Vergara - 1976 - Physiological and morphological adaptability of ri

394 (‘LIA-LATE AND RICE
in that year. It is hoped that a brief summary of our program will meet the
objectives of my participation in this symposium.
Many individuals contributed in a variety’ of ways to the program summarized
herein. Although many of them will not be identified in this paper. their contributions
were significant and are hereby acknowledged.
The author was asked to stress the methodology of our research. Because of
specified page limitations, presentation of research results is restricted and may
at times appear cryptic.
GENERAL APPROACH T0 'l'l-IE PROBLEM
Epidemiological research to monitor disease increase among populations of
plants historically" has evaluated the influence of climatic regimes and time on
various segments of the disease cycle. Primary attention has been devoted to the
influence of temperature, light, relative humidity. and dew periods on sporulation.
spore dispersal. infection. and colonization. Little attention has been given
to the remaining components of the disease triad, the pathogen and the host.
Predictive and interpretative epidemiology can be misleading when the assumption
is made that different varieties of a susceptible complex and different members
of a pathogenic race are prone to react similarly to various climatic regimes.
Despite the irrevocable validity of these statements, and in keeping with the
theme of this symposium. the results presented deal with research in which both
host and parasite were held as constants. Mention should be made. however.
that other facets of our research have demonstrated clearly that differences in the
relative susceptibility‘ of host cultivars (Nelson and Tung, 1973 a, b. c) or in the relative
virulence of parasite populations (Nelson. 1973) affect disease incidence in
a manner similar to that which occurs when climatic parameters become more
or less favorable for disease increase.
The disease cycle is the essence of epidemiology". Propagules depart from infected
tissue. travel to susceptible tissue. enter, colonize. and ultimately produce
more propagates. continuing the cycle. The faster and more efficiently the cycle
moves, the greater the amount of disease. To be sure. the particulars differ for
various diseases. but the general principle is the same.
Our initial approach to the study of the epidemiology of SCLB was to determine
the influence of certain climatic factors on separate portions of the disease
cycle under controlled environment conditions. The separate phases monitored
included sporulation. spore release. spore deposition. infection. and colonization.
This segment of the research was considered essential to our understanding
of changes in disease incidence under field conditions and to a correlation of such
changes in incidence with changes in specific climatic factors.
A second and related phase of our research was concerned ‘with monitoring
disease onset and disease increase under field conditions. Environmental sensing
techniques were used to monitor all of the important climatic factors. permitting
an accurate correlation of climate and disease incidence.