Abstract: Maize (Zea mays) ranks second as food in the world and drought limits its productivity. Plants harbor endophytic bacteria that influence health and drought tolerance. The goal of this research was to estimate the density and diversity of cultivable endophyte bacteria from the root system of seven homozygous maize drought-tolerant and seven drought-susceptible lines in three locations of Mexico during three crop cycles. The density and diversity of bacterial populations was assessed by direct counting on plates and identified by PCR. The results identified three groups of endophytic bacteria: 1) highly frequent (Bacillus subtilis, Bacillus megaterium y Pseudomonas geniculata), 2) frequent (Bacillus firmus, Pseudomonas hibiscola y Sinorhizobium meliloti) y 3) low frequency (Acinetobacter soli, Stenotrophomonas maltophila y Burkholderia gladioli. The analysis of variance (ANOVA) showed significant differences (p≤0.05) in density (Log10 CFU g-1 root) of population by location, crop cycle, days after sowing and maize lines. The density of Bacillus subtilis, Pseudomonas hibiscola at El Batán and Bacillus megaterium, Sinorhizobium meliloti in Tlaltizapán, were significantly higher in drought-tolerant maize lines compared to drought-susceptible lines.

Resumen: El maíz (Zea mays) ocupa el segundo lugar como alimento en el mundo y la sequía limita su productividad. Las plantas albergan bacterias endófitas que influyen en la sanidad y tolerancia a la sequía. El objetivo de esta investigación fue estimar la densidad y diversidad de las bacterias endófitas cultivables de la raíz en siete líneas homocigóticas de maíces tolerantes y siete susceptibles a sequía en tres localidades de México durante tres ciclos del cultivo. La densidad y diversidad de las poblaciones bacterianas se evaluó mediante conteo directo en placas y se identificaron por PCR. Los resultados identificaron tres grupos de bacterias endófitas: 1) altamente frecuentes (Bacillus subtilis, Bacillus megaterium y Pseudomonas geniculata), 2) frecuentes (Bacillus firmus, Pseudomonas hibiscola y Sinorhizobium meliloti) y 3) baja frecuencia (Acinetobacter soli, Stenotrophomonas maltophila y Burkholderia gladioli. El análisis de varianza (ANOVA) mostró diferencias significativas (p≤0,05) en la densidad (Log10 UFC g-1 de raíz) de población por localidad, ciclo de cultivo, días después de siembra y líneas de maíz. La densidad de Bacillus subtilis, Pseudomonas hibiscola en la localidad de El Batán y Bacillus megaterium, Sinorhizobium meliloti en Tlaltizapán, fueron significativamente mayores en las líneas de maíz tolerantes que en las susceptibles a sequía.

Uma das mais importantes doenças da mandioca (Manihot esculenta Crantz) é a bacteriose, causada pela Xanthomonas axonopodis pv. manihotis. Visando caracterizar genes de mandioca envolvidos na resistência a esta doença, um clone genômico do gene de peroxidase (MEPX1) foi isolado por meio de PCR. A sequência de nucleotídeos apresentou homologia com outros genes de peroxidase de plantas, contendo um intron, típico de genes de peroxidase. O produto de translação apresenta o domínio heme-ligante, característico de peroxidases, assim como domínios de fosforilação e glicosilação. A sequência de aminoácidos teve 75% de homologia com genes de peroxidase de Arabidopsis thaliana. Análise em Southern blot de 17 cultivares de mandioca, usando MEPX1 como sonda, apresentou polimorfismos que, além de refletirem a origem geográfica do material, demonstraram associação com resistência ou tolerância a bacteriose, indicando que MEPX1 pode vir a ser explorado como marcador para esta importante doença em programas de melhoramento de mandioca.

Cassava bacterial blight (CBB), caused by Xanthomonas axonopodis pv. manihotis, is considered one of the most important bacterial diseases of cassava (Manihot esculenta Crantz). In order to characterize the cassava genes involved in resistance to this disease, a genomic clone of a cationic peroxidase gene, MEPX1, was isolated by PCR from cassava cultivar MCOL 22. The DNA sequence of MEPX1 showed high homology with other plant peroxidase genes and contained a large intron typical of peroxidase genes. The predicted translation product showed a heme-ligand motif, also a characteristic of peroxidases, as well as phosphorylation, myristoylation and glycosylation sites. The amino acid sequence had 75 % homology with two Arabidopsis thaliana peroxidases. A Southern blot of 17 cassava cultivars, probed with MEPX1, showed multiple hybridization bands. Polymorphisms between cultivars generally reflected geographic origin, but there was also an association with resistance to CBB, indicating that MEPX1 could be a potentially useful marker for this trait.