Bunchy Top Research Articles

‘Candidatus Phytoplasma brasiliense’-related strains associated with papaya bunchy top disease in northern Peru represent a distinct geographic lineage

During the 2015–2016 fruit production season, a papaya bunchy top (PBT) disease was observed in a papaya production farm located at Region de Piura, northern Peru. Affected plants exhibited symptoms of excessive proliferation of auxiliary shoots at the top or near top of the main stem, shortening of internodes, leaf yellowing, and necrosis of leaf veins. The symptom syndrome suggested possible infection by a phytoplasma, and the recent discovery of a phytoplasmal disease in a nearby vineyard also indicated that a phytoplasma reservoir and potential vector(s) were present in the area. Molecular diagnostic assays for phytoplasma detection were therefore employed. Nested polymerase chain reactions and subsequent nucleotide sequence analysis confirmed that phytoplasma infection did occur in the papaya production farm. The phytoplasma strains found to be associated with the PBT disease are affiliated with ‘Candidatus Phytoplasma brasiliense’, a species that had previously never been implicated in a papaya disease anywhere in the world. We provide molecular evidence to suggest that the papaya-infecting phytoplasma strains identified in this study are closely related to a phytoplasma associated with the first grapevine yellows (GY) disease that we recently identified in Peru. The results of our study indicate that these PBT and GY phytoplasma strains in Peru represent an emerging geographic lineage that is distinct from those of all other known ‘Ca. Phytoplasma brasiliense’ strains in the Americas.

Molecular mapping of bunchy top disease resistance in Gossypium hirsutum L.

AbstractCotton bunchy top (CBT) is an aphid transmitted Polerovirus disease and a significant threat to the Australian cotton industry. Symptoms include stunted plant growth, and leaves often display pale green angular patterns at the leaf margins and dark green centers with a leathery texture. Resistance to CBT was evaluated in 206 F2 plants and 76 F2:3 families derived from the resistant cultivar ‘Delta Opal’ crossed to the susceptible cultivar ‘Sicot 70’, and in 25 other cultivars the majority susceptible to CBT. CBT resistance in ‘Delta Opal’ was shown to be controlled by a single dominant locus designated Cbt. A combination of AFLP and single nucleotide polymorphism markers located Cbt on chromosome A10, close to the mapped resistance locus in ‘Delta Opal’ to another Polerovirus disease of cotton; cotton blue disease. The markers identified flanking CBT resistance will provide useful tools for breeders for marker-assisted selection to alleviate the impact of this disease on cotton production.

Banana bunchy top.

Banana bunchy top.

Variability in yellow leaf symptom expression caused by the Sugarcane yellow leaf virus and its seasonal influence in sugarcane

Yellowing of leaf midrib, its extending to adjoining lamina and necrosis of discoloured tissues from the tip portion are the common yellow leaf (YL) symptoms observed in tropical climatic conditions in India. As symptoms of this disease vary among the varieties, the progress of these symptoms was studied in Coimbatore from disease free status in the plant, using a newly devised YL 0-5 disease severity scale. Progress of recovery of symptoms in symptomatic leaves was monitored with a 0-4 symptom severity scale for four seasons. Detailed observations with ten symptomatic varieties have very clearly indicated a clear variation in symptom expression among them. First symptoms were recorded in leaf 1 and 2 in few plants of the cvs CoPant 84211 and B38192. Apart from yellow discoloration of midrib, reddish discoloration, pinkish midrib and laminar discoloration were recorded in cvs B38192, Co 86010 and Co 85019, respectively. Progress of laminar discoloration on both sides parallel to the midrib varied from ~0.5 to 3.0 cm in different varieties. Apart from severe laminar discoloration progressive leaf drying from the tip region along the midrib towards leaf base and bunching of leaves in the crown were identified as the severe form of disease in sugarcane varieties. For such leaf drying with characteristic pattern of ‘V’ or ‘Y’ shape and in a bunchy top, leaf yellowing was recorded up to -7th leaf and drying was recorded up to -1st leaf in severe YL-affected variety B38192. Progressive increase in disease symptom was noticed in most of the varieties till nine months after planting and later a fluctuation in disease expression was noticed among the varieties. Subsequently decrease of yellowing was observed leaving behind the dried laminar region at the tip. The correlation and regression analyses with meteorological parameters established that ~ 50 % of variability in disease severity grades is explained by minimum temperature and relative humidity in the afternoon. This study on the disease symptomology has clearly revealed variation in YL symptom expressions among the varieties and impact of prevailing weather factors on the fluctuation of disease expressions.

Rickettsia-related bacteria associated with papaya plants showing bunchy top disease in Cuba

Papaya bunchy top (PBT) disease has been associated with Rickettsia-related proteobacterium. To study the occurrence of this proteobacterium in Cuba, during 2012, we collected 264 samples from asymptomatic and symptomatic papaya trees in three regions of Cuba. Symptomatic tissue evaluated by transmission electron microscopy revealed Rickettsia-like morphology. PCR using rickettsial sdhA-specific primers amplified a single band with expected size from 95 % of symptomatic plants. Phylogeny confirmed the presence of Rickettsia-related proteobacterium in plant showing PBT disease. This work confirms Rickettsia-related proteobacterium is a generalized pathogen in papaya plant affected by bunchy top disease in Cuba.

ASSOCIATION OF ANTS WITH PINK HIBISCUS MEALYBUG, MACONELLICOCCUSHIRSUTUS (GREEN) AND ITS INFLUENCE ON PREDATORY FAUNA IN MULBERRYECOSYSTEM

ABSTRACT The pink hibiscus mealybug, Maconellicoccus hirsutus (Green) (Hemiptera: Pseudococcidae) is amajor sucking pest of mulberry, infests tender shoot and causes bunchy top which leads to retardedgrowth of the plants. The leaves in the infested shoots become unfit for young age silkworm rearing. Infestation of M. hirsutus is often associated with attendant ants and they help spreading of the pest besides protecting from natural enemies. Thus, a study on the association of ants with M. hirsutus andtheir influence on the predatory fauna in mulberry gardens was carried out in southern Tamil Nadu. Four ant species viz. Monomorium indicum, Solenopsis geminata, Tapinoma sessile and Camponotuscompressus were found to have association with the pink mealy bug in mulberry garden. Among thespecies, M. indicum was found predominant accounting for an average of 37.78 numbers per mealybuginfested shoot whereas the rest of the species S. geminata (3.3), T. sessile (1.67) and C. compressus(0.56) were exhibited least association. The average mealy bug population was comparatively higherin ant attended colonies (61.22) than unattended ones (49.22). The population of predatory faunadecreased significantly (0.96) on ants association compared to the mealy bug infested shoots free fromthe ants (4.75) which indicates the deterring potentiality of the attendant ants. Destruction of thepredominant M. indicum colonies in mulberry ecosystem could help increase the field activities of predatory fauna against M. hirsutus.

First Report of a 16SrV-C Phytoplasma Causing Little Leaf and Bunchy Top of Tossa Jute (Corchorus olitorius) in India.

Jute is the most important phloem fiber crop of the world, and is mainly grown in the South East Asian countries of India, Bangladesh, Nepal, China, Indonesia, Thailand, and Myanmar, and few South American countries. The fiber is used in making sacks, ropes, bags, carpets, shoes, geo-textiles, and home decorations. There are two kinds of jute: tossa jute (Corchorus olitorius L.) and white jute (C. capsularis). In June 2012, symptoms suggestive of phytoplasma infection (little leaf and bunchy top) were noticed on tossa jute in different experimental fields of the CRIJAF research farm, Barrackpore, India, and the incidence of the disease varied from 5 to 20%. The infected plants showed profuse lateral branching with a bushy appearance. In many plants, branching at the apical portion developed a bunchy top symptom with tufts of smaller leaves. Leafy stem was also common in many plants with main stems covered with numerous little leaves. Total DNA was extracted from leaf midveins of 15 symptomatic and 5 asymptomatic plants by using an improved salt concentration and simple sodium acetate CTAB method (1). PCR was carried out with universal P1/P7 primer set followed by nested primer pair R16F2n/R16R2 (3), resulting in DNA amplicons that were 1.8 kb and 1.2 kb, respectively, in all symptomatic samples tested. Phytoplasma was not detected in symptomless samples. The five purified nested products were cloned in a pGEM-T Easy vector (Promega) and sequenced. One of the sequences that proved to be identical was deposited in GenBank (Accession No. KF501045). The consensus sequence was analyzed by NCBI BLAST and found to share 99% similarity with the 16Sr DNA sequence of the alder yellows phytoplasma reference strain (GenBank Accession No. AY028789), which belongs to the 16SrV group. The phylogenetic tree based on the 16SrDNA sequence of phytoplasmas belonging to group 16SrV and other distinct phytoplasma groups also showed that the phytoplasma clustered with members of subgroup 16SrV (4). Subsequently, in silico RFLP analysis of the nested PCR product with the pDRAW32 program using AluI and TruI restriction site used for 16SrV subgroups A, B, C, D, and E indicated that the 16SrV Corchorus strain belonged to subgroup C. RFLP patterns from all symptomatic C. olitorius samples were identical to the 16SrV-C pattern (2). The vector species transmitting the concerned phytoplasma in C. olitorius still needs to be identified. The leaf hopper, Amrasca biguttula biguttula, may be a potential vector as it is often noticed in jute fields. To the best of our knowledge, this is the first report of 16SrV-C phytoplasma associated with tossa jute (C. olitorius) in India. Initiative has to be taken to manage this disease; otherwise, branching of the main stems would badly affect the fiber quality as well as yield.

A multiplex nested PCR assay for simultaneous detection of Corchorus golden mosaic virus and a phytoplasma in white jute (Corchorus capsularis L.)

A multiplex nested PCR assay was developed by optimizing reaction components and reaction cycling parameters for simultaneous detection of Corchorus golden mosaic virus (CoGMV) and a phytoplasma (Group 16Sr V-C) causing little leaf and bunchy top in white jute (Corchorus capsularis). Three sets of specific primers viz. a CoGMV specific (DNA-A region) primer, a 16S rDNA universal primer pair P1/P7 and nested primer pair R16F2n/R2 for phytoplasmas were used. The concentrations of the PCR components such as primers, MgCl2 , Taq DNA polymerase, dNTPs and PCR conditions including annealing temperature and amplification cycles were examined and optimized. Expected fragments of 1kb (CoGMV), 674bp (phytoplasma) and 370bp (nested R16F2n/R2) were successfully amplified by this multiplex nested PCR system ensuring simultaneous, sensitive and specific detection of the phytoplasma and the virus. The multiplex nested PCR provides a sensitive, rapid and low-cost method for simultaneous detection of jute little leaf phytoplasma and CoGMV. Based on BLASTn analyses, the phytoplasma was found to belong to the Group 16Sr V-C.

Identification and molecular characterization of phytoplasmas and rickettsia pathogens associated with ‘Bunchy Top Symptom’ (BTS) and ‘Papaya Bunchy Top’ (PBT) of papaya in Cuba

Two different papaya diseases have been previously reported in Cuba, Bunchy Top Symptom (BTS) associated with a phytoplasma of group 16SrII ‘Candidatus Phytoplasma aurantifolia’ and Papaya Bunchy Top (PBT), associated with a rickettsia. Regarding the regional phytosanitary impact of both diseases for the papaya crop, the present study investigated the occurrence of BTS and PBT in papaya fields in Cuba, and the possible mixed infection of phytoplasma and rickettsia pathogens associated. Papaya plants showing symptoms of BTS or PBT or both, were collected in Las Tunas and Havana provinces from January 2009 to February 2010, and evaluated for phytoplasma and rickettsia by PCR with primers targeting the 16S ribosomal RNA and the rickettsial succinate deshydrogenase (sdhA) genes, respectively. Phytoplasmas and rickettsia were individually detected in 76/86 BTS-symptomatic and 22/22 PBT-symptomatic papaya plants, and simultaneously detected in 5/86 (5.81%) of the BTS-symptomatic and 17/22 (77.27%) of the PBT-symptomatic plants. Conventional and virtual RFLP analyses of the 16S rDNA sequences revealed the presence of phytoplasmas of group 16SrI ‘Candidatus Phytoplasma asteris’ and 16SrII in papaya plants affected by BTS and PBT, and identified two new phytoplasma subgroups, 16SrI-X and 16SrII-N in papayas fields of Las Tunas, which was confirmed by phylogenetic analysis. The partial rickettsia sdhA gene sequences were 100% identical to that of the rickettsia associated with PBT in Puerto Rico. Results confirm that phytoplasmas are consistently associated with both BTS and PBT symptoms, and that mixed infections of phytoplasma and rickettsia pathogens can occur in either BTS or PBT-affected papaya fields, which implies new epidemiological constraints for the disease control.

Identification of a new Polerovirus (family Luteoviridae) associated with cotton bunchy top disease in Australia

Cotton bunchy top (CBT) disease has caused significant yield losses in Australia and is now managed by control of its vector, the cotton aphid (Aphis gossypii). Its mode of transmission and similarities in symptoms to cotton Blue Disease suggested it may also be caused by a luteovirus or related virus. Degenerate primers to conserved regions of the genomes of the family Luteoviridae were used to amplify viral cDNAs from CBT-affected cotton leaf tissue that were not present in healthy plants. Partial genome sequence of a new virus (Cotton bunchy top virus, CBTV) was obtained spanning part of the RNA-dependent-RNA-polymerase (RdRP), all of the coat protein and part of the aphid-transmission protein. CBTV sequences could be detected in viruliferous aphids able to transmit CBT, but not aphids from non-symptomatic plants, indicating that it is associated with the disease and may be the causal agent. All CBTV open-reading frames had their closest similarity to viruses of the genus Polerovirus. The partial RdRP had 90 % amino acid identity to the RdRP of Cotton leafroll dwarf virus (CLRDV) that causes cotton blue disease, while other parts of the genome were more similar to other poleroviruses. The sequence similarity and genome organization of CBTV suggest that it should be considered a new member of the genus Polerovirus. This partial genome sequence of CBTV opens up the possibility for developing diagnostic tests for detection of the virus in cotton plants, aphids and weeds as well as alternative strategies for engineering CBT resistance in cotton plants through biotechnology. © 2012 Australasian Plant Pathology Society Inc.

A historical overview of the appearance and spread of Musa pests and pathogens on the African continent: highlighting the importance of clean Musa planting materials and quarantine measures

AbstractThe genus Musa is not native to Africa. It evolved in tropical Asia, from southwest India eastward to the island of New Guinea. There is a growing circumstantial evidence which suggests that the East African Highland banana and the tropical lowland plantain were cultivated on the African continent since before 1 AD. It is also probable that ABB cooking and AB and AAB dessert cultivars were brought to the continent from India by Arabian traders from 600 AD, and that these were disseminated throughout East Africa. During the colonial era, the main centres of distribution for banana cultivars were botanical gardens, such as Zomba in Malawi, Entebbe in Uganda and Amani in Tanzania. It appears that the very early introductions of Highland banana and plantain arrived in Africa as a relatively clean material without the conspicuous pests and diseases that affect them in Asia. In contrast, several devastating problems now impact the crop in Africa, including nematodes, the borer weevil and diseases, most notably banana bunchy top, banana streak, Sigatoka leaf spots, Xanthomonas wilt and Fusarium wilt. We (a) provide chronological overviews of the first reports/observations of different Musa pests and pathogens/diseases in Africa, (b) highlight specific examples of when a pest or pathogen/disease was introduced via planting materials and (c) give recent examples of how the pests and pathogens spread to new regions via planting materials. In total, these production constraints threaten banana and plantain production throughout the continent and impact those who can ill afford lost production, the small‐holder producer. Our intent in this review is to highlight the significance of these problems and the great importance that infested planting materials have played in their development.

Advances in Small Isometric Multicomponent ssDNA Viruses Infecting Plants.

Multicomponent ssDNA plant viruses were discovered during 1990s. They are associated with bunchy top, yellowing and dwarfing diseases of several economic plants under family Musaceae, Leguminosae and Zingiberaceae. In the current plant virus taxonomy, these viruses are classified under the family Nanoviridae containing two genera, Nanovirus and Babuvirus. The family Nanoviridae was created with five members in 2005 and by 2010, it has expanded with four additional members. The viruses are distributed in the tropical and subtropical regions of Asia, Australia, Europe and Africa. The viruses are not sap or seed transmissible and are naturally transmitted by aphid vector in a persistent manner. The genome is consisted of several circular ssDNAs of about 1kb each. Up to 12 DNA components have been isolated from the diseased plant. The major viral proteins encoded by these components are replication initiator protein (Rep), coat protein, cell-cycle link protein, movement protein and a nuclear shuttle protein. Each ssDNA contains a single gene and a noncoding region with a stable stem and loop structure. Several Rep encoding components have been reported from each virus, only one of them designated as master Rep has ability to control replication of the other genomic components. Infectivity of the genomic DNAs was demonstrated only for two nanoviruses, Faba bean necrotic yellows virus and Faba bean necrotic stunt virus (FBNSV). A group of eight ssDNA components of FBNSV were necessary for producing disease and biologically active progeny viruses. So far, infectivity of genomic components of Babuvirus has not been demonstrated.

Significant plant virus diseases in India and a glimpse of modern disease management technology

India has a diverse agroclimate representing tropical, subtropical and temperate climates with zones ranging from average to high in temperature, humidity and rainfall; from low to scarce rainfall in deserts to cold to very cold plains and upland areas. Thus it is the home of one of the richest flora and fauna in the world. For pests and pathogens, too, tropical and subtropical climates are ideal for growth and development. A majority of the world’s fruits, vegetables, cereals, pulses, oil seed crops, fiber crops, sugarcane, spices, and ornamentals are cultivated in India. Virus diseases and their vectors are also in abundance. Since ancient times, virus-like diseases and management practices have been known in India. This knowledge has now been revived and adopted in organic farming, especially for medicinal and aromatic plants. Current trends for extensive and intensive agriculture, open international agricultural trade, and thus food security and sustained economy have brought new challenges in the fight against virus diseases. In this changing scenario, current diseases of significance are caused by begomoviruses, badnaviruses, cucomoviruses, potyviruses, ilarviruses in crops such as vegetables, fruits, ornamentals, fiber crops, and sugarcane. Variability in the viruses is also common. Briefly reviewed here is the positive effect of an isolate of Rice necrosis mosaic virus; when artificially inoculated on jute and mesta fiber crops enhanced their fiber contents. Diseases of significance, e.g., leaf fleck disease of sugarcane, citrus yellow mosaic disease, banana bunchy top, banana bract mosaic, mungbean yellow mosaic, mosaic in chrysanthemum, gladiolus and orchids are also discussed. Efficient, reliable diagnostic tools have been developed and used extensively. Some of the advanced laboratories have been accredited for virus indexing under the National Certification System for tissue-cultured plants. International standards for phytosanitary measures have been promulgated, and a mandatory nodal agency is in place for the conservation and exchange of germplasm; a Containment Level-4 facility to examine incoming transgenics and a fully equipped laboratory to intercept virus-infected plant material are functional. A National Agricultural Biosecurity System will soon be in place. All these measures are essential to protect agricultural systems and to compete in the international agriculture market. Continued vigilance, disease mapping and adopting the latest technology are required to practice sustainable agriculture.

First report of a 16SrII group phytoplasma associated with die‐back diseases of papaya and citrus in Ethiopia

Citrus orange (Citrus aurantifolia) and papaya (Carica papaya) are amongst the most common fruits grown in Ethiopia and the area devoted to their cultivation has increased considerably in the last six decades (Seifu, 2003). Recently decline disorders of both citrus and papaya have been reported as causing significant yield losses amongst the major farms growing these crops in the country. Symptoms in citrus include leaf interveinal chlorosis, mosaic or mottling, a reduction in the size and curling of leaves. In severe cases, premature fruit fall, twig drying and die-back, and death of the tree. In papaya, the first symptom is a bright yellowing of the upper young leaves; later, symptoms of mosaic, crinkling and leaf tip necrosis develop, followed by a drying of the upper leaves, which progresses to death of the whole plant. Leaf samples showing symptoms from 12 papaya and 6 orange plants were collected from farms in the Melkassa area of east Shewa, during September 2005. Citrus tristeza virus (CTV) has been previously reported in Ethiopia (Khassaye et al., 1977), so citrus samples were tested for CTV by DAS-ELISA, yielding 4/6 positives. DNA was extracted from all plants and indexed in both a nested PCR with phytoplasma generic primers P1/P7 and R16F2n/R16R2, and a simple PCR for papaya bunchy top (PBT) rickettsia using primers PBTF1/PBTR1 (Davis et al., 1998). Nested PCR amplicons were obtained for 11/12 papaya and six citrus samples. Following RFLP analysis, all exhibited identical HaeIII, RsaI and AluI profiles, which were typical of a 16SrII phytoplasma. None of the papaya and citrus samples evaluated was positive for the PBT rickettsia. Sequencing was done by The Sequencing Service (Univ. Dundee, Scotland; http://www.dnaseq.co.uk) using Applied Biosystems Big-Dye Ver 3·1 chemistry, on an Applied Biosystems model 3730 sequencer. The 16S rDNA phytoplasma sequences of a representative sample of papaya (GenBank Acc. No. DQ285659) and citrus (GenBank Acc. No. DQ286576) were identical and their highest similarity (98%) was with papaya yellow crinkle in Australia (GenBank Acc. No. Y10097), a member of the 16SrII group (Candidatus Phytoplasma aurantifolia). This is the first record of phytoplasmas associated with die-back diseases of papaya and citrus in Ethiopia. The finding of a mixed infection of phytoplasma and CTV in some citrus samples will require further studies before any recommendations for disease management can be made. Work in the UK was done under Defra plant health license No. PHF 174D/5185(08/2005). Rothamsted Research receives grant aid from the Biotechnology and Biological Sciences Research Council of the UK.

First report of Banana bunchy top virus infecting banana in Iran

Banana bunchy top disease is one of the most serious diseases of bananas (Musa spp.) worldwide. The disease is caused by Banana bunchy top virus (BBTV), the type species of the Babuvirus genus; (family Nanoviridae). The genome of BBTV is comprised of at least six circular single-stranded DNA (ssDNA) components, each approximately 1 Kb in size. Symptoms of BBTV infection include plant stunting, foliar yellowing and most characteristically, dark green streaks on the pseudostem, petioles and leaves (Harding et al. 1993; Vetten et al., 2005). From 2004 to 2006, a series of field surveys were conducted in the major banana-growing areas in Iran: Mazandaran province (Sari, Babol, Behshahr, and Ghaemshahr) in the north and Hormozgan province (Jask and Varz-Abad) in the south. A total of 164 banana plant samples with bunchy top, stunting and leaf samples with green streak symptoms were collected. Samples were tested for the presence of BBTV with a double-antibody sandwich enzyme-linked immunosorbent assay (DAS-ELISA) using positive control and polyclonal antibodies against BBTV, according to the supplier's instructions (Bio-Rad). Of the samples tested, 27 were positive for BBTV using DAS-ELISA. To confirm BBTV identification, polymerase chain reaction (PCR) was carried out using samples that previously tested positive by ELISA. Forward [F3: 5′-GGAAGAAGCCTCTCATCTGCTTCAGAGAR C-3′; nts 287 to 258] and reverse [FPCR4: 5′-TTCCCAGGCGCACACCTTGAGAAACGA AAG-3′; nts 284 to 313] primers were used to amplify complete BBTV DNA-1 (Furuya et al., 2005). PCR analysis showed fragments of approximately 1 Kb in 19 samples. Furthermore, using primer pairs designed to differentiate BBTV strains (Su et al., 2003), Iranian BBTV isolates were divided into two distinct strains. This is the first report of the occurrence of BBTV in Iran.

Diseases of Tropical Perennial Crops: Challenging Problems in Diverse Environments.

The world’s oldest ecosystems are found in the tropics. They are diverse, highly evolved, but barely understood. Diseases that impact crops in these regions can be significant contraints to production, especially when they occur in lowland environments with high rainfall and uniform, warm temperatures; respites from disease pressure there are often infrequent. Difficulties in managing diseases in the humid tropics are multiplied when the affected crops are perennial. The favorable conditions for disease development and the presence of susceptible host tissue over long periods make diseases of tropical perennial crops serious management challenges. This topic is introduced with a few concepts on the occurrence and development of these pathosystems. Peculiar aspects and scenarios that influence the types of and extent to which different diseases develop are summarized. Measures that are useful on annual or short-term crops may be ineffective against these diseases. They are scientifically interesting problems. New vectors, as for mango malformation, or pathogens, as for bunchy top of papaya, are associated with some of the diseases. And some of the diseases are caused by two or more distinct taxa; for example, citrus greening, mango malformation, Panama disease, and tracheomycosis of coffee. Some of the most important diseases are host-specific and are caused by either coevolved or new-encounter pathogens. Resistance, the most effective tool with which many of these diseases are managed, is usually available in coevolved pathosystems but may be uncommon in new-encounter situations. Inadequate host resistance can be a significant barrier in the management of both coevolved and new encounter diseases. General tactics are described that are useful against diseases of tropical perennials. The successful management of plant disease utilizes several principles and practices, regardless of the host and environment in which it is grown. These include the avoidance, exclusion, and eradication of the causal agents. Host protection is of great importance, as is the identification and incorporation of resistance in the host plant. All of these approaches are discussed with tropical perennial examples.

Cytopathology, Mode of Aphid Transmission and Search for the Casual Agent of Cotton Bunchy Top Disease

AbstractThe cytopathological effects of cotton bunchy top (CBT) disease and its mode of transmission by Aphis gossypii Glover (cotton aphid), were studied. CBT infection affected the leaf epidermal layer producing a loose, ruptured and rough surface morphology with many stomata closed and misshapen. Roots of CBT‐infected plants showed reduced growth, small knots and a dark brown appearance. A single aphid per plant was capable of transmitting CBT at 5%, whereas three aphids per plant transmitted CBT to 50% of the cotton seedlings and 20 aphids per plant transmitted the disease agent to 80% of the cotton seedlings. Aphis gossypii acquired CBT after a minimum acquisition access period of 5 min and transmitted the agent after a minimum inoculation access period of 1 h. Both alate and apterous aphids and nymph instars 2, 3 and 4 of A. gossypii transmitted CBT. This preliminary data suggest that A. gossypii transmits CBT in a semi‐persistent manner. Myzus persicae Sulz (green peach aphid) was unable to transmit CBT. A comprehensive attempt to isolate the CBT agent, using a range of virological techniques including double‐stranded RNA extraction, two‐dimensional gel electrophoresis for viroid, circular DNA test, nanovirus polymerase chain reaction (PCR), luteovirus PCR and enzyme‐linked immunosorbent assay, phytoplasma test, nucleoprotein purification and electron microscopy, was unsuccessful, raising the possibility that CBT may be caused by a unique new pathogen.

Rhizosphere and endophytic bacteria for induction of systemic resistance of banana plantlets against bunchy top virus

Bunchy top is one of the most important viral diseases affecting banana production worldwide. Several approaches have been made to control or combat the bunchy top virus disease in banana, transmitted by the banana aphid, Pentalonia nigronervosa Coq. No tactic is able to completely protect the plants against this viral infection. To ameliorate this problem, an attempt was made to use different bacterial strains, which could be inoculated to the roots of micropropagated plantlets to avoid the post transplanting problems. Virus indexed micropropagated plantlets of banana cv. Virupakshi (AAB) were subjected to root colonization followed by foliar spraying with three bacterial strains viz ., Pseudomonas fluorescens strains Pf1, CHA0 and Bacillus subtilis strain EPB22 along with an un-inoculated control during primary and secondary hardening stage in the nursery and at the time of transplanting, 3rd, 5th and 7th month after planting in the field. Microbe inoculated plantlets showed improved vegetative growth, physiological attributes, PR—proteins and phenol contents besides reducing banana bunchy top disease (BBTD) incidence in the field. These results indicate that, transplant mixes amended with beneficial bacterial strains can enhance growth of banana plants, besides reducing the damage caused by banana bunchy top virus.

PENGARUH WAKTU INFEKSI VIRUS KERDIL PISANG TERHADAP KERENTANAN TIGA KULTIVAR

Effects of time of infection of banana bunchy top virus on susceptibility of three banana cultivars. Banana Bunchy Top, caused by Banana Bunchy Top Virus (BBTV), is one of the most important banana diseases in Indonesia. Approach to reduce disease incidence involves prevention of early infection especially on susceptible cultivars. This study was conducted to evaluate the response of three banana cultivars, Ambon Kuning, Tanduk, and Kepok, to different time of infection of BBTV i.e., one week and three week after adaptation period, and one week during adaptation period. Banana plants used in the study were prepared through in vitro propagation (tissue culture) and virus transmission was done using aphid vector, Pentalonia nigronervosa. In addition to observation on symptom expression, inhibition of plant height, and reduction of leaf size, conformation of virus infection was done through indirect ELISA. Virus concentration on different part of the plant, young leaf, stem, and root, tends to decrease over the time due to the ability of BBTV to move from cell to cell before replication takes place. It is evidenced that BBTV was able to infect banana in all growth stages although the younger plant is more susceptible to BBTV. Although concentration of the virus in the tested plant is considered high, symptoms expression of BBTV infection can be differentiated from moderate to very severe. Response of banana plants to infection of BBTV can be grouped into susceptible (Ambon Kuning), moderate tolerant (Tanduk), and tolerant (Kepok).

PEMETAAN PERSEBARAN PENYAKIT BUNCHY TOP PADA TANAMAN PISANG DI PROVINSI LAMPUNG

Distribution mapping of bunchy top of banana in Lampung Province. Studies on the occurrence of banana bunchy top were conducted in Lampung province from March to May 2003. This study were aimed to make distribution map of banana bunchy top in Lampung. The stratified random sampling were used. The sample comprised 6 districts out of 10 districts in Lampung. Three subdistrics were randomly selected in each district and then 3 villages were also selected in each subdistrict. In each village 3 famer”s gardens were selected as observation area. The distribution map shows that banana bunchy top has spread throughout the 6 districts visually observed, but only 4 districts, that bunchy top incidence could be examined. Banana bunchy top incidence in Bandar Lampung, South Lampung, Central Lampung, and North Lampung were 2.31, 2.23, 1.06, and 0.84 % respectively. Bunchy top virus attacked various types, among them are janten (55.23%), muli (38.88%), kepok (30.47%), ambon (21.52%), raja sere (19.76%), nangka 4.64%), and lilin (3.84%). There were no disease incidence on cultivar tanduk, rejang and susu, thus this fact might be indicated resistance phenomena of these cultivars.