Avena test

Several in vitro tests are suitable for the determination of the growth-regulating activity of hormone-type herbicides, among them the straight growth test of wheat or oat, and the pea curvature test. Both methods yield quantitative results of good reproducibility. The Avena test elaborated by Went cannot be used in this case, but the root growth inhibition test is suitable (Audus, 1949 1951). 

Moreover, when it appeared that the large difference of activity between the antipodes in the avena test (proportion for (+) and —) form = 30 1) was not found in the straight growth test, and most probably had to be ascribed to differences in basipetal transport, it seemed that the asymmetry had no importance for the primary activity itself. 

The slopes of the above equations are the same, indicating the same dependence of inhibition on the hydrophobic character of the drug. The intercepts are different, indicating greater sensitivity of the Avena test. These are arbitrary standards and it would be interesting to place both on the same basis to compare the intrinsic activity of the two classes of inhibitors. An equation similar to 10 was also found for the phenylacetic acids.While both sets of acids are toxic at high concentrations, at much lower concentrations they promote cell elongation. 

Various assay methods have been used to detect the presence of inhibitory substances. These include some of the classical tests used by investigators of growth-promoting substances—i.e., the various Avena coleoptile assays which utilize intact, decapitated, or isolated cylinders and the split pea stem test. Effects on seed germination and seedling shoot or root growth and development have also been measured in addition to other visible expressions of inhibition. Details of many of these tests have been compiled by Mitchell et al. (99). Tests have been carried out in Petri dishes, with various solution culture techniques, and by sand and soil culture. Effects so measured may or may not be similar to those obtained under field situations— i.e., the establishment of inhibition under controlled conditions pro-... 

Another limitation to the studies in Table 1 is the small number of plant species tested. Primarily monocotyledonous plants have been studied, although McClure et al. (26) found ferulic acid inhibitory in soybean. The restriction of studies to monocots is probably because the mechanism of mineral absorption has been more fully elucidated with monocots. Harper and Balke (32) reported some minor differences in the inhibition of K+ absorption by salicylic acid among oats (Avena sativa L.), wheat (Triticum aestlvum L.), barley, and maize roots. 

Fig. 12. Curvature responses of decapitated avena coleoptiles as a function of auxin concentration. (A) curvature obtained in 90min, auxin applied asymmetrically (standard auxin test). (B) curvature produced in 60 min by symmetrical application of auxin upon succeeding transverse electrical stimulation. Bending occurs towards the positive pole, as sketched187 ...

Dihydropyrenophorin, from Drechslera avenae, is a leaf pathogen of both wild and cultivated oats. It causes reddish brown lesions with a necrotic sunken center. At least one compound isolated from broth cultures of this fungus caused comparable lesions on oats and a variety of other plants at 3.2 x 10" M (15). The phytotoxin was characterized by spectrometric analyses and chemical conversion as (-)-dihydropyrenophorin (Vl), an important di lactone macrolide (15). However, the major product obtained in our extraction procedure used to isolate (-)-dihydropyrenophorin was the diol VII (j 6), which was not active in our bioassay tests. 

Biologically, the most interesting aspect of (-)-dihydropyrenophorin is that it causes reddish lesions on Johnson grass at 10 6 10 7, and 10"8 M wherein no other plant species tested shows any sensitivity whatever at these concentrations. Thus, it would appear that VI is host selective. To our knowledge Johnson grass is not a host of D. avenae. 

The antennal olfactory receptor system in several phytophagous insects is very sensitive in the detection of the green odour components. In the Colorado beetle Leptinotarsa decemlineata, the threshold of response for trans-2-hexen-1-ol is circa 10b molecules per ml of air (17). In comparison, at 760 mm Hg and 20 C, 1 ml of air contains about 1019 molecules. The insects tested i.e., the migratory locust Locusta migratoria, the carrot fly Psila rosae (18), the cereal aphid Sitobion avenae (19), the Colorado beetle L. decemlineata (17), Leptinotarsa... 

Maleic hydrazide (4) is not active in the Avena auxin test, and is inhibitory to growth, especially of grasses, at all measurable concentrations. 

The first plant bioassay [Avena sativa L (oat) coleoptile test] was employed by F.W. Went in the 1920 s to demonstrate the existence of and to quantitatively assess the first growth-modifying substance [indole-3-acetic acid (IAA)] isolated from plants.122 Plant bioassays have been extremely useful and intimately linked to the discovery and characterization of the major classes of plant hormones. In fact, many of the bioassays used now were developed for PGRs. Bioassays have been used to screen, evaluate phytotoxicity or plant growth promotion, study mode... 

Test organism Hordeum vulgare (barley), Latuca sativa (lettuce), Pancurn miliaceum (millet seeds), Lycopersicon esculentum (tomato), Cucumis sativus (cucumber), Glycine max (soybean), Brassica oleracea (cabbage), Avena sativa (oat), Lolium perenne (perennial ryegrass), Allium cepa (common onion), Daucus carota (carrot), Zea mays (corn). 

Inhibitor of Avena coleoptile sections and rice seedling test (297)... 

Biotypes with target-site-based resistance to ACCase inhibitors were also selected in wild oat species [Avena fatua, A. sterilis). The resistance patterns were found to be variable. For example, the resistance factors for ACCase from the Canadian A. fatua biotype UMl were 105 for sethoxydim, 10 for tralkoxydim, and 10 for didofop and fenoxaprop, whereas for the Aoena fatua biotype UM33 from Canada the ratios were 10.5 for fenoxaprop, 1.2 for diclofop, 5 for sethoxydim and 1.7 for tralkoxydim. It was proposed that this was due to different point mutations, each being assodated with a characteristic resistance pattern [37]. Another reason could be the frequency of homozygote and heterozygote resistant and susceptible plants within a tested population. 

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