Modified plant architecture to enhance crop disease control: genetic control and possible value of upright fruit position in cucumber

Plant architectural features can facilitate disease control by creating unfavourable environments for pathogen growth or limiting pathogen contact with the host. In the case of Phytophthora capsici infection of cucumber (Cucumis sativus), the susceptible fruit typically lie in contact with soil under warm, moist conditions of a full canopy, an ideal location for exposure to inoculum and disease development. We have shown that increased row spacing, trellising and architectural variants that allow for more open canopies, such as shorter vines, reduced branching, or smaller leaves, can modify microclimate as assessed by temperature at the location of developing fruits. However, only trellising reduced infection rates (<3 % infection vs. 22 % for control). A cucumber accession PI308916, with extremely short internodes and resulting upright position of young fruit, also exhibited reduced disease. Fruit of PI308916 were susceptible when inoculated with P. capsici, indicating that reduced infection likely resulted from decreased soil contact. The compact trait is inherited as a single recessive gene, cp. Like many architectural traits, cp may be pleiotropic; PI308916-derived breeding lines were reported to have poor seedling emergence. PI308916 exhibited inconsistent apical hook formation that co-segregated with short internodes in F₂ and backcross generations, and disorganized internodal cortical cell arrangement. The combined phenotypes suggest either pleiotropy or very tight linkage of genes affecting hormone balance or cell division. The narrow chromosome region recently defined by QTL analysis includes candidate gene homologs of meristem related genes modulating cell division or spacing of lateral shoot organs and genes associated with brassinosteroid signaling or cytokinin content.     

The role of Mycoplasma strain F38 in contagious caprine pleuropneumonia (CCCP) in Kenya

The results of a serological and cultural study of experimental and field cases of contagious caprine pleuropneumonia were consistent with an aetiological role for mycoplasma strain F38. This mycoplasma was isolated from 57 acute cases in 46 outbreaks of CCPP and from 87 experimental contact cases. Clinical data from experimental contact cases were assessed for comparison with field cases.     

The effect of high passage mycoplasma strain F38 on the course of contagious caprine pleuropneumonia (CCPP)

Summary In comparison with an equal number of untreated controls, goats inoculated with high passage culture of mycoplasma strain F38 were significantly less susceptible to contact infection from CCPP cases.

---

Efecto De Un Pasaje Alto De La Cepa De Micoplasma F 38 En El Curso De La Pleuroneumonia Contagiosa Caprina

Resumen En comparación con un número igual de controles sin tratar, cabras inoculadas con un pasaje alto de Micoplasma Cepa F 38 fueron significativamente menos susceptibles al contacto con animales enfermos.

---

L'effet De La Souche De Mycoplasme F38 A Grand Nombre De Passages, Sur L'evolution De La Pleuropneumonie Contagieuse Caprine (CCPP)

Résumé Par comparaison avec un nombre égal d'animaux témoins non vaccinés, les chèvres inoculées avec cette souche sont significativement moins sensibles à l'infection transmise par contact avec des animaux atteints de maladie naturelle.

     

A mycoplasma from acute contagious caprine pleuropneumonia in Kenya

Summary A mycoplasma was isolated from acute caprine pleuropneumonia in Kenya. The organism could be differentiated serologically from the known strains of mycoplasma with which it was compared. When the organism was inoculated into goats it caused pleuropneumonia which was readily contagious, and from which the organism could be reisolated.

---

Resumen Se aisló un micoplasma de casos agudos de pleuroneumonia caprina en Kenia. Los organismos se diferenciaron serologicamente de otras cepas conocidas de micoplasma con las cuales se compararon. Cuando los organismos se inocularon en cabras, la enfermedad se reprodujo y el organismo causal pudo aislarse nuevamente de los casos clínicos.

---

Résumé Un mycoplasme a été isolé d'un cas de pleuropneumonie aigu? de la chèvre au Kenya. Ce germe a pu être différencié sérologiquement des souches connues auxquelles il a été comparé. Lorsqu'il est inoculé à des chèvres saines, il provoque une pleuropneumonie réellement contagieuse et est réisolé à partir des lésions.

     

Low genetic diversity and strong geographic structure in introduced populations of the Eucalyptus foliar pathogen Teratosphaeria destructans

The aggressive Eucalyptus leaf pathogen, Teratosphaeria destructans, causes widespread damage in tropical and subtropical Eucalyptus-growing regions of Indonesia, China, Thailand, East Timor, Vietnam, Lao, and South Africa. Little is known regarding the origin, pathways of dispersal, or reproductive biology of this pathogen. The aim of this study was to investigate the genetic structure of a global collection of T. destructans isolates. This was achieved by developing and using polymorphic microsatellite markers. Low genotypic diversity and a limited number of private alleles were found in all investigated populations, with the highest maximum diversity of 10.7% in isolates from South Sumatra. This supports the hypothesis that T. destructans was introduced to these regions. High levels of clonality were common in all populations, especially in isolates sampled from the recent disease outbreak in South Africa, which were all identical. The global collection of isolates grouped into three distinct clusters, corresponding largely to their sampled regions. Low levels of genotypic diversity, high levels of clonality, and strong geographic structure suggest independent introductions into all the sampled areas from an unknown source. The results imply that strict biosecurity measures are needed to avoid introductions of additional genotypes in these areas.     

Genomic characterization of mating type loci and mating type distribution in two apparently asexual plantation tree pathogens

The Eucalyptus stem canker pathogens Teratosphaeria gauchensis and T. zuluensis (Capnodiales, Teratosphaeriaceae) are found in many tropical regions of the world where their hosts are cultivated for plantation forestry. Population genetic analyses have suggested that some populations undergo recombination, even though their sexual states have never been observed. Against this background, the aim of this study was to characterize the mating type (MAT) locus of these species and thus to better understand the basis of their diversity. Known Mycosphaerellaceae MAT genes were used to identify and investigate the MAT locus in the T. gauchensis and T. zuluensis genomes. Both species were found to be heterothallic and primers were designed to amplify the opposite MAT idiomorphs as well as conserved regions within the MAT1-1-1 and MAT1-2-1 genes. Each Teratosphaeria MAT idiomorph was defined by either the MAT1-1-1 or the MAT1-2-1 gene, and an idiomorph-specific hypothetical protein (MAT1-1-10 and MAT1-2-12). Populations of T. zuluensis from Asia and southern Africa were dominated by a single mating type, whereas the proportions of the different idiomorphs for T. gauchensis in South America and southern Africa were similar. There was no physical evidence of sexual reproduction for either species and it is argued that although recombination may be possible, it is unlikely to form an important part of their life cycles in diseased Eucalyptus plantations. Instead, continuous human-mediated multiple introductions of these species have probably resulted in the current genetic structure of their populations, which holds risk for future disease outbreaks and interspecific hybridization.