CPRT22 Module 5: Genetic Control PDF

CPRT22 Module 5: Genetic Control: Mechanisms of Genetic Manipulation of the Pests and Host Plants: Lesson 5.1: Genetic Manipulation of the Pest: Sterile Insect Technique Genetic Control of Insect Pests Manipulation of genetic component or other inheritance mechanisms in...

CPRT22 Module 5: Genetic Control: Mechanisms of Genetic Manipulation of the Pests and Host Plants: Lesson 5.1: Genetic Manipulation of the Pest: Sterile Insect Technique Genetic Control of Insect Pests Manipulation of genetic component or other inheritance mechanisms in an organism. The most widely used technique under this control method is the sterile male technique in insects or the sterile insect technique (SIT). The procedure involves mass-rearing insects, subjecting them to sterilization by irradiation or chemical mutagens, and releasing large numbers of males to mate with wild females This is an environmentally friendly approach.  Example of chemical sterilant in insects tris-(1-aziridinyl) phosphine oxide is a chemical sterilant used in SIT. Drawback of this chemical: It is mutagenic and carcinogenic to man and animals and poses hazards to man and the environment and should be used with caution. SIT was developed during the 1940s and 1950s and is now a mature technology and widely accepted method for insect population suppression, and in some cases, eradication Examples of Effective SIT SIT programs effectively eradicated the Screwworm in North and Central America, and the Mediterranean fruit fly in Florida and other locations The fruit fly population's suppression in mango using SIT and MAT using methyl eugenol as lure and malathion as poison - in Guimaras, Iloilo by the collaboration of Philippine Nuclear Research Institute (PNRI) and the National Mango Research and Development Center in 1996-1998 Lesson 5.2: Mechanisms of Host Plant Resistance to Insect Pests Host Plant Resistance to Insect Pests Resistance is the heritable property that enables a plant to inhibit pest population growth or recover from an injury caused by populations not inhibited from growing. Genes from the wild relatives of crops and novel genes, are deployed in different crops to make the plants resistant, which is an effective weapon to minimize insect losses pests.  The resistance of plants to insects Enables a plant to avoid or inhibit host selection: Inhibit oviposition and feeding, Reduce insect survival and development; and tolerate or recover from an injury from significant damage. two ways by which plants become resistant to insect pest attacks ecological resistance and genetic resistance Ecological resistance is considered a false resistance or pseudo resistance because it is under the primary control of the crop's environment. Genetic resistance is a right or real resistance because it is governed by resistance genes inherent to various introduced sources. two ways by which plants become resistant to insect pest attacks Two types of ecological resistance, namely: phenological asynchrony and induced resistance. In phenological asynchrony, the crop's susceptible stage does not coincide with the pest population's peak such that the plant escapes the damage.(In a real sense, the crop has no resistance to the pest). On the other hand, induced resistance is brought about by the plants' proper care, such as fertilization and other farm practices that make them resistant to insect pest attacks. Mechanisms of Genetic Resistance to Insect Pests Genetic resistance is a type of resistance under the primary control of the plant's genetic factors and is considered real resistance. Painter (1951) classified insect resistance mechanisms into three: non-preference, antibiosis, and tolerance. Non-preference was later named as antixenosis by Kogan and Ortman (1978). Antixenosis occurs when a pest is less likely to find or feed on a resistant plant. Antibiosis occurs when feeding on a resistant plant harms the pest's health or fitness. In general, this is caused by chemicals in the plant tissue which can either directly kill, slow the development of, or reduce the reproductive capacity of a pest Antibiosis includes all adverse physiological effects of a temporary or permanent nature resulting from a plant's ingestion by an insect. Resistance is due to toxic substances/biochemicals present in plants. Antibiosis The effects that toxic substances may have on insects include failure to emerge, failure to pupate, abnormal growth, malformed adults, reduced fecundity or egg- laying ability, restlessness and other behavior, and ultimately, death. Antibiosis resistance often results in increased mortality or reduced longevity and reproduction of the insect. Tolerance Tolerance occurs when a plant can continue to thrive despite being attacked. Lesson 5.3: Host Plant Resistance to Diseases defined as the host plant's ability to exclude or overcome a pathogen's effect entirely or to some degree.  The use of resistant varieties, if available, is perhaps the best pest control method for managing pest and disease problems. Different varieties of a given plant species vary in their reaction to a specific plant pathogen. International and National Plant Breeding Institutions where resistant varieties are developed In rice These varieties are high yielding and have resistance or moderate resistance to major pests and diseases like rice stemborer, brown planthopper, green leafhopper bacterial blight, and rice blast: NSIC Rc 216 (Tubigan 17), Rc 160, and Rc 300 (Tubigan 24) and Rc 222. PhilRice scientists bred Rc 160, RC 216, RC 300, whileIRRI scientists bred Rc 222 (Tubigan 18)s. Rice tungro disease-resistant lines were also released by NSIC (formerly Philippine Seed Board) under the popular name, Matatag lines  Mechanisms of Host Plant Defense Against Plant Pathogens Pre-formed resistance is also called a passive type of resistance while induced resistance is an active resistance mechanism. Tolerance is the host plant's ability to reduce the effect of infection on its fitness regardless of the level of pathogen multiplication so it can still have its normal yield despite the disease infection.  Pre-formed resistance mechanisms include structural barriers to penetration such as thick plant cuticle, waxy cuticle, partially closed stomates, lignified and suberized cell layers, corky cell layers, and pre-existing compounds catechol and protocatechuic acid in red onion scales (Ilag and Ilag 2002). Pre-formed resistance can also be due to a lack of nutrients in the plants required by the pathogen tissues that block pathogen invasion. These characteristics are in the genetic makeup of the host plant. Induced resistance The pathogen induces these mechanisms upon infection. includes mechanical barriers, hypersensitive reaction, phytoalexin production, production of toxic metabolites against the pathogen, and detoxification of toxins produced by the pathogen. Hypersensitive reaction (HR) is the rapid localized death of host cells around the invading pathogen. It results in confinement and even death of the pathogen. The plant produce only minute localized lesions which do not further develop. Phytoalexin is a substance produced by the infected plant that inhibits the development of the pathogen Systemic acquired resistance (SAR) plants infected with one pathogen become more resistant to subsequent infection by another pathogen. It also refers to where a pathogen is inoculated in a portion of the host plant. When the plant is resistant to that pathogen, the initial infection will make the whole plant resistant to that same pathogen. It may result after a hypersensitive reaction, wherein the localized resistance reaction becomes systemic.  Resistance Elicitors The pathogens or parts of the pathogens that can induce plants' resistance are called plant defense activators or resistance elicitors. For example, a mild strain of a virus when inoculated to a healthy plant can protect the plant from an aggressive strain of the same virus. The phenomenon is called cross- protection. The phenomenon is similar to immunization or vaccination in humans. Synthetic compounds have also been reported to activate plant defenses and serve as resistance elicitors Examples of identified plant defense activators isalicylic acid, acetylsalicylic acid (aspirin), dichloroisonicotinic acid and Chitosan These compounds can be injected or sprayed, or drenched into the plants. Chitosan is found effective in inducing resistance of tomato to bacterial wilt, rice to bacterial blight in abaca to bacterial heart rot. Genetic Modification of Crops for Pest Resistance The production of pest-resistant crops takes time, resources, and expertise in plant breeding. It entails several selfings and backcrossing steps. If the resistance gene to be transferred is dominant, it takes at least four backcrossing rounds within seven seasons. If the gene is recessive, this process requires more generations of selfing, and thus nine or more cropping seasons are needed. genetic engineering of crops Is a short cut method of introgressing or transferring a pest resistance gene from a donor to an elite line It introduces specific DNA sequences (e.g., gene/s for insect resistance) into crop plants to enhance insect pests' resistance. The DNA sequences used usually encode proteins with insecticidal activity. Genetic insertion or gene transfer into a plant is followed by selecting the target gene's offsprings. This insertion process does not occur in nature so this is man made where a gene "gun," a bacterial "vehicle" (Agrobacterium tumeraciens), or a chemical or electrical treatment (electroporation) this genetic material inserts itself into the host plant's chromosomes Engineers must also insert a "promoter" gene from a virus as part of the package to make the inserted gene express itself. Genetic engineering for host plant resistance to insects An example of genetically modified crops is Bt corn and Bt cotton. Both GE crops were inserted with the crystalline toxin protein (cry gene) from the bacteria Bacillus thuringiensis that confers resistance to the corn borer and cotton bollworm. Another example of GE crop The PRSV-resistant (Hawaiian) transgenic papaya variety SunUp was developed by transforming somatic embryos with the coat protein (CP) gene of the Hawaiian papaya ringspot virus strain. Advantages of Using Host Plant Resistance to manage pests 1. It has no additional cost to farmers. 2. Resistance is specific to a particular pest. 3. Resistant varieties are compatible with other pest- management techniques 4. Often effects of the use of insect-resistant cultivars are cumulative over time. Effectiveness is long-lasting. 5. It is not hazardous to the environment. Disadvantages of Using Host Plant Resistance 1. It takes time and resources to develop a resistant variety. 2. Resistant varieties are usually only resistant to one or a limited number of pests. 3. Incompatibility of resistance with other agronomic traits. 4. If resistant varieties are widespread and insect densities are high, insects may develop new strains that are not affected by the plant's defenses. 5. There's a lack of resistance to some polyphagous insects. 6. Resistance to one pest is linked with susceptibility to other pests.