Effect of selection methods on seed potato quality

Potato is one of the most important crops in the world. Although it ranks fourth after rice, wheat and maize, the major food crops in the world, either in production or in the economic value, in terms of energy and protein production per hectare and per unit of time, the potato ranks first which is significantly above cereals, pulses and cassava (CIP 1984). In many countries potato is considered a vegetable, but the interest for potato as staple crop increases especially in developing countries, including Indonesia which is the largest potato producer in Southeast Asia. At present, the potato areas in Indonesia varies between 60,000 and 70,000 ha with a total production of about 1.2 - 1.3 million tons per year. The potato has been considered a priority crop in the strategic plan of research and development program of the Indonesian Agency for Agricultural Research Development (IAARD) in the last 30 years because of its potential as alternative carbohydrate source in food diversification and for export markets. The potato originally comes from the cool tropical highlands of the Andes in South America (Horton and Anderson 1992) and therefore the potatoes in Indonesia are mainly grown in the highland areas (> 1,000 m). The main potato variety in Indonesia since the 1980’s is Granola, which covers 80 to 85% of the potato area. The moderate resistance of Granola to PLRV and PVY appear to have contributed in making it a successful variety in Indonesia (Chujoy 1995). Seed is the most costly component of potato production, and potato profitability often depends on access to quality seed. Seed accounts for 30-40% of the total costs of potato production in Indonesia (De Putter, et al. 2014; Pronk, et al. 2017a; Van den Brink, et al. 2015). High quality seed is relatively expensive and is not affordable by most farmers. Therefore, most potato farmers often use potato seed tubers saved from their previous crops. Small tubers are usually selected and saved for seeds for planting in the following season. This unhygienic practice results in carrying over diseases (e.g. viruses and bacteria contained in the small seed tubers) with the result that yields decrease over time. Farmers will need to buy seed tubers from other farmers or traders when their own seed stock has degenerated due to build up diseases. The degeneration of seed stock depends on the seed selection and also on the variety grown. Varieties differ in levels of resistance to virus infections and virus particle multiplication within the plant (Salazar 1996). One method to reduce the degeneration rate is through so-called positive selection (Gildemacher, et al. 2007). In this method, the best potato plants in a field are marked before crop senescence and they serve as mother plants for seed potatoes used in the following season. Positive selection in Kenya gave an average yield increase in farmer-managed trials of 34%, corresponding to a 284 € increase in profit per hectare at an additional production cost of only 6 € /ha (Gildemacher, et al. 2011). Within the vegIMPACT program demonstration trials have been carried out to show farmers the potential benefits of positive selection on the seed potato quality in the subsequent season. The demonstrations showed potato farmers the importance of plant selection in one planting season in order to obtain good quality seeds in the following planting season. Positive selection is a technique to maintain good quality seeds by reducing the degeneration rate of farm saved seed. This technique potentially reduces the costs for the most costly input, i.e. seed potatoes, in potato production