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Root colonizing Trichoderma fungi can stimulate plant immunity, but net effects are strain × cultivar-specific and changing ambient conditions further contribute to variable outcomes. Here, we used four Trichoderma spp. to inoculate seeds of four common bean (Phaseolus vulgaris) cultivars and explored in three different experimental setups the effects on fungal anthracnose after leaf inoculation with Colletotrichum lindemuthianum. Plants growing in pots with field soil under greenhouse conditions exhibited the highest and those in the open field the lowest overall levels of disease. Among 48 Trichoderma strain × bean cultivar × setup combinations, Trichoderma-inoculation enhanced disease in six and decreased disease in ten cases, but with the exception of T. asperellum B6-inoculated Negro San Luis beans, the strain × cultivar-specific effects on anthracnose severity differed among the setups, and anthracnose severity did not predict seed yield in the open field. In the case of Flor de Mayo beans, Trichoderma even reduced yield in anthracnose-free field plots, although this effect was counterbalanced in anthracnose-infected plots. We consider our work as a case study that calls for stronger emphasis on field experiments in the early phases of screenings of Trichoderma inoculants as plant biostimulants.

Most of the commercial papaya genotypes show susceptibility to water deficit stress and require high volumes of irrigation water to yield properly. To tackle this problem, we have collected wild native genotypes of Carica papaya that have proved to show better physiological performance under water deficit stress than the commercial cultivar grown in Mexico. In the present study, plants from a wild Carica papaya genotype and a commercial genotype were subjected to water deficit stress (WDS), and their response was characterized in physiological and molecular terms. The physiological parameters measured (water potential, photosynthesis, Fv/Fm and electrolyte leakage) confirmed that the papaya wild genotype showed better physiological responses than the commercial one when exposed to WDS. Subsequently, RNA-Seq was performed for 4 cDNA libraries in both genotypes (susceptible and tolerant) under well-watered conditions, and when they were subjected to WDS for 14 days. Consistently, differential expression analysis revealed that after 14 days of WDS, the wild tolerant genotype had a higher number of up-regulated genes, and a higher number of transcription factors (TF) that were differentially expressed in response to WDS, than the commercial genotype. Thus, six TF genes (CpHSF, CpMYB, CpNAC, CpNFY-A, CpERF and CpWRKY) were selected for further qRT-PCR analysis as they were highly expressed in response to WDS in the wild papaya genotype. qRT-PCR results confirmed that the wild genotype had higher expression levels (REL) in all 6 TF genes than the commercial genotype. Our transcriptomic analysis should help to unravel candidate genes that may be useful in the development of new drought-tolerant cultivars of this important tropical crop.

Phaseolus vulgaris line A193 has been shown to be widely resistant to Colletotrichum lindemuthianum, including race 1472, one of the most virulent races of C. lindemuthianum characterized. Resistance to C. lindemuthianum race 1472 in P. vulgaris line A193 was investigated in segregating F2 and F2.3 populations from a cross between A193 and Flor de Mayo Bajio (a commercial cultivar highly susceptible to C. lindemuthianum). Resistance to 1472 in A193 was determined to be conditioned by a single dominant gene. Inoculation of crosses between A193 and cultivars Michigan Dark Red Kidney and Perry Marrow with race 1472 suggest that resistance in A193 is conditioned by the Co-1 gene. Inoculation of the cross A193 × Perry Marrow with C. lindemuthianum race 2, demonstrated that resistance to race 2 in Perry Marrow is also conditioned by a single dominant gene and is distinct to resistance in A193 or Michigan Dark Red Kidney. Three AFLP markers (ECAG/MACC-1, EACA/MAGA-2, EAGG/MAAC-8) linked in repulsion to the Co-1 locus were identified by screening the A193 × Flor de Mayo F2 population with 314 random amplified polymorphic DNA, amplified fragment length polymorphism, and restriction fragment length polymorphism markers. The two most closely linked markers should be useful in marker-assisted selection for Co-1.

The role of jasmonic acid (JA) on mycorrhizal colonization by Glomus fasciculatum in tomato plants was examined using mutant plants overexpressing prosystemin (PS) or affected in the synthesis of JA (suppressor of prosystemin-mediated responses 2, spr2). The degree of mycorrhizal colonization was determined by measuring frequency (F%) and intensity (M%) of colonization and arbuscule abundance (A%). Gene expression and biochemical analyses were also performed in roots to detect changes in carbon (C) partitioning. Colonization was similar in mycorrhizal PS and wild-type roots, except for a higher A% in the former. Conversely, colonization was severely reduced in roots of spr2 mutants. No association was found between levels of expression of genes coding for systemic wound responsive proteins (or SWRPs) and other defense-related proteins in roots and mycorrhization levels in these plants. On the other hand, the degree of mycorrhizal colonization correlated with changes in the transcriptional regulation of a number of genes involved in sucrose hydrolysis and transport, cell wall invertase activity and mycorrhizal-specific fatty acid content in roots. The results obtained suggest that one of the mechanisms by which JA might operate to modulate the mycorrhization process could be through its influence on the regulation of C partitioning in the plant. The significant colonization increase observed in mycorrhizal spr2 plants supplied with exogenous methyl jasmonate supports its role as a positive regulator of the symbiosis.

The pathotypes of 17 isolates of Colletotrichum lindemuthianum from the central region of Mexico were characterized to determine the genetic relationship among isolates from this region and other regions of Mexico, and to evaluate the resistance present in the elite germ plasm collection of Phaseolus vulgaris at INIFAP. Eight pathotypes were identified, including pathotype 292, which is reported for the first time in Mexico. The lack of isolates infecting cultivar TU carrying the Co-5 resistance gene suggests that this cultivar is a useful source of resistance. Six pathotypes produced susceptible reactions on only differential cultivars of Middle American origin, one pathotype on a single cultivar of Andean origin, and one pathotype on cultivars of both Middle American and Andean origin. Comparison of amplified fragment length polymorphism (AFLP) genotypes of 21 isolates confirmed suggestions that populations of C. lindemuthianum are comprised of asexually reproducing clonal lineages. Analysis of five different pathotypes of C. lindemuthianum on 21 elite genotypes of P. vulgaris identified four genotypes from different races of P. vulgaris resistant to all five pathotypes. This information will allow breeders and farmers to select the resistant genotypes most suited to their needs.

This study analyzes the morphological and genetic characteristics of three sympatric populations of Prosopis from Argentina. Although morphological and geographical data suggest that Prosopis chilensis var. riojana is an interspecific hybrid of Prosopis chilensis var. chilensis and Prosopis flexuosa var. flexuosa, no correlation was found between morphological traits and genetic distances generated by random amplified polymorphic DNA - polymerase chain reaction (RAPD-PCR). Genetic similarity is greater among P. chilensis var. chilensis and P. flexuosa var. flexuosa than between either of these two taxa with P. chilensis var. riojana. Also, P. chilensis var. riojana has unique genetic markers that are absent from its putative parents. Additionally, dendrograms generated by unweighted pair group method with arithmetic means (UPGMA) and Neighbor-Joining clustering criteria group P. chilensis var. chilensis and P. flexuosa var. flexuosa apart from P. chilensis var. riojana. Possibilities for the lack of congruence between morphol- ogy and RAPD markers are discussed. The results obtained are insufficient to conclusively establish the origin of P. chilensis var. riojana; however, the morphological and genetic traits observed suggest this taxon is well differenti- ated from P. chilensis var. chilensis and P. flexuosa var. flexuosa. Resume : Les auteurs analysent les caracteristiques morphologiques et genetiques de trois populations sympatriques de Prosopis, en Argentine. Bien que les donnees morphologiques et genetiques suggerent que le Prosopis chilensis var. riojana soit un hybride interspecifique du Prosopis chilensis var. chilensis et du Prosopis flexuosa var. flexuosa ,i l n'y a aucune correlation entre les traits morphologiques et les distances genetiques generees par l'amplification au hasard de l'ADN polymorphique - reaction en chaine polymerase (RAPD-PCR). La similitude genetique est plus grande au sein des P. chilensis var. chilensis et des P. flexuosa var. flexuosa, qu'entre chacun de ces taxons avec les P. chilensis var. riojana. De plus, le P. chilensis var. riojana possede des marqueurs genetiques uniques qui sont absents chez les parents putatifs. Qui plus est, les dendrogrammes generes par groupe de paires non-ponderees en utilisant la moyenne mathematique (UPGMA) et les criteres de regroupement des voisins relies (« neighbor-joining ») regroupent le P. chi- lensis var. chilensis et le P. flexuosa var. flexuosa separement du P. chilensis var. riojana. Les auteurs discutent ce qui pourrait expliquer le manque de congruence entre la morphologie et les marqueurs RAPD. Les resultats obtenus ne suffisent pas pour etablir de facon concluante l'origine du P. chilensis var. riojana; cependant, les caracteres morpholo- giques et genetiques observes suggerent que ce taxon serait bien distinct du P. chilensis var. chilensis et du P. flexuosa var. flexuosa. Mots cles : distances genetiques, hybridation, morphologie, Prosopis, RAPD, taxon rare.

Macrophomina phaseolina infects a wide range of plant species. In the case of Phaseolus vulgaris (the common bean), the fungus causes charcoal rot which can lead to severe losses especially under arid conditions. In order to combat the disease, it is necessary to have information on the population structure of the pathogen in terms of pathogenesis on different species which may be grown simultaneously or successively within a region. Previous reports have demonstrated the heterogeneity of the pathogen both in terms of morphological characteristics and molecular genotype; however no systematic attempt has been made to compare pathogenesis of different isolates in relation to genotype, species of origin or geographical location. With this aim 84 isolates of M. phaseolina from different plant species in different geographical regions of Mexico were analysed by inoculation on a set of P. vulgaris cultivars differing in reaction to the fungus and by determination of their amplified fragment length polymorphism (AFLP) genotype. Forty three distinct pathotypes were identified, only two of which were found in more than one species. All 84 isolates had distinct AFLP genotypes and cluster analysis showed a tendency of the isolates to form groups related to geographical origin or species of origin.

The life cycle of flowering plants alternates between a predominant sporophytic (diploid) and an ephemeral gametophytic (haploid) generation that only occurs in reproductive organs. In Arabidopsis thaliana, the female gametophyte is deeply embedded within the ovule, complicating the study of the genetic and molecular interactions involved in the sporophytic to gametophytic transition. Massively parallel signature sequencing (MPSS) was used to conduct a quantitative large-scale transcriptional analysis of the fully differentiated Arabidopsis ovule prior to fertilization. The expression of 9775 genes was quantified in wild-type ovules, additionally detecting >2200 new transcripts mapping to antisense or intergenic regions. A quantitative comparison of global expression in wild-type and sporocyteless (spl) individuals resulted in 1301 genes showing 25-fold reduced or null activity in ovules lacking a female gametophyte, including those encoding 92 signalling proteins, 75 transcription factors, and 72 RNA-binding proteins not reported in previous studies based on microarray profiling. A combination of independent genetic and molecular strategies confirmed the differential expression of 28 of them, showing that they are either preferentially active in the female gametophyte, or dependent on the presence of a female gametophyte to be expressed in sporophytic cells of the ovule. Among 18 genes encoding pentatricopeptide-repeat proteins (PPRs) that show transcriptional activity in wild-type but not spl ovules, CIHUATEOTL (At4g38150) is specifically expressed in the female gametophyte and necessary for female gametogenesis. These results expand the nature of the transcriptional universe present in the ovule of Arabidopsis, and offer a large-scale quantitative reference of global expression for future genomic and developmental studies.

El mejoramiento del girasol (Helianthus annuus L.) depende en gran medida de la introducción de diversidad genética proveniente de material silvestre. El objetivo de este trabajo fue construir un mapa de ligamiento basado en marcadores AFLP a partir de una población F2:3 derivada de un cruzamiento inter-subespecífico de girasol (H. annuus var. macrocarpus x H. annuus ssp. texanus Heiser), así como detectar posiciones de loci de caracteres cuantitativos (QTL) a través del enfoque analítico de mapeo por intervalos. Se evaluaron los siguientes caracteres contrastantes entre girasoles cultivados y silvestres, presumiblemente relacionados con la domesticación: altura de planta, número de capítulos (ramificación) y diámetro de capítulos por planta, número y peso de aquenios por capítulo, días a floración, días a madurez fisiológica y contenido de aceite de aquenios. La evaluación fenotípica se llevó a cabo en condiciones de campo, con un diseño de bloques incompletos con dos repeticiones. Se consideró un nivel de significancia estadística de amplitud genómica de 0.05 en la detección de los QTL. Para establecer los valores críticos de los estadísticos de prueba se hicieron pruebas de permutación sólo con los grupos de ligamiento con puntuaciones LOD (logaritmo de la razón de verosimilitudes) > 1.5. Además, para cada carácter se hizo un análisis de varianza por locus individual no ligado, con lo cual se identificaron cuatro loci no ligados que afectan el número de aquenios por capítulo y los días a madurez fisiológica, con P < 0.001. Se identificó un QTL significativo con amplitud genómica de 0.017 para peso de aquenios que podría representar una región del genoma relacionada con la domesticación, y cinco QTLs posibles en cinco caracteres. Los QTLs detectados, que incluyen los hipotéticos, explicaron de 7.1 a 11.9 % de la varianza fenotípica.

La soya [Glycine max (L.) Merrill] posee bajos niveles de diversidad genética en comparación con otras especies autógamas. Por lo anterior y con el fin de determinar si existe la necesidad de introducir nuevo germoplasma para generar nuevas variedades, se evaluó la diversidad genética de 24 líneas elite de soya para el trópico húmedo de México y nueve introducciones de otros países, mediante marcadores moleculares tipo AFLP. Los resultados revelaron que las líneas e introducciones no se agruparon de acuerdo a su origen geográfico, además de indicar un alto nivel de polimorfismos (60 %). Los genotipos de México son altamente similares a los de Brasil. El índice dediversidad genética fue bajo (31 %), y semejante a los reportados en otros estudios con RFLP y RAPD. Aunque la muestra de genotipos no representó a la totalidad del germoplasma de soya cultivada en el trópico húmedo de México, se considera que existe suficiente diversidad genética para generar nuevas variedades, ya que tres líneas mexicanas fueron más divergentes a nivel molecular que los materiales considerados filogenéticamente distintos de otros países (basados en características morfológicas y fisiológicas) utilizados como testigos.