Comparison of Field, Greenhouse, and Detached-Leaf Evaluations of Soybean Germplasm for Resistance to Phakopsora pachyrhizi

Abstract

Fourteen soybean accessions and breeding lines were evaluated for resistance to soybean rust caused by the fungus Phakopsora pachyrhizi. Evaluations were conducted in replicated experiments in growth chambers using detached leaves and under greenhouse and field conditions. In growth-chamber experiments, inoculation of detached leaves with 1 × 106 spores/ml resulted in a significantly (P < 0.0001) higher total number of pustules and spores per unit leaf area than inoculations with lower spore concentrations. Amending agar medium with plant hormones significantly (P < 0.0001) aided retention of green leaf color in detached leaves. Leaf pieces on a medium containing kinetin at 10 mg/liter had 5% chlorosis at 18 days after plating compared with leaf pieces on media amended with all other plant hormones, which had higher levels of chlorosis. Leaf age significantly affected number of pustules (P = 0.0146) and number of spores per pustule (P = 0.0088), and 3- to 4-week-old leaves had a higher number of pustules and number of spores per pustule compared with leaves that were either 1 to 2 or 5 to 6 weeks old. In detached-leaf and greenhouse screening, plants were evaluated for days to lesion appearance, days to pustule formation, days to pustule eruption, lesion number, lesion diameter, lesion type, number of pustules, and spores per pustule in 1-cm2 leaf area. Plants also were evaluated for diseased leaf area (in greenhouse and field screening) and sporulation (in field screening) at growth stage R6. There were significant (P < 0.0001) differences among genotypes in their response to P. pachyrhizi infection in the detached-leaf, greenhouse, and field evaluations. Accessions PI 594538A, PI 417089A, and UG-5 had very low levels of disease compared with the susceptible checks and all other genotypes. Detached-leaf, greenhouse, and field results were comparable, and there were significant correlations between detached-leaf and greenhouse (absolute r = 0.79; P < 0.0001) and between detached-leaf and field resistance (absolute r = 0.83; P < 0.0001) across genotypes. The overall results show the utility of detached-leaf assay for screening soybean for rust resistance.

Resistance to Asian soybean rust in soybean lines with the pyramided three Rpp genes

“…Management strategies such as the use of fungicides, the adoption of a free host period, and the use of genetic resistance are important for controlling ASR (Yorinori 2008). The development of soybean varieties resistant to ASR is considered the most economical control strategy; therefore it is important to facilitate its management (Twizeyimana et al 2007, Pierozzi et al 2008. However, resistance is not always durable due to pathogen variability (Oliveira et al 2005), and there is a large regional pathogenic diversity in the ASR pathogen population in Brazil (Freire et al 2008, Kato and Yorinori 2008, Soares et al 2009, Akamatsu et al 2013).…”

Comparison of Detached Leaf Evaluations in Different Age of Transgenic Tomato Expressing Antimicrobial Peptide Gene (Ace-AMP1) Resistant to Early Blight Disease Caused By Alternariasolani

“…Sterilization of leaf samples reduced the saprophytic populations and similarly [13]. Antimicrobial peptide genes have high antimicrobial activity against various pathogenic fungi and are the potential genes to be transformed into plants for transgenic development [14] [2]. In the present study, transgenic plant 10-7 showed higher resistant and moderate resistant was observed in 7-2, 13-19 and 1-3 when compared to the other lines.…”

Use of a trap garden to find additional genetically distinct isolates of the rust fungus Phragmidium violaceum to enhance biological control of European blackberry in Australia

“…Nonetheless, despite these inconsistencies there was overall a good correlation between leaf-disk and field results. Detached-leaf bioassays have also been shown to produce results comparable to assays performed using whole plants in a growth chamber or greenhouse during screening of soybean genotypes with the rust Phakopsora pachyrhizi (Twizeyimana et al 2007) and oat cultivars with Puccinia coronata (Jackson et al 2008).…”