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Influence of Potato Varieties and Alternate Application of Fungicides with Different Modes of Action on Potato Solanumtuberosum L Late Blight Phytophthorainfestans Mont de Bary Tuber Yield in Central Ethiopia

Adina Getinet, Mashilla Dejene and Bekele Kassa

The experiment was conducted at Holetta Agricultural Research Center and on-farm at TikurEnchini during 2017 crop season to test the influence of potato varieties and alternate application of fungicides on potato late blight severity and tuber yield in three potato varieties, namely Belete, Gudene and Jalene were used as factor A, fungicide application sequences (Mancozeb, Ridomiland Trust-Cymocop) as factor B fungicide application sequences included fungicide sprays, which were applied as sole and alternate application sequences. Each plot (9m2 with 40 plants per plot) consisted of six rows with 10 plants per row and with spacing of 75 cm between rows and 30 cm between plants. The spacing between plots and adjacent replications was 1 m and 2 m, respectively. The treatments were arranged in a randomized complete block design in factorial experiment with three replications. Disease severity, yield and yield-related data were collected from the four central rows of each experimental plot. The result indicated that variety, fungicide, locations and their interactions significantly reduced late blight severity and increased tuber yield and yield components. The final percent disease severity reached a maximum value of 89.17%, 83.33% and 71.67% on the unsprayed variety Belete, Jalene and Gudene, respectively. All fungicide application sequences reduced the progress of the disease as compared to unsprayed control, but TRM and RRR spray sequence highly reduced the progress of the disease as compared to other application sequences.  Higher tuber yield was recorded on the variety Belete (56.84 tons ha-1), followed by Gudene and Jalene. In this study, TRM and RRR spray sequence retarded late blight development consistently when combined with all varieties and the highest yields were obtained from plots sprayed with TRM and RRR spray sequences. The mean relative yield loss calculated for the control plots due to late blight ranged from 30.35 to 52.16%. The highest (298,231 ETB/ha) net benefit was maintained from Belete sprayed with TRM spray sequence.  The least (73,446 ETB/ha) net benefit next to the absolute control (52,887 ETB/ha) was Jalene sprayed with TTT spray sequence. The highest (3341.7%) Marginal rate of return was maintained from Belete sprayed with TRM spray sequence. On the other hand,the lowest marginal rate of return was obtained from variety Gudene and Jalene sprayed three times with Trust-Cymocop. Therefore, application of these fungicides alone is not recommended in controlling potato late blight, especially for the tested varieties and locations. The overall results indicated that alternate application of fungicide significantly reduced late blight epidemics, improved potato productivity and profitability, thus, the fungicide application sequence is recommended for the study areas and for areas with similar agro-ecologies.