Evaluation of the performance of groundnut genotypes and their resistance to groundnut rosette virus.
Makweti, Lutangu Jethrow.
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The groundnut or peanut is one of the important legume crops of tropical and semi-arid tropical countries, where it provides a major source of edible oil and vegetable protein. The crop is mainly grown by smallholder farmers with little inputs, resulting in low yields of 700 kg/ha compared to Asia and south America which records 3500 kg/ha and 2500 kg/ha respectively. The low yields are due to a number of abiotic and biotic factors with diseases being a major constraint. Amongst the diseases, groundnut rosette disease can cause up to 100% yield loss when infection occurs. The objectives of this study were to; (i) evaluate the ICRISAT elite lines for rosette resistance using artificial inoculation, (ii) determine the effect of genotype by environment interaction of landraces and elite lines and select for stability and high yield, and (iii) determine the genotype by trait interaction for the landraces so as to select potential genotypes for use as parents in the breeding programme. To achieve objective one, glasshouse and field inoculation experiments were conducted using the infector row technique. In the glasshouse, the results revealed that ICGV SM 08503 and ICGV SM 01514 were resistant and showed 0% disease incidence while ICGV SM 01711, ICGV SM 09547, ICGV SM 09537, ICGV SM 08501 and ICGV SM 09545 showed moderate resistance with scores ranging from 1.1 to 1.7. ICGV SM 02724, ICGV SM 10005 and ICGV SM 08560 showed high susceptibility with scores as high as 4.6. However, the susceptible genotypes ICGM SM 10005, ICGV SM 02724 and ICGV SM 08560 showed low incidences of the disease in the field evaluation. At 60 days after sowing (DAS), the incidence ranged from 9.9% to 16.5% while at 80 DAS, it ranged from 18.6% to 23.8%. The highest score for disease incidence at 100 DAS was 27.3% for genotype ICGV SM 08560. The rest of the genotypes had 0% incidence. The yield per hectare ranged from as low as 0.32 ton/ha to as high as 1.03 ton/ha. ICGV SM 10005 recorded the lowest yield while ICGV SM 01711 was the highest yielding genotype with 1.03 ton/ha. For the genotype x environment study, a total of 11 groundnut genotypes from ICRISAT comprising of nine elite lines and two released cultivars as controls were evaluated over ten environments spread across the three agro-ecological zones of Zambia in the 2016/17 season. Additive main effect and multiplicative interaction (AMMI) and genotype and genotype by environment interaction (GGE) biplot models showed that ICGV SM 01711 and ICGV SM 02724 were high yielding recording 2.08 t/ha and 1.99 t/ha, respectively, compared to the average mean of 1.67 t/ha across all environments and showed relative stability. ICGV SM 10005 and ICGV SM 08560, which are Spanish genotypes, yielded 1.67 t/ha and 1.60 t/ha, respectively, compared to Luena (control) which yielded 1.23 ton/ha. ICGV SM 10005 had better relative stability over ICGV SM 08560 and Luena. Genotype x trait analysis, correlation and path coefficient analysis on a total of eight landraces, two pre-released cultivars and five released cultivars showed a strong and highly significant correlation for grain yield with number of pods per plant, yield per plant, shelling percentage and 100-seed weight with r values of 0.86, 0.90, 0.94 and 0.23, respectively, at P<0.001 but 100-seed weight’s correlation was not significant. The path coefficient analysis revealed that yield per plant, shelling percentage, number of pods per plant, 100-seed weight and days to maturity had a positive direct effect on grain yield while days to flowering had negative direct effect on grain yield. Genotype by trait (GT) biplot captured 83.00% of the variation due to genotype by trait interactions. Two land races, Kasele and Chalimbana performed relatively well in relation to MGV 4 and it was recommended that these could be hybridized with genotypes that have complementary features so that beneficial alleles are combined for improvement of the crop, while genotypes ICGV SM 01514, ICGV SM 01711 and Chishango can be used as sources of resistance genes.