O objetivo deste trabalho foi avaliar a diversidade e as relações genéticas entre linhagens e variedades de sorgo sacarino (Sorghum bicolor) do banco de germoplasma do Instituto Nacional de Investigações Florestais, Agrícolas e Pecuárias, México, por meio de marcadores AFLP e SSR. Os marcadores moleculares revelaram robustez dos perfis de amplificação e permitiram diferenciar os 41 genótipos de sorgo sacarino avaliados. A análise da frequência e da distribuição dos fragmentos polimórficos permitiu detectar alelos únicos (AFLP) e raros (SSR) em diversos genótipos (RBSS‑8, RBSS‑9, RBSS‑25, RBSS‑32 e RBSS‑37), o que indica que estes marcadores podem estar associados a uma característica que ainda não foi determinada ou podem ser úteis para a identificação destes genótipos. As relações genéticas indicaram a presença de pelo menos dois tipos de sorgo sacarino: um grupo de genótipos modernos usados para a produção de açúcar e biocombustíveis, e outro grupo formado por genótipos antigos e modernos utilizados para a produção de xaropes. Genótipos de sorgo sacarino podem ser usados para o desenvolvimento de novas variedades com maior conteúdo de açúcar e caldo.

The objective of this work was to evaluate the diversity and genetic relationships between lines and varieties of the sweet sorghum (Sorghum bicolor) germplasm bank of the National Institute for Forestry, Agriculture and Livestock Research, Mexico, using AFLP and SSR markers. The molecular markers revealed robust amplification profiles and were able to differentiate the 41 genotypes of sweet sorghum evaluated. Analysis of the frequency and distribution of polymorphic fragments allowed for the detection of unique (AFLP) and rare (SSR) alleles in several genotypes (RBSS‑8, RBSS‑9, RBSS‑25, RBSS‑32, and RBSS‑37), indicating that these markers may be associated with a feature that has not yet been determined or may be useful for the identification of these genotypes. The genetic relationships indicated the presence of at least two types of sweet sorghum: a group of modern genotypes used for sugar and biofuel production, and another group consisting of historic and modern genotypes used for the production of syrups. Sweet sorghum genotypes may be used to develop new varieties with higher sugar and juice contents.

Triazolic fungicides were applied to sorghum genotypes at several rates during the grain filling period to determine the control of grain mold. After harvest, grain samples were taken and put in potato dextrose agar. Fungicide application in the anthesis stage promoted more healthy seeds (44.32%), and the application of any fungicide increased significantly healthy seeds (15.4 to 18.89%). The fungicide doses of 62.5 and 125 ppm gave a greater healthy seed number, which was 19.5 to 21.5% superior than the control rate.

Para determinar el control de los mohos del grano, fueron aplicados fungicidas triazólicos a genotipos de sorgo en diversas dosis durante el periodo de llenado del grano. Después de la cosecha, muestras de grano fueron tomadas y puestas en PDA. La aplicación de los fungicidas en la etapa de antesis promovió más semillas sanas (44.32%), y la aplicación de cualquier fungicida incrementó significativamente las semillas sanas (15.4 a 18.89%). Las dosis de fungicida de 62.5 y 125 ppm un número mayor de semillas sanas, el cual fue superior al testigo en 19.5 a 21.5%.

Experiments were carried out at College Station, USA, and Rio Bravo and Celaya, Mexico, under irrigated conditions during 2002 and 2003. Six sorghum hybrids and three male-sterile lines were planted at each location. Claviceps africana isolates were applied every other morning. Panicles were inoculated using a hand atomizer until runoff with a suspension of 1.6 x 10(6) conidia mL-1. Ergot severity was measured at milk stage. Bartlett's test was performed to determine homogeneity of variances among years. The results showed variability in susceptibility to ergot among genotypes at a single planting date, at planting dates within a year, locations and years. Ergot severity was statistically greater in 2002 in both hybrids and A-lines. Celaya had the greatest amount of ergot on hybrids, followed by College Station and Rio Bravo. In general, A-lines had the greatest severity. ATx2752 had the lowest ergot severity (22.8%), while ATx635 and ATx623, had 27.4% and 36.2%, respectively. Sorghum hybrid AP2233 was the most susceptible, and NC+8R18 showed the least amount of ergot severity.

Los experimentos se llevaron a cabo en College Station, EUA, Río Bravo y Celaya, México, bajo condiciones de riego durante 2002 y 2003. Seis híbridos de sorgo y tres líneas andro-estériles se sembraron en cada localidad. los aislados de Claviceps africana se aplicaron cada dos días. Las panojas se inocularon usando un atomizador manual hasta escurrimiento total con una suspensión de 1.6 x 10(6) conidios mL-1. La severidad del cornezuelo fue evaluada en el estado lechoso. La prueba de Bartlett se utilizó para definir homogeneidad de varianzas entre años. Los resultados indicaron variabilidad en la susceptibilidad a la enfermedad entre genotipos en una misma fecha de siembra, entre fechas de siembra dentro de un mismo año, entre localidades y años. La severidad del cornezuelo fue estadísticamente mayor en 2002, tanto en híbridos como líneas andro-estériles. Celaya mostró el mayor valor de severidad en híbridos, seguida de College Station y Río Bravo. En general, las líneas andro-estériles mostraron la mayor severidad de la enfermedad. ATx2752 presentó la menor severidad (22.8%), mientras que ATx635 y ATx623, mostraron 27.4 y 36.2%, respectivamente. El híbrido AP2233 fue el más susceptible y NC+8R18 mostró la menor severidad a la enfermedad.

This study was conduced in Rio Bravo, Tamaulipas, and Celaya, Guanajuato, Mexico, in which pathogenicity of two isolates of ergot (Claviceps africana) obtained from the same two locations, were evaluated on six hybrids and three male sterile sorghum lines. Also, a genetic analysis was performed in twelve isolates of the fungus using AFLPs markers. The analysis of variance indicated significant differences between isolates for pathogenicity (evaluated as the floral infection percentage in sorghum genotypes), differences between genotypes, locations, planting dates, and years. The genetic analysis showed a great genetic intrapopulation variation (60% genetic diversity) and the occurrence of different ergot genotypes; nevertheless, there was a high genetic similarity (> 94%) by the clonal character. In general, three groups of ergot genotypes are affecting sorghum in Mexico, one in the Bajio area (Guanajuato and Jalisco), another in Tamaulipas, and the third one in Sinaloa.

El estudio se desarrolló en Río Bravo Tamaulipas y Celaya Guanajuato, México, donde se evaluó la patogenicidad de dos aislamientos del cornezuelo (Claviceps africana) obtenidos en las mismas localidades, en seis híbridos y tres líneas androestériles de sorgo. Además, se realizó un análisis genético de doce aislamientos del hongo utilizando marcadores AFLPs. El análisis de varianza indicó diferencias significativas entre aislamientos para patogenicidad (evaluada por los porcentajes de infección floral en los genotipos de sorgo), diferencias entre genotipos, localidades, fechas de siembra y años de evaluación. El análisis genético mostró gran variación genética intrapoblacional (diversidad genética 60%) y la ocurrencia de diferentes genotipos de cornezuelo, aunque es evidente su carácter clonal por los altos porcentajes de similitud genética (> 94%). En general pueden distinguirse tres grupos de genotipos afectando al sorgo en México, uno en el Bajío (Guanajuato y Jalisco), otro en Tamaulipas y un tercero en Sinaloa.