Search

Silverleaf whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is one of the most notorious invasive insect pests, infesting more than 900 species of plants and spreading more than 200 viral diseases. This polyphagous agricultural pest harbours diverse bacterial communities in its gut, which perform multiple functions in whiteflies, including nutrient provisioning, amino acid biosynthesis, and virus transmission. The present exploratory study compares the bacterial communities associated with silverleaf whitefly infesting cassava, also known as cassava whitefly, collected from two different zones (zone P: plains; zone H: high ranges), from Kerala, India, using next-generation sequencing of 16S rDNA. The data sets for these two regions consisted of 1 321 906 and 690 661 high-quality paired-end sequences with mean length of 150 bp. Highly diverse bacterial communities were present in the sample, containing approximately 3513 operational taxonomic units (OTUs). Sequence analysis showed a marked difference in the relative abundance of bacteria in the populations. A total of 16 bacterial phyla, 27 classes, 56 orders, 91 families, 236 genera, and 409 species were identified from the P population, against 16, 31, 60, 88, 225, and 355, respectively, in the H population. Arsenophonus sp. (Enterobacteriaceae), which is important for virus transmission by whiteflies, was relatively abundant in the P population, whereas in the H population Bacillus sp. was the most dominant group. The association of whitefly biotypes and secondary symbionts suggests a possible contribution of these bacteria to host characteristics such as virus transmission, host range, insecticide resistance, and speciation.

Elephant foot yam (Amorphophallus paeoniifolius (Dennst.) Nicolson), is an important edible tropical tuber crop, belonging to the family Araceae. Corms produced by this plant is very big and they are rich in starch, protein, mineral, vitamins, and dietary fiber but has acridity problem. This crop is susceptible to virus and phytoplasma diseases which affects crop growth and corm yield. Even though this crop has high commercial value, the problems like susceptibility to viral diseases, acridity problems, and lack of genetic diversity made hindrance in their exploitation. These issues can be resolved only by improving the characters through genetic transformation. To achieve genetic transformation in this important crop, a study was conducted to optimize various parameters for efficient Agrobacterium-mediated genetic transformation using embryogenic calli with vectors having gus reporter gene. Calli were developed using petiole and leaves of in vitro plantlets of elephant foot yam cultivar Gajendra and experiments were conducted to evaluate the sensitivity of calli to different doses of antibiotics viz. geneticin, hygromycin, ticarcillin. It was observed that complete death and discoloration of the calli were obtained with 25 mgl(−1) geneticin and 10 mgl(−1) hygromycin. The lowest lethal concentration of ticarcillin against Agrobacterium growth was found to be 500 mgl(−1) which did not affect calli growth. Optimized parameters for efficient transformation in elephant foot yam include 100 μM acetosyringone concentration with 2 days of co-cultivation at temperature 22 °C using LBA4404 strain. The putative transformants were characterized for the integration of the gus gene using PCR and nucleic acid spot hybridization. The optimized protocol is simple and reproducible and may be adapted for other cultivars also. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s13205-021-02824-6.

Elephant foot yam (Amorphophallus paeoniifolius) is a vegetatively propagated stem tuber crop. In this investigation we describe a highly competent and reproducible in vitro propagation of the plant from corm bud, petiole and young leaf explants. Friable callus was initiated from all the explants on modified MS medium (half the concentration of NH4NO3 and KNO3) supplemented with 0.5 mg l-1 each of benzyl amino purine (BAP), α-naphthalene acetic acid (NAA) and 2,4-dichloro phenoxy acetic acid (2,4-D). Shoot regeneration from calli was optimal on modified MS medium supplemented with 5.0 mg l-1 BAP and 1.0 mg l-1 NAA. Microcorms, capable of producing micro shoots all over the surface, were induced from the callus at a frequency of 90% on shoot regeneration medium supplemented with 5% sucrose. Rooting was 100% on modified liquid MS medium augmented with 5.0 mg l-1 Indole 3- butyric acid (IBA). A 100% survival rate of plantlets on transplantation to soil: sand: coir pith mixture was recorded.Keywords: Callus, elephant foot yam, in vitro, microcorms, regeneration, somatic embryoAfrican Journal of Biotechnology, Vol 13(49) 4508-4514

The genetic variability in starchy Curcuma species was assessed using Random Amplified Polymorphic DNA (RAPD) technique. The RAPD pattern generated by 20 primers revealed a high degree of polymorphism. A total of 274 bands were generated of which 264 were polymorphic. All the species were separated into 3 clusters using UPGMA. C. aromatica, C. leucorrhiza, and C. brog formed a cluster within which C. longa and C. zedoaria formed a subgroup. C. harita was genetically distinct from all the other Curcuma species. Since it is difficult to distinguish different species by leaf morphology, the RAPD pattern has high utility in identification of starchy Curcuma species.

Cassava (Manihot esculenta Crantz.) is the most important vegetatively propagated food staple in Africa and a prominent industrial crop in Latin America and Asia. Its vegetative propagation through stem cuttings has many advantages, but deleteriously it means that pathogens are passed from one generation to the next and can easily accumulate, threatening cassava production. Cassava-growing continents are characterized by specific suites of viruses that affect cassava and pose particular threats. Of major concern, causing large and increasing economic impact in Africa and Asia are the cassava mosaic geminiviruses that cause cassava mosaic disease in Africa and Asia and cassava brown streak viruses causing cassava brown streak disease in Africa. Latin America, the center of origin and domestication of the crop, hosts a diverse set of virus species, of which the most economically important give rise to cassava frog skin disease syndrome. Here, we review current knowledge on the biology, epidemiology, and control of the most economically important groups of viruses in relation to both farming and cultural practices. Components of virus control strategies examined include: diagnostics and surveillance, prevention and control of infection using phytosanitation, and control of disease through the breeding and promotion of varieties that inhibit virus replication and/or movement. We highlight areas that need further research attention and conclude by examining the likely future global outlook for virus disease management in cassava.

A reverse transcription polymerase chain reaction assay using potyvirus specific primers designed from the core of the coat protein was carried out, and a cDNA fragment of 327 bp was obtained from most of the potyviruses infecting the tropical tuber crops. Reverse transcription polymerase chain reaction (RT-PCR) products were sequenced and found to be derived from the expected virus. Specific cDNA probe was generated from the amplicon, and the probe was then successfully used for the diagnosis of the potyviruses infecting the major tuber crops through biotinylated nucleic acid spot hybridisation. The specific probe developed could detect the potyviruses infecting tuber crops namely SPFMV, DsMV and DAV from sweet potato, aroids and yams respectively.Key words: Coat protein, potyvirus, reverse transcription polymerase chain reaction, nucleic acid spot hybridisation.

The development of Catenaria anguillulae on the immobilized juveniles of Heterodera cajani was studied. Within 2 h of inoculation, the zoospores of C. anguillulae congregated at the oral openings of juveniles and in 13–15 h the germ-tube passed from the side of the stylet, growing up to the tail region. After 1 h the mycelium became septate at regular intervals and swelling of the sporangia commenced, attaining full size in 40–50 min as it touched the nematode body. At this stage, second septation occurred with rhizoids developing along with growing mycelium. After nearly 5 h of the second stage of septa formation, grouping of fat globules into groups of 4–6 occurred, along with the initiation of discharge-tubes. Precisely within 30 min, 8–12 smaller globules were rearranged in circular forms, followed by half-moon shape 17 min later. Zoospore differentiation, vesicle formation and release of zoospores occurred within 50 min of the half-moon stage.