Sources of resistance to cassava root rot caused by Fusarium spp.: a genotypic approach

Abstract

The development of cassava cultivars resistant to root rot (PRM) is a viable strategy for disease control. The objectives of this study were to identify stable sources of PRM resistance and to estimate genetic parameters. Inoculation with Fusarium spp. (Fspp) species was performed in 697 accessions and five environments that were then assessed for symptom severity in the peel (cortex and periderm) and root pulp. The environment and genotypes was considered to have random effects via analysis of mixed models. The resistance stability, resistance adaptability, and resistance stability + adaptability for Fspp were assessed using the harmonic means of genotypic value (Si), relative performance of genotypic values (Ai), and harmonic mean of the relative performance of genotypic value (Zi), respectively. About 10 % of the accessions were considered resistant to Fspp. Discrepancies in the accession classification for PRM resistance in the root peel and pulp indicate the existence of different defense mechanisms in these parts of the root. The individual heritability and mean genotypic heritability through environments were of low magnitude, resulting in medium accuracy selective magnitude. Despite the existence of strong genotype × environment interaction (G × E), accessions with high adaptability and stability were identified. The 22 accessions resistant to PRM in the peel and pulp enabled significant and balanced disease reduction on Zi estimates (−48.18 and −46.42 %, respectively). The lack of complete resistance and continuous distribution of PRM suggest quantitative inheritance of resistance. The Zi method is a useful approach in the capitalization of G × E interaction for disease resistance.