Germination causes

Seedlings rot near soil line and fall over seeds do not germinate. Cause Damping-off. Keep soil moist, but not soggy. Thin seedlings and spray with compost tea as soon as first true leaves open to help prevent problems. 

Abscisic acid is a general plant-growth inhibitor. It induces dormancy and prevents seeds from germinating causes abscission of leaves, fruits, and flowers and causes stomata to close. High concentrations of abscisic acid in guard cells during periods of stress induced by drought probably have a role in stomatal closure. 

Encecalin (I) causes a dwarfing of lettuce shoots at concentrations from lOppm and up. On the other hand, eupatoriochromene (II) causes very little dwarfing of the seedling but does inhibit germination of lettuce at lOOppm and above. The concentration of these two chro-raenes in yellow starthistle may indeed allow for some effect to be exerted on the surrounding plant community. 

Effects of Sesquiterpene Lactones on Seed Germination. Sesquiterpene lactones are common constituents of the Asteraceae but are also found in other angiosperm families and in certain liverworts (31,32). These highly bitter substances exhibit a wide spectrum of biological activities (J 3) which include cytotoxicity, anti-tumor, anti-microbial, insecticidal (34) and molluscicidal (35) properties. Furthermore, they are known causes for livestock poisoning and contact dermatitis in humans (33). Structure-activity relationship studies on sesquiterpene lactones have demonstrated that biological activity frequently depend on the presence of the cr... 

The germination and growth of velvet leaf (Abutllon theophrastl Medic.), a weed causing severe problems in corn and soybean fields, is inhibited by tomentosin (28) and axivalin (29), two lactones isolated from seeds of povertyweed (Iva axillaris Pursh) (44). 

The activity in the aqueous extract was also effectively partitioned into a diethyl ether organic phase. At this step, relative inhibition increased compared to the methanol extract. The organic phase extract caused 96, 93, and 89% inhibition of C . album hypocotyl length, root length, and germination, respectively (data not shown). 

Table I. Comparison of soil samples with regard to total number of microorganisms isolated and the percentage of total causing severe toxicity (growth rating < 2 or germination < 75% of controls) to cucumber (Cucu), barnyard grass (Bygr), and cress...

Soil % causing growth rating s. 2 % reducing germination 75%... 

Many authors note that test conditions have a strong influence on results, and activity varies widely with a variation in concentration of the germination stimulant. A relatively high concentration of a stimulant often causes inhibition of germination. Preconditioning the seed in the presence of a germination stimulant can also cause inhibition of germination. 

The enzymes in wheat, and hence in flour, that often cause problems in the bakery are present in the seed to make nutrient available to the seed. Similarly, this is why sprouted wheat causes problems if it is allowed to get into flour. Thus, the a-amylase is low in mature wheat grains but rises rapidly on germination. In bread, a low, but not too low, level of a-amylase is desirable since it produces sugars to feed the yeast and opens up the structure. Deliberate additions of malt flour were once common, but are now rarely made, to increase the amylase level. 

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