Tuber Dry Matter Research Articles

Variation in antioxidant status and productivity in andigena potato clones

Potato can be a valuable source of antioxidants in the human diet, and genetic variability exists for antioxidant contents. The present study was carried out to evaluate the extent of variability in coloured flesh potatoes from andigena clones. There were significant differences among clones in ascorbic acid, phenols, total carotenoids and anthocyanins. During the two crop seasons, purple fleshed andigena potato clone JEX/A-122 was found to be superior in ascorbic acid, phenols and anthocyanins, followed by JEX/A-121. However, total carotenoids content in all the evaluated clones in general was less than half to that of yellow fleshed control variety Kufri Surya. Tuber dry matter in JEX/A-121 and JEX/A-122 was moderate (19.6 %) and statistically at par with that of Kufri Surya (21.1 %). Effect of growing season was also noticed on antioxidants status. The clones JEX/A-121 and JEX/A-122, superior in antioxidants showed significantly lower biological yield (226 and 246 g plant−1) as compared to commercial varieties Kufri Surya and Kufri Pukhraj (661 and 665 g). Tuber yield in JEX/A-121(166 g plant−1) and JEX/A-122 (156 g plant−1) was also significantly lower than the variety Kufri Surya and Kufri Pukhraj (410 and 416 g plant−1). The poor plant canopy and low yield in these clones was attributed to low leaf area, early senescence and reduced photosynthesis efficiency. Lower productivity in these clones negates the possibility of their direct exploitation towards either nutrient enhancement in potato driven food chains or as natural colourants. The genetic variability reported in this paper, however, provides impetus for future breeding work directed specially at enhancing the antioxidative matrix by targeted selections.

Storage behaviour and cooking quality of Indian potato varieties

Tubers of forty four indigenous potato varieties were assessed for storage behaviour at room temperature, tuber dry matter content and cooking quality during 2010, 2011 and 2012. The maximum, minimum temperatures and relative humidity during storage period ranged between 26 to 40°C, 17-28°C and 18 to 82%, respectively. The lowest total weight loss was recorded in variety Kufri Pushkar (7.7%) followed by Kufri Lalima (7.9%), Kufri Surya (8.3%), Kufri Red (9.2%), Kufri Dewa, Kufri Sheetman (9.3%), Kufri Chandramukhi, Kufri Jyoti (9.5%), Kufri Sindhuri (9.6%), Kufri Kuber (9.7%), Kufri Chipsona-1 (9.8%), Kufri Kundan (9.9%) and Kufri Chamatkar (10.0%). Highest tuber dry matter content (%) was observed in Variety Kufri Kundan (24.2) followed by Kufri Himsona (23.7), Kufri Frysona (23.6), Kufri Kuber (22.7), Kufri Chipsona-2 (22.3). Kufri Khasigaro (22.0), Kufri Sheetman (21.9), Kufri Chipsona-3 (21.7) and lowest in Variety Kufri Khyati and Kufri Pukhraj (16.1%). Of the total varieties, 14 were adjudged as floury, 15 mealy, 14 waxy and one (Kufri Ashoka) as soggy. The total weight loss had highly significant and positive correlation with sprout weight/Kg tubers (r = 0.76**), physiological weight loss (r = 0.97**). Based on the results potato varieties namely, Kufri Chamatkar, Kufri Chipsona-1, Kufri Chandramukhi, Kufri Dewa, Kufri Jyoti, Kufri Kuber, Kufri Kundan, Kufri Lalima, Kufri Lauvkar, Kufri Pushkar, Kufri Red, Kufri Safed, Kufri Sheetman, Kufri Sindhuri possessed excellent keeping quality with medium to long tuber dormancy, low storage losses, medium to high tuber dry matter and good flavour. The information generated in this study can be utilized in the breeding programme. This can also help the farmer to choose and cultivate the potato varieties as per demand of the consumers.

Diversity of crop development traits and nitrogen use efficiency among potato cultivars grown under contrasting nitrogen regimes

Potato (Solanum tuberosum L.) requires abundant nitrogen (N) to perform well and has low nitrogen use efficiency (NUE). We assessed phenotypic variation among 189 potato cultivars for NUE and the association between NUE and ecophysiological variables describing canopy development (CDv), under high and low N input. In 2009 and 2010, 189 cultivars were grown with N supply (soil N + fertiliser N) of 75 or 180 kg N/ha at Bant, the Netherlands. CDv was assessed weekly as the percentage of soil covered by green potato leaves (%SC). Data were analysed using a model that described CDv as a function of thermal time, based on the Beta function and estimates of cardinal temperatures. Nitrogen significantly affected model-derived, biologically relevant, curve-fit parameters for each cultivar. The t 1 (i.e., thermal time required to reach maximum soil cover (Vx)) was higher at low than at high N. Other parameters were higher at high than at low N, especially Vx and the period over which it was maintained. Nitrogen also affected tuber dry matter yield, tuber size and weight distributions, N content and N uptake but not tuber dry matter percentage. The total area under the %SC curve was highly correlated with yield in both years. Cultivars performing well under high N also performed well under low N. There was large variation in NUE component traits among cultivars; maturity type partially explained this variation. Variables of the CDv model captured this variation, N effects on light interception and its correlation with yield.

Response of potato to full and deficit irrigation under semiarid climate: Agronomic and economic implications

Yield, cost, and revenue functions of potato (cv. Agria) were developed from field experiments in 2007–2008, which were designed to determine the response of tuber yield to no irrigation for two weeks at tuber bulking (TB) and tuber ripening (TR). Deficit-irrigated treatments were compared to a well-irrigated control (C) throughout the growing season. The yield-profit maximization methodology of English (1990) was reviewed and a new procedure based on optimization software was proposed. Treatment with deficit irrigation at TB achieved marketable yield 12% lower than that obtained in the well-irrigated control (60.5Mgha−1), whereas deficit irrigation at TR reduced tuber yield by 42%, compared to the control. However, yield reduction was compensated by an increase in tuber dry matter in the deficit-irrigated treatments. The results of the newly proposed yield-profit maximization procedure show that when land is limiting, the level of water applied at which net income per unit of land is maximized (Wl) fits the yield maximizing (Wm) strategy, while when water is limiting, the level of water applied at which net income per unit of water is maximized (Ww) would result in as much water saving as 10–15% of total applied water. The results also suggest that the target yield that was obtained in the treatment with deficit irrigation at tuber bulking (53.6tha−1) was in the range of 500–560mm of water application. We concluded that deficit irrigation at tuber bulking for two weeks is a suitable scenario for potato farming, with potential benefits resulting from reduced irrigation costs.

Yield and water use efficiency of early potato grown under different irrigation regimes

Potato grown for early or off-season production plays a crucial role in the economy of several areas in the Mediterranean countries. Irrigation is important for determining yield and earliness, thus a better investigation of plant response under various pedo-climatic conditions can help to improve resource use efficiency and farmer income. A two-year field research (2009-2010) was carried out in Apulia region, southern Italy, on cv Spunta grown under three irrigation regimes: full irrigation (I100), 50% of full irrigation (I50) and rainfed (I0). Treatments were arranged in a randomized complete block design with three replicates. Plant water status, plant growth and, at harvesting, water use efficiency, yield and quality parameters were quantified. Water stress significantly affected yield response: as an average of the two years, a marketable yield decrement of 25.9 and 63.6% was observed in I50 and rainfed compared with I100 treatment, respectively. On the contrary, tuber dry matter and specific gravity increased moving from irrigated treatments to the rainfed one and varied also as a function of experimental year. The results confirmed that irrigation is required for early potato cultivation because rainfall is not sufficient to meet crop water needs. In addition, the study indicated that the irrigation regime reduced by 50% of crop water requirements was able to furnish satisfactory yield, with tuber quality characteristics similar or even better than those obtained under full irrigation.

Reciprocal effects in potato (Solanum tuberosumL.) x Andigena-Tuberosum intergroup hybridization under shortdays

Six Tuberosum and five Andigena parents were used to generate 23 Tuberosum × Andigena direct and 23 reciprocal progenies. These progenies were evaluated for total yield, marketable yield, tuber number, average tuber weight and per cent tuber dry matter in second and third clonal generations. Evaluation of progenies in field was done in Randomized Complete Block Design with split plot taking direction of cross (Andigena versus Tuberosum as female) as sub-plot and parental combination as main-plot. Significant variation was recorded in progenies for the characters studied. Results revealed that that reciprocal cross differences in inter group crosses were in general not significant for all the characters. The lack of reciprocal cross differences in short-day length environment in Indian plains shows that crosses can be attempted in either direction while breeding cultivars for Indian plains.

An ecophysiological model analysis of yield differences within a set of contrasting cultivars and an F1 segregating population of potato (Solanum tuberosum L.) grown under diverse environments

The generic ecophysiological model ‘GECROS’ simulates crop growth and development as affected by genetic characteristics and climatic and edaphic environmental variables. We used this model to analyse differences in tuber yield of potato in five cultivars covering a wide range of maturity types and 100 individuals of a diploid F1 population segregating for maturity type. Six field experiments were conducted, in which contrasting nitrogen availabilities were created to represent six environments. Values of five genotype-specific model-input parameters were estimated and calibrated. Variation among the 100 F1 genotypes was as wide as, or slightly wider than, that among the five contrasting cultivars for any of the five parameters values but not for tuber yield. For the 100 F1 genotypes, the model accounted for 86% of genotypic differences in across-environment average tuber yield and 89% of environmental difference in across-genotype average yield. But the percentage in the genotypic differences in yield for a given experiment accounted for by the model ranged from 2% to 65%. Model analysis identified Nmax (i.e. total crop N uptake) and tuber N concentration as key components affecting tuber yield for all six experiments. Genotypes with higher Nmax and lower tuber N concentration exhibited higher tuber dry matter yield. The development of potato ideotypes for any specific environments should prioritize optimising N-related traits.

Effect of Different Defoliation Systems of Ryegrass–Clover on Yield and Selected Quality Parameters of Organic Potatoes (Solanum tuberosum L.) for Industrial Processing at Harvest and After Storage

The nitrogen supply plays an important role in achieving quality characteristics in organic potato farming. Different defoliation systems of ryegrass–clover may influence the amount of fixed nitrogen available to the tubers. In a field experiment, the effect of different defoliation systems (cutting, mulching and a combination of them) of the pre-crop ryegrass–clover on selected quality attributes of organically grown potatoes, destined for processing into French fries (cv. Agria) or crisps (cv. Marlen), were conducted in two consecutive years (2003 and 2004). Parameters studied included compounds related to the sensory properties of potato food (tuber dry matter, starch, reducing sugars) as well as nutritional quality (nitrogen, minerals). Selected agronomic parameters such as total tuber yields and tuber size distribution were also compared. Furthermore, the influence of additional slurry fertilisation and 4 months of storage on these parameters were investigated. Total yields and portion of tuber yield 50–60 mm were significantly affected by the pure mulching variant in 2003. In 2003, the starch concentration at harvest, as well as after storage, was above the required minimum of 22% (cv. Marlen) and 19% (cv. Agria), while in 2004, this was slightly beneath these values. In 2004, a significant increase of starch concentration by the pure cutting variant was observed. In both years, mulched ryegrass–clover caused a decrease in tuber DM contents of 2.10 and 3.54%, respectively, compared to the cutting systems. Fertilisation significantly decreased DM and starch concentration. In 2004, the reducing sugar concentration of tubers of cv. Marlen from the pure cutting system was with 2.1 g kg−1 FM above the required maximum of 1.5 g kg−1 for crisps. In addition, storage led to a three to fivefold increase of reducing sugars concentrations in the tubers in this year. After slurry fertilisation, 8.8% higher N contents and up to 36% higher K concentrations were measured. Mulching of the pre-crop combined with slurry application led to an up to 61% higher tuber K concentration compared to the cutting system. The results indicate that different defoliation systems of the pre-crop ryegrass–clover and slurry fertilisation had only minor effects on internal tuber quality attributes. Quality parameters were more affected by the prevailing weather conditions in combination with the genotype of different potato cultivars.

Potato Crop Response to Genotype and Environment in a Subtropical Highland Agro-ecology

Potato response to environment, planting date and genotype was studied for different agro-ecological zones in Lesotho. Field experiments were conducted at four different sites with altitudes ranging from 1,655 to 2,250 m above sea level during the 2010/2011 and 2011/2012 summer growing seasons. Treatments consisted of three cultivars that varied in maturity type, two planting dates and four sites differing in altitude and weather patterns. Various plant parts were measured periodically. To understand and quantify the influence of abiotic factors that determine and limit yields, the LINTUL crop growth model was employed which simulated potential yields for the different agro-ecological zones using weather data collected per site during the study period. Observed actual crop yields were compared with model simulations to determine the yield gap. Model simulations helped to improve our understanding of yield limitations to further expand potato production in subtropical highlands, with emphasis on increasing production through increased yields rather than increased area. Substantial variation in yield between planting date, cultivar and site were observed. Average tuber dry matter (DM) yields for the highest yielding season were above 7.5 t DM ha−1 or over 37.5 t ha−1 fresh tuber yield. The lowest yield obtained was 2.39 t DM ha−1 or 12 t ha−1 fresh tuber yield for cultivar Vanderplank in the 2011/2012 growing season at the site with the lowest altitude. Modelled potential tuber yields were 9–14 t DM ha−1 or 45–70 t ha−1 fresh yield. Drought stress frequently resulted in lower radiation use efficiencies and to a lesser degree harvest indices, which reduced tuber yield. The site with the lowest altitude and highest temperatures had the lowest yields, while the site with the highest altitude had the highest yields. Later maturing cultivars yielded more than earlier maturing ones at all sites. It is concluded that the risk of low yields in rain-fed subtropical highlands can be minimised by planting late cultivars at the highest areas possible as early as the risks of late frosts permit.

Soil Macronutrients Influence Antioxidant Status in Early Season Potatoes

Potatoes, a good source of antioxidant can prove low cost supplement in Indian diet for Fig ht against malnourishment, which is presently growing at alarming rate. Qualitative parameters viz. antioxidants, starch, dry matter, secondary metabolites etc. in potato are influenced by genotype and environmental conditions. The antioxidants contents can be enhanced significantly by employing suitable variety, cultivation regimes and environmental stresses. Present research reports the identification of antioxidant affluent variety, effect of macronutrients on antioxidants content in tubers per say and compound antioxidants yield in short duration crop under heat stress condition. Among prevalent ten potato varieties, Kufri Surya was adjudged best with maximum ascorbic acid (20.4mg 100g FW−1) and carotenoids contents (44.0μg 100g FW−1) and moderate phenols in fully matured tubers. The results indicated that Kufri Surya tubers harvested at infancy (60 day) could achieve moderate levels of ascorbic acid (11.0 mg 100g FW−1), maximum phenols (59.9 mg 100g FW−1) and highest tuber dry matter (18.4%) with 240 kg N ha−1. Application of 240 kg N ha−1 had better tuber yield (9.2 t ha−1), highest total phenols yield (5.5 kg ha−1) and comparable ascorbic acid productivity (1.01 kg ha−1). Likewise, ascorbic acid and tuber dry matter were increased significantly by phosphorous and potash nutrients, whereas total phenols improved marginally. The highest tuber yield (8.9 t ha−1), compounded yield of ascorbic acid (1.51kg ha−1) and total phenols (4.98 kg ha−1) were harnessed with 60 kg P2O5 and 100 kg K2O ha−1. The findings suggest that macronutrients N, P2O5 and K2O applied @ 240, 60 and 100 kg ha−1, respectively were most appropriate levels for harnessing optimum antioxidants yield with >18.0% tuber dry matter in 60 days early crop of potato variety Kufri Surya.

EFFECTS OF CARBON DIOXIDE AND PHOSPHORUS SUPPLY ON POTATO DRY MATTER ALLOCATION AND CANOPY MORPHOLOGY

□ Data on combined effects of elevated carbon dioxide concentration (CO2) and phosphorus fertilization (P) on potato are scarce. Growth chamber studies (E1 and E2) that used three P and two CO2 levels were conducted. Leaf, stem, tuber, and stolon dry matter increased with P. Lateral-stem production was sensitive to P with a minimum 2.5-fold increase in mass. Leaf length increased an average 20.2% in E1 and 38.2% in E2 and leaf area increased an average 336% in E1 and 470% in E2 across CO2 levels. Tuber dry mass increased 22% in E1 and 38.2% in E2 in response to elevated CO2 and total dry mass by 14.1 and 15.4%. Tissue P contents increased with P but were unaffected by CO2. Effects of P on canopy branching were associated with plant N status. The studies suggest elevated CO2 levels are unlikely to alter potato P requirements on a unit mass basis.

Seasonal light interception, radiation use efficiency, growth and tuber production of the tuber crop Plectranthus edulis

Plectranthus edulis (Vatke) Agnew (Lamiaceae) is an ancient Ethiopian crop that produces below-ground, edible tubers on stolons. It is grown from seed tuber pieces. There is thus far little quantitative information on dry matter production of this crop and parameters determining growth and yield. The objective of this study was to understand and quantify the growth of P. edulis, and identify the processes determining and limiting yield. Two similar experiments were carried out at two sites (Awassa and Wondogenet in southern Ethiopia) in a split-plot design with five blocks and cultivar (Lofuwa and Chankua) as main factor and sampling date [20 2-weekly sampling dates from 14 to 280 days after planting (DAP)] as split factor. The crop was unknown at the start and showed an unusual growth pattern, for which reasons growth was analysed at a basic level.Maximum tuber weights were achieved 238 DAP in both cultivars and at both sites, and we consider the period up to 238 DAP as the growth period and the remaining time until the last sampling as the period of in situ storage, as is common farmers’ practice. Tuber dry weights at 238 DAP were c. 900–1000gm−2 and tuber dry matter concentrations 19–21%, corresponding to c. 4.5–4.9kgm−2 fresh tuber yield. Two processes limited the dry matter production: radiation interception by the crop and the conversion of the intercepted radiation into dry matter.Only about one third of the incident radiation was intercepted by the green leaves due to late emergence (c. 4 weeks), a slow development of the canopy after emergence until full ground cover was attained (c. 20 weeks), a short period during which ground cover was complete (c. 2 weeks) and a long period of declining ground cover starting 8 weeks before the end of the growing period.The radiation use efficiency (RUE) was established for the crops in Wondogenet and was only 1.59gMJ−1 PAR, on average across sampling dates. RUE varied across the growing period, increasing after emergence until early after tuber formation to about 2.7gMJ−1 PAR, then again decreasing because of a temporary stagnation (cv. Chankua in Awassa) or decrease (all other cultivar×site combinations) in total crop dry weight, starting 168 DAP in Awassa and 182 DAP in Wondogenet and lasting several weeks. During this period crop biomass decreased because the loss in canopy dry matter – especially stem dry matter – was not yet compensated for by an increase in tuber dry matter. Later, tuber production more than outweighed the decrease in canopy dry weight, and total dry weight and RUE increased again. During this last period the green stems might have significantly contributed to crop photosynthesis. The relative allocation of the total dry matter produced to the tuber varied between 81 and 99% at 238 DAP. Keeping the tubers in the soil after 238 DAP reduced tuber dry weights by 37–54% in 6 weeks.

Nitrogen Use by Yam as Affected by Mineral Fertilizer Application

Soil fertility decline and high N demand during plant growth are cited as main causes of low yield in yam (Dioscorea spp.). As information regarding fertilizer N use in yam is lacking, a field experiment was undertaken in 2006 and repeated in 2007 in central Côte d'Ivoire using 15N (15NH415NO3) labeled fertilizers to monitor N uptake and fertilizer use efficiency in D. alata. The 15N‐labeled fertilizer was added in two splits (at 90 and 130 d after planting) for a target tuber yield of 40 Mg fresh tuber ha−1. The application of mineral fertilizers increased total biomass production and tuber yield as well as N uptake from native soil organic matter. The recovery of 15N‐labeled fertilizer applied at 90 and 130 d after planting was not significantly different but the year affected 15N recovery by the plant. The maximum 15N recoveries calculated from the sum of the 15N recovery measured at both application dates were 46 and 23% in 2006 and 2007, respectively. Leaf dry matter and leaf N uptake were higher in 2006 than in 2007, but tuber dry matter was not different between years at the final harvest. Up to 170 kg N ha−1 was returned to the soil through the fallen shoots, indicating an important recycling of N for soil fertility replenishment. Thus, crop succession or intercropping are encouraged in a yam cropping system. Our results also show that the application of mineral fertilizers had a strong “priming effect” on the native soil N in both years.

Chlorpropham Affects Processing Quality of Potato During Storage

Undesirable storage conditions lead to physical and chemical quality loss in stored potatoes (Solanum tuberosum L.), which affects consumer acceptability. This study evaluated the effects of temperature on storage stability and processing quality of chlorpropham-treated potato cvs. Kufri Chipsona-1 and Kufri Pukhraj stored at 2 or 11°C and approximately 90% relative humidity (RH). Postharvest application of chlorpropham (40 mL·Mt−1 twice) was effective in checking sprouting and maintaining low reducing sugar levels in ‘Kufri Chipsona-1’ tubers stored at 11°C, approximately 90% RH up to 6 months. French fries and chips prepared from ‘Kufri Chipsona-1’ had lower moisture content, oil uptake, and higher yield than from ‘Kufri Pukhraj’. French fries and chips prepared from potatoes stored at 2°C had higher moisture content and oil uptake; those from potatoes stored at 11°C had lower values. There was a negative relationship between tuber dry matter and oil uptake during storage at 11°C. ‘Kufri Chipsona-1’ was best for processing into french fries and chips and potato products were found to be highly acceptable for up to 6 months of storage.

Differential response of potatoes (Solanum tuberosum L.) to salinity in an arid environment and field performance of the seed tubers grown with fresh water in the following season

Ten potato varieties, commonly grown in the Mediterranean region, were grown on sandy soil in an arid desert area of Israel. The potatoes were drip-irrigated with three water sources: fresh water (control – ENV1), saline water from a local well (intermediate salinity – ENV2) and the local well water enriched with NaCl (high salinity – ENV3). The average salinity levels expressed as the electrical conductivity (EC) measured in the soil extracts from the root zone were 2.35, 5.1 and 8.5dSm−1 for the ENV1, ENV2 and ENV3 treatments, respectively. Salinity stress decreased fresh tuber yields, increased tuber dry matter and soluble solids, increased tuber electrolyte content and lowered osmotic potential (OP) of the tuber sap in all varieties. ANOVA and Fisher's LSD pair-comparisons revealed highly significant differences among the varieties in all traits. Correlation analyses showed negative associations between tuber yield and tuber traits (dry matter, DM; total soluble solids, TSS, EC and OP). Positive associations were found between tuber DM and TSS, EC and OP. There was no positive association between early maturation or yielding capacity and tolerance to salinity. Vivaldi, a high-yielding variety and Almera, a low-yielding variety were found significantly less susceptible to salinity than Mondial, a late-maturing and high-yielding variety, and Charlotte, an early-maturing and low-yielding variety. The significant differences in the response to salinity stress indicated genotypic variation in the response to salinity and support the potential of breeding for tolerance to salinity in potatoes.When seed tubers of the three irrigation treatments were grown with fresh water irrigation during the following season, there were no significant differences in plant growth or tuber yields from the three seed sources in most varieties indicating the possibility of using saline water for the production of potato seed tubers.

Effect of Manure Application Timing on Potato Yield, Quality, and Disease Incidence

This study was established to determine whether the timing of liquid dairy manure application prior to planting potatoes influenced potato crop performance and the occurrence and severity of common scab (Streptomyces spp.) and verticillium wilt (Verticillium dahliae). Four potato (Solanum tuberosum L.) varieties with varying levels of resistance to common scab and verticillium wilt were planted on a site treated with manure applied at 280,500 L ha−1 to separate plot areas 18, 6, or 1 month before potato planting in each of 2 years. Total tuber yield for 2001 showed a significant interaction between time of manure application and variety, with more scab-susceptible varieties (Russet Norkotah and W-1151R) showing lower yields compared to the fertilizer control when the manure application was made 1 month before planting. In 2002, the proportion of U.S. No. 1 tubers was significantly lower when manure was applied 1 month before planting, especially for W-1151R. Tuber dry matter was significantly reduced by manure application in both years, but was not consistently related to time of manure application. Total yield was significantly decreased as common scab levels increased, and this relationship was primarily driven by the low yield/high scab levels associated with W-1151R and Russet Norkotah planted 6 or 1 month after manure application in 2001. Late-season verticillium evaluations showed highest levels in 2001 when manure was applied 1 month before planting to susceptible varieties Superior and Russet Norkotah. This experiment showed that when manure was applied immediately ahead of potato planting yields, and quality of some varieties decreased in 1 of 2 years. Therefore, it may be safer to apply manure at least 18 months prior to planting potatoes.

Produtividade, qualidade de tubérculos e incidência de doenças em batata, influenciados pela aplicação foliar de silício

O objetivo deste trabalho foi avaliar o efeito da aplicação de silício por via foliar, na forma de ácido silícico estabilizado, sobre a incidência de doenças, produtividade e qualidade de batata. Foram realizados três experimentos: um com a cultivar Agata e outro com a Atlantic, em Botucatu, SP; e um com a cultivar Agata, em Itaí, SP. Utilizou-se delineamento de blocos ao acaso, com oito repetições. Os tratamentos consistiram de: testemunha (sem aplicação de Si) e aplicação de Si via foliar, na dose 2 L ha-1, de produto comercial com 0,8% de Si solúvel como concentrado estabilizado de ácido silícico. A dose de Si foi parcelada em quatro aplicações durante o ciclo da cultura. A aplicação de Si reduz a severidade da requeima e a incidência de canela-preta, além de aumentar a produtividade e o teor de matéria seca dos tubérculos. O fornecimento de Si via foliar aumenta a produtividade de tubérculos, independentemente de seus efeitos sobre a incidência de doenças.

Evaluation of Yield and Yield Attributes of Five Sweet Potato (<i>Ipomoea batata</i> (L)Lam) Varieties in Owerri - Imo State

Five sweet potato varieties (Ex –igbariam local, TIS 86/0356, TIS 8441, TIS 87/0087, and TIS 2532.OP.1.13) were evaluated for yield and agronomic performance in Imo State University Farm, Owerri. The experiment was laid out in a randomised complete block design with three replications. The planting density was 33,000 plants/ha and NPK (15:15:15) fertilizer was applied blanket at the rate of 100kg/ha. Significant (p= 0.05) differences were obtained in the performance of the varieties in fresh tuber yields, vigor at six weeks after planting, leaf area/plant, fresh biomass, tuber dry matter and biomass dry matter yields. Variety TIS 86/0356 gave significantly (p= 0.05) the highest mean fresh tuber yield of 7.38 t/ha and a significantly (p=0.05) high mean biomass dry weight of 3.08 t/ha, whereas the variety TIS 8441 gave the lowest mean fresh tuber and biomass dry matter yields of 1.28t/ha and 1.29t/ha, respectively. Variety TIS 86/0356 was therefore recommended for sweet potato growers in the region.Key words: Sweet potato, varieties, yield evaluation.

Phenotypic analysis of tuber yield- and maturity-related traits in white yam (Dioscorea rotundata)

Inadequate yield potential of available varieties and their long growth periods are two of the factors limiting yam ( Dioscorea spp.) production. Identifying yield- and maturity-related traits and breeding for them will enhance production. Ten morphological/physiological traits: time of shoot emergence, time of tuber initiation, plant height, shoot dry weight, time of shoot senescence, tuber fresh weight (tuber yield), tuber number/plant, tuber parenchyma colour, tuber dry matter content and tuber dormancy period were assessed in eight accessions of D. rotundata (white Guinea yam) on the field in 2008 and 2009. Shoot dry weight and plant height were identified as the major tuber yield-related traits. Early field emergence and tuber initiation, short tuber dormancy period and low tuber dry matter content may also be related to tuber yield. High yielding accessions were low in tuber dry matter content. Moreover, early and late maturing accessions could be separated by time of attainment of uniform parenchyma colour within a tuber, length of tuber dormancy period and time of shoot senescence. Accessions were identified that may be used as parents for developing mapping populations for some of the traits assessed in the study. Key words: Dioscorea rotundata , tuber maturity, tuber dormancy, dry matter content, yield related traits, senescence.

Effect of harvesting interval on biomass yield and chemical composition of taro (Colocasia esculenta (L.) Schott) for feeding pigs in Laos

Cheap feedstuffs with acceptable protein content are needed for the improvement of pig performance in developing countries, and the utilization of traditional crops is one possible solution. Taro (Colocasia esculenta (L.) Schott) was grown for two seasons in Vientiane, Lao PDR, and was subjected to three harvesting frequency treatments. The treatments applied were harvesting leaves and petioles at intervals of 4 (H4), 6 (H6) and 24 (H24) weeks, respectively. The tubers were harvested at the last harvest occasion. Leaf, petiole and tuber dry matter (DM) yield, leaf proportion (DM basis) and chemical composition of the leaves and petioles were determined. Treatments H4 and H6 yielded significantly more leaf and petiole DM than treatment H24 in both years. Total leaf DM yield was 2146, 1654 and 364kgha−1 in 2007 and 1483, 1341 and 691kgha−1 in 2008 for treatments H4, H6 and H24, respectively. Tuber DM yield was not affected by the treatments and was on average 3667 and 2732kgha−1 in 2007 and 2008, respectively. Leaf proportion did not generally differ between treatments and was on average 52 and 62% in 2007 and 2008, respectively. The leaves contained between 160 and 260gkg DM−1 crude protein (CP) which was much higher than in the petioles. Although significant, the difference between treatments was small, which was due to the high rate of leaf turn-over (5 weeks). Ash content of the leaves was 112–145gkg DM−1, and crude fiber (CF) was a 173–206gkg DM−1. The total essential amino acid content of taro leaf ranged from 40 to 45g, 16gN−1. It is concluded that taro leaves are a potential protein feed resource for growing pigs, and that leaves can be harvested frequently with no detrimental effect on tuber yield.