Agriculture Reference
In-Depth Information
Lighting Procedure
Intensity . Provide high light intensities from both cool white luorescent tubes and incandescent bulbs.
Light intensity may be described in foot candles (f.c.), lux or umol m -2 S -1 . The following light conversion
factors can be used: lux x 0.0929 = f.c.; f.c. x 10.764 = lux; f.c. umol m -2 S -1 x 5,166 = f.c. Light of 3,100
f.c. or 600 umol m -2 S -1 from incandescent bulbs is acceptable for growth chamber testing. The use of lower
intensity light may result in inadequate anthocyanin development and, therefore, indistinct seedling pig-
mentation difference. Low light intensity can also affect plant height and internode length. High-pressure
sodium lighting is also used, especially in greenhouses. Soybean plants grown for photoperiod evaluation
for lowering should be grown only in luorescent light.
Photoperiod. A 24 h photoperiod (continuous light) should be used for wheat, oats, sorghum, corn,
ryegrass, lettuce, alfalfa, and soybean, except for the metribuzin and photoperiod tests. A 16 h photoperiod
(16 h of light followed by 8 h of dark) is required when evaluating the reaction of soybean seedlings to
metribuzin. Garden bean, kidney bean, and bentgrass samples should be grown under a 20 h photoperiod
(20 h of light followed by 4 h of dark). Sweetclover samples may be grown under either at 20 or 24 h pho-
toperiod. Berseem clover samples should be grown under a 12 h photoperiod (12 h of light followed by 12
h of dark). When testing the lowering response of soybean varieties, photoperiods of 13 1/2, 15 1/2, and 18
h may be used, depending on the maturity group of the varieties involved.
Temperatures
Samples of all species, except bentgrass and berseem clover, should be grown at 25°C. Cooler temperatures
usually encourage anthocyanin development. Therefore, if the light intensity is inadequate, the temperature
in the chamber can be lowered to compensate for the lower light intensity.
Table 9.3 summarizes the appropriate procedures for growth chamber tests of crops grown for varietal
identiication.
Evaluation of Seedlings and Plants
Alfalfa plants can be evaluated for lower color (purple, variegated or yellow) (Fig. 9.18) and the number of
days from planting until lowering. This procedure can be used to differentiate varieties and detect off-type
plants. Five weeks are required to complete this test (AOSA, 2010).
Figure 9.18. Purple, variegated and yellow alfalfa lowers.
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