Abstract
Angular leaf spot (ALS) is one of the most severe diseases of common bean. However, there is as yet no standardization of the phenological stage, inoculum concentration, diagrammatic scale (DS), and day of assessment for screening ALS resistance in bean lines. The present study aimed to evaluate the potential for assessment of ALS severity in common beans using the Leaf Doctor app and inoculation at the V2 phenological stage under two inoculation concentrations. The experiment was carried out in a completely randomized design in a 3 × 2 × 2 factorial arrangement with three cultivars (AND 277, IAC-Milênio, and IAC-Carioca), two monosporic isolates (31-31 and 10-59), and two inoculum concentrations (2 × 104 and 4 × 104 conidia/mL). Disease severity was evaluated from 11 to 15 days after inoculation (d.a.i) using a diagrammatic scale and the Leaf Doctor. The results showed that 15 d.a.i., the concentration of the inoculum was no longer significant and that the isolates showed no significant difference in terms of pathogenicity. Moreover, in 15 d.a.i. it was possible to separate the cultivars into three phenotypic classes: resistant (AND-277), moderately susceptible (IAC-Milênio) and susceptible (IAC-Carioca). Considering the diagrammatic scale of notes, the cultivar AND 277 had a score of 2.3, while for the image evaluation, it was observed that only 0.65% of the total leaf area was affected by the disease. For this reason, 15 d.a.i. was recommended as the better day for evaluation, and the concentration of 2 × 104 conidia/mL may be adopted in order to reduce the amount of inoculum needed for the experiment. In addition, the evaluation with the Leaf Doctor app increases accuracy and improves discrimination between resistant and susceptible cultivars. Key words: Pseudocercospora griseola, Phaseolus vulgaris, digital analysis, disease resistance.
Highlights
Common bean (Phaseolus vulgaris L.) is one of the grains most consumed by humans throughout the world (Assefa et al, 2019)
The results were significant for the cultivar factor for all the days of evaluation and approaches used due to differences in the degree of resistance of the cultivars
The Tukey mean test showed there was a significant difference between susceptible cultivars only from 13 to 15 d.a.i., and all cultivars were considered resistant until 12 d.a.i. (Table 1)
Summary
Common bean (Phaseolus vulgaris L.) is one of the grains most consumed by humans throughout the world (Assefa et al, 2019). Regarding the consumption of beans, Brazil stands out as the largest consumer of this. In addition to being the largest consumer, Brazil is the third largest producer of beans in the world (FAOSTAT, 2021). The estimated production of the last bean crop in Brazil was about 3.1 million tons, with an average yield of 1.074 kg/ha (CONAB, 2021). Bean yield is affected by several factors, and in Brazil, disease is one of the main problems. Braun, is one of the most serious diseases in common beans; it may cause yield losses of up to 80% (Nay et al, 2019a; Librelon et al, 2020)
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