México ocupa actualmente el cuarto lugar mundial en producción de sorgo. En el estado de Sonora, este cultivo es uno de los más productivos. Los mayos, un pueblo amerindio que habita en el sur del estado mexicano de Sonora, ha estado promoviendo sistemas sustentables de producción agrícola. La aplicación de bioderivados de exoesqueletos de crustáceos como el quitosano (QUI) y microorganismos promotores del crecimiento vegetal, endomicorrízicos, simbiontes, benéf icos, y antagonistas, en algunos cultivos han mostrado ser una alternativa en el proceso de germinación y mejoras de rendimientos de cosecha; sin embargo, con relación al sorgo de grano, son limitados lo estudios sobre el efecto de éstos bioderivados como el QUI y consorcios microbianos. El objetivo de la investigación consistió en evaluar en sorgo de grano, el efecto de quitosano (100 y 50%) y un consorcio microbiano (en conjunto e individual forma con QUI) contra fertilización tradicional, en la región indígena del Mayo en Basconcobe, Etchojoa, Sonora, en la inducción fenológica, rendimiento y calidad proteica del grano. Se utilizó un diseño experimental de bloques al azar, con siete tratamientos a evaluar y cinco repeticiones Como variables respuesta se midieron: tasa de germinación, clorof ila total, y en madurez f isiológica la altura de planta, longitud de panoja, rendimiento ha-1 y proteína en grano. Los resultados indican que, en rendimiento y calidad proteica del grano de sorgo, el tratamiento más ef iciente (con P < 0.05), fue con QUI 100% + consorcio microbiano utilizando al 50% una fertilización regional. Estos resultados expresan la posibilidad de utilizar el quitosano como un biofertilizante de origen marino conjuntamente con un microbiano en un sistema de producción de sorgo.
Vascular wilting diseases have become one of the most serious diseases of tomato (Lycopersicon esculentum) throughout the Baja California Peninsula. Since the winter of 2004, a disease with symptoms characteristic of those caused by a Fusarium species has been observed in commercial fields near La Paz and Todos Santos in the state of Baja California Sur (BCS). Symptoms include typical one-sided wilting and dark brown vascular discoloration. Upper stem tissues and wilted seedlings were disinfested by immersion in a 1.0% aqueous solution of sodium hypochlorite for 2 min, rinsed in sterile water, and placed on Komada's medium (pH 6.8) at 22 ± 3°C. After 72 h, hyphal growth was recovered and subcultured on carnation leaf agar and potato dextrose agar and incubated at 25°C in 12-h light/dark cycles. Identification was based on colony morphology, conidial characteristics, and molecular techniques. White cottony mycelium, reddish coloration of the medium, ovoid two-celled macroconidia, and large macroconidia, all characteristic of F. oxysporum, were observed (2). Polymerase chain reaction and restriction fragment length polymorphisms with restriction enzymes EcoRI, RsaI, and HaeIII were used to characterize 24 isolates (sampled during January 2005) from La Paz (Fol-LaP) as formae speciales lycopersici and assigned to vegetative compatibility group 0030 (1). Confirmation of pathogenicity and race determination for the Fol-LaP isolates were as described previously (3). Mexican isolates of races 2 and 3 (one each) were included as positive controls. Conidial suspensions of 7 × 105 CFU/ml were used to inoculate differential tomato cvs. Bonny Best (Millington Co., universally susceptible), Tequila F1 (Vilmorin, race 1 resistant), Rio Grande (Harris Moran, race 1 and 2 resistant), and Sebring (Rogers, race 1, 2, and 3 resistant). Plants at the first true-leaf stage were inoculated by dipping their roots in the conidial suspension. Inoculated seedlings were transplanted into pots containing a sterile 5:1:1 mixture of sand/vermiculite/soil (v/v/v) and maintained in the greenhouse at 25 to 28°C under natural daylight. An equal number of plants of each cultivar dipped in water were used as controls. The experimental design was a completely randomized type with six replications (pots) containing four seedlings per pot. The test was done twice. The most susceptible plants inoculated by root-dipping developed typical symptoms of wilt, slight vein clearing on outer leaflets, stunting, dark brown vascular discoloration, and death. F. oxysporum was recovered from all symptomatic plants, whereas noninoculated tomato seedlings showed no symptoms. According to differential infection and symptomatology observed on infected cultivars, 62.5% of the isolated strains were identified as race 2, 25% as race 3, and 12.5% as an undetermined race isolated from Sebring. The presence of race 3 in BCS has important epidemiological implications since it has been reported on tomato in Sinaloa (4). The potential spread of the pathogen on introduced transplants represents a risk to tomato crops on the peninsula. To our knowledge, this is the first report of F. oxysporum f. sp. lycopersici race 3 in the state of BCS, Mexico. References: (1) G. Cai et al. Phytopathology 93:1014, 2003. (2) P. E. Nelson et al. Fusarium species. Pennsylvania State University Press, University Park, 1983. (3) B. A. Summerell et al. Plant Dis. 87:117, 2003. (4) J. G. Valenzuela-Ureta et al. Plant Dis. 80:105, 1996.
Since November 2001, geminivirus-like symptoms (stunting, reduced leaf size, and leaf curling “chino”) have been observed in tomato (Lycopersicon esculentum Mill.) plantings in Baja California Sur, Mexico. Samples of symptomatic plants were collected from commercial fields and analyzed by traditional and molecular methods for the presence of geminiviruses. Inocula prepared from infected plants were experimentally transmitted to tomato seedlings and Datura stramonium by mechanical inoculation and whitefly transmission. Leaf curling and interveinal chlorosis symptoms similar to those found in the field were observed in inoculated tomato and D. stramonium. DNA from infected plants was extracted and analyzed by polymerase chain reaction (PCR) and electrophoresis using degenerate primers PALIv1978/PARIc494 (1). PCR fragments of the expected size (1.1 kb) for the common region (CR) were obtained from 28 of 64 plants, cloned and sequenced (GenBank Accession No. AY336088). Comparisons of CR sequences with the NCBI database by using BLAST and MegAlign (DNASTAR, London) indicated that the Baja Californian isolates were New World bipartite begomoviruses sharing the highest nucleotide sequence identity (93%) with a partially characterized geminivirus (Tomato severe leaf curl virus (ToSLCV); GenBank Accession No. AF130415) from Guatemala. References: (1) M. R. Rojas et al. Plant Dis. 77:340, 1993.
Since 2000, a phytoplasma-like disease (locally known as “permanent yellowing”) was observed on tomatoes (Lycopersicon esculentum Mill.) grown in the Valle de San Quintín in northern Baja California Peninsula. Affected plants showed general chlorosis, severe stunting, upwardly rolled leaves, bronzing of mature leaves, purple discoloration of veins, “little leaf”, abnormal floral structures, and excessive branching of axillary shoots. Total DNA extracted from symptomatic and asymptomatic plants was used in nested (n)-PCR assays driven by phytoplasma-universal primer pair P1/P7 (3), followed by primer pair R16F2n/R16R2 (1) targeting the 16S ribosomal RNA gene of the putative phytoplasma. PCR conditions (direct and nested) were conducted as previously described (l,3). Restriction fragment length polymorphism (RFLP) patterns of nPCR-amplified products (≈ 1.25-kbp 16S rDNA fragments) digested with enzymes AluI, MseI, HhaI, and HpaII showed that 85% (17 of 20) of PCR-positive tomato samples had restriction patterns typical of phytoplasmas belonging to the aster yellows group, subgroup B (16SrI-B) “Candidatus Phytoplasma asteris” (2). Only 10% (2 of 20) of the samples were associated with a phytoplasma related to the 16SrXIII-A Mexican periwinkle virescence group (formerly group 16SrI, subgroup I). None of the symptomless plants tested positive. Subsequently, these results were confirmed by nPCR using 16SrI specific primer pair P1/Aint (4) and specific primers rp(I-B)F1/rp(I-B)R1 that amplify the ribosomal protein (rp) gene operon of aster yellows phytoplasma subgroup B (16SrI-B[rp-B]) (1). The presence of the phytoplasmas in symptomatic plants was confirmed by scanning electron microscopy. Characteristic yellow symptoms could be experimentally reproduced by graft inoculation of tomato seedlings (cv. Maya) with tissue of field-infected plants. Symptoms similar to those of field-grown diseased plants were observed consistently in most of the plants, and when graft transmitted from tomato to periwinkle (Catharantus roseus (L.) G. Don), symptoms of virescencent, small flowers were observed. In contrast, no symptoms were observed on plants grafted with tissues from healthy plants. In Baja California, it appears that at least two distinct phytoplasmas are involved in the disease complex. To our knowledge, this is the first molecular evidence of the presence of a phytoplasma associated with yellows-type diseases in the major tomato cultivation areas of the peninsula. References: (1) I.-M. Lee et al. Phytopathology 93:1368, 2003. (2) I.-M. Lee et al. Int. J. Syst. Evol. Microbiol. 54:1037, 2004. (3) B. Schneider et al. Page 369 in: Molecular and Diagnostic Procedures in Mycoplasmology. Academic Press, San Diego, CA, 1995. (4) C. D. Smart et al. Appl. Environ. Microbiol. 62:2988, 1996.
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