Abstract Brown leaf spot disease, caused by the fungus Ragnhildiana diffusa, is responsible for losses in pecan orchards and quantification is essential in order to conduct epidemiological studies to establish levels of productivity losses, and assess control strategies. Therefore, the aim of this study was to develop and validate a diagrammatic scale for assessing the severity of brown leaf spot in pecan. 240 symptomatic leaflets were collected from adult trees in Anta Gorda, in the Brazilian state of Rio Grande do Sul, and used to assess the current percentage severity of the disease. The scale was based on the minimum and maximum observed severity of the disease, with six graduations defined according to the Weber-Fechner Visual Stimulus Law. The scale therefore consisted of eight levels (1.5, 4.6, 10.6, 17.3, 39.5, 65.1, 77.5, and 98%). The estimates of eight evaluators provided a basis for validating the scale. They made estimates of disease severity on 40 symptomatic digitalized pecan leaflets first, without using the scale and then referring to it. The scale provided greater precision, accuracy, and reproducibility of estimates and should result in more reliable epidemiological studies.

RESUMO Os objetivos deste trabalho foram desenvolver um protocolo de estabelecimento e quantificar o crescimento in vitro de plântulas de louro-pardo (Cordia trichotoma (Vell.) Arráb. Ex Steud.) oriundas de sementes, para a produção de explantes assépticos. Para o estabelecimento in vitro, estudou-se o efeito do tempo de embebição e de diferentes protocolos de desinfestação das sementes. A embebiçao fez-se em água destilada e autoclavada por 0, 24, 48, 72, 96 ou 120 horas. Para a desinfestação de sementes sem tegumento, testou-se a imersão em álcool etílico 70% por 30 segundos, seguida da imersão em solução de hipoclorito de sódio a 2% ou 5% por 0, 5, 10, 15 ou 20 minutos. Foram avaliadas as percentagens de desinfestação e germinação e o tempo médio de germinação. O crescimento de explantes de louro-pardo foi quantificado nos meios de cultura 1/2MS e WPM, através do número de folhas e raízes emitidas e do comprimento da parte aérea e da raiz primária aos 7, 14, 21 e 28 dias após a inoculação. A embebição das sementes de louro-pardo por até 24 horas favoreceu a retirada do tegumento sem afetar a desinfestação e germinação. A retirada do tegumento e a imersão das sementes em solução de álcool etílico 70% por 30 segundos foram suficientes para a produção in vitro de plântulas assépticas. Plântulas de louro-pardo apresentaram melhor crescimento em meio de cultura WPM, sem a adição de reguladores de crescimento.

ABSTRACT The objectives of this work were to develop an in vitro establishment protocol and to quantify growth of louro-pardo (Cordia trichotoma (Vell.) Arráb. Ex Steud.) seedlings to produce asseptic explants. Seed imbibition and disinfection were studied for in vitro seedling establishment. Seeds were imbibed in distilled and autoclaved water for 0, 24, 48, 72, 96 or 120 h. Seeds without tegument were submerged in a 70% alcohol solution for 30 s and in a hypochloride solution of 2% or 5% for 0, 5, 10, 15 or 20 min. Percentages of disinfection and germination and mean germination time were evaluated. Seedling growth of louro-pardo was quantified in 1/2MS and WPM culture mediums. Number of emerged leaves and roots and length of shoot and primary root were evaluated at 7, 14, 21 and 28 days after inoculation. Imbibition of louro-pardo seeds until 24 hours made easy tegument excision without affecting disinfection and germination. Seed-tegument excision and immersion in a 70% alcohol solution for 30 s were enough for an acceptable production of in vitro asseptic seedlings. Louro-pardo seedlings grow satisfactorily in a WPM culture medium without growth regulators.