Inheritance of resistance to oat crown rust in recombinant inbred lines

Abstract

Crown rust is the main disease affecting oats (Avena sativa L.), and genetic resistance has been the chief method utilized to control this disease. A population composed of 135 recombinant inbred lines, F5:6, generated by crossing the oat cultivar UFRGS 8 with the genotype Pc68/5*Starter, was assessed on the inheritance of resistance to crown rust (Puccinia coronata f. sp. avenae P. Syd. & Syd.). The evaluation of resistance in F5:6 seedlings was based on the type of infection resulting from inoculation with the race SQPT of P. coronata f. sp. avenae. The proportion of Resistant: Susceptible seedlings (R:S) was 62:64, which indicates that inheritance was governed by a single gene. The assessment of resistance inheritance in adult plants was performed in the field during the years 2004 and 2005. The distinction between resistant and susceptible classes was based on the final severity (FS) as well as the area under the disease progress curve, which was normalized and corrected (AUDPC*c). F5:6 and F5:7 were evaluated under field conditions in 2004 and 2005, demonstrating a ratio of approximately 1R:3S, which fits with a typical two genes inheritance model.

Epidemiological and histological components of crown rust resistance in oat genotypes

“…The virulence of P. coronata isolates from southern Brazil towards the Pc68 gene conferring resistance to P. coronata in oat genotype Pc68/5*Starter has previously been reported by Leonard and Martinelli (2005) and Graichen et al (2010). This oat genotype shows no disease in the early stages of development but pustules are present after flowering at the end of the plant growth cycle.…”

“…where: y i = % leaf area affected by crown rust (severity at the i th observation; t i = time in days after sowing at the i th observation, n = period of days from the onset and latest assessment of the disease, and c = the longest epidemic period among the genotypes tested (from Graichen et al 2010). …”

Puccinia coronata f. sp. avenae: a threat to global oat production

“…The relationship between crown rust resistance in oat and Pca virulence displays typical gene‐for‐gene characteristics, with resistance conferred by multiple single dominant resistance genes, each displaying different specificities towards pathogen isolates (Chong et al ., ). To date, more than 100 crown rust resistance ( Pc ) genes have been described in oat (Table S1, see Supporting Information) (Gnanesh et al ., ; Graichen et al ., ; Tan and Carson, ; USDA‐ARS CDL, ), although the lack of molecular information makes it difficult to determine whether some of these genes may be the same or are alleles at a common locus. In contrast with this wealth of R genes, no effectors have yet been identified in Pca , and the knowledge of rust pathogen Avr proteins remains limited to Melampsora lini , the causal agent of flax rust, and Hemileia vastatrix , the causal agent of coffee leaf rust (Maia et al ., ; Ravensdale et al ., ).…”

Phenotypic and genetic characterization of partial resistance to crown rust in Avena sativa L.

“…The area under the disease progress curve (AUDPC) was estimated by the trapezoidal integration of the curve for each individual plant from the six basic generations. The AUDPC values were normalized and corrected (AUDPCnc) by dividing the values by the number of days until the final severity reading for each genotype and multiplying the resulting values by the number of days until the final severity evaluation of the experiment, according to Graichen et al (2010), as shown below:…”

“…With respect to the predominant oat rust races that are found in Brazil, the most promising resistance gene is Pc68, due to the low incidence of virulent pathotypes that have been found to affect it (Leonard and Martinelli 2005). However, Graichen et al (2010) reported that the resistance that is provided by Pc68 has been overcome in Brazil. Unfortunately, the effectiveness of genes that provide specific resistance to P. coronata f.sp.…”