Assessment of Comparative Virulence and Resistance in Soybean Using Field Isolates of Soybean Rust

Abstract

<p class="4Body">A major impediment to breeding for resistance to Asian soybean rust (<em>Phakopsora</em> <em>pachyrhizi</em>) is the lack of stable sources of resistance, due to high variability in the pathogen. The objectives of this study were to assess comparative virulence of five diverse field isolates from major soybean producing areas in Uganda, and identify lines with resistance to isolates of soybean rust in seedling and adult plants under screen house and field conditions respectively. When inoculated with the five field isolates, all twelve lines evaluated showed diverse and mixed reactions, suggesting each location differed in soybean rust races and/or virulence. Experimental sites growing many diverse soybean lines yearly had the greatest diversity of soybean rust. The effectiveness of specific resistance genes was restricted to certain locations and gene R<em>pp2</em> previously resistant was ineffective producing a susceptible tan reaction at the seedling stage. A positive correlation between mean lesion density at the seedling stage and adult plant severity indicated that using field isolates to screen for seedling resistance can be a useful breeding approach to extrapolate resistance in adult plants. Overall, these results emphasise the relevance of using field isolates from the target areas to evaluate lines for soybean rust resistance.</p

Soybean production in eastern and southern Africa and threat of yield loss due to soybean rust caused byPhakopsora pachyrhizi

“…One isolate, 72‐1 from Australia, induced both RB and TAN lesions on the same leaflets of eight different soybean accessions (Bromfield et al ., ). Other studies have reported mixed reactions in different rust populations, especially when using a bulk pathogen population or a mixture of isolates (Miles et al ., ; Yamanaka et al ., ; Maphosa et al ., ). These reactions could result from a mixture of races in the inoculum (Bonde et al ., ) that may imply more diverse virulence of the different isolates in a given population.…”

“…In the 2005 and 2006 growing seasons, 25 different soybean accessions, four among them bearing Rpp1 to Rpp4 , were found to be susceptible to rust populations originating from Uganda, except for accession PI 230970 ( Rpp2 ) (Oloka et al ., ). However, TAN‐type lesions were recently observed on PI 230970 ( Rpp2 ) when inoculated with five isolates of P. pachyrhizi in field trials in Uganda (Maphosa et al ., ), suggesting a change in virulence of Ugandan rust populations within a period of less than 10 years. In other studies, Twizeyimana et al .…”

Evaluation of Cowpea Genotypes for Virus Resistance Under Natural Conditions in Uganda

“…To identify host resistance, it is important to evaluate different genotypes under field conditions in different environments (Goenaga et al, 2011;Maphosa et al, 2013;Oloka et al, 2008). This study was therefore undertaken to study the reaction of 105 cowpea genotypes to natural virus infection to identify sources of resistance for breeding.…”

Prevalence of pathotypes of <em>Phakopsora pachyrhizi</em> Syd. causing Asian soybean rust in India

“…The differentials EC-241778 and JS-335 individually recorded no reaction to 14 and 16 different isolates, respectively. Twizeyimana and Hartman (2012) and Maphosa et al (2013) in the case of soybean rust. The clustering of different isolates based on morphological traits clearly indicated the presence of three pathotypes under Indian conditions.…”