Disease-free Planting Material Research Articles

Somatic Embryogenesis in Theobroma cacao L.

Theobroma cacao L. is a tropical tree originating in the Amazon, where it grows naturally in the shade of tropical rainforests. Cacao sub-products, such as butter and powder, are produced as principal components of chocolate and contain important nutritional compounds such as polyphenols and flavonoids. However, bean production is decreasing because plantations are antiquated and unproductive. Cacao propagation has been traditionally performed through classical propagation methods, such as grafting or rooted cuttings, but those methods are not sufficient to obtain large quantities of planting material with the desired genetic quality and optimal plant health. In the search for solutions to this problem, somatic embryogenesis (SE) is a vegetative method used for cacao propagation that has the potential to be explored. SE is a type of clonal propagation by which totipotent cells in the somatic tissue can develop into embryos and subsequently convert into plants.This method offers significant technological advantages because it is possible to obtain a large quantity of disease-free planting material with good agronomic characteristics and genetic stability. In T. cacao, tow techniques of in vitro micropropagation have been reported as direct and indirect SE. Indirect SE requires the additional step of cell dedifferentiation, unlike direct SE, which does not require this step. Here, we report a protocol using direct and indirect SE techniques using two types of culture methodologies-solid and liquid culture media.

Standardization of rapid multiplication protocol in petaloid male sterile lines of African marigold (Tagetes erecta) through in vitro culture

Marigold (Tagetes erecta L.) is one of the farmer’s first choice for commercial cultivation. It is commonly propagated through seeds, but some ornamentally high valued petaloid and gynomonoecious lines can only be maintained through vegetative propagation. Therefore, the objective of the present investigation was to develop efficient in vitro protocol for mass multiplication of commercially high valued petaloid male sterile cultivars. Nodal segments were chosen as explant from two thermotolerant marigold cultivars, viz. Siracole Orange and Siracole Yellow. Explants were pre-treated with carbendazim (0.2%) + metalaxyl (0.2%) + 8-hydroxy quinoline citrate (200 mg/l) for 60 minfollowed by surface sterilization with 0.1% HgCl2 for 4 min to eliminate the microbial contamination. Highest culture establishment (82.2%) and earliest bud emergence (3.88 days) was recorded in Murashige and Skoog (MS) medium supplemented with BAP (0.5 mg/l) and NAA (0.05 mg/l). Maximum (6, 28, 122 and 404 shoots/explant) proliferation with healthy shoots and free from callus was obtained on MS medium supplemented with 0.5 mg/l BAP + 0.1 mg/l NAA + 2.5 mg/l AgNO3 in 30, 60, 90 and 120 days after culture respectively. Maximum elongation (2.10 cm) wasobserved on MS media devoid of growth regulators (control). Highest rooting percentage (96.50%), maximum number of roots (23.37), rapid root induction (5.25 days) and high ex vitro survival (91.25%) was noted in ½ MS medium supplemented with 0.5 mg/l IBA. Highest plant survival (98.10%) and superior plant growth was observed when rooted plants were shifted to low-cost polypropylene glasses instead of traditional glass bottle system. This protocol is highly useful for mass multiplication of true-to-type, disease free planting material as well as helpful in long termmaintenance of germplasm lines.

Designing and Evaluation of Bagasse Powered Preheating Device for Seed Cane Hot-water Treatment Plant

As a solution for the energy crisis facing today, the biomass from the sugarcane industry plays major role as an energy source in developing countries. Sugarcane (Saccarhum officinarum) is a globally important source of commercial sugar, which accounts for over 75 percent of the world sugar production. It is estimated that, 30 percent of wet bagasse is produced in a normal sugar mill. Sugarcane bagasse has a heating value of 16792.44 kJ/kg. There is a high potential for using bagasse as a biomass energy source of agricultural sector when considering its thermal properties and the availability. Due to non-availability of disease-free healthy planting materials, sugarcane productivity in Sri Lanka has decreased. Hot water treatment of sugarcane planting material is practiced to control systemic diseases of sugarcane such as ratoon stunting disease and smut. Operating of the existing hot water treatment plants require high electricity for the initial heating process which is very costly and time consuming. This research is focused on designing and evaluating of a bagasse powered pre-heating device for seed cane hot water treatment plant for saving energy and time. The flue gas generated by burning of bagasse was used as the energy source for steam generation inside the pre-heating device. The pre-heating device was designed by combining the concepts of water tube boiler and shell boiler so that the device is named as the combined steam generator. Specifications of the preheating device were calculated according to the heat energy requirement of feed water, steam and fuel energy. Conceptual design for the new pre-heating device was developed considering the system requirements. Based on the concept, a detail design of each part of the device was developed with properly defined dimensions, using a parametric 3D modeling software and simulation process carried out using finite element analysis (FEA). Then the preheating device was completely assembled with fabricated parts. According to the evaluation results, efficiency of the combined steam generator was 80.14%. So the time and the electric energy consumption are reduced by 37% and 99.17% respectively. Keywords: Seed cane, Bagasse, Hot water treatment, Biomass energy, Steam

English

Taro leaf blight disease has recently been reported in Cameroon to cause between 50 and 100% yields loss of taro in most of the agro-ecological crop growing regions. This has led to a significant reduction in disease-free planting materials, edible crop and increased. The Meristem culture technique has been used to produce crop plants free of viruses and fungi especially in vegetative propagated colocassia plants. This aimed at applying in-vitro micro-propagation technique for sustainable production of four local taro cultivars in Cameroon. This study was conducted at the Root and Tuber Tissue Culture Laboratory, of the Institute of Agricultural Research for Development (IRAD), Bambui from April 2015 to November 2016. Micro-plants from four local taro cultivars were produced in vitro from apical meristem tips. The tip meristems were excised from corms of the four local taro cultivars. The excised explants were surface sterilized with alcohol and sodium hypochlorite in sequence steps at different concentrations. Meristems were cultured at establishment stage on Murashige and Skoog (MS) medium with 30 g of sugar, 1.1 ml of 6-benzylaminopurine and 7 g of agar. Shoots proliferation was induced in MS with 2.2 ml of 6-benzylaminopurine (BAP). Result shows a significant difference at p≤0.5 in number of shoots, petiole length, open leaf and corm diameter among the cultivars and no significant variation in mean number of senescence leaf with respect to all the cultivars, at 60 days of shoot tip culture. At rooting stage, taro shoots were cultured on MS media supplemented with 10 ml of 0.1 mg/ml naphthalene acetic-acid (NAA). Roots were produced on all the cultivars with excellent mean growth rate of 14.7 ± 0.69 recorded in cultivar with dark green petiole and small leaves.   Key words: Taro cultivars, in-vitro micro-propagation, benzylaminopurine, naphthalene acetic-acid, Murashige and Skoog.

Effect of Sucrose and Growth Regulator’s Level on Ginger Micropropagation

Ginger is most important cash crop of the hilly region of Nepal. However, availability of disease free planting material (rhizome) is the major problem faced by Nepalese farmers. Tissue culture is the only option to produce disease free rhizome of ginger. Suitable culture media combination is most important for the production of planting material in ginger through tissue culture. Therefore, effect of different level of sucrose and growth regulators on micro-propagation of ginger was studied using local collection ‘Kaski Local’. Early stage bud was used as explant. MS basal media with different level of sucrose and growth regulators was used as tissue culture media. 30 g/L sucrose, 30 g/L sucrose+5mg/L BA, 30 g/L sucrose+5 mg/L BA+0.5 mg/L NAA, 60 g/L sucrose+5mg/L BA, 60 g/L sucrose+5 mg/L BA+0.5mg/L NAA, 90 g/L sucrose+5 mg/L BA was used in this study. The explants were surface sterilized, cultured and incubated at 25±2°C, 90-95% relative humidity and 14:10 hours light:dark photoperiod for 8 weeks. Increased level of the sucrose increased the rhizome weight, however, addition of NAA produced more positive effect for this. MS basal media with 60 g/L sucrose+5 mg/L BA+0.5 mg/L NAA produced higher rhizome weight.Journal of Nepal Agricultural Research Council Vol.3 2017: 45-48

Community phytosanitation to manage cassava brown streak disease

Cassava viruses are the major biotic constraint to cassava production in Africa. Community-wide action to manage them has not been attempted since a successful cassava mosaic disease control programme in the 1930s/40s in Uganda. A pilot initiative to investigate the effectiveness of community phytosanitation for managing cassava brown streak disease (CBSD) was implemented from 2013 to 2016 in two communities in coastal (Mkuranga) and north-western (Chato) Tanzania. CBSD incidence in local varieties at the outset was >90%, which was typical of severely affected regions of Tanzania. Following sensitization and monitoring by locally-recruited taskforces, there was effective community-wide compliance with the initial requirement to replace local CBSD-infected material with newly-introduced disease-free planting material of improved varieties. The transition was also supported by the free provision of additional seed sources, including maize, sweet potato, beans and cowpeas. Progress of the initiative was followed in randomly-selected monitoring fields in each of the two locations. Community phytosanitation in both target areas produced an area-wide reduction in CBSD incidence, which was sustained over the duration of the programme. In Chato, maximum CBSD incidence was 39.1% in the third season, in comparison with an incidence of >60% after a single season in a control community where disease-free planting material was introduced in the absence of community phytosanitation. Kriging and geospatial analysis demonstrated that inoculum pressure, which was a function of vector abundance and the number of CBSD-infected plants surrounding monitored fields, was a strong determinant of the pattern of CBSD development in monitored fields. In the first year, farmers achieved yield increases with the new varieties relative to the local variety baseline of 94% in Chato (north-west) and 124% in Mkuranga (coast). Yield benefits of the new material were retained up to the final season in each location. The new variety (Mkombozi) introduced under community phytosanitation conditions in Chato yielded 86% more than the same variety from the same source planted in the no-phytosanitation control location. Although there was an 81% reduction in CBSD incidence in the new variety Kiroba introduced under community phytosanitation compared to control conditions in Mkuranga, there was no concomitant yield increase. Variety Kiroba is known to be tolerant to the effects of CBSD, and tuberous roots of infected plants are frequently asymptomatic. Community phytosanitation has the potential to deliver area-wide and sustained reductions in the incidence of CBSD, which also provide significant productivity gains for growers, particularly where introduced varieties do not have high levels of resistant/tolerance to CBSD. The approach should therefore be considered as a potential component for integrated cassava virus management programmes, particularly where new cassava plantations are being established in areas severely affected by CBSD.

Production of virus-free orchid Cymbidium aloifolium (L.) Sw. by various tissue culture techniques.

Orchids are affected by many viruses resulting in poor growth, yield and quality, and an overall decline in population. Cymbidium mosaic virus (CymMV) is one of the common orchid viruses found in Cymbidium species but it infects different orchid genera. In this study Cymbidium aloifolium was propagated in vitro using MS medium at different strength (1.0, ½, and ¼) with or without 0.5 mg/l BAP (6-benzylaminopurine) and 0.5 mg/l NAA (Naphthalene acetic acid). To provide disease-free planting material, source plant for in vitro propagation needs to be screened for pathogenic viruses. In the present study, in vivo-grown source (mother) plants and tissue culture-derived plants of C. aloifolium were tested for CymMV virus using Double antibody sandwich enzyme linked immunosorbent assay (DAS-ELISA). All the tissue cultured plants were found to be 100% virus-free whereas the in vivo grown source plants were highly affected by CymMV virus (83.33%). The virus-free in vitro plantlets were multiplied in large scale and then acclimatized on earthen pot containing a mixture of cocopeat, litter and clay in the ratio of 3:2:1. Eighty five percent of acclimatized plantlets survived making this method an efficient mass production system for high quality virus-free C. aloifolium for commercial floriculture and germplasm preservation.

Technological Advances in Huanglongbing (HLB) or Citrus Greening Disease Management

Huanglongbing (HLB), previously citrus greening disease, is the most destructive of citrus species causing major threat to the world citrus industry. The disease was reported from China in 1919 and now known to occur in more than 40 different countries of Asia, Africa, South and North America. Three species of gram negative bacterium namely Candidatus Liberibacter asiaticus, Candidatus Liberibacter africanus and Candidatus Liberibacter americanus are the casual organisms of HLB, respectively prevailing in the continent of Asia, Africa and South America. It is one of the most extensively researched subjects in citriculture world. HLB was detected in 2004 and 2005, respectively in San Paulo of Brazil and Florida of USA: the two leading citrus production hub of the world causing huge economic loss within 5 years of first detection. Since then research on HLB detection and management was further accelerated in American continents. This paper presents the scientific advancement made on detection, spread, economic losses caused by HLB in different parts of the world and controlling management strategies. Remarkable achievements have been made on HLB detection techniques including iodine test, qPCR and more recently in spectroscopy. While efforts are being made to develop resistance varieties using conventional and biotechnological tools management strategy which includes reduction of inoculums source, vector control and replant with disease-free planting materials still remains major option for HLB control. Citrus intercropping with guava have shown promising results for vector reduction.Journal of Nepal Agricultural Research Council Vol.1 2015, pp.41-50

English

Cassava (Manihotes culenta Crantz) is among major food and income security crops in sub-Saharan Africa. However, high seed dormancy and delayed germination limit seed propagation. Using traditional stem cutting causes loss of superior genotypes and decreases productivity as a result of low multiplication ratio (1:10) and viral and bacterial diseases.Thus, the aim of this study was to optimize and screen efficient in vitro protocols for rapid multiplication and production of disease-free cassava planting materials through nodal culture technique. The experiment was laid out in a 5 x 5 factorial arrangement in Completely Randomized Design with five cassava genotypes (Warima, Munafa, SLICASS 6, Coco cassada and SLICASS 7) and five BAP supplemented MS medium (0, 0.02, 0.1, 1.0 and 2.0 mg/L), replicated three times. Results revealed that, BAP supplement significantly (p<0.001) influenced numbers of leaves and shoots compared to plantlet height growth traits of nodal cassava explants in culture. Virus indexing of infected plants from screen house using species specific primer pairs, OjaRep/EACVMRep and OjaRep/ACMVRep, confirmed the presence of East Africa Cassava Mosaic Virus (EACMV) and the African Cassava Mosaic Virus (ACMV) at an amplicon of approximately 650bp and 400bp, respectively. The study demonstrated the effectiveness of cytokinin supplemented MS medium in enhancing growth of cassava; and the adequacy and effectiveness of the PCR technique in identifying ACMV and EACMV using nodal cuttings. Future studies will involve molecular characterization of the EACMV strain(s) existing in the country. Key words: Cassava, nodal culture, virus indexing.

Effect of different growth regulators on in vitro micro-propagation of Kufri Frysona

In the present investigation, experiment was conducted for in vitro micro-propagation with different concentration of growth regulators in different explants Sprouts and Shoot tips of potato cultivar Kufri Frysona. The maximum survival percentage (40) of sprouts and (100%) of shoot tips were obtained when the explants were surface sterilized with 0.2% bavistin &amp; 0.4% streptocyclin (45minutes) and 0.1% mercuric chloride (60seconds). Sterilized explants were inoculated on MS basal supplemented with various growth regulators and established successfully. The maximum shoot induction (62.5±1.44%) in 11.3±0.33 days and (74.0 ± 2.13 %) in 10.0 ± 0.50 days were reported on medium PM1 (BAP 0.25 mg/l) in sprouts and shoot tip explants respectively. The sprouted explants were further sub-cultured on MS media supplemented with various growth regulator alone and in combination for in vitro multiplication. In Kufri Frysona (11.2) shoots were obtained on MS medium fortified with 0.25mg/l BAP + 0.01mg/l IAA on 42th day of subculture. In vitro rooting was observed on MS basal medium supplemented with 2.0 mg/l NAA in Kufri Frysona after 10 days. Rooted plantlets were successfully hardened in green house using different types of potting mixture and finally transferred to field. The protocol will be very useful for large-scale production of disease free planting material of potato (S. tuberosum) in future.

Optimising plant bed performance through adaptive research with the Australian sweetpotato industry

A key driver of Australian sweetpotato productivity improvements and consumer demand has been industry adoption of disease-free planting material systems. On a farm isolated from main Australian sweetpotato areas, virus-free germplasm is annually multiplied, with subsequent 'pathogen-tested' (PT) sweetpotato roots shipped to commercial Australian sweetpotato growers. They in turn plant their PT roots into specially designated plant beds, commencing in late winter. From these beds, they cut sprouts as the basis for their commercial fields. Along with other intense agronomic practices, this system enables Australian producers to achieve worldRSQUOs highest commercial yields (per hectare) of premium sweetpotatoes. Their industry organisation, ASPG (Australian Sweetpotato Growers Inc.), has identified productivity of mother plant beds as a key driver of crop performance. Growers and scientists are currently collaborating to investigate issues such as catastrophic plant beds losses; optimisation of irrigation and nutrient addition; rapidity and uniformity of initial plant bed harvests; optimal plant bed harvest techniques; virus re-infection of plant beds; and practical longevity of plant beds. A survey of 50 sweetpotato growers in Queensland and New South Wales identified a substantial diversity in current plant bed systems, apparently influenced by growing district, scale of operation, time of planting, and machinery/labour availability. Growers identified key areas for plant bed research as: optimising the size and grading specifications of PT roots supplied for the plant beds; change in sprout density, vigour and performance through sequential cuttings of the plant bed; optimal height above ground level to cut sprouts to maximise commercial crop and plant bed performance; and use of structures and soil amendments in plant bed systems. Our ongoing multi-disciplinary research program integrates detailed agronomic experiments, grower adaptive learning sites, product quality and consumer research, to enhance industry capacity for inspired innovation and commercial, sustainable practice change.

Mass in-vitro micro propagation of banana (Musa sp.)

Production of Banana is constrained by many biotic as well as abiotic factors. The production of disease free planting material of banana by meristem culture technique is an urgent need.An experiment has been designed to develop a suitable and efficient protocol for plant regeneration in banana through micro propagation.The surface sterilization of banana plant is the most difficult practice.So it is very important to optimize the concentration and duration of different sterilants for explants surface sterilization. The best sterilants for the surface sterilization of the explant of banana were 0.1 per cent HgCl 2 for 5 min duration followed by NaOCl (40 %, commercially available) solution for 8 min duration and 70 per cent ethyl alcohol for 2 min. And the best medium for establishment of banana explant was supplemented with 3mg/l BAP, 0.2mg/l IAA with 30 mg ascorbic acid followed by Proliferation with 5mg/l BAP,0.5mg/ l IAA with 30 mg ascorbic acid and 10 mg/l BAP,0.5 mg/l IAA with 30 mg ascorbic acid.Significantly highest number of roots and greater root length were produced by 0.5 mg/l IAA + 0.5 mg/l IBA. How to view point the article : Kumari, Namrata and Misra, Pragati (2016). Mass in-vitro micro propagation of banana (Musa sp.). Internat. J. Plant Protec., 9(1) : 204-210.

The distribution and incidence of banana Fusarium wilt in subsistence farming systems in east and central Africa

Bananas (Musa spp.) are major staple and cash crops in the Great Lakes region of Africa. Yet, banana yields in this region are among the lowest in the world due to a wide range of abiotic, biotic and socio-economic causes. Cropping systems which could contribute to soil fertility replenishment, pest and disease suppression and climate change mitigation might improve banana yields and contribute to uplifting the livelihoods of millions of people in the region. In this context, a survey was conducted over two seasons in banana-based subsistence farming systems in Rwanda, Burundi, north-western Tanzania (Kagera and Kigoma regions) and eastern Democratic Republic of Congo (South Kivu province), to investigate the distribution and incidence of banana Fusarium wilt as related to cropping systems, edapho-climatic and socio-economic factors. Banana Fusarium wilt incidence was found generally high in the region, 54.1% of all farms had disease incidence higher than 40%, with Tanzania having the highest number of farms with high disease incidence (63.6%). Statistical analysis (chi-squared test of association) and GIS mapping, by layering Fusarium wilt incidence over selected predictor maps, showed that disease incidence was lower in farms growing cultivar mixtures (p < 0.01) and at higher altitudes (>1600masl) (p < 0.05), and a significant association of Fusarium wilt and farm age was observed whereby disease incidence was highest in farms aged between 10 and 30 years (p < 0.05). Additionally, this study reports for the first time the occurrence of Fusarium oxysporum f. sp. cubense race 2 in Rwanda and Burundi, and suggests that strategies for banana Fusarium wilt management in east and central Africa should include raising farmers’ awareness on pathogen spread mechanisms and enhancing their access to disease-free planting materials.

Development of a loop-mediated isothermal amplification assay for rapid and sensitive detection ofSporisorium scitamineumin sugarcane

Smut disease caused by Sporisorium scitamineum is one of the most destructive sugarcane diseases worldwide. The pathogen spreads primarily through infected sugarcane setts, and hence, the use of disease-free planting materials is essential for preventing disease development in the field. In this study, a species-specific loop-mediated isothermal amplification (LAMP) assay was developed for rapid and accurate detection of S. scitamineum. Based on the differences in internal transcribed spacer (ITS) sequences of S. scitamineum, a set of four species-specific primers, F3, B3, FIP and BIP, were designed by using a panel of fungal and bacterial species as controls. After optimization of the reaction conditions, the detection limit of LAMP assay was about 2 fg of the S. scitamineum genomic DNA in 25 µL reaction solution, 100-fold lower than that of conventional polymerase chain reaction. The assay showed high specificity to discriminate all S. scitamineum isolates from nine other fungal and bacterial pathogens. The LAMP assay also detected smut infection from young sugarcane leaves with no visible smut-disease symptoms. The findings from this study provide a simple, highly sensitive, rapid and reliable technique for early detection of S. scitamineum, which may be useful for sugarcane quarantine and production of smut-free seedcanes. This is the first report of LAMP-based assay for the detection of S. scitamineum in sugarcane.

Protocols for Improvement of Black Pepper (Piper nigrum L.) Utilizing Biotechnological Tools.

Black pepper, Piper nigrum L., the "King of spices" is the most widely used spice growing in the South-Western region of India. The humid tropical evergreen forest bordering the Malabar Coast (Western Ghats is one of the hot spot areas of plant bio-diversity on earth) is its center of origin and diversity. However, the crop faces constraints like rampant fungal and viral diseases, lack of disease free planting material, hence biotechnological tools can be utilized to address these problems and strides have been made successfully. The standardization of micropropagation, somatic embryogenesis, in vitro conservation, protoplast isolation, and genetic transformation protocols are described here. The protocols could be utilized to achieve similar goals in the related species of Piper too.

Adoption of IPM Practices in Grape, Tree Fruit, and Nut Production in the Western United States

To determine the prevalence of IPM adoption in perennial crop production in the Western United States, this review examined peer-reviewed scientific literature, extension reports, and studies conducted by or on behalf of commodity groups or other agriculture interests that were published since the year 2000. Based on 32 sources of data, IPM adoption is widespread in production of tree fruits, nuts, and vines, with a large percentage of growers using many prevention, avoidance, monitoring, and selective-suppression practices – known as the PAMS approach. In the wine grape industry in California, quarantine, certified disease-free planting material, and leaf pulling are practiced broadly to prevent or avoid disease. Wine grape growers in California monitor frequently to track insect vectors of disease and employ area-wide management practices. Seventy to ninety percent of California pear growers and >90% of Oregon and Washington pear producers monitor for insect pests. Hazelnut, walnut, and almond production in Oregon and California rely heavily on pest-control professionals to monitor pest activity. Across a wide range of crops, infrastructure to model pest population development based on weather data are well established and depended upon by producers. Suppression using pesticides has declined drastically (from 40–90%) in Oregon hazelnut production, California almond and fresh-market grape production, and California, Oregon, and Washington pear production. Sixty to seventy percent of walnut and pear producers in California, Oregon, and Washington are considering the impacts to human health and environment when making suppression and management decisions. Western perennial crops and practices are unique, and the findings documented in this review may not be applicable nationally.

Protocols for In Vitro Propagation, Conservation, Synthetic Seed Production, Embryo Rescue, Microrhizome Production, Molecular Profiling, and Genetic Transformation in Ginger (Zingiber officinale Roscoe.).

Ginger is a rhizomatous plant that belongs to the family Zingiberaceae. It is a herbaceous perennial but cultivated as annual, with crop duration of 7-10 months. Ginger is native to India and Tropical South Asia. The tuberous rhizomes or underground stems of ginger are used as condiment, an aromatic stimulant, and food preservative as well as in traditional medicine. Ginger is propagated vegetatively with rhizome bits as seed material. Cultivation of ginger is plagued by rhizome rot diseases, most of which are mainly spread through infected seed rhizomes. Micropropagation will help in production of disease-free planting material. Sexual reproduction is absent in ginger, making recombinant breeding very impossible. In vitro technology can thus become the preferred choice as it can be utilized for multiplication, conservation of genetic resources, generating variability, gene transfer, molecular tagging, and their utility in crop improvement of these crops.

Cassava brown streak disease and the sustainability of a clean seed system.

One method of reducing disease in crops is the dissemination of disease‐free planting material from a multiplication site to growers. This study assesses the validity and sustainability of this method for cassava brown streak disease, a threat to cassava crops across East Africa. Using mathematical modelling, the effects of different environmental and control conditions on pathogen spread were determined in a single‐field multiplication site. High disease pressure, through large vector populations and disease in the surrounding area, combined with poor roguing practice, resulted in unsuccessful disease suppression. However, fields may produce sufficiently clean material for replanting if these factors can be overcome. Assessing the sustainability of a low‐pressure system over multiple harvests, well‐managed fields were found to maintain low disease levels, although producing sufficient cuttings may prove challenging. Replanting fields from the previous harvest does not lead to degeneration of planting material, only cutting numbers, and the importation of new clean material is not necessarily required. It is recommended that multiplication sites are only established in areas of low disease pressure and vector population density, and the importance of training in field management is emphasized. Cultivars displaying strong foliar symptoms are to be encouraged, as these allow for effective roguing, resulting in negative selection against the disease and reducing its spread. Finally, efforts to increase plant multiplication rates, the number of cuttings that can be obtained from each plant, have a significant impact on the sustainability of sites, as this represents the primary limiting factor to success.

Light-emitting diodes (LED) increase the stomata formation and chlorophyll content in Musa acuminata (AAA) ‘Nanicão Corupá’ in vitro plantlets

Micropropagation of banana by means of different morphogenetic routes is an important source of genetically uniform, pest- and disease-free planting materials of Musa spp. Morphogenesis of in vitro grown plants are affected by light quality, light quantity and photoperiod. Light-emitting diode (LED) lighting systems have several unique advantages, including their peak spectral output, which closely coincides with the red absorption peak of chlorophyll and the reported wavelengths for maximum photosynthetic efficiency. The present study was aimed to investigate the effect of two LED lighting treatments (white LED and deep red/white LED) compared to conventional fluorescent lamps on the stomata formation and chlorophyll (Chl) levels in micropropagated banana plantlets through organogenesis. Both LED lighting evaluated increased the levels of total Chl, Chl-a and Chl-b in banana in vitro plantlets, indicating no statistical difference between them, but being higher then plantlets subjected to fluorescent lamps. The number of stomata was also increased equally by both LED lighting treatments, indicating increased formation of stomata in both abaxial and adaxial leaf surfaces when compared to fluorescent lamps. Although all treatments presented 100 % survival in the acclimatization phase, LED lighting show promising for micropropagation of banana due to its known superior light quality, low energy consumed, little heat generated and long operating lifetime.

Screening for sweet potato (Ipomoea batatas L.) leaf curl virus (SPLCV) and its elimination using thermotherapy-meristem tip culture technique

Despite its high potential for food security, production of sweet potato (Ipomoea batatas L.) is constrained by viruses which reduce yield by 90%. It is, therefore, essential to detect and eliminate these viruses in elite clones before dissemination to farmers. In this study, we used visual symptomatology and polymerase chain reaction (PCR) techniques to detect Sweet potato leaf curl virus (SPLCV) and eliminated the virus using thermotherapy-meristem tip culture. Visual symptomatology revealed virus associated symptoms, including vein clearing, interveinal chlorosis, chlorotic spots, upward leaf curling, leaf narrowing, purpling, blistering and leaf yellowing in all 22 accessions grown on the field. The disease incidence varied between accessions with US003 having the lowest (20%), while ten accessions had the highest (90%). The severely diseased accessions were tested for SPLCV using PCR technique. The technique detected the virus in 30 % of the accessions. Plants that tested positive to PCR assay were grown in the chamber at 35 °C for 4 weeks followed by meristem culture. The regenerants were indexed for SPLCV. Fifty-two percent (52.4%) of the regenerants were successfully cleaned of the virus. Virus indexing and elimination will enhance the dissemination of disease-free planting materials to farmers. DOI: http://dx.doi.org/10.4038/jas.v10i1.8034 The Journal of Agricultural Sciences, 2015, vol.10, no1: p.1-9