R. Beltrán

Controle biológico de Monosporascus cannonballus com Chaetomium

Melon collapse caused by Monosporascus cannonballus is one of the main diseases that affect this cucurbit. The objective of this research was to study the biological control of M. cannonballus by Chaetomium. Infested substrates with 0.5, 1, 2, 4 and 8 x 105 CFU g-1 were introduced in plates where seeds of melon type Piel de Sapo cv. PS 1430 were sowed in seeding trays after two weeks of incubation. The seedlings were transplanted to pots with a similar substrate, infested additionally with 2.5 x 104 CFU of Chaetomium per gram and 20 CFU of M. cannonballus per gram of substrate. Three controls were considered: one infested with Chaetomium alone, another with M. cannonballus and one without any treatment. The experimental design was completely randomized with five replicates. General disease index and control percentage were evaluated forty-five days after transplant. The General disease index varied according to the increased Chaetomium concentration. The results demonstrated that 4 and 8 x 105 CFU of Chaetomium g-1 were equivalent to 0.9 and 0.6, respectively. The statistical analysis showed that 4 and 8 x 105 CFU g-1 of Chaetomium concentration were the most efficient treatments, with control percentage higher than 55 %, indicating the potential of Chaetomium to control M. cannonballus.

Comparative Epidemiology of Monosporascus Root Rot and Vine Decline in Muskmelon, Watermelon, and Grafted Watermelon Crops

Disease progression and soil population dynamics of Monosporascus cannonballus ascospores were studied and compared through the entire growing season in muskmelon, watermelon, and watermelon grafted onto Cucurbita rootstock crops. In muskmelon and watermelon, there was a decrease of ascospore counts in soil from transplanting until first symptoms of vine decline were observed. This decrease probably was related to ascospore germination and subsequent root infection. Later, there was a remarkable increase of ascospore counts in a parallel way to the quick development of vine decline symptoms, which lead to plant death. In these crops, root colonization adjusted to first-order linear equations and vine decline progression best correlated with exponential and logistic models. In contrast, there were no symptoms of vine decline on grafted watermelon. Furthermore, the isolation of M. cannonballus from Cucurbita roots was considerably lower, perithecia were never observed, and ascospore soil populations remained stable. These results suggest that disease control by grafting onto genus Cucurbita seems to be related primarily by the increased resistance of its root system to infection by M. canonballus, and provide further evidence of the use of grafting as a disease management measure for this disease.

Incidence of Verticillium wilt of artichoke in Eastern Spain and role of inoculum sources on crop infection.

Surveys of 94 artichoke fields throughout the artichoke production areas of Comunidad Valenciana (eastern Spain) were conducted from 1999 to 2002 to determine the incidence and distribution of Verticillium wilt.Verticillium dahliae was isolated from 80.9% of the sampled fields, and detected in all artichoke-growing areas, with a mean disease incidence of 53.8% infected plants. The disease was found to cause severe damage to cv. ‘Blanca de Tudela’, which is the most important artichoke cultivar grown in Spain, and was also observed on the seed-propagated cv. ‘Imperial Star’. In field trials to study the role of infected planting material and soil inoculum on infection of artichoke plants during the cropping season,V. dahliae was transmitted from infected stumps to the plants, confirming that the use of infected stumps could have greatly contributed to the dissemination of the pathogen. Inoculum density ofV. dahliae in soil had an effect on crop infection, in that a higher number of microsclerotia per gram of soil resulted in a higher percentage of infected plants. In addition, yield of cv. Blanca de Tudela was significantly affected byV. dahliae infection, showing that a higher percentage of infection corresponded with lower yield.

Effect of dsRNA on growth rate and reproductive potential of Monosporascus cannonballus

The effect of double stranded RNA (dsRNA) infection on growth rate and the reproductive potential of Monosporascus cannonballus was studied in 21 isolates collected in cucurbit growing areas of Spain and Tunisia. The isolates were incubated on potato dextrose agar (PDA) under different conditions of temperature, pH, and water potential (Ψ(s)). They showed optimal growth temperatures over the range of 27-34°C and perithecia formation was obtained mainly at 25 and 30°C, although some isolates were able to produce perithecia at 35°C. All isolates were able to produce perithecia in a broad range of pHs (4-8). Regarding the effect of Ψ(s,) the isolates were more tolerant to grow on KCl than on NaCl. For each solute, radial growth decreased progressively as Ψ(s) decreased and was severely limited at -5.0 to -6.0MPa. Perithecia formation was highest at -0.5MPa, decreased at -1.0MPa and occurred just in some isolates at -2.0MPa. Nine of the M. cannonballus isolates harboured dsRNA with 2-6 bands each and a size range of 1.9-18.0Kb. Phenotypical data were subjected to multivariate factorial analysis. Most of the isolates clustered in two groups corresponding with the presence/absence of dsRNA elements. Isolates without detectable dsRNA produced more perithecia. However, isolates with dsRNA produced lower number of perithecia depending on the pH, Ψ(s,) or solute used. These results improve our understanding of the behaviour and growth of this pathogen in soil, and can be useful to implement effective disease control.

Análisis de Distintos Tipos de Azúcares en el Método de Extracción de Ascosporas de Monosporascus cannonballus en Suelo

The objective of this work was to test different kinds of sugar for the extraction of ascospores of M. cannonballus. The ascospores of this ascomycete involved in melon (Cucumis melo) collapse can be recovered from soil by a physical method using a gradient of sucrose (50% concentration). The use of commercial sucrose represents a high cost per sample. This is the reason for research into a cheaper substitute sugar. In this work, we compared dextrose, commercial cane sugar and dessert sugar. Average ascospores/g of soil recovered with all these sugars were not statistically different, using the Tukey Test (P=0.05). The use of commercial cane sugar is recommended for its efficacy and low cost in every sample (R

Population Dynamics of Monosporascus cannonballus Ascospores in Marsh Soils in Eastern Spain

0.042).