Characterization, Purification and Antiserum Production of Sweet Potato Feathery Mottle Potyvirus (SPFMV)

Characterization, purification and production of antiserum against sweet potato feathery mottle potyvirus (SPFMV) were carried out in this study. Characterization of the virus involved host range reaction, inclusion bodies determination, virion morphology and determination of coat protein molecular mass. Initial serological detection of potyviruses infection was carried-out by Indirect ELISA using an Agdia® commercial kit for potyvirus on samples of sweet potato collected from major growing areas in Peninsular Malaysia, Sabah and Sarawak. Experimental results of this study showed, potyviruses are present in most of the major sweet potato growing areas in Peninsular Malaysia and some areas in Sabah and Sarawak. The SPFMV isolate used in this study was single probed by aphid and vectored to healthy Ipomoea setosa three times. The initial infection symptom on I. setosa was characterized by veinal chlorosis of actively growing leaves. In subsequent leaves, the veinal chlorosis was concentrated to major veins. Progressively the veinal chlorosis was restricted to midvein. Subsequent new foliar growth was symptomless. Host reaction results showed, I. nil produced symptoms of faint vein clearing and crinkling after inoculation. Symptomless I. purpurea tested positive in Indirect ELISA, thus showing latent infection in this host. The rest of the indicator plants did not show any virus symptom and tested negative in the ELISA test. These results indicated that the virus isolate in this study has a narrow host range and restricted to the Convolvulaceae family only. Cytoplasmic inclusions (Cis), a major characteristic of the poty group, were observed under light microscopy. In the infected cells, the Cis were stained dark blue (Azure A) and were usually located beside the plant cell nuclei

Epidemiological and Molecular Characterisation of Citrus Huanglongbing (HLB) Disease in Malaysia

Citrus huanglongbing (HLB) disease is considered as one of the most destructive diseases of citrus in Asian, African and American countries. It is caused by Candidatus Liberibacter species. In Asian countries, the causal agent is Candidatus Liberibacter asiaticus. Surveys of the HLB disease on infected citrus trees were carried out in the major citrus growing areas in Peninsular Malaysia namely Selangor, Pahang, Kelantan and Pahang. The occurrence of HLB disease was confirmed by polymerase chain reaction (PCR) and transmission electron microscope (TEM) tests. Candidatus Liberibacter asiaticus was detected positive in samples collected from honey mandarin (Citrus reticulata), pummelo (C. grandis), Mexican lime (C. aurantifolia), mandarin (C. suhueinsis), calamondin (C. madurensis), Cleopatra (C. reticulata), Troyer citrange (Poncirus trifolia X C. sinensis) and citrirnelo (P. trifolia X C. paradise). Field-infected citrus trees showed typical symptoms of HLB disease such as intervienal chlorosis, green vein, dieback of twigs, lopsided fruit shape, small fruit size and premature fruit drop easily. All the major citrus growing areas in Peninsular Malaysia were found infected with HLB disease. The percentage mean estimate disease incidence ranged from 28.3 - 53.8% and 0.0 - 46.03% depending on localities and citrus species, respectively. The seriousness of the disease justified further studies on the epidemiology and molecular characterization of the causal agent, Candidatus Liberibacter asiaticus in Malaysia. HLB vector, Diaphorina citri were more abundant in the lowland areas such as Selangor and Terengganu. It was absence in Cameron Highland, Pahang but moderate level was recorded in Lojing Highland, Kelantan. Further study on characterization and strain differentiation of Malaysian Candidatus Liberibacter asiaticus isolates was carried out. Based on their biological (pathological) properties, Malaysian isolates exhibited six types of HLB symptoms such as olive green of leaves, green vein, vein yellowing, mottling, stunted and dieback of twigs. In terms of disease incidence and disease severity reactions, Malaysian isolates showed sigmoid pattern of disease progress curves and caused polycyclic type of disease. Based on their aggressiveness, Malaysian isolates could be classified into three groups i.e. severe, moderate and mild. In terms of molecular properties, all isolates produced intense accumulation of starch granule inside the tissue of infected leaves. TEM study revealed that Malaysian isolates were pleomorphic and consisted of two types of bodies i.e. elongated and spherical forms. The body lengths ranged from 100-1200 nm depending on their body shape and the isolates. Differentiation of their modal length and composition ratio revealed that the Malaysian isolates could be classified into two groups i.e. group 1 comprises of GFB-T and GFB-S and group 2 comprises of GFB-PK. Characterization of their 16s rDNA gene sequences revealed that Malaysian isolates produced about 1 156-1 167b.p of nucleotide sequences. Gene sequences between Malaysian isolates showed high percentage of nucleotide similarity that ranged from 96-99%. Similar trends were observed on their genetic distances. Analysis of outer membrane protein (OMP) gene also showed differences between Malaysian isolates tested, namely GFB-Mandarin and GFB-Pummelo. A study on host preference of D. citri and susceptibility of citrus species against GFB-T isolate indicated that D. citri most preferred to colonize and feed on jasmine orange (Munaya paniculata) followed by sour orange (C. aurantium), pummelo and honey mandarin. Host susceptibility study revealed that jasmine orange and pummelo were resistant to HLB infection while sour orange was found to be tolerant. Calamondin was susceptible and honey mandarin was very susceptible to HLB infection. The effect of calcium, zinc and copper application on plants' recovery and severity following infection of HLB disease showed slight protection against the HLB bacterium but was inconsistent in some cases. Citrus trees treated with combination of calcium and zinc at 600 ppm, and 10 ppm respectively resulted to significant increase (P10.05) in terms of fruit production and total soluble solid (TSS) content. This treatment also resulted in reduction of AUDPC value of disease severity and also improved mean leaf length, mean leaf width and mean leaf area. To date, there is no successful treatment available throughout the world including Malaysia to control HLB disease in the orchards. Perhaps the combination of present treatment together with good agriculture practices could improve the efficiency of HLB management in the orchards by enhancing tree immunity, delaying disease onset to prolong lifespan of citrus trees

Enhanced nutritional programme: an innovative approach to controlling plant diseases in the tropics

Mineral nutrients are essential for the normal growth and development of both plants and microorganisms and play a crucial role in plant–pathogen interactions, which could be beneficial or detrimental to plant health. Excessive nutrient uptake causes toxicity in plants, so meeting optimal nutrient requirements is very important in the prevention of plant nutrient-deficiency symptoms. In most cases, mineral nutrients represent the primary lines of plant defense against plant pathogens and are directly affected by the plant host, pathogens, and environmental factors. In general, mineral nutrients may affect disease resistance through induced defenses, including by the production of toxins, metabolites, and lignin. The application of an enhanced nutritional programme (ENP) to minimize the deleterious effects of phytopathogens has become a hot topic of discussion around the world. Furthermore, various reports from several countries have shown that the application of mineral nutrients such as calcium (Ca), copper (Cu), and zinc (Zn) in a disease-control programme could enhance crop production and quality, suppress various plant diseases, and promote plant growth. Thus, the aim of this chapter is to discuss conventional disease control methods in the tropics with special reference to major diseases in rice, oil palm, and citrus, as well as limitations on their control. Moreover, the potential application of an ENP as part of a disease control programme in plantation crops in Malaysia is also discussed

Symptomatology and range of the blood disease bacterium A2 HR MARDI strain (Ralstonia syzygii subsp. celebensis) on selected hosts

Bacterial wilt disease is one of the major diseases in banana. In Malaysia, banana blood disease (BBD) is caused by the blood disease bacterium (BDB) A2 HR MARDI (Ralstonia syzygii subsp. celebensis). This disease bears similarities in symptomatology with Moko disease which caused by Ralstonia solanacearum and BBD in Indonesia, which caused by BDB R229. To determine the symptoms and host range of BDB, a pathogenicity test and host range study were carried out. In this study, there are four stages of external and internal symptoms which were observed. The pathogenicity of the bacterium cultures was then tested on banana, tomato and heliconia plantlets to determine the host range for BDB. To reconfirm that the banana was infected with BDB, re-isolation of BDB from the infected banana plants and Koch’s postulates test were performed. The results showed that there were symptoms of wilting and yellowing of leaves, which eventually caused plants death in the banana plantlets but no symptoms appeared in tomato and heliconia. The results indicate that BDB A2 HR MARDI is host-specific pathogen, only infecting banana similar to BDB R229 and is not as a broad range pathogen as R. solanacearum

The Role of Crop Protection in Sustainable Potato (<em>Solanum tuberosum</em> L.) Production to Alleviate Global Starvation Problem: An Overview

Among food crops in terms of consumption, potato ranks fourth, most important and valuable crop worldwide in terms of production and area harvested after maize, wheat and rice. In the coming years, potato production must keep pace with global population expansion nutritiously and sustainably which can partially be achieved by reducing the yield losses caused by the destructive pest and disease activities to the crop. The challenge of 70–80% total microbial crop yield loss posed by pathogens must be addressed for sustainable potato production in order to properly alleviate the global starvation problem. Potato as a food security crop can help to achieve the four food security requirements: food availability, quality, accessibility and stability. Health benefits of potato have shown the presence of phytochemicals as well as resistant starch which serve as anticancer and antidiabetic. The role of potato in the global food security should not be over emphasized, hence in this chapter we want to give an overview on the global hunger and food security at present, and the role played by potato as a food security crop. In addition, potato yield losses caused by pests and diseases especially phytopathogens, their etiology and the role of crop protection in sustainable potato production to alleviate global starvation problem will be discussed

Detection of Candidatus Phytoplasma Asteris’ (16srI) Associated with Bitter Gourd Leaf and Floral Malformations in Malaysia

Bitter gourd vines (Momordica charantia) exhibiting symptoms of leaf and floral malformations including reduced leaf and flower size and shortened internodes were observed in farmer’s fields in Selangor, Malaysia. The causal agent was detected by nested and semi nested Polymerase Chain Reaction (PCR) using phytoplasma universal primers based on 16SrRNA and SecA gene sequences. Sequence analysis of 1.2 kb and 480 bp amplicons of the 16SrRNA and SecA gene respectively confirmed the presence of phytoplasma DNA associated with Candidatus phytoplasma asteris (Group16SrI) in the symptomatic bitter gourd samples. Phylogenetic analysis of the 16SrDNA and SecA sequences placed the bitter gourd phytoplasma in the 16SrI phytoplasma group. &nbsp;This is the first report of phytoplasma infection in bitter gourd in Malaysia

Evaluation of resistance in response to infection of Southern corn leaf blight disease and determination of secondary metabolites produced during the interaction

In Malaysia, corn is produced in small scale due to many diseases affecting this crop and by planting susceptible hybrids. Southern corn leaf blight (SCLB) is a foliar disease caused by a fungus Cochliobolus heterostrophus. This research was aimed to evaluate resistance in selected inbred lines in response to infection of SCLB disease, and to determine the plant secondary metabolites produced during the interaction. Only one isolate (CH001) was used for this study. This isolate was identified using morphological and molecular methods, the aggressiveness of the isolate was also determined. Based on morphology and molecular results, this isolate was identified as C. heterostrophus. Pathogenicity test result showed that, the isolate was very aggressive with mean disease severity index (DSI) of 60%. Based on assessment of resistance in selected inbred lines of corn, line SLBR5 was the most resistant line with DSI mean of 20.30% at the fifth week after inoculation, line SLBS3 was the most susceptible line with DSI mean of 51.70%. The concentration of peroxidase (PO), polyphenols oxidase (PPO) and total phenolic content (TPC) were determined. In PO, resistant line SLBR5 produced higher compounds with 6320, 7600 and 5800 mgGAE/g at the 1st, 2nd and 3rd week after inoculation, respectively. Susceptible line, SLBS3 was found to produce less with 1640, 1800 and 1920 mgGAE/g at the same assessment periods. For PPO, line SLBR5 also produced higher PPO with 2440, 2560, and 2760 mgGAE/g at the 1st, 2nd and 3rd week after inoculation, respectively. Line SLBS2 produced less PPO with 1080, 1240 and 880 mgGAE/g at the same period. Similarly, in TPC, line SLBR5 produced the highest TPC with 15720, 15960 and 17720 mgGAE/g at the 1st, 2nd and 3rd week after inoculation, respectively. Line SLBS3 produced less TPC with 11960, 10240 and 10840 mgGAE/g at the same assessment periods

Leaf nutrient status in relation to severity of Ganoderma infection in oil palm seedlings artificially infected with Ganoderma boninense using root inoculation technique

Basal stem rot (BSR) caused by Ganoderma spp., a basidiomycete fungus, is a major devastating disease of oil palm, especially in Malaysia and Indonesia. Several factors were reported to influence the outbreak of BSR disease which include nutrient status, age of palm, types of soil, previous crop and replanting techniques. Elemental nutrient is known to have some beneficial effects on plant disease control. Over many years, macro- and micro-nutrient application has been totally overlooked in oil palm fertiliser programmes in relation to outbreak of BSR disease incidence. A study was conducted to determine leaf nutrient concentrations in relation to severity of Ganoderma infection in oil palm seedlings artificially inoculated with G. boninense using root inoculation technique. This study was conducted at Universiti Putra Malaysia (UPM), Serdang which involved a total of 210 Durax Pisifera (DXP) oil palm seedlings. After inoculation, external and internal symptoms developing on seedlings and disease severity index (DSI, four disease classes of 0, 1, 2 and 3) were recorded. At 15 months of inoculation, leaf samples were collected and macro-nutrient such as Nitrogen (N), Phosphorus (P), Potassium (K), Calcium (Ca) and Magnesium (Mg) and micro-nutrient such as Copper (Cu), Zinc (Zn), Manganese (Mn), Iron (Fe) and Boron (B) were analysed. Analysis of variance (ANOVA) was performed to test the difference between leaf nutrient concentrations in relation to DSI, followed by comparison means using Least Significant Difference (LSD) test at 0.05 significant levels. A total of 25.0% of inoculated seedlings were dead due to G. boninense infection. Significant difference of leaf nutrient concentration in relation to DSI was observed. Leaf macro-nutrient concentration of N, K, and Ca showed significant difference (p<0.05) while P and Mg showed no significant difference in relation to BSR disease development. Meanwhile, leaf micro-nutrient concentration of Cu, Mn and B showed significant difference (p<0.05) while Zn and Fe showed no significant difference. Among significant nutrients, Ca and Cu were found higher in healthy seedlings (DSI - 0) compared to infected seedlings (DSI – 1, 2 or 3). This study suggested that formulation of fertiliser consists mainly of Ca and Cu are needed in order to reduce BSR disease incidence in oil palms

Citrus Huanglongbing disease: disease symptoms Biology of candidatus liberibacter asiaticus vector and disease management

Symptoms Biology of Candidatus Liberibacter asiaticus Vector and Disease Management Managing citrus huanglongbing diasease (HLB) in the field is a major challenge to the citrus growers worldwide. Furthermore, the difficulties in managing diseases in the topics are also associated with environmental factors such as high humidity and rainfall, warmer climate and high inoculum pressure and vector in the orchards. Hence, deep understanding on the etiology and epidemiology of the disease is an effective way to control the spread of the disease. This book is divided into nine chapters to address current issues in the development of sustainable management of HLB in Malaysia. It is a joint effort by four authors from Faculty of Agriculture, Universiti Putra Malaysia, each with a wide expertise in their fields; Khairulmazmi Ahmad and Kamaruzaman Sijam are in plant pathological research while Rita Muhammad and Dzolkhifli Omar are experts in entomological research. This book is a must for anyone working in the citrus production, especially plant quarantine officers, plant pathologists, extension officers and university students