Forewarning Rice Blast in India

3. VALIDATION OF MODELS DEVELOPED AT DRR
The regression equations developed for the data of 2001, 2002, 2003
revealed that independent variables influence the rice leaf blast differentially during
different years, thereby making it difficult to select a good equation. For example,
during 2002 the combined linear effects of T , Rh and Leaf wetness (L ) contributed
Min E W
to the variation in rice blast severity, whereas during 2003, it was T , T , R and Rf.
Max Min W
Similarly, other weather variables in different combinations effected rice blast severity
in different years of study. However, T was found an important predictor in 2002
Min
and 2003. Therefore, the models developed were validated to find a best-fit model
for better forewarning. Out of all the equations, the regression equation developed
based on the pooled leaf blast and weather data of the duration 2001-2003 at
Medchal was observed to be the best-fit equation, which was validated on 2002-
2003 data of DRR. Tsai and Su (1984) also stated that combined data of various
years resulted in equations, which gave better agreement between observed and
predicted values than equations derived from data of individual years.
The best validation model used for forecasting the disease is:
LB = 14.5 + 0.90 LB + 0.10 T – 1.41 T –0.10 Rf + 1.20 R + 0.29
N P Max Min W
Rh –0.18 Rh M E
R2 = 0.92
Where: LB = Leaf blast in next week
N
LB = Leaf blast during previous week
P
T = Maximum temperature during previous week
Max
T = Minimum temperature during previous week
Min
Rf = Rain fall during previous week
R = Rainy days during previous week
W
Rh = Morning relative humidity during previous week
M
Rh = Evening relative humidity during previous week
E
The validation models were developed for leaf blast at Medchal, Hyderabad,
during 2001-2003 and at DRR, Rajendranagar during 2002-2003. The observed
and predicted values were given in Fig. 7.
The dependent neck blast variable and independent weather variables of the
years 2002 and 2003 of DRR subjected to the validation on the three years blast /
weather data (2001-2003) of Medchal resulted in best fit equation. Observed and
predicted values of neck blast at DRR and Medchal are given in the Fig. 8.
NB = -25.61 + 0 .79 NB + 1.8 T –2.5 T + .38 Rh N P Max Min E
R2 = 0.90
Where: NB = Neck blast in next week
N
NB = Neck blast during previous week
P
T = Maximum temperature during current week
Max
T = Minimum temperature during current week
Min
= Evening relative humidity during current week
Rh E
Forewarning Rice Blast in India
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