on, 
9D 
EFFECTS OF STRESS, AND PUBESCENCE ON PLANT LEAF AND CANOPY 
REFLECTANCE! 
Harold W.Gausman, David E.Escobar, and Romeo R.Rodriguez, 
Plant Physiologist and Biological Technicians, respectively, 
USDA, ARS, Weslaco, Texas USA 
  
ABSTRACT: 
Nematode-stressed cotton (Gossypium hirsutum L.) had less reflec- 
tance than nonstressed plants over the 0.5- to 2.5-um waveband. 
Iron deficiency of grain sorghum (Sorghum bicolor (L.) Moench) 
and lead toxicity of Mexican squash plants (Cucurbita pepo L., 
cv Tatume) increased visible light reflectance at the 0.55- and 
0.65- um wavelengths, as compared with controls, because they 
reduced leaf chlorophyll contents. As severity of ozone (03) 
damage increased on cantaloupe (Cucumis melo L., var cantalu- 
pensis Naud., cv Perlita), leaf reflectance increased because of 
dehydration. Consequently, the 1.65- and 2.2-um wavelengths 
(highly sensitive to leaf water content) should be useful to 
detect O3-damaged plants. Frozen sour orange (Citrus aurantium 
Linn.) leaves had about 15 percentage points less near-infrared 
light (0.75 to 1.35 um) reflectance than nonfrozen leaves within 
5 h after the freeze treatment ended. Reflectance measurements 
were better than photographs for detecting early freeze damage. 
The hypodermis (water storage tissue) of succulent Peperomia's 
(Peperomia obtusifolia A.Dietr.) leaves was shown to be respon- 
sible for the lack of a reflectance peak centered at about the 
2.2-um wavelength. Sensor bands encompassing either the 1.6- or 
2.2-um wavelengths should be useful to distinguish succulent from 
nonsucculent plant species. Silverleaf sunflower's (Helianthus 
argophyllus Torr. and Gray) white dense pubescence greatly re- 
flected visible light, as compared with sparsely hairy common 
sunflower (Helianthus annus L.), but its absorptance in the 
near-infrared region was higher because of light entrapment in 
this waveband. In addition, color infrared photography showed 
that pubescent silverleaf sunflower plants had a characteristic 
"pinkish" response as compared with a darker magenta response 
of other plant species. 
Stressed leaves had a compact cellular arrangement in their meso- 
phyll; whereas, nonstressed leaves of the same chronological age 
had a spongy mesophyll. Compact leaves had lower infrared reflec- 
tance than spongy leaves. 
Chlorotic (iron deficient) grain sorghum areas 2.8 (1.1 ha) 
or larger, in otherwise homogeneous fields, were identified from 
LANDSAT-1 MSS5 data. 
  
  
  
  
  
  
  
1) Soil and Water Conservation Research, ARS, USDA, Weslaco, 
Texas. Studies reported on were supported in part by the 
National Aeronautics and Space Administration under Contract 
Nos. R-09-038-002 and S-70251-AG, Task 3.