AUDPC is an epidemiological indicator of the amount of accumulated disease over time. Those genotypes showing

Thank you very much for your answer.. 

My question is that the AUDPC is just measure of rate of disease development over time but it is not a true measure to classify disease susceptible and resistant  varieties. We may compare the rate of disease development between varieties but final disease severity of particular variety is ultimate value taken into consider in classifying into the susceptible and resistant varieties

What is your opinion on this?

Indeed you may consider dy / dt of the disease as an indicator of possible tolerance / susceptibility. You can use a epidemiological model of plant disease evolution. AUDPC only give us the accumulated disease.

AUDPC becomes important when you do not have absolute resistance in your test material and then you can have relatively better tolerant genotypes which is somehow resisting the rate of pathogen spread on host. This can be by restricting the rate of sporulation and spread of the lesion on the host tissue. So as a second choice you will go for genotypes with low AUDPC (off course it can not be the replacement of absolute resistance).

AUDPC should not be considered alone and is particularly useful for quantitative resistance. Rate of increase is really important for resistance as your final severity does not indicate when the infection started or how much further it developed after the "final" score. I have seen some people making early final scores that to me suggest that the disease could still have effected yield and possibly quality after this reading. Has anyone got a model that considers the growth rate or maturity rate of the hybrid/cultivar when comparing AUDPCs?

Thank you very much for your reply @David Nowell

Yes you are right.. The AUDPC should not be consider alone as an indicator of possible tolerance / susceptibility varieties. The AUDPC is just give a rate of disease development which indicate the rate of disease increase/decrease in particular variety. but Final disease index/Disease severity at the maturity should be consider as measure the disease quantitatively in field conditions.

There are certain model developed in wheat that disease phenotype scores should be stopped at soft-dough stage/milking stage of crop growth stage where leaves become yellowing and drying due to physiological maturity not due to the disease incidence.

AUDPC could be a measure of Varietal tolerance/Susceptiblity and is  Progress of disease over time. It again depend upon the objective of study to consider AUDPC or some other papameters.

Thank you for your answer. 

My question is among AUDPC AND DISEASE SEVERITY, WHICH ONE IS THE ULTIMATE PARAMETER TO CONSIDER TO  CLASSIFY VARIETIES INTO DISEASE SUSCEPTIBLE OR AS RESISTANT ONES. 

Hello Chethana,

AUDPC is a method to measure a qauntitative resistance. Always quantitative resistance is incomplete resistance and it is explained interms of reduced susceptability (No plant is immune to quantitative disease traits). If the disease resistance you are working with is a quantitative in nature and you are using AUDPC as a measure of disease quantification than in my opinion you can use AUDPC to differentiate your genotypes.

At the end of your experiment it definately gives you a value for both R & S genotypes, that will tell you how less susceptability of R genotype is as compared to S.

I hope i cleared your point.

Good luck

Uday 

In case of Bipolaris sorokiniana (spot blotch) disease of wheat the idea of calculating AUDPC is to make quantitative assessment of disease spread over time. For identifying donors final severity is the best but for breeding material (segregating) AUDPC values give an idea of comparative score. The adverse effect of infection and severity would depend on several other parameters (time or stage of disease appearance, rate of spread & severity and final score) that limits yield through component traits. Maturity duration, leaf angle, canopy colour and stay green habit are indirect traits that also account for host resistance. 

Simply based on AUDPC it is not advisable to classify genotypes for resistant or susceptible but one should also take into account final disease severity.

Thank you very much sir for the very useful answer.

I am agree fully with you answer sir.  Thank you 

AUDPC may be an indicator but not usable in isolation. The disease severity at the crop stages that affect crop yield is the real indicator for resistance or susceptibility. if yield loss is below threshold level and leaves are showing lower values for disease severity, it may be considered as resistance. otherwise mean values based on dd scale can be used to identify resistant genotypes

Yes You can consider disease resistant/tolerant on the basis of AUDP. It is also a measure of disease progress over time and  magnitude of disease.You can also consider final score but at that time may be crop stage will be at over mature.There will be some other environmental effects as well.

@SK SINGH, Thank you very much for your answer

@Baidya Nath Maho, Thank you very much for your opinion.

AUDPC is a just indicate the rate of disease development/spread overtime in particular variety. Disease severity indicates that  % of disease incidence in a particular variety.

The disease scoring scheme for the spot blotch designed in such a way that one should stop scoring for the disease at a soft dough stage before maturity of plants. as many as five disease score (double digit score) were taken in a 7 days interval between each scores. Double digit scores were used for calculation of disease severity by using a formula 

DS= (D1/9)x (D2/9) x 100 for each score to obtain the individual disease severities (DS). DS were used to calculate the AREA UNDER DISEASE PROGRESS CURVE(AUDPC)

AUDPC is an indicator of disease accumulation over time in a crop plant. It can be a good indicator for selection for resistance as has taken care of all disease effects on the plant over all the period of growth. This means that selection for resistance using AUDPC is selection based on total resistance of plants.

Definitely we can use AUDPC as resistance indicator. If we can combine other resistance components also we can effectively assess the resistance.