Incidence, Distribution and Characteristics of Major Tomato Leaf ...

Incidence, distribution and characteristics of major tomato leaf curl and mosaic virus diseases 134
5.3.2.1 Tomato Yellow Leaf Curl Virus (sensu lato) Incidence and
Spread under Different Experimental Treatments
5.3.2.1.1 Tomato Yellow Leaf Curl Virus Incidence
Taking all three trials, i.e. I (March-July 1999), II (August – Nov.1999), and III
(Nov.1999 – February 2000), there was less TYLCV disease incidence in trial II and
III than in trial I due to a dual effect consisting of treatment effects (n1-n6) in Figure
5.12, and weather changes, as shown also in figure 5.13. Thus, during trial I (Figure
5.10), disease progress curves with sigmoid-like pattern were observed for all
treatment plots except for plots with tomato-bean intercrop and no dimethoate
application (n3), which produced a pattern characteristic of a monocyclic disease
spread (Thresh, 1998). A monocyclic disease starts off with a direct increase in
number of infected plants over time, but gradually slows down and stabilizes at a
certain level without rising again. From the results, it was clear that uprooting
combined with dimethoate (n5), which had a significantly low disease incidence curve
(Figure 5.10), was the most effective in controlling TYLCV. The same treatment (n5)
also had low disease incidence in August to November 1999 (trial II) as shown in
figure 5.11