duced by artificial drying, although the impairment mechanisms remain poorly understood. The impairment of lipid body alignment along the plasma mem-Although several chemical and molecular mechabrane during artificial drying of maize (Zea mays L.) seed has been associated with decreases in germination and vigor. In this study, nisms associated with desiccation tolerance have rewe question further its potential functions as well as the alignment ceived attention in the last decade, few studies have mechanisms. Ears of hybrid maize [B73 ϫ (H99 ϫ H95)] were haraddressed ultrastructural changes during this event. vested at about. 550, 500, 400, and 320 g H 2 Ok g Ϫ1 fresh weight (fw) Klein and Pollock (1968) observed that polysomes disand subjected to preconditioning (PC) (ear drying at 35؇C and 0.47 m appeared and ribosomes appeared free in cell cytoplasm s Ϫ1 airflow rate) for 0, 12, 24, 36, and 48 h before fast drying (shelled of embryo axes of lima beans (Phaseolus lunatus L.) seed, 35؇C and 5.10 m s Ϫ1 airflow rate) treatments to decrease seed during maturation. Depletion of plastid starch during moisture content (MC) to about 130 g H 2 Okg Ϫ1 fw. In a cross section acquisition of desiccation tolerance has been reported of the embryo radicle, alignment of lipid bodies (LB) occurred firstin mustard (Sinapis alba L.) embryos (Fisher et al., 1988) in the root cap, followed by outer quiescent center (QC) cells and and in radicle cells of Brassica campestris L. embryos

germination and vigor as maturation progresses. Maize ears harvested from 400 to 500 g H 2 Okg Ϫ1 fw could be Maize (Zea mays L.) seed quality is often reduced because of safely dried down to 120 g H 2 Ok g Ϫ1 fw with temperadrying injury, although the causes and impairment mechanisms are tures around 40ЊC (Kiesselbach, 1939;Washko, 1949; poorly understood. In this study, we investigated changes in embryo McRostie, 1949;Navratil and Burris, 1984), whereas drying rates and their effect on the acquisition of desiccation tolerance in maize seed. Ears of hybrid maize [B73 ϫ (H99 ϫ H95)] were ears harvested at MC Ͻ 2 5 0gH 2 Ok g Ϫ1 fw could be harvested at about 550, 500, 400, and 320 g H 2 Ok g Ϫ1 fresh weight dried at 50ЊC (Navratil and Burris, 1984). Nevertheless, (fw) and subjected to preconditioning (PC) (ear drying at 35؇C and maize ears harvested as early as 30 d after silking and 0.47 m s Ϫ1 airflow rate) for 0, 12, 24, 36, and 48 h before fluidized dried slowly are able to withstand desiccation (Knittle bed (FB) drying (shelled seed, 35؇C and 5.10 m s Ϫ1 airflow rate)and Burris, 1976;Peterson, 1997). This may illustrate treatments to decrease moisture content (MC) to about 130 g H 2 O the importance of drying rate. kg Ϫ1 fw. Additionally, ears were entirely dried under PC (35C) and Maize seed is composed of different tissues, which unheated-air (NH) conditions. At the four harvests, different drying appear to dry at different rates because of their position. rate phases were evident in embryos of seed dried entirely at PC Under field drying conditions, embryo moisture remains (35C) conditions. A slower drying phase coincided with the PC period, about 150 g H 2 Ok g Ϫ1 fw higher than whole seed as it which increased with increasing maturation. Under FB drying, embryo MC declined at a faster rate down to about 400 g H 2 Ok g Ϫ1 fw, drops from 400 to 300 g H 2 Okg Ϫ1 fw. Then, the embryo followed by an intermediate drying rate down to about 200 g H 2 OMC decreases rapidly to equilibrium with whole seed kg Ϫ1 fw, and a slower drying rate below this point. As embryo MC at about 150 g H 2 Okg Ϫ1 fw (Struve, 1958). This phenomdeclined to 400 g H 2 Okg Ϫ1 fw at slower drying rates, either with PC enon has also been reported under artificial drying and or field drying, the ability to withstand the faster drying rates of the preconditioning (slow drying before fast drying) treat-

SU MMARYSix pairs of isogenic lines of sorghum (Sorghum bicolor L. Moench) were sown in field plots in Montecillo, State of Me´xico (2240 m altitude), in 2005 and 2006. Crosses A (Y)rB (X) were done in each pair. In A-lines, the length of pistil, stigma, style and ovary, as well as the ovary width, were measured. In B-lines, pollen diameter, viability (cytoplasm density) and production were evaluated. Pollen germination and pollen tube growth in the pistils of the A-lines, were quantified in vivo with aniline blue and epifluorescence 18 h after pollination (HAP), while fertilized pistils were counted at 96 HAP. Histological studies on both pollinated and non-pollinated pistils were performed in one male-sterile line. Seed yield, mean-seed weight, seeds per panicle and seed set (SS; seeds/flower/ panicle) were determined at harvest. Pollen viability was the variable most related to pollen germination and pollen tube growth. Stigma receptivity was not associated with its morphology

In A‐lines of sorghum (Sorghum bicolor L. Moench), seed production under field conditions with manual pollination is generally lower than that in self‐pollinated B‐lines. This may be associated with floral differences. Six pairs of A/B‐lines and four R‐lines were evaluated during 2005 and 2006 at Montecillo, State of México (2240 m altitude). Rachis length, number of primary branches and fertile flowers per panicle, 100‐seed weight, seed number, seed yield and seed set per panicle were evaluated. In the A‐lines, the pistil characteristics were also measured and in the male‐fertile lines, the size of anthers and the amount and size of viable pollen were recorded. Compared with the A‐ and B‐lines, the R‐lines exhibited significantly higher (P ≤ 0.05) numbers of flowers, seed set and seed yield per panicle and they also produced more pollen grains of larger size and with greater viability during their longer flowering period (FP). Between A‐ and B‐lines, there were differences (P ≤ 0.05) in most of the yield traits, which also interacted with year. The proportion of viable pollen in B‐ and R‐lines (75 %) was not considered to be a factor that might account for their low seed production. Chilling temperatures (3.5–8.4 °C) during the FP could have affected stigma receptivity in the three different line types and thus may have reduced seed set in the male‐fertile lines.

No abstract

Zea mays and Sorghum bicolor are important crops for animal and human nutrition worldwide. In the Central Highland Valley of Mexico, both crops are extremely important, and research is aimed toward increasing yield, disease resistance, and crop adaptation from 1,900- to 2,700-m elevation. In a 3-year field breeding experiment (2004 to 2006), leaf blight and vascular wilt symptoms were frequently observed in contiguous plots of maize and sorghum crops in Montecillo, Mexico and maize plots in Tecamac, Mexico. To identify and characterize the causal agent of these symptoms, isolations were conducted on leaves from areas where healthy and diseased tissues converged. Leaf sections of 1 cm2 from both crops were disinfested, placed on casamino acid-peptone-glucose (CPG) medium, and incubated at 28°C. After 48 h, only yellow colonies were observed and 12 isolates were selected for further characterization. Physiological and biochemical tests indicated that the isolates were nonfluorescent on King's B medium, and API 50 CHE (bioMérieux, Marcy l'Etoile, France) revealed that they were negative for gelatin hydrolysis, indole production, acid production from raffinose and positive for utilization of glycerol, D-glucose, mannitol, arbutine, esculine, salicine, cellobiose, maltose, melibiose, D-fucose, and D-arabitol; all characteristics of Pantoea agglomerans. Further identification of these isolates was accomplished by DNA analysis. For DNA analysis, 1.4-kbp fragments of the 16S rRNA gene were amplified with primer set 8F/1492R (3) and sequenced with U514F/800R universal primers (2). Five sequences were obtained and deposited in GenBank (Accession Nos. EF050806 to EF050810). A phylogenetic tree was constructed using the UPGMA method (mega version 3.1). Results of the phylogenetic analysis grouped the species P. ananatis, P. stewartti, and P. agglomerans into three clusters. The five unknown sequences were grouped into the P. agglomerans cluster. There was a 98 to 99% similarity of the five 16S rRNA gene sequences with P. agglomerans strain type ATCC 27155. Pathogenicity of the 12 isolates was confirmed by injecting 108 CFU mL–1 of inoculum into stems of 3-week-old maize cv. Triunfo and sorghum cold tolerant hybrid (A1×B5)×R1 seedlings in the greenhouse at 28°C and 80% relative humidity. Also, seedlings were inoculated with water, nonpathogenic isolates of P. agglomerans from maize (GM13, and HLA1), and not inoculated as negative controls. Three replications were included for each isolate and control. All test strains developed water-soaked lesions on juvenile leaves at 8 days postinoculation and were followed by chlorotic to straw-colored leaf streaks and then leaf blight symptoms at 3 weeks postinoculation. All negative control seedlings did not develop symptoms. In addition, the 12 isolates were infiltrated at 107 CFU mL–1 into tobacco leaves that displayed a hypersensitive response at 4 days, indicating the presence of the type III secretion system (1). Isolates were reisolated, and the 16S rRNA gene fragments were 100% similar to their original isolate sequences. P. agglomerans has been reported to affect other crops, including chinese taro in Brazil (2007), onion in the United States (2006) and South Africa (1981), and pearl millet in Zimbabwe (1997); however, to our knowledge, this is the first report of P. agglomerans associated with leaf blight and vascular wilt symptoms in maize and sorghum in the Central Highland Valley of Mexico. References: (1) J. Alfano and A. Collmer. Annu. Rev. Phytopathol 42:385, 2004. (2) Y. Anzai et al. Int. J. Syst. Evol. Microbiol. 50:1563, 2000. (3) M. Sasoh et al. Appl. Environ. Microbiol. 72:1825, 2006.

-The objective of this work was to evaluate the genetic diversity of nine maize races (Zea mays ssp. mays) from Northwestern Mexico and one population of teosinte of the Balsas race (Zea mays ssp. parviglumis). A total of 649 alleles were identified, with an average of 20.9 alleles per locus using 31 microsatellite loci; 84.3% of them were polymorphic loci with a 0.49 expected heterozygosity. Graphic representation of principal coordinate analysis (PCoA) showed broad variation and population distribution. The highest probabilistic value obtained with the ∆K criterion confirmed the existence of five population groups clustered by the Bayesian model. This grouping coincided with the population distribution observed in the PCoA graph. Maize races examined retain broad genetic diversity among and within the evaluated populations.Index terms: Zea mays, conservation strategies, landraces, microsatellites, plant breeding. Diversidade genética e estrutura das raças de milho nativo do Noroeste do MéxicoResumo -O objetivo deste trabalho foi avaliar a diversidade genética de nove raças de milho (Zea mays ssp. mays) do Noroeste do México e uma população de teosinto da raça Balsas (Zea mays ssp. parviglumis). Foram identificados 649 alelos, uma média de 20,9 alelos por locus, utilizando 31 loci microssatélites. Desses, 84,3% eram polimórficos e apresentaram heterozigosidade esperada de 0,49. A representação gráfica da análise de fatores principais (PCoA) mostrou ampla variação e distribuição populacional. O maior valor probabilístico obtido com o critério ΔK confirmou a existência dos cinco grupos populacionais agrupados com o modelo bayesiano. Esse agrupamento coincide com a distribuição populacional observada no gráfico PCoA. As raças de milho examinadas apresentam ampla diversidade genética entre e dentro das populações avaliadas.Termos para indexação: Zea mays, estratégias conservacionistas, raças nativas, microssatélites, melhoramento vegetal.

Mesoamérica es considerada el centro de origen y diversidad del maíz (Zea mays L.). La teoría multicéntrica del origen y diversidad del maíz define cinco centros de origen-domesticación, a partir de los cuales se conformaron cuatro macro regiones o centros de diversificación primaria de este cereal, de donde fueron emergiendo las diversas razas y la concentración de su diversidad. Un centro de diversidad genética se define como aquella área geográfica donde existe diversidad morfológica, genética, o ambas, para una determinada especie, que se caracteriza por albergar poblaciones de los parientes silvestres y que constituye una reserva genética. El objetivo de este estudio fue validar de manera empírica las regiones geográficas de México que conforman con la definición de centro de diversidad genética para el caso del maíz. Se utilizó análisis espacial para examinar la diversidad y distribución de 24,126 colectas de maíz nativo y 1,106 registros de parientes silvestres (Teocintle: 692 y Tripsacum: 414) colectadas durante el periodo 1926-2014, disponibles en los bancos de germoplasma y herbarios de las instituciones de investigación y enseñanza agrícola nacionales e internacionales ubicados en México y, mediante el uso de sistemas de información geográfica y modelación. En apego a los criterios y definiciones considerados en la teoría multicéntrica de origen y diversidad del maíz, se definieron y validaron empíricamente 19 regiones geográficas que se consideran centros de diversidad genética del maíz nativo de México.