Genetic linkage of the aphid resistance gene, Rac, in cowpea

Linkage of the aphid resistance gene, Rac, with various polymorphic loci controlling morphological traits and aspartate amino-transferase isozyme (AAT) was studied in cowpea (Vigna unguiculata L. Walp) with the objective of identifying simply inherited and easily identifiable markers for aphid resistance and to distiguish between Rac1 and Rac2 reported by Pathak (1988). The F2 and F2 - derived F3 populations from crosses IT87S-1459 x Tvu 946 x ICV 5, and IT84S-2246 x Tvu 946 segragating for Rac1 and cross ICV 12 x Tvu 946 segragating for Rac2 were scored for various polymorphic morphological traits. Locus pd, controlling peduncle colour, was found to be linked to both Rac1 and Rac2 (P <0.05). The recombination frequencies estimated by the maximum likehood method were 26 +/- 8.3% and 35 +/- 7.5% for Rac1-pd and Rac2-pd co-segregation, respectively, thus indicating that Rac1 and Rac2 were not different from one another. No linkage was found between aphid resistance genes and the genes controlling other polymorphic morphological traits or AAT isozyme.La relation entre le gene de resistance aux aphids, Rac, avec de nombreux loci polymorphiques qui controlent les traits morphologiques et l'isozyme asparate d'amino transferase (AAT) etait etudie chez le niebe dans l'optique d'identifier les marqueurs facilement heritables et facilement identifiables pour la resistance aux aphides et envue de faire la distinction entre Rac1 et Rac2 tels que precaunise par Pathak (1988). Les populations F2 et F2 - derivees de F3 des croisements IT87S-1459 x Tvu 946 segregues pour Rac2 ont ete cotees pour leurs differents traits morphologiques polymorphiques. Le locus pd, controllant la couleur de pedoncule etait associe au Rac1 et Rac2 (P<=0.05). Les frequences de recombination estimees par une methode de probabilite maximale etaient de 26 +/- 8.3% et de 35 +/- 7.5% pour la co-segregation des Rac1-pd et Rac-2-pd-respectivement; ce qui indique que la Rac2 n'etait pas differents l'une de l'autre. Aucune relation n'a ete revelee entre les genes de resistance aux aphides et les genes qui controllent les autres traits morphologiques polymorphiques ou l'isozyme AAT

Morphological diversity of farmers’ and improved potato (Solanum tuberosum) cultivars growing in Eritrea

Farmers’ and improved potato (Solanum tuberosum L.) cultivars growing in Eritrea are main sources of food and income to many growers. The current study was proposed to characterize 17 farmers’ and 4 imported cultivars of potato using 33 morphological descriptors. Planting was done in two geographically distinct locations, HAC and Asmara, Eritrea. The experiment was laid out in a randomized complete block design with three replications having 18 plants per plot. Plants grown at HAC emerged early (24.52 days) and reach maturity (94.84 days) while at Asmara it took 43.77 and 123.59 days, respectively. However, yield was higher in Asmara (0.49 kg/plant) compared to HAC (0.37 kg/plant). An accession having many and longer stems was associated with more tuber production, but inversely related to yield. Similarly, accessions with higher stem thickness and tuber size were associated with high yields. The PCA analysis indicated that the first four components explained about 85% of the total variability among the studied materials. The PCA clustered the materials in to four main groups (GI, GII, GIII, GIV) mainly explained by flowering patterns and yield related descriptors. The work has provided useful information on morphological characteristics of the farmer’s potato to avoid duplication of resources and identify promising materials for future breeding program

Genetic diversity assessment of farmers’ and improved potato (Solanum tuberosum) cultivars from Eritrea using simple sequence repeat (SSR) markers.

Sixty three potato clones (51 farmers’ and 12 varieties) from Eritrea, 18 and 12 varieties from Kenya and Rwanda, respectively were characterized using 12 highly polymorphic simple sequence repeat (SSR) markers. The study was designed to assess the genetic diversity and varietal distinctness among the different samples. In total, 91 alleles ranging between 2 (STM1053) to 13 (STM0031) alleles per marker were scored. All but 97.8 SSR markers were highly polymorphic with an average PIC value of 0.87 (0.51 to 0.98). All of the 51 farmers’ cultivars were clearly distinct from each other. Samples from Eritrea showed the highest genetic diversity as explained by the diversity index (h). The principal coordinate analysis (PCoA) revealed that the local farmers’ Eritrean samples are different from the Kenyan, Rwandese and even the imported varieties. Genetic distance analysis generated three clusters correlating with the PCoA findings. Cluster I consisted of 45 samples with 6 sub-clusters; Cluster II consisted of 29 samples with a majority (26) from Eritrea while cluster III consisted of 19 samples. Potato materials from Eritrea appeared to cluster separately from the other samples, which reflects a contribution from the Tuberosum germplasm prominent in temperate regions, unlike from the Andigenum germplasm for Kenyan and Rwandan potato materials. Most of the Eritrean samples in cluster I are farmers’ cultivars with intermediate maturity, good performance and better tuber quality characteristics. Cluster II contains mainly the imported variety from Eritrea characterized by late emergence and late maturity. The Kenyan and Rwandese were grouped mainly in Cluster III. In summary, the farmers’ cultivars are distinct from the Kenyan and Rwandese materials and represent more genetic diversity than the varieties imported into Eritrea. This finding is of interest to national breeding program to use the farmer’s materials as source of genetic variation for traits of interest

Controle genético do comprimento do pedúnculo em feijão-caupi Genetic control of peduncle length in cowpea

O objetivo deste trabalho foi estudar o controle genético do caráter comprimento do pedúnculo em feijão-caupi (Vigna unguiculata). Para isso, foi realizado um cruzamento entre os parentais TVx-5058-09C, de pedúnculo curto, e TE96-282-22G, de pedúnculo longo. Os parentais e as gerações F1, F2, RC1 (P1xF1) e RC2 (P2xF1) foram avaliados em delineamento de blocos ao acaso, com quatro repetições. Foram estimados: variâncias fenotípica, genotípica, ambiental, aditiva e de dominância; herdabilidades no sentido amplo e restrito; grau médio de dominância e número mínimo de genes que determinam o caráter. O modelo aditivo-dominante foi adequado para explicar a variação observada. O efeito gênico aditivo foi o mais importante no controle do comprimento do pedúnculo, que é, aparentemente, controlado por cinco genes.<br>The objective of this work was to investigate the genetic control of peduncle length in cowpea (Vigna unguiculata L.). A short peduncle cowpea line (TVx-5058-09C) was crossed with a long peduncle line (TE 96-282-22G). The parents and the F1, F2, RC1 (P1xF1), and RC2 (P2xF1) generations were evaluated in randomized block design with four replications. Genotypic, phenotypic, environmental, additive, and dominance variances for peduncle length were determined. Narrow and broad sense heritability, the degree of dominance, and the minimum number of genes determining peduncle length were estimated. The additive-dominant model was adequate to explain the observed variation. The additive gene effect was the most important in controlling peduncle length, which appeared to be controlled by five genes