Disease Infection Rate

DISEASE INFECTION RATE Infection rate (r) = infection rate is a number that shows how fast the pathogen population is growing. Or a number that shows the development of the pathogen population per unit of time. For example, the rate of population infection with downy mildew (Peronosclerospora maydis)in metro corn varieties and suitable climates, the average is r = 0.45/unit/day, meaning that every day for every 100 plants, 45 plants are attacked by the disease. So the development is very fast. By knowing the magnitude of the infection rate, it can be assumed that the pathogen is very aggressive, the host plant is very susceptible and the climate is very favorable. On the other hand, for the Arjuna corn variety, for example, the r may be only 0.10 /unit/day, in the same climatic environment. It is possible that this is because this variety is more resistant to attacks by pathogens which slows down the rate of infection. From the magnitude of r, it can also be inferred about the nature of the pathogen, whether it grows logarithmically (exponentially) or not. Measurement of the infection rate (r) is carried out several times in a row at certain time intervals, for example: every day, every week, every month or once a year depending on the nature of the pathogen. In pathogenic species that attack short-lived plants and develop relatively quickly, r measurements are carried out every day or week, for example: leaf blight by Phytophthora infestanson potato plants, downy mildew byPeronoscerospora maydis which attacks the leaves of very young maize plants,Helminthosporium maydis, Puccinia maydisboth attack corn leaves on older plants and Ustilago maydiswhich attacks corn fruit. Likewise diseases caused by viruses, mycoplasma, wilt bacteriaXanthomonas solanacearum,Pythiumspp., Sclerotium roflsii,Fusariumspp. which attacks soybeans, peanuts and others. But for root diseases such asArmilaria melleathat attacks rubber or tea plants, calculating the infection rate r maybe once a month is enough. X = proportion (part) of this pathogenic plant can be a leaf, branch branch and others, if the nature of the pathogenic attack is only local, so it does notsystemic. The part of the leaf that is attacked in the form of spots can be estimated as to the area of the spots compared to the total leaf area. For measurements, a number of affected leaves can be taken as an example. Or attacks in the form of spots can be counted how many spots there are at certain times.But if the attack is systemic, then the affected plant itself is considered x. For example, mycoplasma, broom or wilt disease,Xanthomonas solanacearumwhich attacks peanut plants, the attack of both pathogens is systemic, therefore each plant that is attacked is considered one x. So if in a plot there are 100 sample plants and after observation on the first day there are 10 plants that are attacked, then the proportion X1 = 0.10 (10%). Only 90% are still healthy, this can be expressed as 1-X = 0.90. In the next observation the number of plants attacked increased by 5, so the number of plants attacked became 15, so X2=0.15. The number of plants that are still healthy is 1-X2=1-0.15 = 0.85 and so on. Compound interest infection rate The development of compound interest disease is called a disease that develops logarithmically with the formula: r = 1/t2-t1 log e X2/X1 with log base 10, then r = 2.3/t2 ‒ t1 log 10X2/t1 This formula is used if the X (proportion) of infected plants is so small that 1 ‒X (proportion) of those that are still healthy can be ignored. However, if X is relatively large and continues to increase, the proportion (1 ‒X) must be calculated as a correction factor using the following formula: r =2.3/t2 ‒t1 log 10 X2(1 ‒X1)/X1(1 ‒X2 ) or r = 2.3/t2 - t1 (log 10 X2/1-X2 ‒ log 10 X1/1Notes. That infection is not constant at all times but can be slow or fast depending on: the influence of weather, the degree of host susceptibility, the aggressiveness of the pathogen, therefore r varies from time to time. So to measure the infection rate r during the epidemic process in a period of time t, the average value of r1, r2, r3, r4 and so on is taken.All diseases can spread and spread from one area to another, but the speed at which these diseases spread is not the same. Some are slow and some are relatively fast, even though the environmental conditions are quite good. In epidemiology, a distinction is made between diseases that develop relatively quickly, namely classified diseasesinto disease“continuous double flowering”and diseases that develop slowly are classified as diseases“simple flowering" Characteristics of classified diseases“continuous compound interest” 1.The inoculum increases rapidly 2.The progression is logarithmic (exponential) 3.The part of the plant that is initially infected will become a source of infection for surrounding plants 4.The r value may be small at first, but will quickly increase The formula used: log X/1-X Some examples of diseases that can be included in this group include leaf blight,Pyricularia oryzaewhich attacks rice; Other diseases that also attack riceDrechslera oryzaeAndCercospora oryzae;downy mildew Peronosclerospora maydiswhich attacks very young corn plants; leaf spot diseaseHelminthosporium maydisAndPuccinia maydiswhich attacks corn leaves on plants that are already quite large;Cercospora arachidicolaAndCercospora personataboth attack the leaves of peanut plants; Phytophthora infestanswhich attacks potato plants; Oidium attacks rubber leaves; tea leaf pox disease Exobasidium vexanwhich attacks the young leaves of tea plants; rust disease, Phacopspora pachyrrhiziwhich attacks soybean leaves and others.All of the diseases mentioned above reproduce asexually with conidia which are mainly spread through the medium of wind Characteristics of DiseaseWhich“simple flowering" 1.The amount of inoculum relatively does not increase (still) 2.The development (spread) of the disease is relatively slow, not exponential 3.Plants that are initially infected do not become a source of infection for subsequent plants 4.The r value is relatively low The formula used: log 1/1Some examples of diseases that are included in this group include diseasesSoil fungi such as:Pythiumspp.,Fusarium oxysporum, Sclerotium rolfsii , diseasecaused by nematodes, which attack the base of the stems of rubber and tea plants, namely:Armilaria mellea and others. The increase in the number of infected plants is not caused by an increase in the amount of inoculum in the soil, but rather because the inoculum has been distributed more or less evenly in the soil. The amount of inoculum is not always constant, some die or some become saprophytes, if there is no host plant.