Efecto del origen del material de siembra y el sistema de cultivo en la severidad e incidencia del anublo bacterial, el anublo fungoso y el superalargamiento de la yuca

Data on max. and min. severity of attacks by Xanthomonas campestris pv. manihotis, Choanephora cucurbitarum, and Sphaceloma manihoticola were gathered on commercial plantations located in 4 regions of Sucre, Colombia. Regional clones Venezolana and Preta were used. In the region of Bongo, neither X. campestris pv. manihotis nor C. cucurbitarum were observed; S. manihoticola was absent in the region of Hato Nuevo. These regions are therefore considered apt for cassava cultivation. The max., min., and total severity means, as well as the percentages of incidence on diseased plantations, were higher when cuttings from meristem culture were used as planting material. Severity indexes and percentages of incidence of S. manihoticola were higher in multiclonal lots than in monoclonal lots; susceptible clones should not be planted next to intermediately resistant clones, since the severity indexes in the latter may increase. The lowest disease incidence and severity were observed in cassava intercropped with maize, since the maize acted as a live barrier avoiding spores of the causal agent to be deposited on susceptible host plant tissues. This cropping system is recommended for areas where S. manihoticola is endemic. (CIAT

Nuevo metodo para transporte de material vegetativo indexado de yuca (Manihot esculenta Crantz)

Cassava vegetative material is distributed by sending seedlings obtained from meristem cultures in test tubes. Although this material is accepted worldwide, losses occur due to seedling weakness and the delay to obtain adult seedlings in the field (normally between 3 and 4 yr). To overcome this problem, a system has been developed in which cuttings from indexed plants, obtained from meristem culture, are wrapped in waxed paper or paper towels, placing their tips on cotton saturated with a mixture of captan- benomyl (3000 ppm) at the end of the cuttings. They are then packed in groups in cardboard boxes for distribution. Dehydration is therefore avoided; cuttings also remain viable for over 15 days, enough time to be transported anywhere in the world. Bud germination and cutting rooting are achieved at 15 days and reach 100 percent. The seedlings obtained can be transplanted directly in the field just 1 mo. after their establishment. Adult plants can be obtained after a yr, which is highly advantageous considering previous losses and the time necessary to obtain adult plants in the field from seedlings in test tubes. (Full text-CIAT

Enfermedades en cultivos de yuca asociados con maiz y name en Cordoba, Bolivar, Sucre y Atlantico

The incidence and severity of several diseases affecting cassava in monoculture and in association with maize and/or yam in the departments of Cordoba, Bolivar, Sucre, and Atlantico (Colombia) were assessed. Leaf spots (brown leaf spot, white leaf spot, blight leaf spot) and CBB were the most common diseases. The distribution of CBB, anthracnose, superelongation, and E.T. disease (cord-like formations) in this region is discussed. Healthy planting material (not infected with bacterioses or superelongation) should be used. Cuttings taken from crops infected with superelongation should be immersed for 10 min. in a solution with benomyl (3g/l), captafol (4 g/l), or Sistemin (2 cc/l). Cassava/maize intercropping was excellent in areas where bacterioses is endemic. Bacterioses-infected monocropped cassava can be pruned towards the end of the rainy season to reduce disease severity. In intercropped cassava/yam, the yam competition reduced the cassava stand; therefore this practice is not recommended. (CIAT

Erradicacion de patogenos de semilla sexual de yuca (Manihot esculenta Crantz) mediante el tratamiento con microondas

The effect of microwaves on the eradication of fungal and bacterial pathogens in cassava sexual seed was investigated. Healthy mature fruits were collected and dried under ambient conditions. Seeds were selected according to specific wt. by placing them in a glass of water and discarding those that floated. The selected seeds were placed in distilled water, submitted to microwave drying (2450 MHz) for 120 s and dusted with thiram (1 g/100 g seed). Colletotrichum spp., Diplodia manihotis, Fusarium spp., Cladosporium spp., Aspergillus spp., Penicillium spp., Neurospora spp., Xanthomonas campestris pv. manihotis, and Bacillus spp. were eliminated by this procedure. Germination was over 90 percent as natural seed latency was broken. The efficacy of the microwave treatment depends on the optimum temp. to be reached (77 degrees Celsius). (CIAT

La pudricion negra de la yuca (Manihot esculenta) causada por Scytalidium sp

The symptoms caused in cassava by Scytalidium sp. and Diplodia manihotis are described and compared. NE Brazil and the northern coast and Valle del Cauca of Colombia are zones with appropriate ecological characteristics for an optimum disease development. Scytalidium sp. affected both roots and stems and therefore it is recommended to use healthy cuttings for planting as well as quarantine measures to avoid its introduction in noncontaminated zones but with conditions appropriate for its development. Etiological, epidemiological, and control studies are currently being conducted with respect to this pathological problem of cassava. (CIAT

Sistema integral de produccion de yuca para La Colorada (Magdalena) una zona infestada de Diplodia manihotis y Fusarium oxysporum

The predominant farming system in La Colorada (Magdalena, Colombia), where cassava is a subsistence crop, is briefly reviewed. The intensive land use has caused soil leaching and infestation with root pathogens such as Diplodia manihotis and Fusarium oxysporum and cassava production has decreased from 15 to 3-4 t/ha. Therefore, CIAT has developed a technological package that yields over 19 t/ha with resistant clones and 10-12 t/ha with susceptible clones. Indications of the technological package are given as to clones, cuttings to be used, preemergent weed control, and manures. (CIAT

International congress of plant pathology

DNA polymorphism and variation in virulence of #Xanthomonas axonopodis pv. #manihotis (Xam), the causal agent of cassava bacterial blight, were studied within a pathogen population from Venezuela. Collections were made in several fields at different sites within an edaphoclimatic zone where cassava is a major crop. DNA polymorphism was assessed by RFLP analysis, using an Xam plasmidic DNA sequence (ptbB) as a probe to determine the relatedness of 91 Venezuelan isolates. A high degree of polymorphism existed among the isolates, whether collected from the same or different fields. Based on a multiple correspondence analysis, the Xam population was distributed into eight clusters and no correlation was observed between genetic diversity and geographic origin. One set of haplotype strains representing the range of variability detected in Venezuela was further characterized by another RFLP analysis using two repetitive genomic probes (pBS6 and pBS8) to establish the usefulness of these probes and their complementarity with the ptbB probe. Variation for virulence was observed in the Xam Venezuelan collection by inoculating a set of cassava cultivars with 28 isolates of the pathogen, each representig a haplotype. Understanding the genetic and pathogenic variation in the pathogen population is useful for designing cassava bacterial blight management strategies. (Résumé d'auteur