Epidemiology of Bean common mosaic virus and Alternaria alternata in 12 Phaseolus vulgaris genotypes

Abstract

Research objective was to assess phytosanitary response and epidemiological behavior in 12 <em>Phaseolus vulgaris</em> genotypes and develop etiological-epidemiological methodologies applicable to plant breeding studies. In 2020 spring-summer season, assessments were conducted at flowering (June) and fructification stages (August). Severity was evaluated with a 6-class logarithmic-diagrammatic scale setup in App-Monitor<sup>®</sup> v1.1. Genotype health was determined using an Integrated Damage Index (IDI), weighted and adjusted for disease severity and coverage-plant vigor (IV), which was estimated with images (RGB, 14mpx) captured with dron-Phantom-3 at 5 m height from genotype centroid. In SAS v9.4, t-test and ANOVAs, followed by Tukey (<em>p</em> = 0.05), were performed for different experimental settings. Disease spatial patterns were analyzed with kriging and omnidirectional variograms in SURFER v10. Forty-three total samples were used for isolation, pathogenicity testing, and molecular identification with universal primers ITS1/ITS4, NIb2F/NIb3R, PBL1v2040/PCR1c for eukaryotes, Potyvirus and Begomovirus, respectively. Final data matrix included 22 variables, 859 observations and 18,898 metadata. <em>Alternaria alternata</em> and <em>Bean common mosaic virus</em> (BCMV) were identified in 100% of samples analyzed with 99% homology. <em>Vaquita Negro</em>, <em>Garrapato</em> and <em>Canario</em> were statistically the most susceptible genotypes (37.3 - 58% severity) for BCMV, while <em>Canario</em> and <em>Tipo Flor de Mayo </em>(41.4-42.7%) were for <em>A. alternata</em> (<em>p</em> = 0.05). <em>Oti</em> and <em>Negro Perla</em> had higher climatic adaptability and tolerance to both pathogens with IV > 0.7 and IDI < 0.43. Spatially, BCMV presented random dispersion of foci and a block-edge effect with continuous contagion of up to 5.6 meters. <em>Vaquita Negro </em>and <em>Bayo Mecentral</em> showed uniform virus spread, presumptively due to high viral transmissibility by seed. In contrast, except for <em>Tipo Flor de Mayo</em> and <em>Canario</em>, which exhibited significant coalescence of foci, <em>A. alternata</em> had spatial dependence of less than 8 plants. Wind and hail damage significantly favored <em>A. alternata</em> infection (<em>p</em> = 0.05) suggesting its opportunistic condition.