Identification of sources of resistance and inheritance to Fusarium wilt (Fusarium oxysporum f.sp. sesami) resistance in sesame

Abstract

Fusarium wilt (Fusarium oxysporum f.sp sesame) is one of the most destructive soil borne diseases in sesame in Uganda. Breeding for resistance and use of resistant varieties is the most economic and environmentally friendly solution to the disease since majority of sesame growers are resource constrained. However, resistant varieties are not readily available to farmers and none of the released varieties in Uganda is resistant to the disease. Therefore, there is need to identify sources of resistance to the pathogen, which is the cornerstone to successful development of resistant varieties in addition to understanding the genetics of resistance to determine the best strategy for resistance breeding. Thus, studies were undertaken with the objectives of determining the resistance level of sesame genotypes to Fusarium wilt in Uganda and inheritance pattern of Fusarium wilt among selected sesame genotypes. To determine the resistance levels of sesame genotypes to Fusarium wilt, 30 sesame genotypes that included released varieties, improved elite pure lines, and introductions were screened in the screenhouse under high pathogen pressure following artificial inoculation. Results from the study revealed that sesame genotypes responded differently to the pathogen, with genotype effect being significant (P≤0.001) for disease incidence. Two genotypes (EM15-1-5 and Sesim 2) were rated moderately resistant (37.3% and 33.8% respectively) whereas seven genotypes were moderately susceptible and 21 susceptible including Sesim 1. In order to understand the gene action controlling resistance to the disease a Full-diallel (8 x 8) design was used consisting two moderate resistant, two moderate susceptible and 4 susceptible parents to generate F1 progenies. Fifty six F1 progenies (crosses and their reciprocals) and parents were evaluated against isolate SEFU2. Results revealed that both additive and non-additive gene actions contributed to controlling resistance to Fusarium wilt. However, non-additive effects were more predominant (moderate Baker’s ratio (53.9%) and low Coefficient of Genetic Determination narrow sense (h2 = 45.1%)). The high significant reciprocal effects for disease incidence observed among reciprocal crosses suggest that maternal effects also influenced (P≤0.001) resistance to Fusarium wilt. From the studies undertaken, the two genotypes (Sesame 2 and EM15-1-5) identified as moderately resistant could be used as resistant donors. Sesim 2 (with EM% GCA effect 7.32, and DI% GCA effect -4.02) and parent EM15-1-5 (with EM% GCA effect 3.07%, and DI% GCA effect -11.58%) were identified as good combiner parents for transmitting resistance and are recommended for use in breeding for Fusarium wilt resistance. It was also discovered that both additive and non-additive genes contributes towards resistance to Fusarium wilt but with non-additive gene effects being more predominant. Therefore, selection of resistant genotypes should be done during later generations of breeding.