Pathogenic and genetic characterizations of 96 isolates of Macrophomina phaseolina from Mexico and other countries were carried out in order to define the pathogenic and genetic patterns of diversity and to gain insights into the pathogenic and genetic specialization in this fungus. Isolates were collected from different hosts in Mexico (23 isolates), Italy, Australia, Japan, Argentina, USA, Colombia and Brazil (73 isolates). Pathogenicity was evaluated in seeds of two Phaseolus vulgaris L. cultivars under in vitro conditions, while genotype was determined on the basis of amplified fragment-length polymorphisms (AFLPs). The most frequent pathotypes were 4095 (15 isolates) and 0 (nine isolates), while 59 isolates had a unique pathotype (61%). Cluster analysis showed two contrasting groups of isolates on the basis of pathogenicity, where one group mainly included the most aggressive isolates from Mexico and Colombia. The AFLP analysis produced 418 amplified products and 92.8% were polymorphic. Cluster analysis showed no clear association between AFLP genotype and geographical origin. When subgroups of isolates were re-analysed, we found a clear differentiation between Mexican and non-Mexican isolates. Results confirmed the significant pathogenic and genetic diversity of Macrophomina and showed a clear differentiation between Mexican isolates from all others.

Entre los años 9000 y 5000 a. C. en diferentes partes del mundo se domesticaron diversas especies vegetales, entre ellas el frijol común (Phaseolus vulgaris L). La importancia de identificar el centro de origen y de domesticación de una especie como P. vulgaris radica en que esas áreas son fuente primaria de poblaciones con genes útiles para el mejoramiento genético y de interés para el entendimiento de la evolución, diversificación y conservación de la especie. El conjunto de conocimientos recabados hasta hoy, como la edad de los restos fósiles y las características morfológicas, agronómicas y genéticas, establecen que el frijol común se originó en Mesoamérica y posteriormente se domesticó entre los 5000 y 2000 años a. C. en dos sitios del continente Americano: Mesoamérica (México y Centroamérica) y los Andes (Sudamérica). A partir del frijol silvestre se formaron dos acervos genéticos domesticados distintos, Mesoamericano y Andino. El uso de nuevas herramientas biotecnológicas y genómicas han ofrecido evidencias definitivas sobre el origen, domesticación y diversidad de P. vulgaris.

Common bean diversity has been classified into two major gene pools, Middle American and Andean. Each Landraces and bean (Phaseolus vulgaris L.) cultivars grown in pool can be further subdivided into three races (Singh Mexico are diverse, as are consumer preferences and agroecological et al., 1991b). The main races grown in Mexico are the production environments. Mexican common bean cultivars were analyzed using amplified fragment length polymorphism (AFLP) finger-Middle American: Mesoamerica, Jalisco, and Durango, printing to examine the genetic relationships within and among races, as well as the Nueva Granada race from the Andean based on the genotyping of 112 bred cultivars developed in Mexico.pool. This last race was probably introduced into Mexico Molecular analysis of dry bean germplasm will be useful to corroborate in pre-Columbian times. previous cultivar characterizations and establish the genetic basis of The knowledge of genetic diversity patterns can inimproved germplasm, to facilitate the use of that diversity, and to crease the efficiency for conservation, utilization, and implement the use of markers in selection. Germplasm included 111 genetic improvement of common bean (Beebe et al., cultivars belonging to Mesoamerica (25), Jalisco (39), Durango (28), 2000; Rosales-Serna et al., 2003). Different methodoloand Nueva Granada (19) races, which are commonly cultivated throughgies and traits, such as morphological (Cá rdenas, 1984; out the bean-producing areas of Mexico. A Mexican P. coccineus Singh et al., 1991a; Rosales-Serna et al., 2003), biochemispecies cultivar (Blanco Tlaxcala) was also included for comparison. Broad genetic diversity was found within bean races, and diversity cal (Singh et al., 1991a, 1991c), and molecular (Beebe values between races were similar. Most of the Nueva Granada germet al., 2000; Metais et al., 2000; Rosales-Serna et al., plasm was clearly different from that of all other races, whereas the 2003) have been suggested for the evaluation of genetic P. coccineus cultivar was distinct from all P. vulgaris cultivars. A diversity in common bean. Bean cultivars have also been dendrogram based on the AFLP analysis did not clearly match with classified by seed type, growth habit, morphology, phethat made on the basis of racial classification. This mismatch was nology, and reaction to photoperiod (Voysest, 2000; Roprobably due to genetic recombination between Andean (Nueva Grasales-Serna et al., 2003). Molecular markers are useful nada) and Mesoamerican (Jalisco, Durango, and Mesoamerica) genefor cultivar identification, due to the fact that they are pools. Utilization of contrasting parents for specific crosses has also not influenced by variable environmental conditions or contributed to broadening the genetic basis of common bean.

Fifty morphological characteristics, fruit production over 3 years (from 1999 to 2002) and the amplified fragment length polymorphism (AFLP) technique were used to analyse a set of 48 guava (Psidium guajavaL.) accessions cultivated in Mexico, in order to characterize their genetic relationships. Germplasm was collected from the Calvillo-Cañones region and planted in Huanusco, Mexico. The study included twoP. cattleianum(Sabine) and twoP. friedrichsthalianum(Berg-Niedenzu) accessions from Costa Rica as outgroups. Principal component analysis (PCA) explained less than 30% of total variation and 14 characteristics from trees (1), leaves (2) and fruits (11) were the most informative. PCA analysis separated the germplasm into three major groups of accessions based on fruit size and weight, stem diameter and leaf size. Significant differences in fruit yield were detected among accessions and years, whereP.guajavaproduced 36 kg/year/tree of fresh fruit whileP. cattleianumandP. friedrichsthalianumshowed fruit yield lower than 7 kg/year/tree. The fruit yield broad sense heritability was 0.25. The AFLP analysis produced two clusters ofPsidiumaccessions, the first includedP. cattleianumandP. friedrichsthalianum, and the secondP. guajavaaccessions. This is the first report about the use of AFLP marker methodology for the genetic characterization of Mexican native guava germplasm and the results based on phenotypic and productive characteristics suggest that germplasm was selected from open pollinated trees.

a partir del sexto día de la inoculación y el desarrollo de la enfermedad se explicó por un modelo de regresión lineal simple (Y = 1.123 + 0.1133X). No se detectó la formación de apresorios pero sí la síntesis de una capa mucilaginosa asociada con los tubos germinativos. El proceso infectivo del hongo se manifestó con la penetración de las hifas intra e inter-celularmente y con la producción de acérvulos a partir de los 12 días después de la inoculación. Los síntomas de la antracnosis se asociaron con la degradación de polifenoles, plasmólisis, necrosis y desintegración celular Palabras Clave: Persea americana L., antracnosis, patogenicidad, patogénesis. ANALYSIS OF Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. INFECTION OF AVOCADO FRUITSABSTRACT -The pathogenesis of Colletotrichum gloeosporioides (Penz.) Penz. & Sacc. from the state of Michoacán, México was characterized in avocado (Persea americana L.) fruits cv. 'Hass'. The fungus caused typical disease symptoms of 'anthracnose' ten days after inoculation. Fungal infection rate was significantly different (p≤0.05) between treatments since the sixth day after inoculation and the disease development was explained by one simple linear regression model (Y = 1.123 + 0.1133X). No appresoria were found but one mucilagous layer associated to germ tubes was detected. Fungal infective process started with intra and intercellular penetration by hyphae and after, acervuli were produced twelve days after inoculation. Anthracnose symptoms were associated with poly-phenol degradation, plasmolysis, necrosis and cell disintegration