Transmission of Colletotrichum truncatum and Macrophomina phaseolina by lima bean seeds

Abstract

The fungi Colletotrichum truncatum and Macrophomina phaseolina are among the main pathogens associated with lima bean seeds in Brazil, and they are the causal agents of anthracnose and charcoal rot, respectively. The aim of this study was to verify the seed-seedling transmission of C. truncatum and M. phaseolina in artificially inoculated lima bean seeds. Potato-dextrose-agar (PDA) media with different hydric potentials were obtained after the addition of mannitol. Isolates of C. truncatum and M. phaseolina were peaked to these media. Forty grams of seeds were distributed over the fungal mycelium, remaining there for different exposure periods, as a function of each treatment: T1: 0.0 MPa without inoculum for 48 h; T2: 0.0 MPa for 48 h; T3: -0.2 MPa for 48 h; T4: -0.4 MPa for 48 h; T5: -0.6 MPa for 72 h; T6: -0.8 MPa for 96 h and T7: -1.0 MPa for 120 h. The seeds were incubated at 25 ºC under a 12-hour photoperiod. Germination in a paper roll, emergence of seedlings in sand and seed health in PDA were evaluated. T4 provided the best conditions to temporarily prevent seed germination, promoting a greater incidence of seeds infected by C. truncatum and a greater percentage of diseased plants. M. phaseolina reduced seed germination, independently of the inoculated treatment. Both fungi were transmitted from the seeds to the seedlings of lima bean, causing symptoms in various aerial parts. C. truncatum and M. phaseolina transmission rate was 83.1% and 76.46%, respectively.

Colletotrichum truncatum transmission via lima bean seeds

“…The inoculation methods used in this study were based on the literature on the Phaseolus genus, which showed distinct changes in the quality aspect of P. lunatus seeds depending on the exposure time in each inoculation method (Figures 3 and 4). Mota et al (2019) evaluated the transmission of C. truncatum in lima bean seeds with symptoms in cotyledons, stems, and leaves, finding a maximum of 96.8%, and 94.2%, respectively, seven days after sowing (DAS). The symptoms became more severe 14 and 21 DAS from seeds inoculated by different osmotic potentials with mannitol.…”

Feijão-fava: doenças virais e fúngicas

“…Colletotrichum truncatum é eficientemente transmitido através de sementes de feijão-fava, alcançando uma taxa de transmissão de 83% quando as sementes são inoculadas artificialmente em meios de cultura com diferentes potenciais hídricos (MOTA et al 2019). Em sementes de feijão-fava naturalmente infectadas, a incidência máxima observada foi de 10%, enquanto a incidência média entre as amostras foi próxima a 1%.…”

“…O patógeno é considerado um dos mais destrutivos nas regiões tropicais e subtropicais, principalmente nas condições ambientais de climas áridos e semiáridos do Nordeste brasileiro. Essa doença tem se destacado em muitas partes do mundo, principalmente pela grande dificuldade de controle e por provocar redução no estande das plantas no campo, baixa qualidade de sementes, morte e maturação precoce das plantas (LODHA & MAWAR 2020;MOTA et al 2019).…”

“…Em sementes de feijão--fava, incidência máxima de 18,2% (média 1,5%) foi encontrada em 34 amostras de sementes coletadas em pequenos produtores rurais e feiras-livres em cidades da região do Nordeste do país (MOTA et al 2017). Sementes de feijão-fava inoculadas artificialmente em meios de cultura com diferentes potenciais hídricos apresentaram taxa de transmissão de 83% (MOTA et al 2019). Esses dados revelam a elevada capacidade de M. phaseolina ser disseminada por sementes.…”

REACTIONS OF LIMA BEAN (Phaseolus lunatus L.) ACCESSIONS TO Colletotrichum truncatum

“…Although adapted to edaphoclimatic conditions of the Brazilian Northeast, lima bean has a low yield due to the occurrence of diseases and lack of modern technologies for its production (SANTOS et al, 2002;FEIJÓ et al, 2017;SOUSA et al, 2018). Among the diseases, anthracnose caused by Colletotrichum truncatum is frequently found in Brazilian bean crops (MOTA et al, 2019).…”