Epidemiology of lentil rust in Ethiopia with special reference to disease progress and yield loss assessment

[摘要] English: Rust [Uromyces viciae-fabae (Schroet.)] is one of the major diseases of lentil (Lensculinaris Medik.) in the world causing major crop losses when conditions are conducivefor disease development. Effective lentil rust management depends on knowledge of, e.g.,disease - yield relationships, dynamics of rust epidemics, accurate phenotyping ofresistance, and components of resistance.Sequential analyses of lentil rust epidemics were performed by assessing crop anddisease parameters in five field rust epidemics. The five epidemics produced similarshapeddisease progress curves that varied significantly in the rate of temporalprogression (rL) and area under the disease progress curve (AUDPC). The epidemics didnot affect crop growth; however, they had significant influences on seed yield, pods perplant and seed mass at crop growth stages between early flowering and early podformation. The rust also significantly affected harvest index and days to maturity. Resultsdemonstrated that a seed yield loss of up to 41.7% could occur and the effect of rust onseed yield of lentil can be predicted with AUDPC and critical-point models using diseaseseverity assessed on the upper canopy layer in the early flowering stage. Every 1%increase in rust severity reduced seed yield by 8.39%. Rust severity �?4.7% at the criticalstage will significantly reduce seed yield.To assess the effect of rust on the value of infected lentil straw as animal feed, atrial was conducted to evaluate its degradability in rumens of Zebu cows. Following 6 hof incubation, samples of all treatments lost �?40% of the total dry matter, degradationreaching ca. 65% at 72 h. Rust did not decrease degradability of dry matter in the rumen.The nitrogen (N), phosphorus (P) and the total crude protein (TCP) content in rust infected straw was higher than those of healthy straw. Seeds from healthy plantscontained more P than the seeds from rusted plants. The rust had no effect on seed Ncontent.Inoculation and incubation techniques resulting in uniform spore deposition andinfection, thereby obtaining reproducible and accurate data on host responses, arerequired for quantitative studies. To achieve this, a spore-settling tower was developed,and uniformity of spore deposition was assessed by dispersing 1, 2, 4 and 8 mgurediniospores of U. viciae-fabae into the tower. Uniform spore deposition was obtainedwhen 8 mg spore quantity was discharged into the tower and allowed a settling period of3 min. A linear relation was found between mass of spores discharged into the tower andspores deposited/cm2. Uniformity of spore deposition increased as the spore amountdischarged increased.In experiments quantifying the effects of temperature on germination of U. viciaefabae,a high percentage (�?80%) of spore germination was observed after 3 h ofincubation on 1.5% water agar at 10, 15, 20 and 25°C, with an optimum (99%) at 20°C.At this sampling time the length of germ tubes ranged from 66 μm (10°C) to 196 μm(20°C). For minimum infection of lentil cultivar EL-142 at 20°C, a dew period of at least3 h was required, whereas maximum infection occurred with a dew period of 24 h.Components of resistance to U. viciae-fabae, namely, latent period, infectionefficiency, pustule size and spore production were evaluated in the lentil cultivars Gudo,R-186, FLIP-87-66L and FLIP-89-60L and EL-142 (susceptible check) in a glasshouse.The cultivars were also compared for area under the disease progress curve (AUDPC),area under the pustule density curve (APDC), apparent infection rate (rG), and disease severity under field conditions. Gudo and R-186 had significantly smaller and fewerpustules, lower spore yield and longer latent period than EL-142. FLIP87-66L wasintermediate for infection efficiency and pustule size. In addition, significant differenceswere found between cultivars for AUDPC, APDC, disease severity and rG. Estimates ofAUDPC, APDC, disease severity and rG were reduced in Gudo, R-186 and FLIP-87-66Lcompared with the susceptible check EL-142. FLIP-89-60L also showed low AUDPC,APDC and disease severity. Some of the components obtained in the field weresignificantly correlated with each other and those measured in the glasshouse. Most of thecomponents studied in the glasshouse were correlated with AUDPC and disease severity.Data indicated the existence of incomplete (partial) resistance in the test cultivars, and thepossibility of using infection efficiency, latent period, spore production and pustule sizeas selection criteria in the evaluation of partial resistance to rust in lentil. Since there wasan interdependence of the components, selection based on more than one componenthelps obtain lines with higher levels of partial resistance. The AUDPC, disease severityand rG could also be used for selecting lines with partial resistance in the field.Histological studies showed that the resistance mechanism in the lentil cv. Gudo againstU. viciae-fabae is a combination of hypersensitive and pre-penetration types.Furthermore, cv. Gudo had a higher percentage of early aborted colonies than thesusceptible cultivar.

[发布机构] University of the Free State