ABSTRACT Azotobacter vinelandii is a Gram negative that undergo a morphological and physiological differentiation process to form cysts resistant to desiccation. The main components of a cyst are alkylresorcinols (ARs), phenolic lipids of 21 to 23 C. These lipids are homologous to plant ARs, where they have been reported to have antifungal properties. The objective of this study was to evaluate the antifungal capacities of vegetative cells and cysts of A. vinelandii AEIV. The cysts were visualized by optical microscope and the detection of ARs was performed by thin layer chromatography. Antagonism bioassay were carried out between vegetative cells and cysts against Fusarium brachygibbosum, Aspergillus niger and Colletotrichum gloeosporioides. We confirmed the induction of cysts and the presence of ARs of A. vinelandii AEIV. We observed that using 1×103 cysts reduced up to 76.3% (p < 0.05) the growth of the three phytopathogenic fungi and this result was not observed when using vegetative cells or the strain blocked in the synthesis of ARs. This shows that the cysts exert an antagonistic effect on phytopathogenic fungi and do so through the ARs, considering the development of an effective strategy to control pests in fungi that affect postharvest fruits.

ABSTRACT In Mexico, Creole corn has presented problems related to seed rot. Therefore, the objective of this study was to determine the frequency of fungi associated with Creole corn seeds. From January to February 2019, 13 Creole corn samples were collected from several localities in Guerrero, Mexico. The samples were processed in PDA culture medium and the frequency of each fungus was estimated based on cultural characteristics and taxonomic keys. Considering symptomatic corn seed samples, Fusarium oxysporum was recorded in eight samples at 97.2%, followed by F. graminearum, isolated from race “Olotillo 1” at 94.4% and from race “Cónico pepitilla” at 58.3%. Phomopsis sp. was isolated at 100% from race “Olotillo 2”. Gibberella moniliformis was isolated from “Elotes Occidental 1” at 83.3%, while the least frequent isolate (19.4%) from “Pepitilla” was Sarocladium strictum, which was recorded in three samples at the low values of 11.1% and 2.8% for races “Arrocillo 2” and “Pepitilla”, respectively; Talaromyces variabilis was found in two samples at 11.1% and 2.8% from “Arrocillo 2” and “Cónico pepitilla”, respectively; Stenocarpella macrospora was isolated at 72.2% from “Pepitilla”. Aspergillus flavus was obtained from “Cónico Pepitilla” at 16.7%, while Setosphaeria turcica and Emericella sp. were less frequently isolated. Considering asymptomatic seeds of race “Cónico pepitilla”, F. oxysporum was isolated at 8.3%, Fusarium acuminatum at 8.3% and Gibberella moniliformis at 41.7%; from asymptomatic seeds of “Olotillo 1” and “Olotillo 2”, Phomopsis sp. was isolated at 50% and Rhizoctonia solani at 50%, respectively. In the present study, the fungi F. oxysporum, Phomopsis sp., G. moniliformis and F. graminearum were most frequently associated with Creole corn seeds.

RESUMO No México, o milho crioulo apresenta problemas de podridão das sementes. Portanto, o objetivo desta pesquisa foi determinar a frequência de fungos associados a sementes de milho crioulo. De janeiro e fevereiro de 2019, 13 amostras de milho crioulo foram coletadas em localidades de Guerrero, México. As amostras foram processadas em meio de cultura BDA e a frequência de cada fungo foi estimada com base nas características culturais e chaves taxonômicas. Nas amostras sintomáticas de sementes de milho, Fusarium oxysporum foi registrado em oito amostras com 97,2%, seguido por F. graminearum isolado na raça de milho “Olotillo 1” com 94,4% e na raça “Cónico pepitilla” com 58,3%. Phomopsis sp., foi isolado 100% na raça “Olotillo 2”. Gibberella moniliformis, foran isolados de “Elotes Occidental 1” com 83,3% e o menos frequente (19,4%) em “Pepitilla” foi Sarocladium strictum registrado em três amostras com valores baixos de 11,1% e 2,8% na raça de milho “Arrocillo 2” e “Pepitilla”, Talaromyces variabilis em duas amostras com 11,1% e 2,8% em “Arrocillo 2” e “Cónico pepitilla”. Stenocarpella macrospora foi isolado em 72,2% da raça de milho “Pepitilla”. Aspergillus flavus em “Cónico Pepitilla” com 16,7%, Setosphaeria turcica e Emericella sp., foi isolado com menor frequência. Em sementes assintomáticas da raça “Cónico pepitilla” foi isolado F. oxysporum com 8,3%, Fusarium acuminatum 8,3%, Gibberella moniliformis em 41,7%, em sementes assintomáticas de “Olotillo 1” e “Olotillo 2” Phomopsis sp., foi isolado em 50% e Rhizoctonia solani com 50%. Neste estudo, os fungos F. oxysporum, Phomopsis sp., G. moniliformis e F. graminearum foram os mais frequentemente associados às sementes de milho crioulo.

RESUMO A doença manchada de vinagreira causada por Corynespora cassiicola afeta a produção de cálice no México. O objetivo deste estudo foi avaliar vinte e dois genótipos de vinagreira contra C. cassiicola em casa de vegetação. Com base nas área abaixo da curva de progresso da doença (AACPD) foi possível detectar genótipos suscetíveis, tolerantes e resistentes. Dada a incidência nas folhas, os genótipos suscetíveis foram Conpoz, Sudlaz, Morcot e Sudigua (valores de AACPD 7379,2 a 5891,7); tolerantes foram Conayu e Chinxal (AACPD 1341,6 e 1313,2). Enquanto isso, pela severidade nas folhas, os suscetíveis foram Sudigua, Conpoz e Morena2 (AACPD de 788,4 a 436,3); tolerantes foram Almatech, Crioxal, Rojatec e Conayu (37,7 a 28,76 de AACPD). Enquanto, avaliando a incidência em cálices, genótipos suscetíveis foram; Morena2, Morena, Conpoz, Descop e Chinayu (AACPD de 6572,1 a 2319,4); para a gravidade suscetível foram Morena2, Descop, Morena, Cabxal, Chinayu e Conpoz (AACPD de 3355,4 a 779,2). A incidência e severidade nos cálices detectaram genótipos resistentes, que foram Almatech, Criolaz2, Criocot, Criolaz, Rojatec, Criopoz, Crioxal, Chinxal e Conayu (0,0 de AACPD). Neste estudo, foram detectados genótipos tolerantes e resistentes à mancha foliar e cálice causada por C. cassiicola em vinagreira.

ABSTRACT Roselle spot caused by Corynespora cassiicola affects calyx production in Mexico. The aim of the present study was to evaluate twenty-two roselle genotypes against C. cassiicola under greenhouse conditions. The area under the disease progress curve (AUDPC) was used to detect susceptible, tolerant and resistant genotypes. Considering the incidence in leaves, susceptible genotypes were Conpoz, Sudlaz, Morcot and Sudigua (AUDPC values of 7379.2 to 5891.7); tolerant genotypes were Conayu and Chinxal (AUDPC 1341.6 and 1313.2). Based on the severity in leaves, susceptible genotypes were Sudigua, Conpoz and Morena2 (AUDPC from 788.4 to 436.3); tolerant genotypes were Almatech, Crioxal, Rojatec and Conayu (37.7 to 28.76 AUDPC). Assessment of the incidence in calyces indicated that susceptible genotypes were Morena2, Morena, Conpoz, Descop and Chinayu (AUDPC from 6572.1 to 2319.4); for the severity in calices, susceptible genotypes were Morena2, Descop, Morena, Cabxal, Chinayu and Conpoz (AUDPC from 3355.4 to 779.2). Incidence and severity on calyces evidenced resistant genotypes, which were Almatech, Criolaz2, Criocot, Criolaz, Rojatec, Criopoz, Crioxal, Chinxal and Conayu (0.0 AUDPC). In the present study, tolerant and resistant genotypes were detected to leaf and calyx spot caused by C. cassiicola in roselle.

Abstract. Blackberry gray mold, induced by Botrytis cinerea, is a fruit disease that causes important economic losses. The present study evaluated nine fungicides belonging to different chemical groups, alone and in combination with potassium silicate, using the dose recommended on the label for the control of B. cinerea in the field. The incidence and severity of the disease were evaluated, as well as the degrees Brix, silicon concentration, and yield. The experiment was carried out twice. Incidence and severity percentages were converted to area under the disease progress curve (AUDPC). Combined with potassium silicate, the fungicide azoxystrobin significantly reduced incidence and severity, showing the lowest percentages in the last evaluation of these variables. In the first repetition, the incidence and severity values were 4% (AUDPC = 1320) and 0.1% (AUDPC = 298.5), respectively. In the second, 3% (AUDPC = 1099) and 0.1% (AUDPC = 214.5) respectively. The concentration of soluble solids and fruit yield increased (12.4 and 13.6 t ha-1 in the first and second repetition, respectively). The results indicate that potassium silicate enhances the effect of fungicides under field conditions and can thus be considered a management alternative against the gray mold disease in blackberries.

Resumen. El moho gris de la zarzamora causado por Botrytis cinerea, es una enfermedad que afecta los frutos y causa pérdidas económicas importantes. En la presente investigación se evaluaron nueve fungicidas pertenecientes a diferentes grupos químicos, solos y en combinación con silicato de potasio utilizando la dosis recomendada en la etiqueta para el control de B. cinerea en campo. Se evaluó la incidencia y severidad de la enfermedad, además de grados Brix, concentración de silicio y rendimiento, el experimento se realizó dos veces. Los porcentajes de incidencia y severidad se transformaron a área bajo la curva del progreso de la enfermedad (ABCPE). El fungicida azoxystrobin combinado con silicato de potasio redujo la incidencia y severidad significativamente, presentando los menores porcentajes en la última evaluación de dichas variables. En la primera repetición, los valores de incidencia y severidad fueron de 4% (ABCPE= 1320) y 0.1% (ABCPE= 298.5), respectivamente, y en la segunda 3% (ABCPE=1099) y 0.1% (ABCPE=214.5), respectivamente. Por lo tanto, aumentó la concentración de solidos solubles y rendimiento (12.4 y 13.6 t ha-1 en la primera y segunda repetición, respectivamente). Con base en los resultados obtenidos, se determinó que el silicato de potasio potencializa el efecto de los fungicidas bajo condiciones de campo, por lo tanto, puede ser una alternativa de manejo contra el moho gris en zarzamora.

Resumen La especie Solanum lycopersicum L. muestra variación en intensidad de color, forma y tamaño de fruto, hábitos de crecimiento, por lo que es importante identificar variedades sobresalientes en características agronómicas y someterlos a un proceso de mejoramiento genético. El objetivo del presente estudio fue evaluar el efecto de la inoculación con Klebsiella variicola, K. quasipneumoniae y K. pneumoniae en plantas de 19 ecotipos de tomate. Se estableció un experimento en un diseño de bloques completos al azar bajo un arreglo factorial generalizado con cinco repeticiones en condiciones de bioespacio. Las variables evaluadas fueron días a floración, peso fresco de fruto, longitud de raíz, peso fresco de raíz, volumen de raíz, peso seco de raíz y número de semillas. El análisis de varianza mostró diferencias significativas en las fuentes de variación cepas de bacteria y ecotipos de tomate. Los resultados indicaron variación en el sistema radicular, características agronómicas y componentes de rendimiento de fruto con la aplicación de bacterias promotoras de crecimiento vegetal en ecotipos nativos de tomate. Las cepas bacterianas favorecen la producción de frutos de tomate con atributos para ser comercializados.

Summary The species Solanum lycopersicum L. shows variation in intensity of color, fruit shape and size, growth habits, so it is important to identify outstanding varieties in agronomic characteristics and subject them to a genetic improvement process. The objective of this study was to evaluate the effect of inoculation with Klebsiella variicola, K. quasipneumoniae and K. pneumoniae in plants of 19 tomato ecotypes. An experiment was established in a randomized complete block design under a generalized factorial arrangement with five replications under biospace conditions. The variables evaluated were days to flowering, fresh fruit weight, root length, fresh root weight, root volume, dry root weight and number of seeds. The analysis of variance showed significant differences in the sources of variation bacterial strains and tomato ecotypes. Results indicated variation in the root system, agronomic characteristics and fruit yield components with the application of plant growth promoting bacteria in native tomato ecotypes. Bacterial strains favor the production of tomato fruits with attributes to be commercialized.

Summary The mining activity has left mine tailings with high quantities of heavy metals and metalloids. Due their extreme toxicity, they represent a hostile environment for microbial colonization; however, there are metalotolerant bacteria in these mining wastes, and this is attributed to mechanisms of bioaccumulation and biotransformation of metals. The native bacteria from El Fraile mine tailings have developed adaptation mechanisms that allow them to persist in a toxic environment, thus, the objective of this study was to isolate and identify bacteria with the ability to tolerate, bioaccumulate or biotransform heavy metals. Our study was based on descriptive observations, we isolated 141 strains from water, leachate, soil, and rhizosphere and stems of plants from El Fraile mine tailings, Guerrero, Mexico. Bacterial tolerance was determined by the minimum inhibitory concentration in different metallic salts, the capacity of bioaccumulation of Ag, Pb, Cr, and Cd, and by the biotransformation of As (III) and Cr6+; in addition, representative bacteria were identified using 16S rRNA gene sequences. The results of the 141 strains analyzed showed ascending tolerance to Cd2+ 2 mM, Cu2+ 5 mM, Pb2+ 9 mM, Zn2+ 9 mM, Ag2+ 10 mM, As3+ 30 mM, and As5+ 45 mM. Only 9.24 and 39% of the strains bioaccumulated Zn2+, Pb2+ and Ag2+. In regard to biotransformation, 9% oxidized As3+ to As5+, and 7 and 24% reduced As5+ to As3+ and Cr6+ to Cr3+, respectively. The genera that prevailed were Chryseobacterium sp., Staphyloccoccus sp., Stenotrophomonas sp., Acinetobacter sp., Bacillus sp., Serratia sp., and Enterobacter sp. These results showed that in El Fraile mine tailings, there are bacterial strains capable of bioaccumulating and biotransforming heavy metals and metalloids; therefore, further studies must be conducted to know their potential in the processes of bioremediation of areas polluted with metals.

Resumen La actividad minera ha dejado depósitos de jales ricos en metales pesados y metaloides. Por su toxicidad extrema, representan un ambiente hostil para la colonización microbiana; sin embargo, en estos residuos mineros existen bacterias metalotolerantes y esto se atribuye a mecanismos que destacan la bioacumulación y biotransformación de metales. Por lo tanto, las bacterias nativas que viven alrededor de los jales El Fraile, han desarrollado mecanismos de adaptación que las hace persistente en un ambiente tóxico; por tal motivo, el objetivo de este trabajo fue aislar e identificar bacterias capaces de tolerar, bioacumular o biotransformar metales pesados y metaloides. El estudio fue observacional descriptivo y se logró aislar 141 cepas de agua, lixiviados, suelo, rizosfera y tallos de plantas de los jales El Fraile, Guerrero, México. Se determinó tolerancia por concentración mínima inhibitoria en distintas sales metálicas, capacidad de bioacumulación de Ag, Pb, Cr, Cd y biotransformación de As (III) y Cr6+; algunas bacterias se identificaron mediante la secuencia del gene 16S ARNr. Los resultados de las 141 cepas analizadas mostraron tolerancia ascendente a Cd2+ 2 mM, Cu2+ 5 mM, Pb2+ 9 mM, Zn2+ 9 mM, Ag2+ 10 mM, As3+ 30 mM y As5+ 45 mM. Solo 9.24 y 39% de las cepas bioacumularon Zn2+, Pb2+ y Ag2+. En la biotransformación solo 9% oxidaron As3+ a As5+, 7 y 24% redujeron As5+ a As3+ y Cr6+ a Cr3+, respectivamente. Los géneros que prevalecieron fueron Chryseobacterium sp., Staphyloccoccus sp., Stenotrophomonas sp., Acinetobacter sp., Bacillus sp., Serratia sp., y Enterobacter sp. Por lo tanto, existen cepas bacterianas en la zona minera El Fraile capaces de bioacumular y biotransformar metales pesados y metaloides; por lo que es necesario realizar más estudios que permitan conocer su potencial en los procesos de biorremediación de sitios contaminados con metales.

Abstract. Several Corynespora cassiicola isolates obtained from roselle (Hibiscus sabdariffa) and nine associated weeds to this crop were morphological and phylogenetically analyzed. The fungal isolates were divided into two groups: group one included 37 isolates obtained from H. sabdariffa and eight obtained from other host plants including Solanum lycopersicum, Chromolaena odorata, Senna alata, Eugenia oerstediana, Passiflora viridiflora, Momordica charantia, Ricinus communis and Gossypium hirsutum; in this case, the predominant colonies were gray, dense texture and polygonal in shape. Group two included two isolates obtained from H. sabdariffa and one from Hyptis suaveolens; in this group the colonies were mainly cream and pale brown, dense and round. Comparative analysis with isolates of C. cassiicola from other countries showed that group one isolates were mainly associated with those isolated from the Solanaceae family, while those from group two were related to those of the Cucurbitaceae family. To our knowledge, this is the first study on the morphological and genetic characterization of C. cassiicola in Mexico.

Resumen. Se analizaron morfológica y filogenéticamente diferentes aislados de Corynespora cassiicola obtenidos de jamaica (Hibiscus sabdariffa) y nueve malezas asociadas al cultivo. Los aislados fúngicos se dividieron en dos grupos: el grupo uno incluyó 37 aislados obtenidos de H. sabdariffa y ocho obtenidos de otros hospedantes como Solanum lycopersicum, Chromolaena odorata, Senna alata, Eugenia oerstediana, Passiflora viridiflora, Momordica charantia, Ricinus communis y Gossypium hirsutum; en este caso, las colonias predominantes fueron de color gris, textura densa y forma poligonal. El grupo dos, incluyó a dos aislados obtenidos de H. sabdariffa y uno de Hyptis suaveolens; en este grupo, las colonias fueron principalmente de color crema y café pálido, densas y redondeadas. El análisis comparativo con aislados de C. cassiicola de otros países mostró que los aislados del grupo uno referidos anteriormente se asociaron principalmente con aquellos aislados de la familia Solanaceae, mientras que los del grupo dos se relacionaron con los de la familia Cucurbitaceae. Para nuestro conocimiento este es el primer estudio sobre la caracterización morfológica y genética de C. cassiicola en México.

Abstract. In recent years, Corynespora cassiicola induced spotted of roselle threatens calyx production. The objective was to determine if some bacterial strains inhibit the development of C. cassiicola in vitro and under biospace conditions. The inhibition of development was due to the dual confrontation of the bacteria: food (20), amphibian skin (41), tailings (22), air (seven) and rhizosphere (10) against the fungus. Plants of jamaican “Creole” variety were sown and artificially inoculated with C. cassiicola. From the beginning of symptoms of the disease, the selected bacterial strains with the highest percentage of inhibition were inoculated. AUDPC was evaluated. Only seven strains inhibited the development of the fungus in vitro from 62.7 to 100%: Klebsiella pneumoniae (M10-1 and M10-10), Acinetobacter lwoffii (A5), Sphingomonas paucimobilis (NF21), Serratia marcescens (M13ACD), S. liquefaciens (M8ACD) and Acinetobacter sp. (5H2). Regarding leaf severity, the M10-1 and M10-10 strains reduced AUDPC by 9.5 and 12.6%, respectively, followed by NF21 (AUDPC 14.5), the control registered the highest levels (AUDPC 45.7). For the severity in calyces, the AUDPC analyzes of all the strains exercised control by reducing severity levels (17.1-8.6 AUDPC).

Resumen. En años recientes, el manchado de la jamaica inducido por Corynespora cassiicola amenaza la producción de cálices. El objetivo fue determinar si algunas cepas bacterianas inhiben el desarrollo de C. cassiicola in vitro y bajo condiciones de bioespacio. La inhibición del desarrollo fue por confrontación dual de las bacterias: alimentos (20), piel de anfibios (41), jales mineros (22), aire (siete) y rizosfera (10) contra el hongo. Se sembraron plantas de jamaica variedad “criolla” y se inocularon artificialmente con C. cassiicola, a partir del inicio de síntomas de la enfermedad se inocularon las cepas bacterianas seleccionadas con mayor porcentaje de inhibición. Se evaluó la ABCPE. Solo siete cepas inhibieron del 62.7 al 100% el desarrollo del hongo in vitro: Klebsiella pneumoniae (M10-1 y M10-10), Acinetobacter lwoffii (A5), Sphingomonas paucimobilis (NF21), Serratia marcescens (M13ACD), S. liquefaciens (M8ACD) y Acinetobacter sp. (5H2). En relación a la severidad en hojas las cepas M10-1 y M10-10 redujeron el ABCPE en un 9.5 y 12.6%, respectivamente, seguido de NF21 (14.5 de ABCPE), el control registró los mayores niveles (45.7 de ABCPE). Para la severidad en cálices, los análisis del ABCPE de todas las cepas ejercieron control al reducir niveles de severidad (17.1-8.6 ABCPE).

Abstract The development of maize genotypes (Zea mays L.) for forage production in rainfed conditions is incipient, because no specific varieties have been disseminated for this purpose. The objective was to identify hybrids with forage potential for rainfed conditions in the state of Guerrero, Mexico. 25 maize genotypes were evaluated under rainfed conditions, under an experimental design of randomized complete blocks with three replications. The experimental unit consisted of four furrows 5 m long, 0.8 m wide between furrows, 0.17 m between plants to obtain a population density of 73 529 ha-1 plants. It was fertilized with the formula 120N-60P-00K. The characters studied were: plant height, cob height, plant weight, cob weight, yield of green, grain and dry fodder. The results indicated highly significant differences in the characters studied. Experimental trilinear hybrids H-H562xHCF2-91, H-H565xHCF2-91, H-H516xHCF2-91, simple cross hybrid 329x97 and control H-564C stood out in green forage yield and single cross hybrids 1275x1277, 1278x1276, hybrids Experimental H-H516xHCF2-91 and H-H565xHCF2-91 expressed higher dry forage yield.

Resumen El desarrollo de genotipos de maíz (Zea mays L.) para producción de forraje en condiciones de secano es incipiente, debido a que no se ha difundido variedades específicas para tal fin. El objetivo fue identificar híbridos con potencial forrajero para condiciones de secano del estado de Guerrero, México. Se evaluaron 25 genotipos de maíz en condiciones de secano, bajo un diseño experimental de bloques completos al azar con tres repeticiones. La unidad experimental consistió de cuatro surcos de 5 m de longitud, 0.8 m de ancho entre surcos, a 0.17 m entre plantas para obtener una densidad de población de 73 529 plantas ha-1. Se fertilizó con la fórmula 120N-60P-00K. Los caracteres estudiados fueron: altura de planta, altura de mazorca, peso de planta, peso de mazorca, rendimiento de forraje verde, de grano y de forraje seco. Los resultados indicaron diferencias altamente significativas en los caracteres estudiados. Los híbridos trilineales experimentales H-H562xHCF2-91, H-H565xHCF2-91, H-H516xHCF2-91, híbrido de cruza simple 329x97 y el testigo H-564C destacaron en rendimiento de forraje verde y los híbridos de cruza simple 1275x1277, 1278x1276, híbridos experimentales H-H516xHCF2-91 y H-H565xHCF2-91 expresaron mayor rendimiento de forraje seco.

RESUMO A mancha de folhas e cálices da jamaica, causada por Corynespora cassiicola, é a principal limitante fitossanitária da cultura da vinagreira (Hibiscus sabdariffa) no Estado de Guerrero, México, provocando perdas significativas na produção. Para seu controle, se avaliou a eficácia biológica de vários produtos químicos (convencionais e alternativos) na safra de 2014 e 2015. O estudo foi conduzido nos municípios de Ayutla e Tecoanapa, Guerrero, sob condições de campo e de pressão do inoculo natural. As Substâncias químicas (tratamentos) foram aplicadas em intervalos de 7 e 14 dias. Em cada tratamento, a gravidade nas folhas e cálices, bem como o peso fresco e seco para cada unidade experimental foi registrado. O ensaio se estabeleceu num desenho experimental de blocos causalizados com quatro repetições. Os dados foram submetidos a análise de variância e testes de separação (Tukey-Kramer, α = 0.05). A menor severidade da doença e o maior ganho no peso fresco e seco de cálices foi observado nos tratamentos com mancozebe, clorotalonil e benomyl alternado com oxicloreto de cobre.

RESUMEN El manchado de hojas y cálices de la jamaica, causado por Corynespora cassiicola, se considera la principal limitante fitosanitaria del cultivo de jamaica (Hibiscus sabdariffa) en el Estado de Guerrero, México, causando pérdidas significativas de la producción. Para su control, se evaluó la efectividad biológica de diversas substancias químicas (convencionales y alternativas) durante los ciclos de producción 2014 y 2015. El estudio se realizó en los municipios de Ayutla y Tecoanapa, Guerrero, bajo condiciones de campo y presión natural de inóculo. Las substancias químicas (tratamientos), se aplicaron a intervalos de 7 y 14 días. En cada tratamiento, se registró la severidad en hojas y cálices, así como el peso fresco y seco de cada unidad experimental. El ensayo se estableció bajo un diseño bloques al azar con cuatro repeticiones. Para el análisis de los datos se realizó un análisis de varianza y pruebas de separación de medias (Tukey-Kramer, α=0.05). La menor severidad de la enfermedad y mayor peso fresco y seco de cálices se obtuvo en plantas tratadas con mancozeb, clorotalonil y benomilo alternado con oxicloruro de cobre.

Abstract Spotted leaves and calyces of roselle (Hibiscus sabdariffa L.) induced by Corynespora cassiicola, is currently considered the main disease for this crop in Mexico. Given its importance, it is necessary to have a standardized method to quantify the disease severity. Therefore, the objective of this study was to develop and validate two diagrammatic logarithmic scales to quantify the severity of this disease. Naturally infected roselle leaves and calyces were collected in Guerrero state commercial plantations, and the actual severity of each of these organs was assessed. The proposed scales, designed from 2LOG program, comprised six classes in leaves: 0=0, 1=(>0-2-4), 2=(>4-7-12), 3=(>1219-29), 4=(>29-42-57) and 5=(>57-70-≤100); in calyces: 0=0, 1=(>0-3-5), 2=(>5-10-18), 3=(>1830-46), 4=(>46-63-77) and 5=(>77-87-≤100). The accuracy, precision and reproducibility of the estimates were verified. For leaves and calyces, one evaluation was carried without scale, and two others evaluations were done with scale, each seven days apart. Evaluators showed better levels of accuracy, precision and reproducibility with the scales. The results suggest that the proposed scales are appropriate to estimate the severity of spotted leaves and calyces of roselle.

Resumen El manchado de hojas y cálices en jamaica (Hibiscus sabdariffa L.), inducido por Corynespora cassiicola, actualmente es considerada la principal enfermedad de este cultivo en México. Dada su importancia, es necesario contar con un método estandarizado para cuantificar la severidad de la enfermedad. Por lo anterior, el objetivo del presente estudio consistió en desarrollar y validar dos escalas logarítmicas diagramáticas para cuantificar ésta enfermedad. Para ello, se colectaron hojas y cálices de jamaica infectados de manera natural en plantaciones comerciales del estado de Guerrero, y se calculó la severidad real de cada uno de éstos órganos. Las escalas propuestas, diseñadas con el programa 2LOG, comprenden seis clases, en hojas: 0=0, 1=(>0-2-4), 2=(>4-7-12), 3= (>12-19-29), 4= (>29-42-57) y 5=(>57-70-≤100); en cálices: 0=0, 1=(>0-3-5), 2=(>5-10-18), 3=(>18-30-46), 4=(>46-63-77) y 5=(>77-87-≤100). Asimismo, se verificó la exactitud, precisión y reproducibilidad de las estimaciones. Se hizo una evaluación en hojas y cálices sin utilizar las escalas, y otras dos evaluaciones utilizando las escalas, a intervalos de siete días. Los evaluadores mostraron mejores grados de exactitud, precisión y reproducibilidad con el uso de las escalas. Los resultados sugieren que las escalas propuestas son apropiadas para estimar la severidad del manchado de hojas y cálices en jamaica.

The distribution and frequency of organisms associated with the "black leg" of roselle was studied in 2011 in Guerrero, where 12 commercial plots were evaluated. The identification was based on cultural characteristics and taxonomic keys. Molecular characterization was performed by amplifying the internal transcribed spacer region (ITS) of the rDNA. The isolated organisms were Phytophthora parasitica, Macrophomina phaseolina, Fusarium oxysporum, Fusarium incarnatum, Fusarium solani, Phomopsis longicolla, Glomerella cingulata and Colletotrichum truncatum. P. parasitica was the most frequent specie (72.4 %), distributed in 10 of the 12 sites, followed by F. oxysporum widely distributed but with low frequency (10.6 %), M. phaseolina was isolated from four sites with frequency 10.9 %. F. incarnatum, F. solani, P. longicolla, G. cingulata and C. truncatum showed low frequency (0.4 to 2.4 %) and distribution. Molecular analysis corroborated the identification of organisms. In pathogenicity tests, P. parasitica, M. phaseolina and F. incarnatum were pathogenic. This is the first report in Mexico for M. phaseolina and F. incarnatum as pathogen of roselle.

Se estudió la distribución y frecuencia de organismos asociados a la "pata prieta" de la jamaica en Guerrero durante el 2011, se evaluaron 12 parcelas comerciales. La identificación se hizo con base en características culturales y claves taxonómicas. La caracterización molecular se efectuó amplificando la región intergenética transcripcional (ITS) del rDNA. Los organismos aislados fueron Phytophthora parasitica, Macrophomina phaseolina, Fusarium oxysporum, Fusarium incarnatum, Fusarium solani, Phomopsis longicolla, Glomerella cingulata y Colletotrichum truncatum.La mayor frecuencia (72.4 %) se obtuvo con P. parasitica distribuido en 10 de 12 sitios, seguido por F. oxysporum de amplia distribución pero de baja frecuencia (10.6%), M. phaseolinase aisló de cuatro sitios con frecuencia de 10.9 %. F. incarnatum, F. solani, P. longicolla, G. cingulata y C. truncatum presentaron baja frecuencia y distribución (0.4 a 2.4 %). Los análisis moleculares corroboraron la identificación de los organismos. En pruebas de patogenicidad, P. parasitica, M. phaseolina y F. incarnatum fueron patogénicos. Este es el primer reporte en México para Macrophomina phaseolinay Fusarium incarnatumcomo patógenos de la jamaica.