How Planting Density Affects Number and Yield of Potato Minitubers in a Commercial Glasshouse Production System

Commercial potato minituber production systems aim at high tuber numbers per plant. This study investigated by which mechanisms planting density (25.0, 62.5 and 145.8 plants/m2) of in vitro derived plantlets affected minituber yield and minituber number per plantlet. Lowering planting density resulted in a slower increase in soil cover by the leaves and reduced the accumulated intercepted radiation (AIR). It initially also reduced light use efficiency (LUE) and harvest index, and thus tuber weights per m2. At the commercial harvest 10 weeks after planting (WAP), LUE tended to be higher at lower densities. This compensated for the lower AIR and led to only slightly lower tuber yields. Lowering planting density increased tuber numbers per (planted) plantlet in all grades. It improved plantlet survival and increased stem numbers per plant. However, fewer stolons were produced per stem, whereas stolon numbers per plant were not affected. At lower densities, more tubers were initiated per stolon and the balance between initiation and later resorption of tubers was more favourable. Early interplant competition was thought to reduce the number of tubers initiated at higher densities, whereas later-occurring interplant competition resulted in a large fraction of the initiated tubers being resorbed at intermediate planting densities. At low planting densities, the high number of tubers initiated was also retained. Shortening of the production period could be considered at higher planting densities, because tuber number in the commercial grade > 9 mm did not increase any more after 6 WA

Basic studies on the production and performance of potato minitubers

Minitubers are small seed potato tubers that can be produced year-round in glasshouses on in vitro propagated plantlets planted at high density. The research reported in this thesis studied the agronomical and physiological principles of the production of minitubers and their performance under Dutch field conditions. The minitubers had fresh weights between 0.125 and 4.000 g.More than 3000 minitubers per m 2were produced in 10 weeks (average fresh weights 1 - 2 g), when tubers were harvested 4, 7 and 10 weeks after planting, using a non-destructive harvesting technique in the first two harvests. Removing tubers in the first harvest resulted in initiation of new tubers because more potential tuber sites became available that were not subjected to the dominance of rapidly growing tubers. Part of the newly initiated tubers grew to a harvestable size within three weeks, but the number of tubers in harvestable sizes did not increase thereafter, whereas part of the undersized tubers was resorbed. The second harvest stimulated growth of tubers that otherwise would have been resorbed or would have remained too small.Almost all minitubers ≥0.5 g survived storage at 2 °C for 1.5 years. After 6 months of storage, growth of plants from minitubers was still poor. Largest leaf areas were achieved after 10 - 11 months of storage, highest stem numbers, progeny tuber weights and harvest indices after 14 - 15 months of storage for cv. Agria and after 18 - 19 months for cv. Liseta.The performance of minitubers was affected considerably by their weight. Lighter tubers had a longer dormant period, partly because of a slower sprout growth up to 2 mm (used to assess the end of dormancy). Plants from lighter tubers took longer to emerge and at emergence had thinner stems, lower root weights, and higher shoot:root ratios. Crops from lighter minitubers produced lower yields because of less radiation intercepted (slower ground cover) and a lower harvest index. Multiplication factors per planted tuber were lower in crops from lighter minitubers because fewer plants emerged or survived, and fewer progeny tubers and lower weights were produced per plant. Yield variation within a crop was higher in crops from lighter minitubers, but - when properly nursed - variation in yield over years was not affected by the weight. Effects of minituber weight generally became less clear in the higher weight ranges. Differences in performance between minitubers and conventional tubers were attributed to weight and age of seed tubers, presprouting method and crop husbandry.Minitubers can be used in the first year of potato seed production programmes to speed up multiplication and to increase the quantity of seed from new cultivars

How weather during development of common bean (Phaseolus vulgaris L.) affects the crop’s maximum attainable seed quality

Weather conditions affect the seed quality of major crops including common bean. This study aimed to evaluate whether seed quality is affected through weather effects on the quality achievable at the end of seed filling (PM) or through changes in quality during maturation drying in the period between PM and harvest maturity (HM). The research also aimed to establish relationships between seed yield and seed quality. Twenty-four common bean (Phaseolus vulgaris L.) crops from two cultivars were sown on different dates in Eldoret and Kitui, Kenya. Seed quality was quantified as the percentage of viable seeds determined with a tetrazolium test, and as vigour measured by electrical conductivity (EC). Over the range  of weather conditions during our study, high temperatures were more detrimental to seed quality than little rainfall. The two cultivars differed in susceptibility to high temperatures. High temperatures and little rainfall seemed to reduce seed quality mainly through reducing maximum quality attainable during the course of crop development. The quality in general did not change significantly between PM and HM, but in some cases the proportion of viable seeds increased between PM and HM, especially when ambient temperatures were relatively low. For seed samples free from mechanical damage, EC appeared to be an unsuitable criterion to detect quality differences at HM, because in almost all seed lots quality was indiscriminately classified as ‘good’, whereas viability varied between 69 and 100%. Production conditions leading to low seed yields or seeds of low weight resulted in a low percentage of viable seeds but conditions resulting in fairly high yields or heavy seeds did not guarantee a high percentage of viable seeds

Analysis of Seed Potato Systems in Ethiopia

This study aimed to analyze the seed potato systems in Ethiopia, identify constraints and prioritize improvement options, combining desk research, rapid appraisal and formal surveys, expert elicitation, field observations and local knowledge. In Ethiopia, informal, alternative and formal seed systems co-exist. The informal system, with low quality seed, is dominant. The formal system is too small to contribute significantly to improve that situation. The informal seed system should prioritize improving seed quality by increasing awareness and skills of farmers, improving seed tuber quality of early generations and market access. The alternative and formal seed systems should prioritize improving the production capacity of quality seed by availing new varieties, designing quality control methods and improving farmer’s awareness. To improve overall seed potato supply in Ethiopia, experts postulated co-existence and linkage of the three seed systems and development of self-regulation and selfcertification in the informal, alternative and formal cooperative seed potato systems. Resumen Este estudio tuvo el propósito de analizar los sistemas de producción de papa en Etiopia, identificar limitantes, y priorizar opciones de mejorar, mediante la combinación de investigación de escritorio, apreciaciones rápidas y estudios formales, encuestas a expertos, observaciones de campo y conocimiento local. En Etiopia co-existen sistemas de semilla informal, alternativo y formal. Domina el sistema informal, con baja calidad de semilla. El sistema formal es muy pequeño como para contribuir significativamente al mejoramiento de esa situación. El sistema informal de semilla debería tener como prioridad el mejoramiento en la calidad de la semilla mediante el aumento en la atención y habilidades de los productores, mejorando la calidad de la semilla-tubérculo de las generaciones tempranas y el acceso al mercado. Los sistemas alternativo y formal de semilla deberían priorizar el mejoramiento en la capacidad de producción de semilla de calidad, mediante la validación de nuevas variedades, el diseño de métodos de control de calidad, y mejorando la atención del productor. Para mejorar el suministro general de semilla de papa en Etiopia, los expertos postularon la co-existencia y asociación de los tres sistemas de semillas y el desarrollo de autorregulación y autocertificación en los sistemas cooperativos de semilla de papa informal, alternativo y formal. Keywords Potato . Seed quality . Seed tuber . Seed system . Quality improvement . Expert elicitation . Solanum tuberosum Introductio

Ontogeny of the tuber crop Plectranthus edulis (Lamiaceae)

Plectranthus edulis (Lamiaceae) is one of the economically important tuber crops of the genus Plectranthus. It is grown in mid and high altitude areas in parts of Ethiopia. The structure of this plant and its development in time has not been described in detail. Two similar experiments were carried out at Awassa and Wondogenet (Southern Ethiopia) with two cultivars (Lofuwa and Chankua) and 20 harvest dates [from 14 to 280 days after planting (DAP)]. The plants were grown from seed tuber pieces and attained a maximum height of about 1.5 m. Plants produced main stems and primary, secondary and tertiary branches, with primary and secondary branches and their leaves constituting the main part of the canopy. Plant components were the seed tuber pieces, sprouts, main stems, branches, leaves, flowers, fruits, seeds, roots, stolons and tubers. Five, partly overlapping, ontogenetic vegetative phases were observed during one crop cycle: emergence, canopy development, stolon initiation and development, tuber initiation and growth, and a phase of canopy senescence. Stolons were formed on main stems and primary branches and originated below ground or above ground (aerial stolons). Aerial stolons were initiated later than below-ground stolons and were much longer (up to 2.5 m). Tubers usually were produced as a swelling on the tip of the stolon and sometimes as a swelling of the middle part of stolons. Tubers were stem tubers with pairs of ''eyes'' (compound buds) being arranged in the same decussate pattern as the axillary buds on stolons and stems. Tubers of cv. Lofuwa were up to 25 cm in length, those of cv. Chankua up to 20 cm, and both with a diameter of about 2 cm. The tubers in the middle of the stolon were longer than the ones at the tip. After tuber initiation, the total number of tubers increased almost linearly during 12 to 14 weeks, and maximum numbers of tubers were attained around 238 DAP, at crop senescence. Also, the number of smaller tubers (<10 or 20 g) increased until 238 DAP. In the period of tuber initiation, the average weight per tuber increased up to 20 to 25 g per tuber. The increase in tuber fresh weight with time was therefore realized by an increase in both tuber number and in average weight per tuber. After crop maturity, farmers keep the tubers unharvested in the soil until they need them. This practice dramatically reduces tuber yield and number, because decreases of 36 to 59% were found in total tuber fresh weight and of 18 to 48% in number of tubers when tubers were kept in the soil in the 6 weeks period between 238 and 280 DA

Effects of shoot tipping on development and yield of the tuber crop Plectranthus edulis

Plectranthus edulis (Vatke) Agnew is one of the tuber crops of the genus Plectranthus that is widely cultivated in Africa and Asia. P. edulis produces below-ground tubers on stolons originating from the stems, comparable to the potato (Solanum tuberosum L.). Farmers apply several laborious cultural practices to enhance shoot growth and yield, among which shoot tipping is very common. Tipping (pinching) is the removal of the shoot apex with one or two pairs of leaves from the main stems and branches. The rationale of this practice, especially when repeated more than once during one cropping season, is not fully understood. One similar experiment with two cultivars was carried out at two locations (Awassa and Wondogenet) in Ethiopia to assess and analyse the effects of shoot tipping and its frequency on crop development and tuber production. Tipping treatments included zero tipping, tipping once, tipping twice and tipping thrice, with the first tipping taking place 68 days after planting (DAP), a stage at which most of the stems reached a height of about 0·15 m, and the remainder following at intervals of 44–46 days. Tipping stimulated stem branching; it significantly increased the number of primary, secondary and tertiary stems in both experiments. Soil cover increased with an increase in the frequency of the tipping in Awassa, because of the tipping effects on the different canopy development variables. Tipping also enhanced the soil cover in Wondogenet, but the crop did not gain any extra benefit from a third tipping. Tipping enhanced early stolon formation, but did not consistently affect the number of stolons per hole later in the growing season. The number of tubers increased with an increase in the frequency of tipping in both cultivars in Wondogenet and in one cultivar in Awassa. Tuber dry matter yield increased with an increase in the frequency of tipping at both sites. Fresh tuber yield in the final harvest at 208 DAP was c. 1·9 kg/m2. Tipping on average increased fresh tuber yield by 17% in Wondogenet, whereas the difference was not detectable in Awassa. Because senescence was delayed slightly by tipping, yield effects of tipping might be larger when harvesting later. In general, there was a positive effect of tipping on canopy development and tuber yield

Indigenous multiplication and production practices of the tuber crop Plectranthus edulis in Chencha and Wolaita, Southern Ethiopia

Plectranthus edulis (syn. Coleus edulis) is a tuber-bearing labiate species cultivated in parts of southern Ethiopia. To learn about traditional cultural practices and their rationale, a survey was conducted among farmers from Chencha and Wolaita experienced in growing this crop. A pre-tested questionnaire was used to interview 48 family heads categorized into three wealth groups per site. Information was checked through group discussions and field observations. In Wolaita, poorer farmers cropped a larger portion of their land to P. edulis than richer farmers. Land was usually prepared for planting between January and April. In Wolaita, the crop was mostly grown in a furrow. In Chencha growing in patches and on flat land also occurred. Farmers mostly used a digging hoe for land preparation. Tuber pieces were planted about 5 cm deep. According to farmers, using tuber pieces resulted in more stems, more progeny tubers and higher yields than using whole tubers. Tubers were broken into pieces 0¿1 day before planting. Tuber pieces were planted with sprouts or after desprouting. Crops were usually fertilized with manure, but in Wolaita sometimes also with compost. Applying fertilizer was thought to give more and bigger tubers. Earthing up took place 1¿3 times (usually twice), to increase yield. Tipping was also done 1¿3 times (usually once), to increase the number of stems. Based on the survey, an overview of the practices and their rationale is compiled for use in further research into this orphan crop