Showing papers by "Central Tuber Crops Research Institute published in 2005"

Post harvest spoilage of sweetpotato in tropics and control measures

Abstract: Sweetpotato storage roots are subjected to several forms of post harvest spoilage in the tropical climate during transportation from farmers' field to market and in storage. These are due to mechanical injury, weight loss, sprouting, and pests and diseases. Sweetpotato weevil is the single most important storage pest in tropical regions for which no control measures or resistant variety are yet available. Several microorganisms (mostly fungi) have been found to induce spoilage in stored sweetpotatoes. The most important among them are Botryodiplodia theobromae, Ceratocystis fimbriata, Fusarium spp., and Rhizopus oryzae. The other less frequently occurring spoilage microorganisms include Cochliobolus lunatus (Curvularia lunata), Macrophomina phaseolina, Sclerotium rolfsii, Rhizoctonia solani, Plenodomus destruens. Microbial spoilage of sweetpotato is found associated with decrease in starch, total sugar, organic acid (ascorbic acid and oxalic acid) contents with concomitant increase in polyphenols, ethylen...

Gelatinisation Properties of Cassava Starch in the Presence of Salts, Acids and Oxidising Agents

Abstract: The effect of various cations, anions, acids and oxidising agents on the gelatinisation properties of cassava starch was studied and wide variation was observed in the pasting and swelling properties. Sodium chloride and sodium thiosulphate slightly lowered the peak viscosity of cassava starch with increase in concentration, whereas with sodium sulphite, calcium chloride and sodium hypochlorite, a more significant decrease in the viscosity and breakdown was observed. Ferrous sulphate, alum, aluminium chloride and acids enhanced the peak viscosity at lower concentrations followed by a decrease at 1% and above. Sodium metabisulphite elevated the viscosity at 0.05 and 0.1%, while sodium hypochlorite lowered the viscosity and breakdown. DSC studies showed that aluminium chloride, sodium sulphite, and sodium thiosulphate brought about an increase in Tonset, Tend and ΔH values at higher concentrations. A decrease in swelling volume was observed from 0.05 to 1% concentration of sodium chloride and above that there was a gradual increase. With sodium sulphite, a significant increase in swelling volume was observed at 2.5 and 5% levels. With 0.05 and 0.1% aluminium chloride and sodium metabisulphite an increase in swelling volume was noticed, but at higher concentrations there was a drastic fall. Sodium chloride, sodium sulphite, sodium thiosulphate and calcium chloride brought about decrease in starch paste clarity with increase in salt concentration, whereas ferrous sulphate, aluminium chloride, sodium hypochlorite, hydrochloric acid and acetic acid improved the starch paste clarity.

Synthesis and Characterization of low DS Succinate Derivatives of Cassava (Manihot esculenta Crantz) Starch

Abstract: Succinylation of cassava starch was carried out in aqueous medium to prepare derivatives with low degree of substitution (DS) and the physicochemical properties of the products were determined. A response surface design was used for the experiment with three levels of each of the three variables viz., concentration of succinic anhydride, reaction time and pH of the reaction medium. The reaction was followed in terms of the DS of the products and reaction efficiency (RE). The degree of substitution of the derivatives varied from 0.001 to 0.022 and reaction efficiency from 2.2 to 46.8%. The DS and RE showed an adequate fit to a second order polynomial model of the variables used. Succinylation brought about increase in the swelling volume, peak viscosity and paste clarity of the starch. However, the pasting temperature and solubility did not show any significant change. The in-vitro α-amylase digestibility of the succinylated derivatives decreased in comparison to that of native starch and this decrease correlated with a corresponding increase in DS.

Microwave‐Assisted Synthesis and Characterization of Succinate Derivatives of Cassava (Manihot esculenta Crantz) Starch

Abstract: The use of microwave heating to prepare very rapidly cassava starch succinates with high viscosity is described. A response surface design was used for the experiment and different factors affecting the succinylation of cassava starch, including concentration of succinic anhydride, reaction time, temperature and moisture content of the medium were investigated. The degrees of substitution of the modified starches increased with an increase in reaction time and were in the range 0.007 - 0.051. The products exhibited higher viscosity, lower pasting temperature, enhanced water binding capacity and reduced swelling and paste clarity than unmodified cassava starch. The results of this study indicated that succinylation of starch can be achieved in shorter reaction times, which offers a benefit to laboratories and industries involved in developing newer and more versatile uses for cassava starch.

The geographical distribution of allelic diversity, a practical means of preserving and using minor root crop genetic resources

Abstract: This paper addresses the preservation and use of minor root crop genetic resources, mostly aroids and yams. Conservation is fraught with difficulty: ex situ collections are expensive to maintain and methods for on-farm conservation have not been studied. Conventional breeding strategies present serious limitations when applied to these species. Furthermore, the evaluation and distribution of improved material are as problematical as its conservation. The similarities shared by these species regarding their domestication, breeding constraints and improvement strategies as well as farmers' needs, are briefly reviewed. Based on these biological constraints, we propose a practical alternative to current conservation and breeding strategies. This approach focuses on the geographical distribution of allelic diversity rather than localized ex situ and/or in situ preservation of genotypes. The practical steps are described and discussed. First, a core sample representing the useful diversity of the species is assembled from accessions selected for their diverse and distant geographic origins, wide genetic distances, quality, agronomic performances and functional sexuality. Second, the geographical distribution of this core sample, in vitro via a transit centre, allows the direct use of selected genotypes by farmers or for breeding purposes. Third, the distribution of genes is realized in the form of clones resulting from segregating progenies and, fourth, farmers select clones with local adaptation. (Resume d'auteur)

Physicochemical properties of the starchy flour extracted from sweet potato tubers through lactic acid fermentation

Abstract: The efficiency of starch extraction from sweet potato tubers was improved by lactic acid fermentation using a mixed culture inoculum. Study of the properties of the starchy flour showed that there was a significant reduction in the starch content and consequently the soluble and apparent amylose contents of fermented samples from all six varieties used. A fall in peak viscosity and viscosity breakdown was observed for fermented samples, while the pasting temperature was enhanced significantly. The fermented flour showed greater solubility and reduced swelling. Differential scanning calorimetry studies indicated a delay in gelatinisation and a fall in enthalpy of gelatinisation of the starch on fermentation. Unlike cassava, all the properties of the starch from sweet potato tubers, ie viscosity, swelling, solubility, gelatinisation temperature, amylose content and starch content, were affected by fermentation, and variation was also observed among cultivars. Copyright © 2005 Society of Chemical Industry

Anthocyanins in Sweet Potato Leaves-Varietal Screening, Growth Phase Studies and Stability in a Model System

Abstract: The sweet potato genotypes in the CTCRI germplasm collection were screened for anthocyanin content in the young top leaves and the values varied from 20-200 mg/100g fresh weight of the leaf samples, the highest being recorded for the genotype S-406. Total anthocyanin content (TAcy) showed significant difference among genotypes, growth phases, and growing seasons. The TAcy in the leaves reached a peak at 20 days after planting, declined after 35 days, returned to 20 day levels or higher by 50-65 days and remained stable or exhibited a slight decrease by 105 days after planting, for most of the genotypes selected for growth phase studies. Approximately 50-60 % decrease was observed in the TAcy of the frozen/thawed leaf samples. The stability of anthocyanin pigments in a model sugar-citrate solution at ambient (30 ± 2 °C) and refrigerated (8 ± 2 °C) conditions was studied. The solutions stored at low temperature and in dark showed higher retention of pigments. Compared to anthocyanins extracted from grape po...

Standardisation of true cassava seed (TCS) programme with special emphasis on more homogeneous, CMD resistant progenies

Abstract: The propagation of cassava through true seeds (sexual seeds) rather than by clones is a promising option due to its manifold advantages such as enhancing the multiplication rate, keeping the dreaded cassava mosaic disease (CMD) under check, longer seed viability, ease of storage and transport. The high genetic heterogeneity and consequent variation among seedlings is the major stumbling block in sexual propagation. In the present study, a CMD resistant exotic accession MNga-1 and a promising cultivar “Ambakadan” with profuse fruit setting, seed output and male sterility were identified to be promising parents for the TCS programme. The rate of sexual propagation could be more than 20-fold over the traditional clonal propagation. Seed treatment with 1% KNO3 or 300 ppm GA promoted uniform seed germination and seedling vigour and reduced the transplanting period from 45 days after planting (DAS) to 30 DAS. Removal of taproots of seedlings while transplanting enhanced tuber development. Tuber yield of first clones (C1) was significantly superior to that of the seedlings. The dry matter content and starch output of seedlings and first clones were comparable to that of the commercial varieties. Similarly, the HCN and cooking quality of seedlings and first clones were at acceptable levels. In the open pollinated (OP) progenies of the Ambakadan the CMD infection increased drastically due to secondary spread of the pathogen. The hybrid progenies of Ambakadan and the CMD resistant line MNga-1 revealed higher percentage of CMD free seedlings and first clonal progenies in the evaluation trials conducted at CTCRI Thiruvananthapuram and ARS, Peddapuram during 2001–2002 and 2002–2003. Nearly homogeneous hybrid population resistant to CMD could be obtained by systematic roguing at seedling and first clonal stage.

Dioscorea alata, a new host of Sclerotium rolfsii in India

Abstract: Greater yam ( Dioscorea alata ) is an important edible species of Asia, and is mainly used as a subsidiary vegetable. Kerala, West Bengal, Bihar, Orissa, Assam, Gujarat and Maharashtra are the major yam-cultivating states in India. In 2002 leaves of D. alata growing in farmers’ fields in the Pathanamthitta district of Kerala showed black, circular, concentric spots 5–10 mm in diameter in the middle and bottom portion of the vines. As the disease advanced, the central portion of the leaf spots dried and fell out, resulting in shot-hole symptoms. When diseased leaves were placed in a humid chamber, abundant fluffy white mycelia emerged from the leaf spots. When isolated on potato dextrose agar, the diameter of hyphae ranged from 1·5 to 2·7 μ m. Numerous round to ellipsoidal, dark brown-to-black, smooth sclerotia were observed in the culture. Disease symptoms were reproduced when detached D. alata leaves were inoculated with the isolated culture and incubated in high humidity in Petri dishes for 4 days. The pathogen was reisolated from the inoculated leaves. Based on morphological and cultural characteristics (Singh, 1982), the pathogen was identified as Sclerotium rolfsii . A culture has been deposited in the Indian Type Culture Collection of the Indian Agricultural Research Institute, New Delhi (ITCC 5789·04). Sclerotium rolfsii associated with leaf spot of Dioscorea spp. has been reported earlier in Nigeria (Amusa, 1999). There are no previous records of this disease on D. alata from India (Bilgrami & Jamaluddin Rizwi, 1991; Butler, 1997).

Growth analysis of Dioscorea species. (164)

Abstract: Comparative growth analysis was carried out on three edible Dioscorea species in field experiments laid out at Central Tuber Crops Research Institute, Thiruvananthapuram, India, during 1996 and 1997, mainly to elucidate the growth characteristics of recently developed trailing (T) and dwarf (D) varieties of Dioscorea rotundata in comparison with native species of Dioscorea (D. escuelenta and D. alata) under Asian conditions. The leaf area index (LAI) was the highest for D. alata and least for D. escuelenta. The LAI attained maximum values at fifth month in D. escuelenta and D. alata and at sixth month in D. rotundata (T) and D. rotundata (D). The crop growth rate (CGR) of D. rotundata (T) and D. alata were almost similar but significantly greater than that of D. escuelenta and D. rotundata (D). In D. escuelenta, except for a slight decline at Phase 2 [4-5 months after planting (MAP)], the CGR followed a steady increase and attained maximum value at the last phase (6-7 MAP). The CGR peaked at Phase 2 (4-5 MAP) in D. rotundata (T) and at Phase 3 (5-6 MAP) in D. alata and D. rotundata. The early season advantage of CGR in these species might explain their high-yielding nature. In all the species, except D. rotundata (T), net assimilation rate (NAR) showed an increasing trend with advancing crop age. Dioscorea escuelenta possessed the highest NAR and D. alata had the lowest NAR. Significantly highest relative growth rate (RGR) values that declined towards harvest, were computed during the early phases in all the species. With advancing growth, there was significant decrement in LAR, specific leaf area (SLA), and leaf weight ratio (LWR) due to reduction in LAI due to leaf senescence and greater diversion of photoassimilates for tuber development. The LAR, SLA, and LAI of Asiatic species showed significant positive association with rainfall. Highest harvest index (HI) was computed in D. escuelenta closely followed by D. rotundata (D). The HI was significantly lower in D. alata and D. rotundata (T) due to greater canopy size of these species. However, HI of D. rotundata (T) was slightly higher than that of D. alata.