Effect of different soil water pressures in controlling Rhizoctonia solani Kuhn, cause of black scurf of potato and distribution of tuber borne diseases of potato in district Abbottabad [Pakistan]
2000
Ajmal, M.
The effect of different soil water pressures on incidence and severity of black scurf and yield of potato was studied in a pot experiment. The experiment consisted of five treatments replicated eight times in a randomized complete black design. Five different soil water pressures (expressed as available percentage of soil moisture) were 2.82%, 5.63%, 8.45%, 11.26% and 14.8%. Seed tubers of variety Cardinal were planted in 25 cm earthen pots. The soil was inoculated one week before sowing with sclerotia of R. solani at the rate of one petri plate/pot. Treatment T4 with SWP 11.26% showed the highest disease incidence (77.1%) and disease severity (22.3%) while its yield was 86.1 g/plant. Treatment T3 with SWP 8.45% showed highest potato yield (104.3 g/plant) and it was higher by 33.9% than the lowest one (68.9 g) in T1 with SWP 2.82%. Its disease incidence and severity were lower by 6.19% and 8.2% than the highest one. The second best treatment was T2 with SWP 5.63 % which caused 22.5% reduction in disease incidence and 13.2% in disease severity. The regression analysis showed that with 1% increase in water pressure there was 2.56% increase in disease incidence and 1.40% increase in disease severity. The second part of this research included survey of tuberborne diseases of potato in Abbottabad District during summer 1998. At each of the seven localities, five fields were randomly selected and in each field tubers taken from five plants were rated for the incidence and severity of the diseases. Among the three diseases, common scab and black scurf were more widespread than powdery scab. The highest disease' incidence (72.4%) and severity (45.1%) of black scurf were recorded at Mandian. The lowest incidence (2.1%) and severity (4.2%) of the disease were recorded at Thanda Choya and Nawasher, respectively. Common scab incidence was the lowest (43.9%) at Bilal Town and highest (93.3%) at Mandian. Its severity was lowest (30.7%) at Potato Research Centre and highest (89.6%) at Nawasher. Powdery scab showed lowest disease incidence (8.7%) at Thanda Choya and the Highest (23.4%) at Bilal Town. On the other hand its lowest (17.6%) and highest (26.2%) severalties were at Ilyasi Masjid and Potato Research Centre, respectively.
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