Post-harvest impact of cassava brown streak disease in four countries in eastern Africa

Cassava brown streak disease (CBSD) is endemic to the coast of East Africa and the disease continues to spread to new areas in the Great Lakes region. In both these areas CBSD leaf symptoms occur at high incidences. However, it is the associated symptom of necrosis in the starch-bearing tissues that renders the root unfit for human consumption. Where root necrosis occurs, the economic viability of processing into flour is adversely affected. Surveys undertaken in Tanzania, Kenya, Uganda, and Malawi showed that CBSD leaf symptoms were present at high incidences but root necrosis incidence was lower than would be expected. It appears that a form of tolerance to CBSD occurs in which the plants are susceptible to infection by the virus but are less affected by the root symptom. Farmers practise selection for cassava varieties less prone to CBSD root necrosis leading to dependence on a decreasing number of varieties

Effect of time of harvesting and disease resistance in reducing Cassava (Manihot esculenta Crantz) yield losses by two viral diseases

Cassava mosaic disease (CMD) and cassava brown streak disease (CBSD) are two important biotic constraints for cassava (Manihot esculenta Crantz) production in Eastern and Southern Africa. CMD causes a general decline in yield in affected plants of susceptible cassava varieties but CBSD causes rotting of edible roots. Delayed harvesting can increase rotting of roots and making them unfit for consumption or marketing, and thus affecting the livelihoods of poor farmers. This study investigated the effect of interaction between time of harvesting and levels of disease resistance to identify ideal harvesting times for reducing yield losses. The resistant cassava variety Namikonga remained in the field for the duration of the study, up to 24 months after planting without incurring significant yield losses, while the tolerant varieties Kiroba and Kizimbani could only be maintained up to 21 months. Susceptible varieties Mreteta and Albert suffered significant yield losses beyond 15 months. Among the varieties, Kizimbani had the least CBSD and CMD foliar symptoms as well as farmer desirable traits including high root weight, quantity of marketable roots and dry matter content. Harvesting of cassava can depend on the resistance or susceptibility of the varieties grown. Therefore, the above harvesting times for different varieties were recommended for minimizing yield losses due to the diseases and thus maximizing yields to the farmers

Understanding the interactions among the crop plants, a virus, insect vector whiteflies and their endosymbionts

Interactions among the four biotic agents - the host plants, a virus, insect vector whiteflies and their bacterial endosymbionts was investigated in this study. The whitefly Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae) is an important crop pest that is infected by several endosymbiotic bacteria that can play varying roles on their hosts. Both whiteflies and endosymbionts are affected by the host plants they feed on, which in turn affect the fourth agent – the viruses, which are transmitted by the whiteflies. We investigated these interactions on five different host plants – eggplant, tomato, beans, okra and cotton - using a single whitefly species Asia 1 infected with three different bacteria Portiera, Wolbachia and Arsenophonus. B. tabaci Asia 1 transmits the Tomato leaf curl Bangalore virus (ToLCBV) effectively, which was the virus used in the study. We found host plants having a significant impact on whitefly growth and development. Eggplant was most favourable, while okra and tomato were least preferred. The endosymbiont Wolbachia was significantly affected by feeding of B. tabaci on different host plants while Portiera and Arsenophonus were unaffected. When whiteflies fed on ToLCBV-infected tomato plants, the concentration of Arsenophonus increased significantly while other endosymbionts remain unchanged. Understanding these interactions will help in managing both whiteflies and viral diseases

Blind image quality evaluation using perception based features

This paper proposes a novel no-reference Perception-based Image Quality Evaluator (PIQUE) for real-world imagery. A majority of the existing methods for blind image quality assessment rely on opinion-based supervised learning for quality score prediction. Unlike these methods, we propose an opinion unaware methodology that attempts to quantify distortion without the need for any training data. Our method relies on extracting local features for predicting quality. Additionally, to mimic human behavior, we estimate quality only from perceptually significant spatial regions. Further, the choice of our features enables us to generate a fine-grained block level distortion map. Our algorithm is competitive with the state-of-the-art based on evaluation over several popular datasets including LIVE IQA, TID & CSIQ. Finally, our algorithm has low computational complexity despite working at the block-level

CYCD3 D-type cyclins regulate cambial cell proliferation and secondary growth inArabidopsis

A major proportion of plant biomass is derived from the activity of the cambium, a lateral meristem responsible for vascular tissue formation and radial organ enlargement in a process termed secondary growth. In contrast to our relatively good understanding of the regulation of primary meristems, remarkably little is known concerning the mechanisms controlling secondary growth, particularly how cambial cell divisions are regulated and integrated with vascular differentiation. A genetic loss-of-function approach was used here to reveal a rate-limiting role for the Arabidopsis CYCLIN D3 (CYCD3) subgroup of cell-cycle genes in the control of cambial cell proliferation and secondary growth, providing conclusive evidence of a direct link between the cell cycle and vascular development. It is shown that all three CYCD3 genes are specifically expressed in the cambium throughout vascular development. Analysis of a triple loss-of-function CYCD3 mutant revealed a requirement for CYCD3 in promoting the cambial cell cycle since mutant stems and hypocotyls showed a marked reduction in diameter linked to reduced mitotic activity in the cambium. Conversely, loss of CYCD3 provoked an increase in xylem cell size and the expression of differentiation markers, showing that CYCD3 is required to restrain the differentiation of xylem precursor cells. Together, our data show that tight control of cambial cell division through developmental- and cell type-specific regulation of CYCD3 is required for normal vascular development, constituting part of a novel mechanism controlling organ growth in higher plants

Effect of botanicals and insecticides seed treatment and containers on seed longevity of black gram under natural ageing conditions

Good storage is the basic requirement in seed production programme as maintenance of high seed viability and vigour from harvest to planting is of utmost importance in a seed production programme. Therefore, inexpensive, simple and practicable technology to prolong the shelf life of seeds under ambient condition is immensely needed. Hence, an experiment was carried out to study the effect of seed treatment with neem oil, nimbicidin, emamectin benzoate 5 SG, deltamethrin 2.8 EC, novuluron EC on black gram seed quality under ambient conditions. The seeds without any seed treatment were included as control. The treated and untreated seeds were stored in cloth bag and polylined cloth bag. The results revealed that, botanicals and emamectin benzoate seed treatments were significantly superior in controlling the storage insect and maintaining higher seed quality up to 10 months of storage when compared to control. Among the chemicals, the emamectin benzoate 5 SG @ 40 mg kg-1 of seed found better by recording significantly higher germination percentage (80.28), vigour index I (2124) and dry weight of seedlings (43.14 mg) and lower electrical conductivity (0.939 dSm-1) and seed damage (0.00 %) compared to control (78.78%, 2012, 38.90 mg, 0.942 dSm-1, respectively) at the end of 10th month of storage. The emamectin benzoate 5 SG and nimbicidintreated seeds stored in polylined cloth bags were considered as effective seed storage management approach in blackgram

Impact of brown streak necrosis on cassava value addition

The main aim of this study was to investigate the quality and quantities of cassava flour produced and value chain development as a result of cassava brown streak disease (CBSD). Analysis of flour prepared from roots affected to various degrees of CBSD were assessed for various parameters such as starch and carbohydrate content, viscosity, pasting temperature, colour and pH. Values showed significant differences between the grades. There was a strong correlation (R2=0.904) between flour viscosity breakdown and pH value, and with peak viscosity and pH value (R2=0.737). A 25% level of CBSD root necrosis not only increased the conversion ratio of fresh roots to final product, but also presented an additional $41-47/t for the cost of fresh cassava roots if necrotic tissue were removed, representing a significant economic loss that makes cassava processing unprofitable

Fitness costs associated with infections of secondary endosymbionts in the cassava whitefly species Bemisia tabaci

We investigated the dual effects of bacterial infections and diseased cassava plants on the fitness and biology of the Bemisia tabaci infesting cassava in Africa. Isofemale B. tabaci colonies of sub-Saharan Africa 1-subgroup 3 (SSA1-SG3), infected with two secondary endosymbiotic bacteria Arsenophonus and Rickettsia (AR+) and those free of AR infections (AR-) were compared for fitness parameters on healthy and East African cassava mosaic virus-Uganda variant (EACMV-UG) infected cassava plants. The whitefly fecundity and nymph development was not affected by bacterial infections, or the infection of cassava by the virus. However, emergence of adults from nymphs was 50% and 17% higher by AR- on healthy and virus-infected plants, respectively than AR+ flies. Development time of adults also was 10 days longer in AR+ than AR-. The whiteflies were further compared for acquisition and retention of East African cassava mosaic virus-Uganda (EACMV-UG). Higher proportion of AR- acquired (91.8%) and retained (87.6%) the virus than AR+ (71.8%, 61.2%, respectively). Similarly, the AR- flies retained higher quantities of virus (~9 folds more) than AR+. These results indicated that bacteria-free whiteflies were superior and better transmitters of EACMV-UG, as they had higher adult emergence, quicker life-cycle and better virus retention abilities than those infected with bacteria