Variation in the response of melon genotypes to sudden wilt

Summary Differences in the response of melon genotypes to the sudden wilt disease were observed in several field trials conducted during 1993–1994 in the Arava region of southern Israel. Generally, the disease was more severe in the late summer growing season which is shorter and has higher temperatures than the spring and autumn growing seasons. The Oriental pickling melon breeding line P6a was the most tolerant among the entries tested. The response to the disease was also studied using two segregating families and their progenitors. BSK (tolerant) × P202 (susceptible) and P6a (tolerant) × D17 (susceptible). Wilting percentages of F₁, F₂ and backcross families were intermediate between the parents, suggesting an additive mode of gene action.     

In vitro andin vivo evaluation of fungicides for control ofStemphylium botryosum F.lactucae on lettuce leaves

Maneb was the most efficient chemical in inhibiting germination ofStemphylium botryosum f. lactucae sporesin vitro. At 0.1 ppm it inhibited germination of all spores in the original population. Growth on PDA was markedly inhibited by 100 ppm daconil or maneb, withca. 90-95% spore mortality. The inhibitory effects of chemicals at sublethal doses on the rate of colony growth resulted both in retarded radial growth and in prolonged incubation period in culture. Maneb at 100 ppm and daconil at 10⁴ ppm had an inhibitory effect on inoculated leaf discs only when applied immediately after inoculation, whereas sodium dimethyldithiocarbamate (SDMC) inhibited fungal development at 10⁴ ppm both immediately after inoculation and 24 h later. SDMC kept the tissue very fresh during the experimental period. Fungal development in inoculated lettuce heads was prevented by 10³ ppm maneb or SDMC when applied before inoculation, but not when applied 24 h after inoculation, although inin vitro tests germinating spores were more sensitive to maneb than non-germinating ones.     

Finite element modeling of the cyclic wetting mechanism in the active part of wheat awns

Many plant tissues and organs are capable of moving due to changes in the humidity of the environment, such as the opening of the seed capsule of the ice plant and the opening of the pine cone. These are fascinating examples for the materials engineer, as these tissues are non-living and move solely through the differential swelling of anisotropic tissues and in principle may serve as examples for the bio-inspired design of artificial actuators. In this paper, we model the microstructure of the wild wheat awn (Triticum turgidum ssp. dicoccoides) by finite elements, especially focusing on the specific microscopic features of the active part of the awn. Based on earlier experimental findings, cell walls are modeled as multilayered cylindrical tubes with alternating cellulose fiber orientation in successive layers. It is shown that swelling upon hydration of this system leads to the formation of gaps between the layers, which could act as valves, thus enabling the entry of water into the cell wall. This supports the hypothesis that this plywood-like arrangement of cellulose fibrils enhances the effect of ambient humidity by accelerated water or vapor diffusion along the gaps. The finite element model shows that a certain distribution of axially and tangentially oriented fibers is necessary to generate sufficient tensile stresses within the cell wall to open nanometer-sized gaps between cell wall layers.     

The advantage of tbz + iprodione treatment for control of gray mold decay of celery caused by the heterogenic spore population ofBotrytis cinerea in Israel

A combined TBZ — iprodione treatment was more effective in inhibiting growthin vitro ofBotrytis cinerea isolates obtained from decayed celery than either of the fungicides applied separately. This was exhibited for both TBZ-resistant and TBZ-sensitive isolates. TBZ at 500 (μg ml^-1 plus iprodione at 1000 μg ml^-1 reduced celery decay beyond the reduction obtained by each fungicide alone. When applied prior to inoculation, the combined treatment prevented decay by the TBZ-sensitive/iprodione-resistant isolates and reduced initial decay by the TBZ-resistant/iprodione-sensitive isolates to 3–10% of the level without treatment. Under natural infection conditions iprodione showed better decay control than TBZ, and at 1500 μg ml^-1 it reduced initial decay during prolonged storage to 3% of the no-treatment level. Although TBZ (500 μg ml^-1) or iprodione (1000 μg ml^-1) applied separately reduced decay significantly, the combination of lower concentrations of each fungicide was sufficient to eliminate decay development almost totally. The combined treatment also inhibited decay bySclerotinia sclerotiorum, which contributed 3% of the total soft rot in stored celery.     

A survey of mold flora and of the mycotoxin deoxynivalenol in corn imported to ISRAEL

Shipments of corn imported to Israel from the U.S.A. during 1985 were sampled during unloading and examined for the presence of fungi and the trichothecene deoxynivalenol (DON). The most frequent species found on the corn wasAspergillus flavus followed byA. versicolor; three otherAspergilli — A. niger, A. ochraceus andA. fumigatus — were found at a much lower frequency. DON analysis was performed by electron capture detection gas chromatography after derivatization with heptafluorobutyryl imidazole. At fortification levels of 0.1, 1 and 2 μg/g, recoveries of 80—100% were obtained. Although DON was not detected in any of the samples analyzed, the observation (in the shipments) of fungi belonging to the generaFusarium andAspergillus suggests a potential danger of mycotoxin contamination. The relatively high moisture content of the samples increased the likelihood of such a hazard.     

PH—Postharvest Technology: Airflow induced by Falling Cottonseed Particles

Bulk materials falling freely in a chute draw air with them. Experiments were carried out to study the parameters that influence the induced airflow. The bulk material consisted of fuzzy and delinted cottonseeds and hulls. The experimental equipment included a loading, open hopper and an unloading enclosure connected to a chute. An orifice flowmeter was provided in the enclosure wall. The air drawn into the enclosure left it through the flowmeter orifice. The parameters varied during the experiments were the kind and the flow rate of falling particles, and the length, cross-section and slope of the chute. The measured data showed that the airflow rate grows with increasing chute length, cross-section or slope. The airflow rate also increased with the fuzziness of the cottonseed and decreased as the particles' terminal velocity increased. Dimensional analysis was used to formulate an approximate form of the law governing the process. It was found that the terminal velocity of the falling particles characterizes well their aerodynamic properties. Graphs plotted in accordance with the law developed in this work compared favourably with most measured data.