No description available.

No description available.

Zoospore production of Pythium dissotocum Drechs. in the nutrient solution of hydroponically-grown lettuce, in the greenhouse, was shown to be cyclic. The number of zoospores detected in the nutrient solution was lowest around noontime, (11:00-14:00 hr) and highest around 20:00 hr. Growth chamber studies were conducted to determine the effect of different light periods on zoospore production. Under continuous light or continuous darkness, the population of zoospores in the nutrient solution decreased. But under 12 hours light, and 12 hours darkness or two periods of light each for 3 hours, zoospore populations decreased during the light period but increased during the dark period.

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This work encompasses studies on the development of biocontrol strategies to manage the disease lettuce drop, caused by the fungi Sclerotinia sclerotiorum and S. minor, using the mycoparasitic fungus Coniothyrium minitans, and to better understand interactions during mycoparasitism at the biochemical level. Results from field experiments revealed that two applications of C. minitans at manufacturer recommended rates significantly reduced the incidence of lettuce drop caused by S. sclerotiorum but not by S. minor. Applications of other biocontrol products tested did not significantly reduce disease incidence caused by either pathogen. Sclerotium population studies revealed that soil populations of S. sclerotiorum in lettuce production fields ranged from 0.08 to 2.9 sclerotia/100g of soil and were generally aggregated in their distribution. Continued field studies revealed that there was no significant effect of irrigation (sprinkler vs furrow) on either the impact of sclerotium density or the efficacy of C. minitans. Studies on the evaluation of different application rates of Contans against S. minor revealed that two applications of Contans at 5 X manufactures recommended rates significantly reduced the disease incidence. Examination of sclerotial exudates of Sclerotinia spp. revealed that crude exudates from both Sclerotinia spp. stimulated C. minitans spore germination and the stimulation was due to compounds within the polar fraction. Studies on the role of lectin-carbohydrate binding during fungal-mycoparasite interactions revealed that many plant lectins as well as crude proteins extracted from sclerotia of either Sclerotinia spp. induced agglutination of C. minitans spores in vitro. Spore germination of C. minitans stimulated by sclerotial exudates of either Sclerotinia spp. was significantly inhibited in the presence of the lectin Con A but not other plant lectins. In vitro studies on the directional growth of C. minitans preceding mycoparasitism revealed the involvement of G proteins for optimal response of C. minitans toward Sclerotinia stimulus.

This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

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More vegetable seeds are needed for developing countries to produce more vegetables. However, high temperature in these areas limits vegetable seed production. Leaf lettuce (Lactuca sativa L.) was grown in growth chambers at 21°C and exposed to different temperatures (28, 35, 38 and 42°C) for different exposure times (1, 4 and 7 hours) when flowers were at seven stages of development near anthesis.

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Plant growth promoters (PGP) are microorganisms essential for sustainable food production systems by improving the productivity of crops and mitigating environmental impacts. Microorganisms enhance the P availability to plants by mineralizing organic P and solubilizing precipitated phosphates. This work is focused on the effect of inoculation of a commercial product containing a mixture of Bacillus spp. on hydroponically grown lettuce (Lactuca sativa) integrated with tilapia (Orechromis niloticus) aquaculture in a closed-loop system, in comparison with an untreated control. We determined plant growth and crop quality parameters to assess the efficacy of the beneficial microorganisms. A nutrient dynamics analysis was conducted to evaluate the effect of Bacillus inoculation on the changes of nutrient concentration in aquaponics solutions, as well as the phosphorus accumulation in several components (fish, plants, water and solids). We performed a plate-count assay to quantify the number microorganisms present in systems inoculated or not with the commercial Bacillus mixture. In general, nutrient dynamics was affected by the inclusion of the Bacillus mixture in the water. Systems that received the product showed faster decreases in ammonia concentration and faster increase in nitrite and nitrate concentrations than the control. The untreated aquaponics systems showed lower accumulation of phosphorus in the water than systems receiving the Bacillus mixture, which resulted in poor plant growth, low phosphorus accumulation in the leaves and low chlorophyll content. However, the mass balance analysis showed that an external source of phosphorus possibly contributed to the overall P budget in systems receiving the Bacillus mixture. The microbial plate count assay demonstrated an active microbiota in aquaponics systems receiving the treatment while untreated systems showed zero microbial counts. The Bacillus mixture used in the present study appears to have PGP properties and to affect P dynamics in aquaponics systems. However, since the product contained traces of phosphorus in its composition, further analysis will be necessary to distinguish whether the advantageous effects promoted by the Bacillus occurred as a result of a beneficial microbial activity or a fertilizing effect. (C) 2016 Elsevier B.V. All rights reserved.