 inbred lines (22 QPM and 10 non-QPM) with two QPM and two non-QPM testers, using a line x tester design, and these were evaluated with four hybrid checks (two QPM and two non-QPM) at 13 locations in South Africa and Zimbabwe. Significant differences were observed among the hybrids for almost all the traits, indicating that superior hybrids could be identified and selected. Significant genotype by environment interaction effect was detected for almost all the traits which indicated that hybrids performed differently across the tested environments. When average yield for QPM and non-QPM was compared across the 13 sites, the yield reduction was 9.34% due to the QPM trait. Decreased ear placement and increased ear aspect could have contributed to this reduction. Yield reduction was 13% for the two QPM testers crossed with lines compared with means of crosses with two non-QPM testers. The best performing hybrid was a QPM genotype (entry 41), but only four of the top 20 hybrids were QPM. Though most crosses indicated a substantial yield loss due to the QPM trait, the top performing hybrid being a QPM indicates the possibility of yield potential improvement in QPM genotypes. [ABSTRACT FROM AUTHOR]

With its drought tolerant and protein-rich properties, Bambara groundnut [Vigna subterranea (L.) Verdc.], an indigenous African legume crop can contribute immensely to food security. This miracle crop is used as food and for the enhancement of soil fertility in South Africa. Knowledge on the genetic diversity and structure among the Bambara groundnut landraces can pave the way for the effective use and cultivation of this crop in southern Africa, especially South Africa. The aim of this study was to assess the genetic diversity and structure among Bambara groundnut landraces collected across South Africa and compared to a limited number of accessions from southern Africa using SSR markers. Seventy-eight Bambara groundnut accessions were genotyped using 19 Bambara specific SSR markers. SSR loci explored in this study, were all polymorphic. A total of 127 alleles were detected with a mean of 6.7 alleles per locus. Allele diversity and frequency among genotypes varied from 0.21 to 0.85 with an average of 0.62 per locus. Genetic variation as described by the analysis of molecular variance indicated higher genetic diversity (92%) within landraces than between (8%) different landraces. Population structure analysis showed that three subpopulations existed, and most of the South African accessions were restricted to one subpopulation, indicating that Bambara landraces has the ability to form unique haplotypes in different environments. Information harnessed in this study is helpful for further use in breeding programs for crop improvement. [ABSTRACT FROM AUTHOR]

Maize is not inherently tolerant to soil acidity but due to the ever increasing demand for the crop in the developing world, production of maize on acid soils continues to expand. Breeding for maize acid soil tolerance is the best strategy to improve yield under these conditions. Therefore, the current study was done to determine the general combining ability (GCA) of eight acid-soil tolerant and susceptible inbred lines and the specific combining ability (SCA) of cross combinations of these lines for grain yield under acid and non-acid soils. The eight lines were crossed using a diallel mating design to produce 28 single cross hybrids for evaluation under acid and non-acid soils at four sites for two seasons. Line C2 was the best general combiner under both soil environments while A2/C1 and A1/C2 had the highest desirable SCA effects under optimal conditions. Loss in grain yield and sensitivity to low pH stress was higher among genotypes in light textured soils than heavy soils. Non-additive gene action was more important than additive gene action in conditioning grain yield under both environments. Results revealed that it was feasible to improve grain yield under low pH and optimum soils from the set of genotypes used in the current study. [ABSTRACT FROM AUTHOR]

A comparison of the different methods of the estimation of genetic diversity is important to evaluate their utility as a tool in germplasm conservation and plant breeding. Amplified fragment length polymorphism (AFLP), microsatellites or SSR and morphological traits markers were used to evaluate 45 sorghum germplasm for genetic diversity assessment and discrimination power. The mean polymorphism information content (PIC) values were 0.65 (AFLPs) and 0.46 (SSRs). The average pairwise genetic distance estimates were 0.57 (morphological traits), 0.62 (AFLPs) and 0.60 (SSRs) markers data sets. The Shannon diversity index was higher for morphological traits (0.678) than AFLP (0.487) and SSR (0.539). The correlation coefficients obtained by the Mantel matrix correspondence test, which was used to compare the cophenetic matrices for the different markers, showed that estimated values of genetic relationship given for AFLP and SSR markers, as well as for morphological and SSR markers were significantly related (p<0.001). However, morphological and AFLP data showed non-significant correlation (p>0.05). Both data sets from AFLP and SSR allowed all accessions to be uniquely identified; two accessions could not be distinguished by the morphological data. In summary, AFLP and SSR markers proved to be efficient tools in assessing the genetic variability among sorghum genotypes. The patterns of variation appeared to be consistent for the three marker systems, and they can be used for designing breeding programmes, conservation of germplasm and management of sorghum genetic resources. [ABSTRACT FROM AUTHOR]

Langdon durum D-genome disomic substitution lines were used to study the chromosome locations of adult-plant leaf rust resistance genes identified from tetraploid wheat accessions. The accessions are 104 (Triticum turgidumsubsp.dicoccumvar.arras) and 127 (T. turgidumsubsp.durumvar.aestivum). The complete sets of the substitution lines were crossed as female parents with the accessions and F1 double monosomic individuals selected at metaphase I. Segregating F2 individuals were inoculated during the flag leaf stage with pathotype UVPrt2 ofPuccinia triticina. The substitution analysis involving accession 104 showed that the gene for leaf rust resistance is located on chromosome 6B. The analysis with accession 127 indicated that chromosome 4A carries a gene for leaf rust resistance. The two novel genes are temporarily designated asLrac104andLrac127, respectively from accessions 104 and 127. [ABSTRACT FROM AUTHOR]

Forty-five Musa clones, including endemic and introduced cultivars plus hybrids, were evaluated for resistance against the banana weevil, Cosmopolites sordidus, in a field trial in Uganda. The predominant groups of staple crops, East African highland bananas (Musa spp. AAA) and plantains (Musa spp. AAB), as well as plantain-derived hybrids (AAB × AA), showed the highest levels of susceptibility to this pest. These were followed by dessert bananas (Musa spp. AAA), exotic bananas (Musa spp. ABB) and finally diploids of M. acuminata (AA). Hybrids of banana origin were highly resistant. Some East African highland cultivars, especially brewing types (e.g., Kabula, Bagandeseza, Ediirira), showed intermediate levels of resistance. Among the non-highland bananas, high levels of resistance were observed in Yangambi-Km5 (AAA), Cavendish (AAA), Gros Michel (AAA), Kayinja (ABB, Pisang Awak subgroup), Ndiizi (AB, Ney Poovan subgroup) and Kisubi (Ney Poovan subgroup). The highest resistance was observed in banana hybrids TMB2×7197-2, TMB2×8075-7 and the wild banana Calcutta-4 (AA). These were considered the best sources of resistance for a weevil resistance-breeding programme with the two hybrids commonly used as improved male parents. [ABSTRACT FROM AUTHOR]

Information on heterotic patterns of quality protein maize (QPM) inbred lines would help to design appropriate breeding strategies for QPM. The objectives of this study were to assess the genetic relationships and heterotic structure of elite QPM inbred lines adapted to eastern and southern Africa (ESA) using simple sequence repeat (SSR) markers. Thirty-five inbred lines consisting of 32 QPM and three non-QPM inbred lines were genotyped using 40 SSR markers that yielded a total of 217 alleles, with an average of 5.43 and range of 2-10 alleles per marker. The number of alleles per inbred line varied from 40 to 82, with a mean of 51.5. About 81% of the pairwise comparisons between the lines had genetic distance estimates varying from 0.250 to 0.415. The unweighted paired group method using arithmetic averages (UPGMA) clustering algorithm and model-based population structure analysis showed the presence of two to three major groups, mainly consistent with maturity groups and pedigree information. This information can facilitate effective utilization of the QPM inbred lines in breeding programs. [ABSTRACT FROM AUTHOR]

Abstract  : Potato (Solanum tuberosum L.) is a nutritious starchy tuber crop consumed as a staple food in most potato growing countries. Its productivity and production are limited by climate change; thus, it is of utmost importance to tap into the diversity of germplasm resources, therefore, diversifying the potato varieties available for production. The objectives of this study were to determine the phenotypic diversity among the selected Agricultural Research Council-Vegetable, Industrial and Medicinal Plants (ARC-VIMP) potato varieties for tuber yields and processing quality and to determine the correlation between measured traits. Two imported and 22 local potato varieties were planted in three different environments in South Africa. Significant (P < 0.001) differences in the tested varieties across all environments were observed for all measured traits. High broad-sense heritability (> 0.6) was observed for most of the traits, except for fry colour and the yield of unmarketable tubers. Nine ARC varieties and three standard varieties were associated with high tuber yield and quality traits, indicating their suitability for the fresh market and processing industry. Variety Mondial and five ARC varieties were associated with high tuber yield, indicating their suitability for the fresh market. Varieties released between 2004 and 2021 had high tuber yield, dry matter and specific gravity compared to the standard varieties and varieties released between 1980 and 1999, although there were slight differences in the magnitudes of their traits measured. These varieties could be recommended for commercial production for specific markets and for use as potential parents for further genetic improvement of the potato crop. [ABSTRACT FROM AUTHOR]