Effect of seed sources, seed tuber size and seed dressing on the performance of potato and late blight incidence in Uganda.

Uganda has a high potential for potato production. However, very low yields are still obtained. This is primarily due to the quality of the potato seed used. The capacity of certified seed production is too low to satisfy the demand, a gap that has been filled by other informal sources with low-quality seed, partly explaining the low potato yields farmers obtain. Using a randomized complete block design in a split-split-plot arrangement, field trials were conducted at three locations in southwestern Uganda for two consecutive seasons to determine the effect of seed sources, seed size, and seed treatment on potato growth, yields, and late blight incidence. Factors included; three seed sources (certified KaZARDI-control, farmer-saved, and local market), two seed sizes (recommended large: 35-55mm and small: < 35 mm), and two levels of seed treatment (treated with Victory 72 WP fungicide and untreated). Thus, it was a 3 × 22 full factorial experiment. Parameters evaluated included plant height, number of main stems per plant, leaf area, emergence, late blight incidence, and number and yield of small, medium, large and total tubers. In addition, a physical assessment of tubers obtained from the different sources was done before the field experiments to provide a characterization of the physical, physiological, and genetic quality of the seed from the different sources. Data was collected on sprout morphology, tuber size, tuber skin appearance, and the presence of disease or damage. The results showed that certified seed from KaZARDI possessed characteristics of high-quality seed (few short, thick, and strong sprouts; no wrinkles on tuber surface; few diseased tubers; larger seed size tubers and the highest genetic purity) while seed from the farmer-saved and local markets sources exhibited characteristics of low-quality seed (many weak white long sprouts which were branched or hairy, wrinkled on tuber surface, many diseased tubers, smaller seed size tubers, and a high varietal mixture). Furthermore, certified seed from KaZARDI had significantly (P < 0.05) high values for plant height (60.89 cm), emergence (87.60 %), number of medium-size (24.27 %) and large-size tubers (17.31 %) as well as yield of medium-size (2.78 t/ha), large-size (3.59 t/ha) and total tubers (8.60 t/ha). Generally, farmer-saved seed followed while the lowest values for the above parameters resulted from the local market seed. Moreover, large-size seeds exhibited significantly (P < 0.05) higher performance than the small-size seed for plant height (59.03 cm), number of main stems per plant (2.74), the yield of small-size (2.76 t/ha), medium-size (2.63 t/ha) and total tubers (7.89 t/ha). Fungicide-treated seed showed significantly (P < 0.05) better performance than the untreated seed for number (22.93 %) and yield (2.58 t/ha)of medium-size tubers as well as total tuber yield (7.77 t/ha). Some interactions were significant. The combination of large-size certified seed; treated certified seed; treated large-size seed generally resulted in the highest growth and yields. Other better treatment combinations were: large-size farmer-saved seed; small-size certified seed; treated farmer-saved seed; untreated certified seed. The findings of this study suggest that potato seed quality is affected by seed source. Furthermore, the study provides empirical evidence that seed source, seed size, and seed treatment significantly affect potato growth and yields. Therefore, based on the above findings, the use of certified, large-size, fungicide-treated seed is primarily recommended for potato production. However, in the event that certified seed is inadequate and cannot satisfy the demand, the farmer-saved seed could be used provided the seed is of large-size and fungicide treated. Therefore, efforts should be geared towards making certified seed more available and accessible as well as training farmers on seed treatment, production, and management practices that improve and maintain the quality of on-farm-produced potato seed.