Prediction of codling moth egg hatch in Germany and Italy using the Californian forecasting model Bugoff21

The effectiveness of the Californian model Bugoff2 for Cydia pomonella was tested in Germany (4 years) and Italy (2 years), the Italian results confirming the German findings. In the first codling moth generation (air temperatures normally below 30 C) good agreement was found between field observations of egg hatching and the model's forecast. However, the model gave notable differences for the second generation, i.e. 3 weeks in Germany and 1 week in Italy, and a significant difference for the third generation in Italy. These divergencies arise from an overestimation of the development rate of the codling moth in Bugoff 2's heat unit table whenever air temperature exceeds the upper limit for development. As a result of modifications to Bugoff 2, an example of a better simulation of the codling moth egg hatch in Germany and Italy is discussed.     

Detection of potato virus Y in early-harvested potato tubers by cDNA hybridization and three modifications of ELISA1

The standard ELISA method for detection of PVY in dormant potato tubers was compared with recently developed methods: (1) a hybridization technique, using a complementary DNA-probe to PVY^N; (2) three modifications of ELISA (standard monoclonal, Flegg & Clark polyclonal or monoclonal). Sap of six Dutch cultivars secondarily infected with PVY was subjected to these methods directly after lifting and after six subsequent one-week intervals during storage at 20°C. During storage the detectability of PVY decreased, irrespective of the diagnostic method applied. However, decrease was less in susceptible than in resistant cultivars. Although the hybridization technique yielded slightly better results than the standard ELISA procedure, it was time-consuming and involved hazardous reagents. The modifications of ELISA investigated were not, in general, more sensitive than standard ELISA.     

Dietary fat supplementation effects on in vitro nutrient disappearance and in vivo nutrient intake and total tract digestibility by horses

Addition of fat to the diet of the equine is a popular method of increasing energy density of the diet while reducing feed intake. Reducing feed intake is of interest to race horse trainers because additional feed is seen as additional weight and, therefore, a hindrance to performance. Limited information is available regarding the interactions of fat with other dietary components, particularly fiber, in the equine digestive system. The effect of dietary fat on in vitro nutrient disappearance in equine cecal fluid was studied in Exp. 1 using a split-plot design within a 2 x 2 Latin square. Two ponies were fed alfalfa (ALF) alone or alfalfa plus 100 g/d corn oil. Five substrates were used to determine in vitro DM disappearance, OM disappearance, NDF disappearance, and total dietary fiber (TDF) disappearance. The substrates included: ALF, tall fescue (TF), red clover (RC), soybean hulls (SBH), and rolled oats (RO). Fat supplementation did not affect in vitro DM, OM, or NDF disappearance. Addition of fat to the diet increased (P < 0.05) the disappearance of NDF in RO. Among substrates, in vitro DM and OM disappearance were highest (P < 0.05) for RO, followed by SBH, ALF, RC, and TF. In vitro NDF and TDF disappearance were highest (P < 0.05) for SBH, followed by RO, ALF, RC, and TF. In Exp. 2, the effects of varying levels of fat on nutrient intake and total tract digestibility were examined using a 4 x 4 Latin square design. Four mature mares were fed a 60% forage-40% concentrate diet containing different concentrations of fat: 0% supplemental fat control (C); 5% supplemental corn oil (5% CO); 10% supplemental corn oil (10% CO); or 15% supplemental corn oil (15% CO). Treatment did not affect intake of the concentrate portion of the diet or CP, gross energy, or NDF intake. Mares consuming the C diet had the highest (P < 0.05) intake of alfalfa cubes, DM, and OM, followed by those on the 10, 5, and 15% CO treatments, respectively. Treatment did not affect nutrient digestibility. Mares consuming the 15% CO diet had the highest (P < 0.05) fat digestibility, whereas those consuming C had the lowest fat digestibility. Fat in the form of CO generally had little effect on in vitro and in vivo nutrient digestibilities in horses.     

Pathogenic and Nonpathogenic Lifestyles in Colletotrichum acutatum from Strawberry and Other Plants

ABSTRACT Anthracnose is one of the major fungal diseases of strawberry occurring worldwide. In Israel, the disease is caused primarily by the species Colletotrichum acutatum. The pathogen causes black spot on fruit, root necrosis, and crown rot resulting in mortality of transplants in the field. The host range and specificity of C. acutatum from strawberry was examined on pepper, eggplant, tomato, bean, and strawberry under greenhouse conditions. The fungus was recovered from all plant species over a 3-month period but caused disease symptoms only on strawberry. Epiphytic and endophytic (colonization) fungal growth in the different plant species was confirmed by reisolation from leaf tissues and by polymerase chain reaction (PCR)-specific primer amplification. C. acutatum was also isolated from healthy looking, asymptomatic plants of the weed genera Vicia and Conyza. Isolates that were recovered from the weeds caused disease symptoms on strawberry and were positively identified as C. acutatum by PCR. The habitation of a large number of plant species, including weeds, by C. acutatum suggests that, although it causes disease only on strawberry and anemone in Israel, this fungus can persist on many other plant species. Therefore, plants that are not considered hosts of C. acutatum may serve as a potential inoculum source for strawberry infection and permit survival of the pathogen between seasons.     

Induced resistance in host mixtures and its effect on disease control in computer-simulated epidemics

The epidemic simulator EPIMUL was modified and used to study how induced resistance affected the development of epidemics in host mixtures. In the model, induced resistance resulted from the interaction of host tissue with avirulent spores and caused a reduction in the efficacy of virulent spores deposited afterwards. We denned three parameters to describe induced resistance: the level of protection, defined as the magnitude of reduction in the virulent spore efficacy for infecting host tissue; the host surface area protected by an interaction with one avirulent spore; and the duration of protection of the host tissue, in days. In our simulations, induced resistance slowed the epidemics and gave better disease control in the mixtures, even if protection lasted for only 2 days. The disease reduction in the mixture attributable to induced resistance was approximately proportional to the level of protection. The effect of induced resistance increased as the protected area increased. Epidemics were virtually unaffected by induced resistance restricted to the infection site, but the effect of induced resistance initially increased rapidly as larger areas were protected. There was little further gain as the protected area increased from 2·6% to 26%. The influence of induced resistance was reduced when the interactions between virulent and avirulent pathogens were reduced.     

Biological control of Fusarium oxysporum f. sp. lycopersici

Fungi known to produce lytic enzymes were used in an attempt to control wilt of tomato caused by Fusarium oxysporum f. sp. lycopersici (FOL). Some of the fungal species (Penicillium oxalicum, Penicillium purpurogenum and Aspergillus nidulans) damaged hyphae of FOL in vitro and reduced the numbers of microconidia in the soil. Treatments with fungi did not result in a reduction in either chlamydospores of FOL in soil or populations of FOL in the rhizosphere of tomato. P. oxalicum was the most effective agent of biocontrol, and it reduced disease severity in both non-autoclaved (20% decrease) and sterile soil. In sterile soil, P. oxalicum reduced disease with different levels of severity (27% decrease at high levels and 50% decrease at low levels). Disease control by A. nidulans and P purpurogenum was only achieved when disease severity was low in sterile soil (55% and 45%, respectively).     

Windborne spread of ergot disease (Claviceps africana) in sorghum A-lines in Zimbabwe

Ergot disease spread rapidly in Zimbabwe amongst replicated plots of male-sterile sorghum A-lines, from a group of centrally situated and precociously inoculated plants. Prominent secondary conidiation by the pathogen, Claviceps africana , on the surface of exuded honeydew provided airborne spores which were trapped in a Burkard continuous spore trap and showed diurnal peaks of concentration in air close to the primary source of inoculum. The rate of disease spread ( r =0·2; range 0·14–0·58) closely matched that recorded for other plant pathogens such as Phytophthora infestans and Puccinia graminis tritici , and it is concluded that the characteristic secondary conidia of C. africana were the principal epidemiological agents within the experimental area. Ergot spread by windborne secondary conidia has significant epidemiological and economic implications for sorghum hybrid breeding in southern Africa.     

Racial diversity and complexity in regional populations of Erysiphe graminis f.sp. hordei in France over a 5-year period

The evolution of race patterns in three French regional populations of the barley powdery mildew pathogen Erysiphe graminis f.sp. hordei over a 5-year period showed rapid adaptation to newly introduced host resistance genes. In all three regions, the main change consisted of the replacement of initially abundant races by pathotypes differing markedly from them by their virulence gene combinations. This explained the increase in diversity during the first 3 years of the survey, when the second group of pathotypes became more common in the populations, and its subsequent decrease due to the decline of the first group of races. The mean number of virulence genes per isolate did not vary noticeably over time in the three populations, remaining at about four out of 12 genes tested. However, the distribution of the isolates into virulence complexity classes was greatly modified, fitting a binomial distribution by the end of the study, although significant deviations were apparent in the first 2 years (1986 and 1987). The data indicate that selection, migration and recombination are the most important factors shaping race structure and evolution in powdery mildew populations, and that mutation is of limited significance. No convincing evidence was obtained for the existence of stabilizing selection sensu Vanderplank as the mechanism limiting virulence complexity. Implications regarding spatial and temporal deployment of race-specific resistance genes to control powdery mildew are discussed.