Distribution and Variability of Pseudocercospora griseola in Uganda

Abstract

Pseudocercospora griseola the casual pathogen for angular leaf spot (ALS) on common bean (Phaseolus vulgaris) is highly variable with many different races occurring in different agro-ecological zones. Therefore, for an effective breeding program, there is a need to continuously monitor the distribution and variability of the pathogen as a means of guiding breeders on which races to target. A study was conducted to assess the incidence, severity and variability of P. griseola in bean growing districts of Dokolo, Lira, Apac, Sironko, Mbale, Rakai, Lwengo, Bukomansibi, Kabale and Kisoro in Uganda. Forty five out of 80 isolates collected were tested on a set of 12 international bean differentials cultivars for ALS. Molecular markers were also used to elucidate the variability among isolates. In all districts, ALS was found wide spread with a mean incidence of 49.9%. Dokolo district had the highest disease incidence and severity, while Kisoro registered the lowest values respectively. In terms of altitude, incidence (60%) and severity (45%) were high for bean fields located between 1000-1200 m and low disease incidence (33.6%) and severity (20.7%) for fields lying above 1500 m. The standard differential cultivars and molecular markers defined 12 pathotypes and 30 haplotypes respectively. These belonged to Middle America and Andean group with considerably high level of diversity. Our findings indicated the presence of ALS in Uganda with high incidence, severity and variability across districts and altitudes. Hence strategic interventions involving integrated disease management and breeding for durable resistance are required to manage the disease.

Characterization of the common bean host and Pseudocercospora griseola, the causative agent of angular leaf spot disease in Tanzania

“…Because Andean isolates that were virulent on Mesoamerican genotypes were found, this suggests that in Tanzania, both common bean genetic backgrounds need to be improved so as to attain durable resistance. Similar findings have been reported from pathogenic characterization using differential cultivars (Ddamulira et al, 2014); however, in this study, no differential cultivars were used and instead virulence grouping was employed as described by Mahuku et al (2002) in which the affected genotypes were characterized. Further, in this study, there is interaction between Andean isolates with Mesoamerican genotypes where some Andean isolates were shown to be virulent on Mesoamerican genotypes ( Figure 5).…”

“…When grouping of isolates was organized based on altitude or geographical location of the site of collection, the distribution of the gene pools of the pathogen was not correlated with altitude (data not shown) and somewhat do with GPS position where most of the Mesoamerican are from the lake zone. Somewhat different findings were reported in Uganda (Ddamulira et al, 2014) and in other common bean production regions (Sebastian et al, 2006;Sartorato, 2004) where gene pool grouping due to place of origin of the isolate was not observed.…”

“…The binomial characterization of the pathogen using the set of differentials can be supplemented with the molecular characterization of the pathogen which detects the variability of the pathogen population regardless of its host and environment (Ddamulira et al, 2014). Different molecular methods have been used to characterize this pathogen including RAPD markers, ISSR markers and Box primers (Abadio et al, 2012;Ddamulira et al, 2014). Sequences from the Internal Transcribed Spacer region (ITS) and Actin genes were used in a similar study evaluating the taxonomic status of P. griseola (Crous et al, 2006).…”

“…The use of differential cultivars, however, has a major limitation due to variability in environmental conditions (Kolmer et al, 1995;Sebastian et al, 2006). The binomial characterization of the pathogen using the set of differentials can be supplemented with the molecular characterization of the pathogen which detects the variability of the pathogen population regardless of its host and environment (Ddamulira et al, 2014). Different molecular methods have been used to characterize this pathogen including RAPD markers, ISSR markers and Box primers (Abadio et al, 2012;Ddamulira et al, 2014).…”

Prevalence and variability of the common bean rust in Uganda

“…Rust disease incidence and severity maps were developed using GPS survey data points obtained from each sampling location and incidence and severity means generated from data analysis (Ddamulira et al, 2014). The altitude was calculated from the elevation data using Spatial Data Download | DIVA-GIS.…”