Vergara - 1976 - Physiological and morphological adaptability of ri

402 euxiivrs AND RICE
ation periods favored sporulation. while light favored ctmidiophtire formation '.
and (3) sporulatioil could occur after two or more successive unfavorable dew
periods. The latter fact suggests that disease forecasting based on probable
sporulatitm periods would not be entirely accurate if it were predicted solely on
the occurrence of favorable periods.
Effect of relative humidity on sponilation
Race T of H. nraydis, susceptible Texas male-sterile hybrid P-A-C‘
15029‘. the
use of air stones. silica gel. and a calibrated flowmcter were the same as in a
spore release study The 45- >< 40- >< 40- cm sporulatiott box was made of7f8-inch
thick styrofoam and was located in the vestibule of an lSCO environmental
chamber. along with the air controls Air entered the box at about 6600 ml/min
at two points l2 cm above the base on one side and exited at the top, predominantly
on the opposite side. Relative humidity was monitored continuously
with a Hyfigro-djxnamics hygrosensor located among the plants at lesion height.
The sensor was calibrated against wet- and dry-bulb mercury’ thermometers. The
Rll dropped 2 to 5 % when plants were inserted in the box but recovery occurred
within 30 minutes. Thereafter. the RH deviated only i0.5%. Recorded
humidity tvas the average of values recorded at 0.5 hr intervals.
(ireenlitiuse-grtivan potted plants at the 4- or S-leaf stage were spray inoculated
with conidia and placed in a dew chamber at 22°C for l6 hr to secure infection.
Then they were transferred to an lSCt.) E2 environmental chamber at 28°C
and 75 % RH for 80 hr for colonization. Sporulation was inhibited at 75 % RH.
T\velve 4-ft fluorescent lamps were timed for 12 hr light daily Lesions were
marked and measured as per Nelson and Tung. except I5 lesions from the four
plants per pot which were selected from the fourth basal leaf instead of the third
basal leaf. Sporulation periods of 16 hr in darkness at 24°C, under controlled
constant RH. were followed by a mass collection of spores from l5 lesions.
Spores ‘were counted as per Nelson and Tung.
All tniginal data from 38 pots were plotted and a curve fitted by inspection.
Then data for RH above 93 % (34 pots) were placed in six groups with a range in
the individual groups of zero to 0.4 % RH. For linear correlation and regression,
transformation of the conidial means was made to yield a straight line seinilog
type curve.
Microscopic examination revealed the absence of CtiltiditipltOft-BS and conidia
on infected plants at time of removal from 75% RH. 28°C chamber. Upon
removal from the sporulation box no liquid water was present on the lesions or
leaves except from guttation water at a few of the marginal hydathodes. The
number of conidia present after l6 hr in the dark at 24°C is shown in Fig. 3.
Conidia were formed at high RH in the absence of “free“ water. Virtually
no conidia were found at RH less than 93 %. The number of conidia increased
as RH was increased. over the range of 93 to 98 %, RH (r = 0.942. 1% level),
until as many or more \‘