HERITABILITY FOR RESISTANCE TO ROSETTE DISEASE IN EXOTIC VALENCIA GROUNDNUTS

Groundnut rosette disease (GRD) is the most destructive virus disease of Valencia groundnuts ( Arachis hypogaea L.) in sub-Saharan Africa. Cultural, biological and chemical control measures have received limited success due to small scale farmers’ inability to use them. Use of host plant resistance provides the most effective and economically viable management option for the resource poor farmers. This study was conducted to determine heritability for resistance to GRD in Valencia groundnuts. Six crosses; Valencia C (P1) × ICGV-SM 90704 (P2), Valencia C (P1) × ICGV-SM 96801(P2), Valencia C (P1) × ICGV-SM 99566 (P2), NuMex-M3 (P1) × ICGV-SM 90704 (P2), NuMex-M3 × ICGV-SM 96801 (P2), and NuMex-M3 (P1) × ICGV-SM 99566 (P2), were made to generate F1, F2, BC1P1 and BC1P2 populations. Data on GRD severity were collected on a 1-9 score scale. Genetic Advance as a percentage of the mean (GAM) and heritability were estimated using variance components. Phenotypic Coefficient of Variation (PCV) and Genotypic Coefficient of Variation (GCV) estimates were high (20.04-70.1%) in the six crosses, except for Valencia C × ICGV-SM 96801(18.1%) and NuMex-M3 × ICGV-SM 96801(17.1%), which exhibited moderate GCV values. Broad and narrow sense heritability estimates for GRD disease score ranged from 64.1 to 73.7% and 31 to 41.9%, respectively, in all the crosses. GAM was high in all the crosses (21-50.7%), except for Valencia C x ICGV-SM 96801 (14.67), M3 x ICGV-SM 99566 (18%) and NuMex-M3 x ICGV-SM 96801 (13.5%) crosses that exhibited moderate GAM. The study revealed the presence of variability of GRD resistance, implying that genetic improvement of these exotic materials is possible.

GENETIC DIVERSITY AMONG SORGHUM LANDRACES OF SOUTHWESTERN HIGHLANDS OF UGANDA

Sorghum ( Sorghum bicolor L. Moench) is an economic and staple crop in sub-Saharan Africa. The genetic diversity in its germplasm is an invaluable aid for its crop improvement. The objective of this study was to assess the existing genetic diversity among sorghum landraces in the southwestern highlands of Uganda. A total of 47 sorghum landraces, collected from southwestern highlands of Uganda, were characterised using 12 qualitative and 13 quantitative traits. The study was conducted at Kachwekano Research Farm in Kabale District, at an altitude of 2,223 m above sea level, during growing season of December 2014 to August 2015. Panicle shape and compactness were the most varied qualitative traits. Grain yield (1.23 to 11.31 t ha-1) and plant height (144.7 to 351.6 cm) were among quantitative traits that showed high variability. Days to 50% flowering (115 to 130 days) showed the least variability. Results of UPGMA cluster analysis generated a dendrogram with three clusters. Panicle weight, leaf width, stem girth, exertion length, peduncle length, panicle shape and compactness, glume colour and threshability were major traits responsible for the observed clustering (P<0.001). Principal Component Analysis revealed the largest variation contributors.

SSR genetic diversity assessment of popular pigeonpea varieties in Malawi reveals unique fingerprints

Background: Pigeonpea ( Cajanus cajan L. Millsp.) is a drought tolerant legume of the Fabaceae family and the only cultivated species in the genus Cajanus. It is mainly cultivated in the semi-arid tropics of Asia and Oceania, Africa and America. In Malawi, it is grown as a source of food and income and for soil improvement in intercropping systems. However, varietal contamination due to natural outcrossing causes significant quality reduction and yield losses. In this study, 48 polymorphic SSR markers were used to assess the diversity among all pigeonpea varieties cultivated in Malawi to determine if a genetic fingerprint could be identified to distinguish the popular varieties. Results: A total of 212 alleles were observed with an average of 5.58 alleles per marker and a maximum of 14 alleles produced by CCttc019 (Marker 40). Polymorphic information content (PIC), ranged from 0.03 to 0.89 with an average of 0.30. A neighbor-joining tree produced 4 clusters. The most commonly cultivated varieties, which include released varieties and cultivated land races, were well-spread across all the clusters observed, indicating that they generally represented the genetic diversity available in Malawi, although substantial variation was evident that can still be exploited through further breeding. Conclusion: Screening of the allelic data associated with the five most popular cultivated varieties, revealed 6 markers – CCB1, CCB7, Ccac035, CCttc003, Ccac026 and CCttc019 – which displayed unique allelic profiles for each of the five varieties. This genetic fingerprint can potentially be applied for seed certification to confirm the genetic purity of seeds that are delivered to Malawi farmers.