Dispersal of conidia of Fusicladium eriobotryae and spatial patterns of scab in loquat orchards in Spain

Dispersal of conidia of Fusicladium eriobotryae, the causal agent of loquat scab, was investigated in two loquat orchards in Spain from 2010 to 2012. A volumetric spore sampler, horizontally and vertically orientated microscope slides, and rain collectors were placed in loquat fields to trap conidia of F. eriobotryae. No conidia were collected in the volumetric sampler, and highly variable numbers of conidia were collected in the rain gatherers. Large numbers of conidia were collected by microscope slides, particularly by those held in a horizontal orientation compared with those held in a vertical orientation. Approximately 90 % of the F. eriobotryae conidia were collected during rainy periods. Based on ROC and Bayesian analysis, using ≥ 0.2 mm rainfall as a cut-off value resulted in a high probability of correctly predicting actual conidial dispersal, and had a low probability of failing to predict actual conidial dispersal. Based on the index of dispersion and the binary power law, the incidence of loquat scab on fruit was highly aggregated in space between and within trees, and aggregation was influenced by disease incidence. Our results demonstrate, for the first time, that F. eriobotryae is dispersed mainly in rain splash. The results will be integrated into a mechanistic, weather-driven, disease prediction model that should help growers to minimize fungicide application for the management of loquat scab.     

Study of Resistance to Orobanche ramosa in Host (Oilseed Rape and Carrot) and Non-host (Maize) Plants

Orobanche ramosa is a parasitic Angiosperm responsible for severe yield losses in several economical crops. It is a serious threat in oilseed rape in France and Morocco and is appearing in carrot crops in Morocco. In this study, several varieties of oilseed rape and carrot were screened in order to identify resistant cultivars and to characterize the resistance mechanisms involved. All the 15 oilseed rape varieties tested were susceptible. In carrot, the varieties 'Colmar à coeur rouge' and 'Nantaise demi-longue' were susceptible, whereas 'Palaiseau' and 'Buror' were resistant. In the susceptible 'Colmar à coeur rouge' carrot no defence reactions were found and the development of the parasite inhibited carrot tap root formation. In the resistant carrot varieties, the parasite germinated, became attached to the host root but became necrotic before emergence. In 'Buror' carrot, formation of a mechanical barrier was associated with the restriction to the cortex of the parasite. In maize cv. 'Vigni', a non-host of O. ramosa, thickening of xylem vessels, cell divisions in the central cylinder and formation of an encapsulation layer were observed in association with restricted development of Orobanche haustoria.     

Pathogenicity of plant and soil isolates of <Emphasis Type="Italic">Phytophthora parasitica</Emphasis> on tomato and pepper

Crown and root rot of tomato and sweet pepper can be caused by Phytophthora parasitica. In this work, 23 P. parasitica isolates from diseased pepper or tomato plants as well as 54 isolates from 23 monocrop tomato soils (from Spain and Chile) and one from a pepper soil were studied for their host–pathogen response. Results show significant host specificity for the isolates from tomato plants and tomato soils (63 of 64 isolates were unable to cause disease in pepper). None of the pepper plant/soil isolates showed pathogenicity on tomato, and only four of 14 reproduced their pathogenicity on pepper. Only one tomato isolate was pathogenic to both Solanaceae species. Two different inoculation protocols were evaluated (substrate irrigation and stem cutting). All isolates which expressed pathogenicity when stem inoculated also did it when root inoculated, but not vice-versa. Therefore, the recommended test protocol for tomato and pepper breeding programmes is that based on root inoculation by irrigation.     

Unravelling the relationship between a seasonal environment and the dynamics of forage growth in grazed swards

It is well reported in the scientific literature that pastures can have similar net forage accumulation when managed with contrasting structures. However, we hypothesized that the dynamics of forage accumulation in grazed swards is linked to seasonal-environmental conditions. Marandu palisadegrass (Brachiaria brizantha [Hochst. ex A. Rich.] was used as the forage species model. The experimental treatments were four grazing heights (10, 20, 30 and 40 cm) allocated to experimental units according to a randomized complete block design with four replicates and evaluated throughout four contrasting environmental seasons (summer, autumn, winter–early spring and late spring). Under rainy and warm periods, greater net forage accumulation was observed in pastures maintained taller; on the contrary, during the mild and dry periods, net forage accumulation rate reduced as grazing height increased. Such patterns of responses were related to compensations between tiller population density and tissues flows during summer and late spring and the reduced capacity of taller canopies to compensate lower population with greater growth rates during autumn and winter–early spring. Grazed swards changed their patterns of forage growth as they transitioned from favourable to more abiotic stressful conditions, suggesting that seasonal adjustments in grazing intensities are necessary in order to maximize forage production.     

Oxygen-18 enrichment of planktonic foraminifera due to gametogenic calcification below the euphotic zone

Empty shells of spinose planktonic foraminifera on the seabed are significantly enriched in oxygen-18 as compared with the shells of their living counterparts in surface waters. This enrichment is due to gametogenic calcification, which extracts calcium carbonate from deeper and colder waters as the shell sinks below the euphotic zone. JEAN-CLAUDE DUPLESSY.     

Genetic variability and heterotic groups of Brazilian popcorn populations

The development of successful advanced lines and cultivars in maize is dependent on parental selection and assignment to defined heterotic groups. So, the objectives of this study were to evaluate genetic variability and identify heterotic groups among Brazilian popcorn varieties. Thus, diallel crosses of advanced generations of the popcorn hybrids, IAC 112 and Zélia, and of three open-pollinated popcorn varieties, RS 20, Branco, and SAM were performed. Ten hybrid combinations, the five parents, and five check treatments were arranged in a block design with four replicates in two tropical-zone locations (CWb climate). Both additive and non-additive effects were important for grain yield, plant height, ear height, and husk cover. For popping expansion, only the additive effects were important. Hybrid combinations between the local variety (Branco) and F₂ populations (IAC 112 and Zelia) resulted in the third and fourth highest values for popping expansion. The best grain yields were obtained with hybrid combinations involving SAM. Cultivars Zélia, IAC 112, and RS 20 increased popping expansion, whereas cultivar Branco increased grain yield of hybrid combinations. The following conclusions may be drawn: Brazilian popcorn populations have reduced heterosis and genetic variability to popping expansion in relation commercial cultivars; there is genetic variability among Brazilian popcorn populations that allows the exploitation of additive and non-additive effects for grain yield; it is possible to increase grain yield by using local varieties; but it would be difficult to obtain commercial hybrids from local varieties because they have poor performance for popping expansion.     

Sclerotinia resistance in sunflower: I. Genotypic variations of hybrids in three environments of Argentina

Sclerotinia sclerotiorum infections on sunflower capitula produce white rot, one of the most dangerous diseases sunflower bears in all humid areas. Therefore, disease quantification on developed genetic materials is a very important action in sunflower breeding. Given the horizontal type of resistance these evaluations should be made in different environments. Several hybrids obtained after crossing seven female × seven male sunflower inbred lines in a factorial mating design were evaluated for resistance to white rot in two locations in the southeast of the province of Buenos Aires, Argentina. Disease incidence and the symptom appearance index indicated significant genotypic effects and genotype × environment (G × E) interactions. Genotypic effects were a greater source of variance than the G × E interaction effects. The G × E interactions only represented changes in magnitude. These results were used to identify the best genotypes for both resistance factors. Four hybrids showed low disease incidence values under both artificial and natural infections, of which only two had high values of the symptom appearance index at both locations. These hybrids are considered to have adequate resistance attributes for the ascosporic penetration and the mycelium extension in the capitulum tissue and could therefore be sown in the province of Buenos Aires without increasing risks of S. sclerotiorum attacks.     

Influence of fertilization on acrylamide formation during frying of potatoes harvested in 2003

The quality of the potato has been found to vary, when grown under different agricultural and environmental conditions, such as the level of fertilization. Consequently these factors may influence the acrylamide formation during the preparation of French fries. These assumptions were studied on three varieties: Bintje, Ramos, and Saturna from the harvest of 2003. Decreasing N fertilization caused increases in the reducing sugar concentration from 60% up to 100% on DM for all varieties studied. Due to a high correlation between the reducing sugar content and the generation of acrylamide during frying, this resulted in a parallel increase in the acrylamide concentration of the French fries. Thus by lowering the amount of N fertilizer, an increase of 30-65% of the acrylamide generation during frying could be observed. It seems of extreme importance to find an appropriate balance between the level of N fertilizer in order to diminish acrylamide formation but on the other hand to obtain an acceptable tuber and to consider the environmental impact. All results reported should be seen in the perspective of the warm growing season of 2003.     

Quantitation of selected odor-active constituents in dry fermented sausages prepared with different curing salts

The odor-active compounds of dry-fermented sausages with added nitrite or nitrate as curing agents were identified by gas chromatography-olfactometry (GC-O) applying the detection frequency (DF) method. The quantification of these compounds in the sausage was determined by multiple headspace solid-phase microextraction (multiple HS-SPME). There were no specific odor-active compounds related to the use of nitrite or nitrate although there were differences in the DF value of several compounds. The nitrite-added sausages presented higher DF values for ethanol, 1-hexanol, propanoic acid, 2-heptenal, and nonanal while the nitrate-added sausages had higher DF values for phenylacetaldehyde and 3-methyl-butanal. Eighteen compounds were quantified by multiple HS-SPME. Most of them were above their air detection thresholds, but only hexanal, heptanal, and 1-octen-3-ol were in a concentration higher than their oil threshold values. These compounds would probably be the main contributors to the aroma of fermented sausages.