PATHOMETRY
Pathometry is a major tool for developing resistant varieties. Disease management through breeding
resistant cultivars at forefront in countries where resource limitations do not permit high cost plant
protection technology. Description of disease symptoms in standard diagrams, color plates and in words
are essential for disease appraisal. Besides measuring diseased area, the counting of spores has been
tried as an alternative method, especially for fungal diseases. Several workers have employed video
image analysis for assessment of plant disease severity. Disease incidence, severity, and spatial pattern
depend on data obtained from field samples. Linear regression equations often are used to characterize
critical-point models where the independent variable is disease measurement and percentage loss in
yield is the dependent variable. Plants can be evaluated for incidence or severity. Such models provide
loss estimates for a given amount of disease at a given point in time or for any point in time when a
given amount of disease is present.
CROP GROWTH STAGES:
A widely accepted definition of an epidemic is “a change in disease intensity in a host population
over time and space” (Madden et al. 2007). This definition emphasizes that epidemics are dynamic
processes with variable disease rates. How many of these disease rate changes are triggered by the host
population is still an ongoing issue. As an epidemic is driven by the effective reproduction number
(Cintron-Arias et al. 2009), which is the product of the proportion of susceptible tissue, the disease
transmission rate, and the infectious period duration, any modification in the host population, whether
quantitative or qualitative (distribution of plants or of susceptible organs), can have an impacton the
epidemic dynamics. The host population growth is modified during the growing season by architectural
features or by cultural practices. The production of new organ continuously modifies two aspects: the
plant or canopy porosity, as well as the plant’s level of susceptibility when organ susceptibility changes
with age (ontogenic resistance or receptivity). Indirectly, plant growth and structure modify the
microclimatic environment inside the canopy, generating favourable or unfavourable conditions for
pathogens. Organ susceptibility or the susceptibility period may also be modified by cultural practices
disrupting crop-pathogen synchronisation. Spatial heterogeneity in the host population can also be
generated by differences in phenology (e.g. variety,bpruning, sowing date) or growth rate (e.g. soil
variation, vigour, rootstock). There is evidence that these variations within host populations do impact
on disease incidence, severity or spread. However, those effects have rarely been explicitly taken into
account in epidemiological models. Tracking back the impacted pathogen processes from the global
dynamics of an epidemic, and then ranking the host traits involved in their modifications, constitute
achallenge. we: 1) review evidence of epidemic variations attributed to plant growth and architecture in
main pathosystems; 2) identify the pathogen processes impacted, and assess them in different epidemic
contexts; and 3) explore the models able to measure and predict the effect of plant growth and
architecture.Plant growth and architecture.
